Frode Stordal

• Finne, Eirik Aasmo; Bjerke, Jarle W.; Stordal, Frode & Tallaksen, Lena M. (2025). Lichens are more tolerant against winter warming stress than vascular and non-vascular plants: Insights from an alpine field experiment. Journal of Ecology. ISSN 0022-0477. 113(3), p. 518–530. doi: 10.1111/1365-2745.14482. Full text in Research Archive Show summary

  Extreme weather events influence carbon cycling and lead to pervasive changes in ecosystem structure and function. Vegetation at high latitudes and in alpine bioclimatic zones can be particularly sensitive to winter warming events, which are short-lived climatic events where temperatures are unusually high and often include rainfall. With climate change the frequency and severity of winter warming events are increasing. We report here from a field experiment on a lichen-dominated ridge at a high mountain plateau in central Norway. This is a common vegetation type at high latitudes and altitudes, yet little is known about ecophysiological responses to winter warming events in lichens, and how it may differ from responses in bryophytes and vascular plants. We ran a week-long simulation of vegetation stress from winter warming events through thaw–freeze and ice encasement, during late winter in 2021 and 2022. The thaw–freeze treatment had minor effects on summer ecophysiology in lichens (Cladonia mitis, Cetraria islandica and Nephromopsis nivalis), while the species N. nivalis and to a lesser extent, C. mitis had reduced vitality after the ice encasement treatment. Contrastingly, the bryophyte Polytrichum juniperinum, and vascular plant Empetrum nigrum had reduced photosynthetic efficiency and seasonal growth in both thaw–freeze and ice encasement treatments. The ice encasement treatment was overall more lethal and led to reduced NDVI (Normalised Difference Vegetation Index). However, reduction in vitality of vascular and non-vascular plants was not enough to impact overall ecosystem carbon flux. Synthesis: The lichen's stronger tolerance against thaw–freeze and ice encasement than co-existing plants oppose the general effects of summer climate warming, where lichens may succumb under greater plant-growth and warmer soils. This study advocates for the importance of year-round ecology to understand vegetation change under climate change.

• Phoenix, Gareth K.; Bjerke, Jarle W.; Björk, Robert G.; Blok, Daan; Bryn, Anders & Callaghan, Terry V. [Show all 20 contributors for this article] (2025). Browning events in Arctic ecosystems: Diverse causes with common consequences. PLOS Climate. 4(1). doi: 10.1371/journal.pclm.0000570. Full text in Research Archive Show summary

  Arctic ecosystems are experiencing extreme climatic, biotic and physical disturbance events that can cause substantial loss of plant biomass and productivity, sometimes at scales of >1000 km2. Collectively known as browning events, these are key contributors to the spatial and temporal complexity of Arctic greening and vegetation dynamics. If we are to properly understand the future of Arctic terrestrial ecosystems, their productivity, and their feedbacks to climate, understanding browning events is essential. Here we bring together understanding of browning events in Arctic ecosystems to compare their impacts and rates of recovery, and likely future changes in frequency and distribution. We also seek commonalities in impacts across these contrasting event types. We find that while browning events can cause high levels of plant damage (up to 100% mortality), ecosystems have substantial capacity for recovery, with biomass largely re-established within five years for many events. We also find that despite the substantial loss of leaf area of dominant species, compensatory mechanisms such as increased productivity of undamaged subordinate species lessen the impacts on carbon sequestration. These commonalities hold true for most climatic and biotic events, but less so for physical events such as fire and abrupt permafrost thaw, due to the greater removal of vegetation. Counterintuitively, some events also provide conditions for greater productivity (greening) in the longer-term, particularly where the disturbance exposes ground for plant colonisation. Finally, we find that projected changes in the causes of browning events currently suggest many types of events will become more frequent, with events of tundra fire and abrupt permafrost thaw expected to be the greatest contributors to future browning due to their severe impacts and occurrence in many Arctic regions. Overall, browning events will have increasingly important consequences for ecosystem structure and function, and for feedback to climate.

• Zhu, Jiang; Tang, Hui; Fang, Keyan; Stordal, Frode; Bryn, Anders & Gao, Min [Show all 7 contributors for this article] (2025). Human Mediation of Wildfires and Its Representation in Terrestrial Ecosystem Models. Fire. 8(8). doi: 10.3390/fire8080297. Full text in Research Archive Show summary

  Increasing wildfires are causing global concerns about ecosystem functioning and services. Although some wildfires are caused by natural ignitions, it is also important to understand how human ignitions and human-related factors can contribute to wildfires. While dynamic global vegetation models (DGVMs) have incorporated fire-related modules to simulate wildfires and their impacts, few models have fully considered various human-related factors causing human ignitions. Using global examples, this study aims to identify key factors associated with human impacts on wildfires and provides suggestions for enhancing model simulations. The main categories explored in this paper are human behavior and activities, socioeconomic background, policy, laws, regulations, and cultural and traditional activities, all of which can influence wildfires. Employing an integrated and interdisciplinary assessment approach, this study evaluates existing DGVMs and provides suggestions for their improvement.

• Haugvaldstad, Ove Westermoen; Tang, Hui; Kaakinen, Anu; Bohm, Katja; Zwaaftink, Christine Groot & Grythe, Henrik [Show all 9 contributors for this article] (2024). Spatial Source Contribution and Interannual Variation in Deposition of Dust Aerosols Over the Chinese Loess Plateau. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 129(14), p. 1–24. doi: 10.1029/2023JD040470. Full text in Research Archive Show summary

  The Chinese Loess Plateau (CLP) in northern China is home to one of the most prominent loess records in the world, reflecting past eolian dust activity in East Asia. However, their interpretation is hampered by ambiguity in the origin of loess-forming dust and an incomplete understanding of the circulation forcing dust accumulation. In this study, we used a novel modeling approach combining a dust emission model FLEXDUST with simulated back trajectories from FLEXPART to trace the dust back to where it was emitted. Over 21 years (1999–2019), we modeled back trajectories for fine (∼2 μm) and super-coarse (∼20 μm) dust particles at six CLP sites during the peak dust storm season from March to May. FLEXPART source-receptor relationships are combined with the dust emission inventory from FLEXDUST to create site-dependent high-resolution maps of the source contribution of deposited dust. The nearby dust emission areas were found to be the main source of dust to the CLP. Dust deposition across the CLP was found to predominantly occur via wet removal, with also some super-coarse dust from distant emission regions being wet deposited following high-level tropospheric transport. The high topography located on the downwind side of the emission area plays an essential role in forcing the emitted super-coarse dust upward. On an interannual scale, the phase of the Arctic Oscillation in the preceding winter was found to have a strong association with the spring deposition rate on the CLP, while the strength of the East Asian Winter Monsoon was less influential.

• Keetz, Lasse Torben; Lieungh, Eva; Karimi-Asli, Kaveh; Geange, Sonya Rita; Gelati, Emiliano & Tang, Hui [Show all 24 contributors for this article] (2023). Climate–ecosystem modelling made easy: The Land Sites Platform. Global Change Biology. ISSN 1354-1013. 29(15), p. 4440–4452. doi: 10.1111/gcb.16808. Full text in Research Archive Show summary

  Dynamic Global Vegetation Models (DGVMs) provide a state-of-the-art process-based approach to study the complex interplay between vegetation and its physical environment. For example, they help to predict how terrestrial plants interact with climate, soils, disturbance and competition for resources. We argue that there is untapped potential for the use of DGVMs in ecological and ecophysiological research. One fundamental barrier to realize this potential is that many researchers with relevant expertize (ecology, plant physiology, soil science, etc.) lack access to the technical resources or awareness of the research potential of DGVMs. Here we present the Land Sites Platform (LSP): new software that facilitates single-site simulations with the Functionally Assembled Terrestrial Ecosystem Simulator, an advanced DGVM coupled with the Community Land Model. The LSP includes a Graphical User Interface and an Application Programming Interface, which improve the user experience and lower the technical thresholds for installing these model architectures and setting up model experiments. The software is distributed via version-controlled containers; researchers and students can run simulations directly on their personal computers or servers, with relatively low hardware requirements, and on different operating systems. Version 1.0 of the LSP supports site-level simulations. We provide input data for 20 established geo-ecological observation sites in Norway and workflows to add generic sites from public global datasets. The LSP makes standard model experiments with default data easily achievable (e.g., for educational or introductory purposes) while retaining flexibility for more advanced scientific uses. We further provide tools to visualize the model input and output, including simple examples to relate predictions to local observations. The LSP improves access to land surface and DGVM modelling as a building block of community cyberinfrastructure that may inspire new avenues for mechanistic ecosystem research across disciplines.

• Tang, Hui; Haugvaldstad, Ove Westermoen; Stordal, Frode; Bi, Jianrong; Zwaaftink, Christine Groot & Grythe, Henrik [Show all 11 contributors for this article] (2023). Modelling the 2021 East Asia super dust storm using FLEXPART and FLEXDUST and its comparison with reanalyses and observations. Frontiers in Environmental Science. 10. doi: 10.3389/fenvs.2022.1013875. Full text in Research Archive Show summary

  The 2021 East Asia sandstorm began from the Eastern Gobi desert steppe in Mongolia on March 14, and later spread to northern China and the Korean Peninsula. It was the biggest sandstorm to hit China in a decade, causing severe air pollution and a significant threat to human health. Capturing and predicting such extreme events is critical for society. The Lagrangian particle dispersion model FLEXPART and the associated dust emission model FLEXDUST have been recently developed and applied to simulate global dust cycles. However, how well the model captures Asian dust storm events remains to be explored. In this study, we applied FLEXPART to simulate the recent 2021 East Asia sandstorm, and evaluated its performance comparing with observation and observation-constrained reanalysis datasets, such as the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) and CAMS global atmospheric composition forecasts (CAMS-F). We found that the default setting of FLEXDUST substantially underestimates the strength of dust emission and FLEXPART modelled dust concentration in this storm compared to that in MERRA-2 and CAMS-F. An improvement of the parametrization of bare soil fraction, topographical scaling, threshold friction velocity and vertical dust flux scheme based on Kok et al. (Atmospheric Chemistry and Physics, 2014, 14, 13023–13041) in FLEXDUST can reproduce the strength and spatio-temporal pattern of the dust storm comparable to MERRA-2 and CAMS-F. However, it still underestimates the observed spike of dust concentration during the dust storm event over northern China, and requires further improvement in the future. The improved FLEXDUST and FLEXPART perform better than MERRA-2 and CAMS-F in capturing the observed particle size distribution of dust aerosols, highlighting the importance of using more dust size bins and size-dependent parameterization for dust emission, and dry and wet deposition schemes for modelling the Asian dust cycle and its climatic feedbacks.

• Finne, Eirik Aasmo; Bjerke, Jarle W.; Erlandsson, Rasmus; Tømmervik, Hans; Stordal, Frode & Tallaksen, Lena M. (2023). Variation in albedo and other vegetation characteristics in non-forested northern ecosystems: the role of lichens and mosses. Environmental Research Letters. 18(7). doi: 10.1088/1748-9326/ace06d. Full text in Research Archive Show summary

  Vegetation has a profound impact on climate through complex interactions and feedback loops, where especially regulation of albedo, the ratio of reflected to incoming solar radiation, is important at high latitudes. How vegetation albedo varies along environmental gradients in tundra ecosystems is still not well understood, particularly for ecosystems dominated by nonvascular vegetation. We studied broadband shortwave albedo of open boreal, arctic, and alpine ecosystems over a 2000 km long latitudinal gradient (60◦ N–79◦ N) and contrasted this against species composition, vegetation greenness (normalised difference vegetation index—NDVI), momentary ecosystem CO2 fluxes and reindeer (Rangifer tarandus) grazing pressure. High cover of pale terricolous fruticose lichens was the single most important predictor for vegetation albedo, which had a maximum value of 0.389 under clear sky conditions and solar zenith angle 60◦. To our knowledge, this is the highest broadband albedo recorded for a vegetated surface. NDVI was negatively correlated to lichen biomass (rs = −0.56), and albedo (rs = −0.19). Gross primary production and ecosystem respiration varied considerably less between plots and vegetation types than albedo. While it is well-known that Rangifer affects climate-relevant aboveground biomass, we here show that its regulation of surface albedo in northern ecosystems may also be of high importance for land-atmosphere interactions. The data presented here thus advocate for an increased understanding of the important and complex role of herbivores and lichen cover in climate-vegetation interactions.

• Wang, You-Ren; Samset, Bjørn Hallvard; Stordal, Frode; Bryn, Anders & Hessen, Dag Olav (2023). Past and future trends of diurnal temperature range and their correlation with vegetation assessed by MODIS and CMIP6. Science of the Total Environment. ISSN 0048-9697. 904. doi: 10.1016/j.scitotenv.2023.166727. Full text in Research Archive
• Lambert, Marius; Tang, Hui; Aas, Kjetil Schanke; Stordal, Frode; Fisher, Rosie & Bjerke, Jarle Werner [Show all 8 contributors for this article] (2023). Integration of a Frost Mortality Scheme Into the Demographic Vegetation Model FATES. Journal of Advances in Modeling Earth Systems. 15(7). doi: 10.1029/2022MS003333. Full text in Research Archive Show summary

  Frost is damaging to plants when air temperature drops below their tolerance threshold. The set of mechanisms used by cold-tolerant plants to withstand freezing is called “hardening” and typically take place in autumn to protect against winter damage. The recent incorporation of a hardening scheme in the demographic vegetation model FATES opens up the possibility to investigate frost mortality to vegetation. Previously, the hardening scheme was used to improve hydraulic processes in cold-tolerant plants. In this study, we expand upon the existing hardening scheme by implementing hardiness-dependent frost mortality into CLM5.0-FATES to study the impacts of frost on vegetation in temperate and boreal sites from 1950 to 2015. Our results show that the original freezing mortality approach of FATES, where each plant type had a fixed freezing tolerance threshold—an approach common to many other dynamic vegetation models, was restricted to predicting plant type distribution. The main results emerging from the new scheme are a high autumn and spring frost mortality, especially at colder sites, and increasing mid-winter frost mortality due to global warming, especially at warmer sites. We demonstrate that the new frost scheme is a major step forward in dynamically representing vegetation in ESMs by for the first time including a level of frost tolerance that is responding to the environment and includes some level of cost (implicitly) and benefit. By linking hardening and frost mortality in a land surface model, we open new ways to explore the impact of frost events in the context of global warming.

• Pirk, Norbert; Aalstad, Kristoffer; Yilmaz, Yeliz A.; Vatne, Astrid; Popp, Andrea & Horvath, Peter [Show all 12 contributors for this article] (2023). Snow-vegetation-atmosphere interactions in alpine tundra. Biogeosciences. ISSN 1726-4170. 20(11), p. 2031–2047. doi: 10.5194/bg-20-2031-2023. Full text in Research Archive Show summary

  The interannual variability of snow cover in alpine areas is increasing, which may affect the tightly coupled cycles of carbon and water through snow–vegetation–atmosphere interactions across a range of spatio-temporal scales. To explore the role of snow cover for the land–atmosphere exchange of CO2 and water vapor in alpine tundra ecosystems, we combined 3 years (2019–2021) of continuous eddy covariance flux measurements of the net ecosystem exchange of CO2 (NEE) and evapotranspiration (ET) from the Finse site in alpine Norway (1210 m a.s.l.) with a ground-based ecosystem-type classification and satellite imagery from Sentinel-2, Landsat 8, and MODIS. While the snow conditions in 2019 and 2021 can be described as site typical, 2020 features an extreme snow accumulation associated with a strong negative phase of the Scandinavian pattern of the synoptic atmospheric circulation during spring. This extreme snow accumulation caused a 1-month delay in melt-out date, which falls in the 92nd percentile in the distribution of yearly melt-out dates in the period 2001–2021. The melt-out dates follow a consistent fine-scale spatial relationship with ecosystem types across years. Mountain and lichen heathlands melt out more heterogeneously than fens and flood plains, while late snowbeds melt out up to 1 month later than the other ecosystem types. While the summertime average normalized difference vegetation index (NDVI) was reduced considerably during the extreme-snow year 2020, it reached the same maximum as in the other years for all but one of the ecosystem types (late snowbeds), indicating that the delayed onset of vegetation growth is compensated to the same maximum productivity. Eddy covariance estimates of NEE and ET are gap-filled separately for two wind sectors using a random forest regression model to account for complex and nonlinear ecohydrological interactions. While the two wind sectors differ markedly in vegetation composition and flux magnitudes, their flux response is controlled by the same drivers as estimated by the predictor importance of the random forest model, as well as by the high correlation of flux magnitudes (correlation coefficient r=0.92 for NEE and r=0.89 for ET) between both areas. The 1-month delay of the start of the snow-free season in 2020 reduced the total annual ET by 50 % compared to 2019 and 2021 and reduced the growing-season carbon assimilation to turn the ecosystem from a moderate annual carbon sink (−31 to −6 gC m−2 yr−1) to a source (34 to 20 gC m−2 yr−1). These results underpin the strong dependence of ecosystem structure and functioning on snow dynamics, whose anomalies can result in important ecological extreme events for alpine ecosystems.

• Lambert, Marius; Tang, Hui; Aas, Kjetil Schanke; Stordal, Frode; Fisher, Rosie & Fang, Yilin [Show all 8 contributors for this article] (2022). Inclusion of a cold hardening scheme to represent frost tolerance is essential to model realistic plant hydraulics in the Arctic-boreal zone in CLM5.0-FATES-Hydro. Geoscientific Model Development. ISSN 1991-959X. 15(23), p. 8809–8829. doi: 10.5194/gmd-15-8809-2022. Full text in Research Archive Show summary

  As temperatures decrease in autumn, vegetation of temperate and boreal ecosystems increases its tolerance to freezing. This process, known as hardening, results in a set of physiological changes at the molecular level that initiate modifications of cell membrane composition and the synthesis of anti-freeze proteins. Together with the freezing of extracellular water, anti-freeze proteins reduce plant water potentials and xylem conductivity. To represent the responses of vegetation to climate change, land surface schemes increasingly employ “hydrodynamic” models that represent the explicit fluxes of water from soil and through plants. The functioning of such schemes under frozen soil conditions, however, is poorly understood. Nonetheless, hydraulic processes are of major importance in the dynamics of these systems, which can suffer from, e.g., winter “frost drought” events. In this study, we implement a scheme that represents hardening into CLM5.0-FATES-Hydro. FATES-Hydro is a plant hydrodynamics module in FATES, a cohort model of vegetation physiology, growth, and dynamics hosted in CLM5.0. We find that, in frozen systems, it is necessary to introduce reductions in plant water loss associated with hardening to prevent winter desiccation. This work makes it possible to use CLM5.0-FATES-Hydro to model realistic impacts from frost droughts on vegetation growth and photosynthesis, leading to more reliable projections of how northern ecosystems respond to climate change.

• Wang, You-Ren; Buchmann, Nina; Hessen, Dag Olav; Stordal, Frode; Erisman, Jan Willem & Vollsnes, Ane Victoria [Show all 8 contributors for this article] (2022). Disentangling effects of natural and anthropogenic drivers on forest net ecosystem production. Science of the Total Environment. ISSN 0048-9697. 839. doi: 10.1016/j.scitotenv.2022.156326. Full text in Research Archive Show summary

  Net Ecosystem Production (NEP) of forests is the net carbon dioxide (CO2) fluxes between land and the atmosphere due to forests' biogeochemical processes. NEP varies with natural drivers such as precipitation, air temperature, solar radiation, plant functional type (PFT), and soil texture, which affect the gross primary production and ecosystem respiration, and thus the net C sequestration. It is also known that deposition of sulphur and nitrogen influences NEP in forest ecosystems. These drivers' respective, unique effects on NEP, however, are often difficult to be individually identified by conventional bivariate analysis. Here we show that by analyzing 22 forest sites with 231 site-year data acquired from FLUXNET database across Europe for the years 2000–2014, the individual, unique effects of these drivers on annual forest CO2 fluxes can be disentangled using Generalized Additive Models (GAM) for nonlinear regression analysis. We show that S and N deposition have substantial impacts on NEP, where S deposition above 5 kg S ha−1 yr−1 can significantly reduce NEP, and N deposition around 22 kg N ha−1 yr−1 has the highest positive effect on NEP. Our results suggest that air quality management of S and N is crucial for maintaining healthy biogeochemical functions of forests to mitigate climate change. Furthermore, the empirical models we developed for estimating NEP of forests can serve as a forest management tool in the context of climate change mitigation. Potential applications include the assessment of forest carbon fluxes in the REDD+ framework of the UNFCCC.

• Beigaitė, Rita; Tang, Hui; Bryn, Anders; Skarpaas, Olav; Stordal, Frode & Bjerke, Jarle W. [Show all 7 contributors for this article] (2022). Identifying climate thresholds for dominant natural vegetation types at the global scale using machine learning: Average climate versus extremes. Global Change Biology. ISSN 1354-1013. 28(11), p. 3557–3579. doi: 10.1111/gcb.16110. Full text in Research Archive Show summary

  The global distribution of vegetation is largely determined by climatic conditions and feeds back into the climate system. To predict future vegetation changes in response to climate change, it is crucial to identify and understand key patterns and processes that couple vegetation and climate. Dynamic global vegetation models (DGVMs) have been widely applied to describe the distribution of vegetation types and their future dynamics in response to climate change. As a process- based approach, it partly relies on hard- coded climate thresholds to constrain the distribution of vegetation. What thresholds to implement in DGVMs and how to replace them with more processbased descriptions remain among the major challenges. In this study, we employ machine learning using decision trees to extract large- scale relationships between the global distribution of vegetation and climatic characteristics from remotely sensed vegetation and climate data. We analyse how the dominant vegetation types are linked to climate extremes as compared to seasonally or annually averaged climatic conditions. The results show that climate extremes allow us to describe the distribution and eco- climatological space of the vegetation types more accurately than the averaged climate variables, especially those types which occupy small territories in a relatively homogeneous ecological space. Future predicted vegetation changes using both climate extremes and averaged climate variables are less prominent than that predicted by averaged climate variables and are in better agreement with those of DGVMs, further indicating the importance of climate extremes in determining geographic distributions of different vegetation types. We found that the temperature thresholds for vegetation types (e.g. grass and open shrubland) in cold environments vary with moisture conditions. The coldest daily maximum temperature (extreme cold day) is particularly important for separating many different vegetation types. These findings highlight the need for a more explicit representation of the impacts of climate extremes on vegetation in DGVMs. climate extremes , climate thresholds , decision trees , DGVMs , machine learning , vegetation distribution

• Wang, You-Ren; Hessen, Dag Olav; Samset, Bjørn Hallvard & Stordal, Frode (2022). Evaluating global and regional land warming trends in the past decades with both MODIS and ERA5-Land land surface temperature data. Remote Sensing of Environment. ISSN 0034-4257. 280. doi: 10.1016/j.rse.2022.113181. Full text in Research Archive Show summary

  Global surface temperature has been setting new record highs in the recent decades, imposing increasing environmental challenges for societies and ecosystems worldwide. Global warming rates of the 20th century have been documented by a number of studies, nevertheless, the warming rates in the most recent decades in the 21st century are of particular interest for understanding the ongoing climate change. Analyzing temperature trends demands data with high spatial resolution and broad geographical coverage to allow for analyzing trends and changes on a regional scale. Land Surface Temperature data from NASA MODIS with global resolution of 0.05° and Skin Temperature data from European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5-Land reanalysis with global resolution of 0.1° fulfill these demands. In this study, we analyze the remote-sensing-based MODIS data to estimate land surface temperature change rates over the period 2001–2020 in global, continental, and pixel-wise scales with statistical significance indicated. The model-based ERA5-Land data are also analyzed in parallel, extending the period of analysis back to 1981. These two independently-sourced datasets, one from satellites above the atmosphere and one from combining surface modeling and observations, are shown to produce highly consistent results. It is revealed that the trends in the shorter period 2001–2020 are spatially conforming to the trends in the longer period 1981–2020 despite the shorter time length. For the period 2001–2020, we show that the global average land surface temperature rate of change was 0.26 °C-0.34 °C per decade, with substantially different warming rates in different regions. The Arctic, Europe, and Russia show statistically significant warming in both datasets. The Arctic, in particular, warmed at a rate 2.5–2.8 times the global average, and data in the 40-year period 1981–2020 suggest that warming is accelerating in almost all the continents or large regions. Most noticeably, the two independent datasets both indicate that Arctic permafrost regions had the world's highest warming rate at the onset of the 21st century, reaching >2 °C per decade in some areas.

• Falk, Stefanie; Vollsnes, Ane V.; Eriksen, Aud Else Berglen; Stordal, Frode & Berntsen, Terje Koren (2021). Technical note: Quality assessment of ozone reanalysis products and gap-filling over subarctic Europe for vegetation risk mapping. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 21(20), p. 15647–15661. doi: 10.5194/acp-21-15647-2021. Full text in Research Archive
• Horvath, Peter; Tang, Hui; Halvorsen, Rune; Stordal, Frode; Tallaksen, Lena M. & Berntsen, Terje Koren [Show all 7 contributors for this article] (2021). Improving the representation of high-latitude vegetation distribution in dynamic global vegetation models. Biogeosciences. ISSN 1726-4170. 18(1), p. 95–112. doi: 10.5194/bg-18-95-2021. Full text in Research Archive Show summary

  Vegetation is an important component in global ecosystems, affecting the physical, hydrological and biogeochemical properties of the land surface. Accordingly, the way vegetation is parameterized strongly influences predictions of future climate by Earth system models. To capture future spatial and temporal changes in vegetation cover and its feedbacks to the climate system, dynamic global vegetation models (DGVMs) are included as important components of land surface models. Variation in the predicted vegetation cover from DGVMs therefore has large impacts on modelled radiative and non-radiative properties, especially over high-latitude regions. DGVMs are mostly evaluated by remotely sensed products and less often by other vegetation products or by in situ field observations. In this study, we evaluate the performance of three methods for spatial representation of present-day vegetation cover with respect to prediction of plant functional type (PFT) profiles – one based upon distribution models (DMs), one that uses a remote sensing (RS) dataset and a DGVM (CLM4.5BGCDV; Community Land Model 4.5 Bio-Geo-Chemical cycles and Dynamical Vegetation). While DGVMs predict PFT profiles based on physiological and ecological processes, a DM relies on statistical correlations between a set of predictors and the modelled target, and the RS dataset is based on classification of spectral reflectance patterns of satellite images. PFT profiles obtained from an independently collected field-based vegetation dataset from Norway were used for the evaluation. We found that RS-based PFT profiles matched the reference dataset best, closely followed by DM, whereas predictions from DGVMs often deviated strongly from the reference. DGVM predictions overestimated the area covered by boreal needleleaf evergreen trees and bare ground at the expense of boreal broadleaf deciduous trees and shrubs. Based on environmental predictors identified by DM as important, three new environmental variables (e.g. minimum temperature in May, snow water equivalent in October and precipitation seasonality) were selected as the threshold for the establishment of these high-latitude PFTs. We performed a series of sensitivity experiments to investigate if these thresholds improve the performance of the DGVM method. Based on our results, we suggest implementation of one of these novel PFT-specific thresholds (i.e. precipitation seasonality) in the DGVM method. The results highlight the potential of using PFT-specific thresholds obtained by DM in development of DGVMs in broader regions. Also, we emphasize the potential of establishing DMs as a reliable method for providing PFT distributions for evaluation of DGVMs alongside RS.

• Daloz, Anne Sophie; Rydsaa, Johanne Hope; Hodnebrog, Øivind; Sillmann, Jana; Oort, Bob van & Mohr, Christian Wilhelm [Show all 10 contributors for this article] (2021). Direct and indirect impacts of climate change on wheat yield in the Indo-Gangetic plain in India. Journal of Agriculture and Food Research. 4. doi: 10.1016/j.jafr.2021.100132. Full text in Research Archive Show summary

  The Indo-Gangetic Plain (IGP) is one of the main wheat-production regions in India and the world. With climate change, wheat yields in this region will be affected through changes in temperature and precipitation and decreased water availability for irrigation, raising major concerns for national and international food security. Here we use a regional climate model and a crop model to better understand the direct (via changes in temperature and precipitation) and indirect (via a decrease in irrigation availability) impacts of climate change on wheat yields at four sites spread across different states of the IGP: Punjab, Haryana, Uttar Pradesh and Bihar. The results show an increase in mean temperature and precipitation as well as maximum temperature during the growing season or Rabi season (November–April). The direct impact of climate change, via changes in temperature and precipitation, leads to wheat yield losses between −1% and −8% depending on the site examined. Then, the indirect impact of climate change is examined, considering the impact of climate change on water availability leading to a decrease in irrigation. In this case, the yield losses become significant and much higher, reaching −4% to −36% depending on the site examined and the irrigation regime chosen (6, 5, 3 or 1 irrigations). This work shows that the indirect impacts of climate change may be more detrimental than the direct climatic effects for the future wheat yields in the IGP. It also emphasizes the complexity of climatic risk and the necessity of integrating indirect impacts of climate change to fully assess how it affects agriculture and choose the adequate adaptation response.

• Guttu, Sigmund; Orsolini, Yvan J.; Stordal, Frode; Otterå, Odd Helge & Omrani, Nour-Eddine (2021). The 11 year solar cycle UV irradiance effect and its dependency on the Pacific Decadal Oscillation. Environmental Research Letters. 16(6). doi: 10.1088/1748-9326/abfe8b. Full text in Research Archive Show summary

  The stratospheric, tropospheric and surface impacts from the 11 year ultraviolet solar spectral irradiance (SSI) variability have been extensively studied using climate models and observations. Here, we demonstrate using idealized model simulations that the Pacific Decadal Oscillation (PDO), which has been shown to impact the tropospheric and stratospheric circulation from sub-decadal to multi-decadal timescales, strongly modulates the solar-induced atmospheric response. To this end, we use a high-top version of the coupled ocean–atmosphere Norwegian Climate Prediction Model forced by the SSI dataset recommended for Coupled Model Intercomparison Project 6. We perform a 24-member ensemble experiment over the solar cycle 23 in an idealized framework. To assess the PDO modulation of the solar signal, we divide the model data into the two PDO phases, PDO+ and PDO−, for each solar (maximum or minimum) phase. By compositing and combining the four categories, we hence determine the component of the solar signal that is independent of the PDO and the modulation of the solar signal by the PDO, along with the solar signal in each PDO phase. Reciprocally, we determine the PDO effect in each solar phase. Our results show that the intensification of the polar vortex under solar maximum is much stronger in the PDO− phase. This signal is transferred into the troposphere, where we find a correspondingly stronger polar jet and weaker Aleutian Low. We further show that the amplification of the solar signal by the PDO− phase is driven by anomalous meridional advection of solar-induced temperature anomalies over northern North America and the North Pacific, which contributes to a decreased meridional eddy heat flux and hence to a decreased vertical planetary wave flux into the stratosphere.

• Guttu, Sigmund; Orsolini, Yvan; Stordal, Frode; Otterå, Odd Helge; Omrani, Nour-Eddine & Tartaglione, Nazario [Show all 9 contributors for this article] (2021). Impacts of UV irradiance and medium-energy electron precipitation on the North Atlantic oscillation during the 11-year solar cycle. Atmosphere. 12(8). doi: 10.3390/atmos12081029. Full text in Research Archive Show summary

  Observational studies suggest that part of the North Atlantic Oscillation (NAO) variability may be attributed to the spectral ultra-violet (UV) irradiance variations associated to the 11-year solar cycle. The observed maximum surface pressure response in the North Atlantic occurs 2–4 years after solar maximum, and some model studies have identified that atmosphere–ocean feedbacks explain the multi-year lag. Alternatively, medium-to-high energy electron (MEE) precipitation, which peaks in the declining phase of the solar cycle, has been suggested as a potential cause of this lag. We use a coupled (ocean–atmosphere) climate prediction model and a state-of-the-art MEE forcing to explore the respective roles of irradiance and MEE precipitation on the NAO variability. Three decadal ensemble experiments were conducted over solar cycle 23 in an idealized setting. We found a weak ensemble-mean positive NAO response to the irradiance. The simulated signal-to-noise ratio remained very small, indicating the predominance of internal NAO variability. The lack of multi-annual lag in the NAO response was likely due to lagged solar signals imprinted in temperatures below the oceanic mixed-layer re-emerging equatorward of the oceanic frontal zones, which anchor ocean–atmosphere feedbacks. While there is a clear, yet weak, signature from UV irradiance in the atmosphere and upper ocean over the North Atlantic, enhanced MEE precipitation on the other hand does not lead to any systematic changes in the stratospheric circulation, despite its marked chemical signatures.

• Hvidsten, Dag; Frafjord, Karl; Gray, Jeremy S.; Henningsson, Anna Jonsson; Jenkins, Andrew & Kristiansen, Bjørn Erik [Show all 12 contributors for this article] (2020). The distribution limit of the common tick, Ixodes ricinus, and some associated pathogens in north-western Europe. Ticks and Tick-borne Diseases. ISSN 1877-959X. 11(4). doi: 10.1016/j.ttbdis.2020.101388. Full text in Research Archive Show summary

  In north-western Europe, the common tick, <i>Ixodes ricinus</i>, is widely established, its distribution appears to be increasing and the spread of tick-borne diseases is of increasing concern. The project <i>‘Flått i Nord’</i> (Ticks in northern Norway) commenced in spring 2009 with the intention of studying the tick’s distribution and that of its pathogens in northern Norway. Several methods were used: cloth-dragging, collecting from trapped small mammals, and collecting from pets. Since 2010, the occurrence of ticks in the region of northern Norway was determined directly by cloth-dragging 167 times in 109 separate locations between the latitudes of 64 °N and 70 °N (included seven locations in the northern part of Trøndelag County). The northernmost location of a permanent <i>I. ricinus</i> population was found to be Nordøyvågen (66.2204 °N, 12.59 °E) on the Island of Dønna. In a sample of 518 nymphal and adult ticks, the <i>Borrelia</i> prevalence collected close to this distribution limit varied but was low (1–15 %) compared with the locations in Trøndelag, south of the study area (15–27 %). Five specimens (1 %) were positive for <i>Rickettsia helvetica</i>. The length of the vegetation growing season (GSL) can be used as an approximate index for the presence of established populations of <i>I. ricinus</i>. The present study suggests that the threshold GSL for tick establishment is about 170 days, because the median GSL from 1991 to 2015 was 174–184 days at sites with permanent tick populations, showing a clear increase compared with the period 1961–1990. This apparent manifestation of climate change could explain the northward extension of the range of <i>I. ricinus</i>.

• Guttu, Sigmund; Orsolini, Yvan J.; Stordal, Frode; Limpasuvan, Varavut & Marsh, Daniel R. (2020). WACCM simulations: Decadal winter-to-spring climate impact on middle atmosphere and troposphere from medium energy electron precipitation. Journal of Atmospheric and Solar-Terrestrial Physics. ISSN 1364-6826. 209. doi: 10.1016/j.jastp.2020.105382. Full text in Research Archive Show summary

  Energetic particle precipitation is one of the main processes by which the sun influences atmospheric composition and structure. The polar middle atmosphere is chemically disturbed by the precipitation-induced production of nitric oxides (NOx) and hydrogen oxides (HOx) and the associated ozone (O3) loss, but the importance for the dynamics is still debated. The role of precipitating medium energy electrons (MEEs), which are able to penetrate into the mesosphere, has received increased attention, but has only recently begun to be incorporated in chemistry-climate models. We use the NCAR Whole Atmosphere Community Climate Model (WACCM) to study the climate impact from MEE precipitation by performing two idealized ensemble experiments under pre-industrial conditions, with and without the MEE forcing, over the period of the solar cycle 23 (only full calendar years, 1997–2007). Each experiment includes 20 11-year ensemble members, total 220 years. Our results indicate a strong month-to-month variability in the dynamical response to MEE throughout the winter period. We find a strengthening of the polar vortex in the northern hemisphere during December, but the signal decays rapidly in the following months. The polar vortex strengthening is likely attributable to planetary wave reduction due to increased zonal symmetries in upper stratospheric ozone heating, initially triggered by MEE-induced NOx advected into the sunlit regions. We also find a similar early winter polar vortex strengthening in the southern hemisphere during June. Changes in mean meridional circulation accompany these anomalous wave forcings, leading to dynamically-induced vertical temperature dipoles at high latitudes. The associated weakening of the stratospheric mean meridional circulation results in an upper stratospheric polar ozone deficit in early winter. This polar cap ozone deficit is strongest in the southern hemisphere and contributes to a polar vortex weakening in late winter, in concert with increased planetary wave forcing. In both hemispheres, the stratospheric polar vortex signal seems to migrate downwards into the troposphere and to the surface.

• Kumkar, Yogesh; Astrup, Rasmus Andreas; Stordal, Frode & Bright, Ryan M. (2020). Quantifying regional surface energy responses to forest structural change in Nordic Fennoscandia. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 125(15). doi: 10.1029/2019JD032092. Full text in Research Archive Show summary

  In a climate model, surface energy and water fluxes of the vegetated ecosystem largely depend on important structural attributes like leaf area index and canopy height. For forests, management can greatly alter these attributes with resulting consequences for the surface albedo, surface roughness, and evapotranspiration. The sensitivity of surface energy and water budgets to alterations in forest structure is relatively unknown in boreal regions, particularly in Nordic Fennoscandia (Norway, Sweden, and Finland), where the forest management footprint is large. Here we perform offline simulations to quantify the sensitivity of surface heat and moisture fluxes to changes in forest composition and structure across daily, seasonal, and annual time scales. For the region on average, it is found that broadleaved deciduous forests cool the surface by 0.16 K annually and 0.3 K in the growing season owed to higher year‐round albedo and lower Bowen ratio, yet in some locations the local cooling can be as much as 2.4 K and 3.0 K, respectively. Moreover, fully developed forests cool the surface by 0.04 K annually in our domain owed to higher evapotranspiration, reaching up to 0.4 K locally in some locations, whereas undeveloped forests warm annually by 0.14 K owed to much lower evapotranspiration reaching up to 0.8 K for some locations. If regional forests are ever to be managed for the local climate regulation services that they provide, our results are an important first step illuminating the potential adverse impacts or benefits across space and time.

• Vedeld, Trond; Hofstad, Hege; Mathur, Mihir; Büker, Patrick & Stordal, Frode (2020). Reaching out? Governing weather and climate services (WCS) for farmers. Environmental Science and Policy. ISSN 1462-9011. 104, p. 208–216. doi: 10.1016/j.envsci.2019.11.010. Full text in Research Archive Show summary

  High-quality weather and climate services (WCS) can be critical for communicating knowledge about current and future weather and climate risks for adaptation and disaster risk management in the agricultural sector. This paper investigates the structure and performance of weather and climate services for farmers from a governance perspective. Empirically the paper compares the institutional design and operations of agro-meteorological services in Maharashtra/India and Norway through a ‘most different case study’ approach. The two cases were selected to represent great diversity in location, scale and institutional design. A governance approach based on semi-direct interviews and policy and institutional analysis was combined with local survey data of farmers’ perceptions and use of the services. Despite the fact that the context for the two agromet advisory services was very different from a climate-weather, eco-agriculture, and socio-institutional angle, the analysis reveals great similarities in the services structures and critical governance challenges. In both countries the agromet services communicated knowledge that was largely perceived not to be well tailored to farmers’ needs for decisions in specific crops- and farm operations, spatially too coarse to address local issues, and, often unreliable or inaccurate in terms of the quality of data. Farmers did, however, respond positively to specific and locally relevant information on e.g., warnings about high rainfall and spread of pests. Observing such similarities across very diverse contexts enhances the generalization potential, precisely because they evolved under very different circumstances. Similar observations find support in the wider WCS literature. Based on the empirical findings, we propose a more deliberate approach to institutional design of WCS in order to enhance governance performance and co-creation of the services at local, district and national scales. It is suggested that greater participation of farmers and agricultural extension agents in the co-creation of these services is a necessary means of improving the services, supported by the WCS literature. However, we insist that greater participation is only likely to materialize if the deficiencies in institutional design and knowledge quality and relevance are addressed to greater extent than done today. The comparison between the two services shows that Norway can learn from India that a more ambitious scope and multiple forms of communication, including the use of social media/ WhatsApp groups, can facilitate greater awareness and interest among farmers in multi-purpose agromet services for multi-way communication. India can learn from Norway that a more integrated and decentralized institutional design can strengthen the network attributes of the services, foster co-creation, and improve participation of both poor and large-scale farmers and extension agents.

• Myers-Smith, Isla H.; Kerby, Jeffrey T.; Phoenix, Gareth K.; Bjerke, Jarle W.; Epstein, Howard E. & Assmann, Jakob J. [Show all 41 contributors for this article] (2020). Complexity revealed in the greening of the Arctic. Nature Climate Change. ISSN 1758-678X. 10(2), p. 106–117. doi: 10.1038/s41558-019-0688-1. Full text in Research Archive Show summary

  As the Arctic warms, vegetation is responding, and satellite measures indicate widespread greening at high latitudes. This ‘greening of the Arctic’ is among the world’s most important large-scale ecological responses to global climate change. However, a consensus is emerging that the underlying causes and future dynamics of so-called Arctic greening and browning trends are more complex, variable and inherently scale-dependent than previously thought. Here we summarize the complexities of observing and interpreting high-latitude greening to identify priorities for future research. Incorporating satellite and proximal remote sensing with in-situ data, while accounting for uncertainties and scale issues, will advance the study of past, present and future Arctic vegetation change.

• Bhattarai, Bikas Chandra; Burkhart, John; Stordal, Frode & Xu, Chong-Yu (2019). Aerosol Optical Depth Over the Nepalese Cryosphere Derived From an Empirical Model. Frontiers in Earth Science. 7. doi: 10.3389/feart.2019.00178. Full text in Research Archive Show summary

  In the Himalayan region, aerosols received much attention because they affect the regional as well as local climate. Aerosol Optical Depth (AOD) observation from satellite are limited in the Himalayan region mainly due to high surface reflectance. To overcome this limitation, we have conducted a multivariate regression analysis to predict the AOD over the cryospheric portion of Nepalese Himalaya. Prediction using three meteorological variables from ERA-Interim: relative humidity, wind velocity components (U10 and V10) were taken into account for model development as independent variables, while the longest time series AOD observation at Pokhara station is used as dependent variable. Model coefficients were found significant at 95 percent level with 0.53 coefficients of determination for daily values. Correlation coefficients between model output and AERONET observations were found to be 0.68, 0.73, 0.75, 0.83, and 0.82 at Lumbini, Kathmandu Bode (KTM-BO), Kathmandu University (KTM-UN), Jomson, and Pyramid laboratory/observatory (EVK2CNR) AERONET stations, respectively. Model overestimate AOD at Jomsom, and EVK2CNR AERONET stations while slightly underestimates AOD in Lumbini, KTM-UN, and KTM-BO AERONET station, respectively. Both model output and MODIS observation showed that the highest AOD over Nepal is observed during winter and pre-monsoon season. While lowest AOD is observed during monsoon, and post-monsoon season. The result of this research supports that the use of linear regression model yields good estimation for daily average AOD in Nepal. The model that we have presented could possibly be used in other mountain regions for climate research.

• Pall, Pardeep; Tallaksen, Lena M. & Stordal, Frode (2019). A Climatology of Rain-on-Snow Events for Norway. Journal of Climate. ISSN 0894-8755. 32(20), p. 6995–7016. doi: 10.1175/JCLI-D-18-0529.1. Full text in Research Archive Show summary

  Rain-on-snow (ROS) events are multivariate hydrometeorological phenomena that require a combination of rain and snowpack, with complex processes occurring on and within the snowpack. Impacts include floods and landslides, and rain may freeze within the snowpack or on bare ground, potentially affecting vegetation, wildlife, and permafrost. ROS events occur mainly in high-latitude and mountainous areas, where sparse observational networks hinder accurate quantification—as does a scale mismatch between coarse-resolution (50–100 km) reanalysis products and localized events. Variability in the rain–snow temperature threshold and temperature sensitivity of snowmelt adds additional uncertainty. Here the high-resolution (1 km) seNorge hydrometeorological dataset, capturing complex topography and drainage networks, is utilized to produce the first large-scale climatology of ROS events for mainland Norway. For daily data spanning 1957–2016, suitable rain and snowpack thresholds for defining ROS events are applied to construct ROS climatologies for 1961–90 and 1981–2010 and to investigate trends. Differing ROS characteristics are found, reflecting Norway’s diverse climates. Relative to 1961–90, events in the 1981–2010 period decrease most in the southwest low elevations in winter, southeast in spring, and north in summer (consistent with less snow cover in a warming climate) and increase most in the southwest high elevations, central mountains, and north in winter–spring (consistent with increased precipitation and/or more snow falling as rain in a warming climate). Winter–spring events also broadly correlate with the North Atlantic Oscillation, and the Scandinavia pattern—and more so with the Arctic Oscillation, particularly in the southern mountain region where long-term ROS trends are significant (+0.50 and +0.33 daily ROS counts per kilometer squared per decade for winter and spring).

• Horvath, Peter; Halvorsen, Rune; Stordal, Frode; Tallaksen, Lena Merete; Tang, Hui & Bryn, Anders (2019). Distribution modelling of vegetation types based on area frame survey data. Applied Vegetation Science. ISSN 1402-2001. 22(4), p. 547–560. doi: 10.1111/avsc.12451. Full text in Research Archive Show summary

  Aim: Many countries lack informative, high‐resolution, wall‐to‐wall vegetation or land cover maps. Such maps are useful for land use and nature management, and for input to regional climate and hydrological models. Land cover maps based on remote sensing data typically lack the required ecological information, whereas traditional field‐based mapping is too expensive to be carried out over large areas. In this study, we therefore explore the extent to which distribution modelling (DM) methods are useful for predicting the current distribution of vegetation types (VT) on a national scale. Location: Mainland Norway, covering ca. 324,000 km2. Methods: We used presence/absence data for 31 different VTs, mapped wall‐to‐wall in an area frame survey with 1081 rectangular plots of 0.9 km2. Distribution models for each VT were obtained by logistic generalised linear modelling, using stepwise forward selection with an F‐ratio test. A total of 116 explanatory variables, recorded in 100 m × 100 m grid cells, were used. The 31 models were evaluated by applying the AUC criterion to an independent evaluation dataset. Results: Twenty‐one of the 31 models had AUC values higher than 0.8. The highest AUC value (0.989) was obtained for Poor/rich broadleaf deciduous forest, whereas the lowest AUC (0.671) was obtained for Lichen and heather spruce forest. Overall, we found that rare VTs are predicted better than common ones, and coastal VTs are predicted better than inland ones. Conclusions: Our study establishes DM as a viable tool for spatial prediction of aggregated species‐based entities such as VTs on a regional scale and at a fine (100 m) spatial resolution, provided relevant predictor variables are available. We discuss the potential uses of distribution models in utilizing large‐scale international vegetation surveys. We also argue that predictions from such models may improve parameterisation of vegetation distribution in earth system models.

• Justino, Flavio; Kucharski, Fred; Lindemann, Douglas; Wilson, Aaron & Stordal, Frode (2019). A modified seasonal cycle during MIS31 super-interglacial favors stronger interannual ENSO and monsoon variability. Climate of the Past. ISSN 1814-9324. 15(2), p. 735–749. doi: 10.5194/cp-15-735-2019. Full text in Research Archive Show summary

  It has long been recognized that the amplitude of the seasonal cycle can substantially modify climate features in distinct timescales. This study evaluates the impact of the enhanced seasonality characteristic of the Marine Isotope Stage 31 (MIS31) on the El Niño–Southern Oscillation (ENSO). Based upon coupled climate simulations driven by present-day (CTR) and MIS31 boundary conditions, we demonstrate that the CTR simulation shows a significant concentration of power in the 3–7-year band and on the multidecadal timescale between 15 and 30 years. However, the MIS31 simulation shows drastically modified temporal variability of the ENSO, with stronger power spectrum at interannual timescales but the absence of decadal periodicity. Increased meridional gradient of sea surface temperature (SST) and wind stress in the Northern Hemisphere subtropics are revealed to be the primary candidates responsible for changes in the equatorial variability. The oceanic response to the MIS31 ENSO extends to the extratropics, and fits nicely with SST anomalies delivered by paleoreconstructions. The implementation of the MIS31 conditions results in a distinct global monsoon system and its link to the ENSO in respect to current conditions. In particular, the Indian monsoon intensified but no correlation with ENSO is found in the MIS31 climate, diverging from conditions delivered by our current climate in which this monsoon is significantly correlated with the NIÑO34 index. This indicates that monsoonal precipitation for this interglacial is more closely connected to hemispherical features than to the tropical–extratropical climate interaction.

• Smith-Johnsen, Christine; Orsolini, Yvan; Stordal, Frode; Limpasuvan, Varavut & Pérot, Kristell (2018). Nighttime mesospheric ozone enhancements during the 2002 southern hemispheric major stratospheric warming. Journal of Atmospheric and Solar-Terrestrial Physics. ISSN 1364-6826. 168, p. 100–108. doi: 10.1016/j.jastp.2017.12.018. Full text in Research Archive Show summary

  Sudden Stratospheric Warmings (SSW) affect the chemistry and dynamics of the middle atmosphere. Major warmings occur roughly every second winter in the Northern Hemisphere (NH), but has only been observed once in the Southern Hemisphere (SH), during the Antarctic winter of 2002. Observations by the Global Ozone Monitoring by Occultation of Stars (GOMOS, an instrument on board Envisat) during this rare event, show a 40% increase of ozone in the nighttime secondary ozone layer at subpolar latitudes compared to non-SSW years. This study investigates the cause of the mesospheric nighttime ozone increase, using the National Center for Atmospheric Research (NCAR) Whole Atmosphere Community Climate Model with specified dynamics (SD-WACCM). The 2002 SH winter was characterized by several reductions of the strength of the polar night jet in the upper stratosphere before the jet reversed completely, marking the onset of the major SSW. At the time of these wind reductions, corresponding episodic increases can be seen in the modelled nighttime secondary ozone layer. This ozone increase is attributed largely to enhanced upwelling and the associated cooling of the altitude region in conjunction with the wind reversal. This is in correspondence to similar studies of SSW induced ozone enhancements in NH. But unlike its NH counterpart, the SH secondary ozone layer appeared to be impacted less by episodic variations in atomic hydrogen. Seasonally decreasing atomic hydrogen plays however a larger role in SH compared to NH.

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• Yilmaz, Yeliz A.; Pirk, Norbert; Tallaksen, Lena M.; Stordal, Frode; Berntsen, Terje Koren & Bryn, Anders (2026). Cold region land-atmosphere interactions. doi: https:/www.gewexevents.org/meetings/glass2026/program/abstracts/#Y. Full text in Research Archive Show summary

  Environmental change in high latitudes is progressing faster and more intensely than in many other regions of the Earth. A warmer climate has already triggered unprecedented changes in the terrestrial cryosphere, hydrosphere and ecosphere, which feed back to the atmosphere and the hydrologic cycle. Yet, many studies still rely on one-way coupling between the atmosphere and the land surface, thereby neglecting important interactions and feedback mechanisms. To advance our knowledge on climate change in northern environments, LATICE (Land–ATmosphere Interactions in Cold Environments) was established as a strategic research initiative at the University of Oslo in 2015. Since then, it has developed into a collaborative network of researchers from atmospheric and terrestrial research groups. We combine novel observations, process-based model development, and integrated Earth observation frameworks to improve our understanding of high latitude environmental processes and their representation in Earth System Models - particularly the Norwegian Earth System Model (NorESM). The current LATICE infrastructure including flux towers, drone-based measurements, and a cold climate container contributes to expanding our observational data records in cold environments complemented by regionally calibrated satellite products tailored to boreal and Arctic conditions. These coordinated in-situ, airborne, and spaceborne datasets provide important constraints on surface fluxes, snow dynamics, and vegetation processes. On the modelling side, LATICE researchers have been contributing to land surface and hydrological models to better represent cold region processes by including process parameterizations, new plant functional types, and vegetation demography. The integration of observations and models through data assimilation methods, and further exploration of hybrid approaches with machine learning algorithms support improved understanding of land-atmosphere coupling and uncertainty quantification. This presentation highlights key activities and scientific advances within the LATICE community, presents example studies, and discusses future directions for scientific collaboration with the Pan-GLASS community.

• Erlandsson, Rasmus; Finne, Eirik Aasmo; Tømmervik, Hans; Stordal, Frode & Tallaksen, Lena M. (2024). Pan-arctic lichen estimation indicates a shift from herbivory to climate change driven declines in lichen biomass. Full text in Research Archive
• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Filhol, Simon; Gascoin, Simon; Pirk, Norbert & Remmers, Janneke [Show all 9 contributors for this article] (2024). Leveraging Earth observations to model snow cover dynamics over Scandinavia. Full text in Research Archive
• Tallaksen, Lena M.; Stordal, Frode; Pirk, Norbert & Yilmaz, Yeliz A. (2024). Land-Atmosphere Interactions at High Northern Latitudes. Full text in Research Archive
• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Filhol, Simon; Gascoin, Simon; Pirk, Norbert & Remmers, Janneke [Show all 9 contributors for this article] (2024). Using Earth observations to model snow cover over Scandinavia. Full text in Research Archive
• Bryn, Anders; Biagio, Amanda Johansen Di; Kausrud, Kyrre & Stordal, Frode (2024). Naturen må også reddes fra klimaødeleggelse. Full text in Research Archive
• Bryn, Anders; Berntsen, Terje Koren; Horvath, Peter; Isaksen, Ketil; Liahjell, Gunnar Thorsen & Naas, Adam Eindride [Show all 10 contributors for this article] (2024). På vei mot nye høyder: tre- og skoggrensene stiger. Arr - Idéhistorisk tidsskrift. ISSN 0802-7005. p. 87–100. Full text in Research Archive
• Bjerke, Jarle W.; Tallaksen, Lena M.; Stordal, Frode & Yilmaz, Yeliz A. (2023). EMERALD Open Science Day - Summary of Group Discussions. Full text in Research Archive Show summary

  Group discussions, key questions: How to move from single discipline to multidisciplinary studies? Which processes are missing in terms of plant-climate interactions for improving models?

• Lambert, Marius; Tang, Hui; Aas, Kjetil Schanke; Stordal, Frode; Bjerke, Jarle Werner & Fisher, Rosie [Show all 10 contributors for this article] (2023). Winter survival of vegetation in the Arctic-boreal region: Integrating cold hardiness and frost mortality schemes into CLM-FATES. Full text in Research Archive
• Bryn, Anders; Horvath, Peter; Volden, Inger Kristine; Stordal, Frode; Torma, Michal & Tjessem, Ingrid Vesterdal [Show all 7 contributors for this article] (2023). Citizen science for treeline mapping. Full text in Research Archive
• Vollsnes, Ane Victoria; Bryn, Anders & Stordal, Frode (2022). Fotosyntesen redder ikke klimaet. p. 19–19. Full text in Research Archive Show summary

  Gjennom fotosyntesen tar plantene opp mye av de menneskeskapte klimagassutslippene. Tørke, brann, insektutbrudd og vindfall skaper imidlertid problemer for økosystemenes opptak og lagring av karbon.

• Aas, Kjetil Schanke; Lambert, Marius; Tang, Hui; Althuizen, Inge; Berntsen, Terje Koren & Fisher, Rosie [Show all 11 contributors for this article] (2022). Recent high-latitude vegetation developments in CLM-FATES. Full text in Research Archive
• Finne, Eirik Aasmo; Tallaksen, Lena M.; Stordal, Frode & Bjerke, Jarle W. (2022). Effects of winter warming events on vegetation ecophysiology on a low-alpine ridge. Full text in Research Archive
• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Filhol, Simon; Gascoin, Simon; Pirk, Norbert & Remmers, Janneke [Show all 8 contributors for this article] (2022). Evaluating modeled snow cover dynamics over Fennoscandia using Earth observations and reanalyses. Full text in Research Archive
• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Filhol, Simon; Gascoin, Simon; Pirk, Norbert & Remmers, Janneke [Show all 8 contributors for this article] (2022). Evaluating modeled snow cover dynamics over Fennoscandia using Earth observations. Full text in Research Archive Show summary

  The snow cover is an essential part of the climate system in cold regions through its effects on the terrestrial water, energy, and carbon balance. Due to the high spatiotemporal variability of snow, it is challenging to resolve snow cover dynamics in models. Thus, our ability to improve the representation of these dynamics in Earth System Models (ESMs) leans heavily on the accuracy and representativeness of the observational data sets used for model evaluation. The big picture provided by the long-term climate data record from satellites helps us to monitor changes in land cover over large areas. At the same time, rapidly developing drone and terrestrial imaging technology provides higher resolution information over specific areas. This complimentary information from spaceborne, airborne, and terrestrial Earth observations is invaluable for better understanding the complex processes in the climate system. In our work, we are currently exploiting estimates of snow-covered area from different optical sensors onboard polar orbiting satellites that are imaging the Nordic region. Drone and terrestrial images are being explored as a source of validation and calibration data for the satellite products.  Having representative snow cover maps enables us to better evaluate the terrestrial component of the Norwegian Earth System Model (NorESM), namely the Community Land Model (CLM5). With a focus on snow processes, we are conducting an analysis using satellite-based estimates of snow-covered area (MODIS, Sentinel-2, and Landsat 8), snow simulations from CLM5, snow variables from several climate reanalyses (ERA5, ERA5-Land, and MERRA-2), and in-situ data from eddy covariance stations (LATICE flux sites). Two offline CLM5 simulations are conducted with different atmospheric forcing, namely the default data set (GSWP3) and ERA5. We are investigating trends in the snow cover phenology, which we characterize using snow cover duration, first and last days of the snow cover, and consecutive snow cover days for each snow season over the last two decades. This work illuminates a path to integrate Earth observations with Earth system modeling in cold environments to both identify and constrain sources of uncertainty. Acknowledgement: This ongoing study is supported by the LATICE (Land-ATmosphere Interactions in Cold Environments) strategic research initiative funded by the University of Oslo, and the project EMERALD (294948) funded by the Research Council of Norway.

• Lambert, Marius S. A.; Tang, Hui; Aas, Kjetil Schanke; Stordal, Frode; Fisher, Rosie & Bjerke, Jarle W. [Show all 7 contributors for this article] (2022). Towards realistic plant hydraulics and frost damage in the Arctic-Boreal Zone by modelling cold acclimation in CTSM5-Fates (hydro). Full text in Research Archive
• Bryn, Anders; Vollsnes, Ane Victoria & Stordal, Frode (2022). Skogen utfordres i nytt klima. Nationen. ISSN 0805-3782. p. 20–20. Full text in Research Archive Show summary

  Politikk som skal være grønn og klimavennlig kan ikke lene seg for kraftig på de grønne økosystemene. Eller satse på at de kan endres til vår fordel. Det er for risikabelt.

• Vollsnes, Ane Victoria; Eriksen, Aud Berglen; Falk, Stefanie; Stordal, Frode & Berntsen, Terje Koren (2022). Ozone-induced early senescence studied in Trifolium repens genotypes from subarctic grasslands. Full text in Research Archive Show summary

  Previous experiments have shown that several European clovers may develop more visible injuries due to ozone when the night is not dark. At high latitudes, the summer nights are bright, giving the background for the question whether plants adapted to midnight sun also have this response of being more easily injured by ozone when the night is not dark. The plants included in the present experiment are expected to be adapted to light exposure during night, since there is midnight sun from the time they melt out of the snow cover in spring until the end of July, in the sites where they were collected. This constitutes about 50 % of the growing season for grassland species in these areas. Cuttings of two genotypes of white clover (Trifolium repens) collected in two sites in subarctic Norway were cultivated under controlled environment conditions. Using a factorial design, the plants were exposed to two different night-time light conditions and two different ozone exposure levels. We studied the development of visible injuries, foliar chlorophyll concentrations and N concentration as signs of premature senescence due to ozone.

• Orsolini, Yvan J.; Guttu, Sigmund; Stordal, Frode; Otterå, Odd Helge & Omrani, Nour-Eddine (2022). The 11 year solar cycle UV irradiance effect and its dependency on the Pacific Decadal Oscillation. Full text in Research Archive
• Bryn, Anders; Horvath, Peter; Torma, Michal; Naas, Adam Eindride; Volden, Inger Kristine & Liahjell, Gunnar Thorsen [Show all 10 contributors for this article] (2022). Treeline research at Natural history museum (UiO). Full text in Research Archive
• Tang, Hui; Aas, Kjetil Schanke; Finne, Eirik Aasmo; Althuizen, Inge; Fisher, Rosie A. & Tømmervik, Hans [Show all 14 contributors for this article] (2021). The impact of moss and lichen on hydrological cycle at surface: a study using CLM-FATES. Full text in Research Archive
• Vollsnes, Ane Victoria; Stordal, Frode; Falk, Stefanie; Eriksen, Aud Berglen; Kauserud, Håvard & Berntsen, Terje Koren (2021). Field and lab experiments, plant ecophysiology starting from The double punch. Full text in Research Archive
• Vollsnes, Ane Victoria; Falk, Stefanie; eriksen, Aud Berglen; Emberson, Lisa D.; O’Neill, Connie & Stordal, Frode [Show all 7 contributors for this article] (2021). Model parameterisation of subarctic vegetation in climate models, an example from an ozone effect study. Full text in Research Archive
• Orsolini, Yvan J.; Guttu, Sigmund & Stordal, Frode (2021). Impact of Medium-Energy Electron Precipitation on the Middle Atmosphere and on Climate in Decadal Simulations. Full text in Research Archive
• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Filhol, Simon; Gascoin, Simon; Stordal, Frode & Tallaksen, Lena M. (2021). Fennoscandian snow cover dynamics in the MODIS era. Full text in Research Archive
• Tang, Hui & Stordal, Frode (2021). Unravelling the puzzle of Arctic vegetation-climate interactions in Earth System Models. Full text in Research Archive
• Guttu, Sigmund; Orsolini, Yvan J.; Stordal, Frode; Otterå, Odd Helge & Omrani, Nour-Eddine (2021). The 11 year solar cycle UV irradiance effect and its dependency on the Pacific Decadal Oscillation. Full text in Research Archive
• Vollsnes, Ane Victoria; Falk, Stefanie; Eriksen, Aud Else Berglen; Stordal, Frode; Kauserud, Håvard & Berntsen, Terje Koren (2021). Luftforurensning og klimaendringer gir dobbelt stress for vegetasjonen. Naturen. ISSN 0028-0887. 5, p. 265–271. doi: 10.18261/issn.1504-3118-2021-05-10. Full text in Research Archive
• Lambert, Marius; Aas, Kjetil Schanke; Tang, Hui; Stordal, Frode & Parmentier, Frans-Jan (2021). Modelling insights into the effects of hardening during extreme winter root water release. Full text in Research Archive
• Narayanappa, Devaraju; Berntsen, Terje Koren & Stordal, Frode (2021). Simulated runoff and river discharge in CTSM version 5.1: Evaluation over Scandinavia. Full text in Research Archive Show summary

  Reliable representation of terrestrial water and energy balance in global climate models is crucial to better understand the response of the hydrological cycle to climate change. Though the current generation of global climate models have improved substantially, they still fail to represent all terrestrial processes adequately. Specifically simulating runoff and river discharge are important for many applications such as water resources management and future water availability projections. In this study, we use the land surface model component of the Norwegian Earth System Model which is Community Land Model version 5 (CLM5) to evaluate against observation-based estimates of runoff and river discharge data of selected catchments data. For the latest three decades (1985-2015), we compare the CLM5 simulated grid-scale runoff with observation-based gridded runoff estimates (E-RUN version 1.1) and with data from the Global Runoff Data Centre (GRDC). CLM5 is also capable of simulating river discharge to the oceans through the Model for Scale Adaptive River Transport (MOSART) and is applicable across local, regional, and global scales. The 3-hourly 0.5o meteorological forcing for CLM5 was provided by the Global Soil Wetness Project version 3v1, an international land surface modeling project. We also compare the simulated river discharge data with selected station discharge data in Norway and Sweden. I will present the detailed evaluation results at the conference. Briefly, the evaluation analysis suggests the further calibration to hydrologic parameters is needed to improve simulations of runoff and river discharge, especially subsurface runoff.

• Falk, Stefanie; Lombardozzi, Danica; Vollsnes, Ane Victoria; Stordal, Frode; Berntsen, Terje Koren & Eriksen, Aud Else Berglen (2021). OzoneLUNA: Ozone damage in CLM revisited. Full text in Research Archive
• Falk, Stefanie; Vollsnes, Ane Victoria; Eriksen, Aud E Berglen; Emberson, Lisa D.; O'Neill, Connie & Stordal, Frode [Show all 7 contributors for this article] (2021). Charakterisierung der subarktischen Ökozone hinsichtlich der Modellierung von Ozonverschmutzung und Klimarisiken. Full text in Research Archive Show summary

  https://www.dpg-verhandlungen.de/year/2021/conference/smuk/part/up/session/5/contribution/2?lang=en

• Falk, Stefanie; Vollsnes, Ane Victoria; Emberson, Lisa D.; O'Neill, Connie; Eriksen, Aud E Berglen & Stordal, Frode [Show all 7 contributors for this article] (2021). Characterizing subarctic biomes for land surface modeling of pollution and climate risk. Full text in Research Archive Show summary

  Here we assess the importance of characterization of key meteorological variables and air pollution profiles on the modeled susceptibility of subarctic vegetation to ozone. Changes in climate (e.g. temperature, water availability) will manifest in both direct and indirect effects influencing the species' sensitivity to air pollution. A likely increase in frequency of persistent heatwaves in the future, will inflict heat related stress while generating favorable conditions for the formation of ambient air ozone, e.g. due to wildfires. We have monitored ambient air ozone concentrations at the Norwegian Institute of Bioeconomy Research (NIBIO) Environment Centre Svanhovd in Northern Norway in the vegetation period 2018/19. Due to data acquisition problems, ozone concentrations for two weeks in July 2018 were missing from our record. We present a reconstruction based on probability density function with respect to the Swedish and Finnish atmospheric monitoring sites and compare with available surface ozone products for the region. Over all, ozone concentrations did not differ significantly between the two years. While temperatures and global irradiance diverged substantially from the multi annual mean precipitation varied only to some extend. We investigate the difference in uptake of ozone using the DO3SE model, for typical vegetation at the location. We find that bespoke parameterization for subarctic vegetation is essential for an accurate estimation of Phototoxic Ozone Dose (POD) and an assessment of damage risk. Accurate estimates of the start and length of growing season are also crucial. We find that temperature and its derivative vapor pressure deficit are likely the most important climate variables while the variability of ozone concentration within climatologically reasonable limits plays a minor role. The use of subarctic parameterization suggests an improvement in risk assessment as POD values are increased in 2018; corroborated by evidence of visible injury in the Svanhovd ozone garden.

• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Filhol, Simon; Gascoin, Simon; Stordal, Frode & Tallaksen, Lena M. (2021). Probing Fennoscandian Snow Cover Dynamics in the Community Land Model and Climate Reanalyses during the Satellite Era. Full text in Research Archive
• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Filhol, Simon; Gascoin, Simon; Stordal, Frode & Tallaksen, Lena M. (2021). Benchmarking CLM5 snow cover dynamics with MODIS and reanalyses over Fennoscandia. Full text in Research Archive
• Orsolini, Yvan J.; Guttu, Sigmund; Stordal, Frode; Otterå, Odd Helge; Omrani, Nour-Eddine & Tartaglione, Nazario [Show all 9 contributors for this article] (2021). Impacts of UV Irradiance and Particle Precipitation on the North Atlantic Oscillation During the 11-year Solar Cycle. Full text in Research Archive
• Guttu, Sigmund; Orsolini, Yvan J.; Stordal, Frode; Limpasuvan, Varavut & Marsh, Daniel R. (2020). Impact of Medium-Energy Electron Precipitation on Ozone and Middle Atmosphere Dynamics in WACCM Simulations. Full text in Research Archive
• Lambert, Marius Stephane Astrid; Tang, Hui; Stordal, Frode; Aas, Kjetil Schanke & Parmentier, Frans-Jan W. (2020). Causes of plant mortality from extreme winter events: model insights into desiccation processes during frost droughts. Full text in Research Archive Show summary

  Arctic and boreal vegetation has experienced significant change during the last decades. Shrubs have grown larger, and trees expand northwards and move upwards along mountain slopes. Although the overall living biomass has gone up, there are significant areas across the Arctic that experienced a decrease in vegetation productivity in recent years – a phenomenon, called "Arctic browning". Part of the reason for arctic browning is a vulnerability to a growing number of extreme weather events associated with climate change. Extreme winter events can initiate icing, loss of frost tolerance, and frost droughts that lead to vegetation damage and death of tissues. While frost droughts are not as well-documented as summer droughts, they are the cause of a considerable proportion of observed damage. They have been suggested to occur when sudden warm events trigger leaf transpiration combined with deeply frozen soils due to the lack of snow that prevent plants from replenishing leaf water loss from soil. Most terrestrial biosphere models represent plant water transport as one single resistance term, or ignore plant hydraulics completely. As a result, leaf transpiration is too strongly regulated by soil water stress, and the disparity between leaf transpiration and soil water stress as expected in frost droughts can hardly be depicted by the models. Recent incorporation of much more detailed plant hydraulic modules, based on tissue (root,stem,leaf) level traits, however, opens up the possibility to properly represent frost droughts experienced by plants, and to investigate how frost droughts impact land-atmosphere interactions. In this study, we used the FATESHydro, a cohort model of vegetation coexistence and competition, driven by high resolution atmospheric forcing derived from COSMO-REA6, to evaluate how frost droughts impact vegetation mortality in northern Norway over the period 2012-2020. We established a clear link between snow depth and drought intensity. We show that root water exudation at low soil water potentials, rather than leaf transpiration loss at high vapor pressure deficit, explained tissue desiccation during shallow snow covered winters. We describe which areas of our domain (northern Norway) are most vulnerable and have been strongly hit by frost droughts over the period 2012-2020.

• Stordal, Frode (2020). Complexity revealed in the greening of the Arctic. Nature Climate Change. ISSN 1758-678X. doi: 10.1038/s41558-019-0688-1. Full text in Research Archive
• Bryn, Anders; Dalen, Thea Grobstok; Finne, Eirik Aasmo; Heiberg, Hanne; Nilsen, Irene Brox & Parmentier, Frans-Jan W. [Show all 22 contributors for this article] (2020). Natur i endring - en vandreutstilling. Full text in Research Archive
• Lieungh, Eva; Bryn, Anders; Stordal, Frode; Bjerke, Jarle W.; Tonjer, Lea-Rebekka & Bright, Ryan M. (2020). Norske fjell gror igjen i et varmere klima. Aftenposten (morgenutg. : trykt utg.). ISSN 0804-3116. p. 20–21. Full text in Research Archive
• Stordal, Frode (2020). Dissolved organic matter: From atmosphere to rivers and lakes. Full text in Research Archive
• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Filhol, Simon Vincent P; Stordal, Frode & Tallaksen, Lena M. (2020). Fennoscandian snow cover phenology from MODIS, CLM5, and climate reanalyses. Full text in Research Archive
• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Filhol, Simon Vincent P; Stordal, Frode & Tallaksen, Lena M. (2020). Scandinavian snow cover phenology from MODIS, CLM, and reanalyses. Full text in Research Archive
• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Filhol, Simon Vincent P; Stordal, Frode & Tallaksen, Lena M. (2020). The Representation of the Fennoscandian Snow Cover Phenology in Reanalyses and CLM5 during the MODIS-era. Full text in Research Archive Show summary

  Snow plays an important role in cold regions through its effect on the terrestrial exchange of energy, water, and carbon. Accurately simulating snow processes is therefore important in capturing various climate feedbacks in Earth system models. The representation of the subgrid heterogeneity of snow properties (e.g. coverage, depth, density, albedo) are, in addition to accumulation and snowmelt, major sources of uncertainty in the snow modules of land surface schemes. Using multiple data sources is essential to address these uncertainties and to evaluate overall model performance. Unlike in-situ observations, satellite remote sensing products provide unique representative information at the scale of Earth system models. The Moderate Resolution Imaging Spectroradiometer (MODIS) sensor onboard the Aqua and Terra satellites provide a continuous long-term climate record for the last two decades. In this study, two daily snow cover data sets from MODIS (MOD10A1 and MYD10A1) were used to retrieve fractional snow-covered area (fSCA) and several snow cover metrics (e.g. snow cover duration, first and last day of snow) over Fennoscandia for the 2001-2020 water years. We use these retrievals to evaluate the fSCA outputs from multiple reanalyses (ERA5-Land, ERA5, and MERRA-2) and the latest version of the Community Land Model (CLM5) which is the land component of the Community Earth System Model (CESM) and the Norwegian Earth System Model (NorESM). In order to test the accuracy of the MODIS data, we employed Sentinel-2 and Landsat 8 satellite retrievals as well as local‐scale measurements around the Finse Eco-Hydrological Observatory (Finse EcHO), a low-alpine site in central Norway. Lastly, we compared the trends in snow cover metrics with terrestrial water storage anomalies obtained from the Gravity Recovery and Climate Experiment (GRACE) to better understand the regional water cycle dynamics over this region. This study provides a useful starting point for integrating Earth observations into Earth system modeling in cold regions to help identify and constrain sources of uncertainty. Acknowledgement : This study is conducted under the LATICE strategic research initiative funded by the Faculty of Mathematics and Natural Sciences at the University of Oslo, and the EMERALD (project #294948) funded by the Research Council of Norway.

• Guttu, Sigmund; Orsolini, Yvan; Stordal, Frode; Otterå, Odd Helge; Toniazzo, Thomas & Verronen, Pekka T. (2020). Effects of the 11-year Solar Cycle including Medium-Energy Electron Precipitation in WACCM decadal climate predictions. Full text in Research Archive
• Vollsnes, Ane Victoria; Falk, Stefanie; Eriksen, Aud Berglen; Kapperud, Åshild Fandango; Kauserud, Håvard & Stordal, Frode [Show all 7 contributors for this article] (2020). Responses to experimental ozone exposure in some native plant species from Northern Scandinavia. Full text in Research Archive
• Yilmaz, Yeliz; Tallaksen, Lena M. & Stordal, Frode (2020). Hydroclimatological evaluation of CLM5 simulations using multiple data sources for land-atmosphere interaction studies over Scandinavia. Full text in Research Archive Show summary

  Arctic amplification leads to rapid changes in the terrestrial water and energy balances at high northern latitudes. Advances in Earth System Models (ESMs) is improving our understanding of the underlying feedback mechanisms leading to these changes. The representation of the land surface in ESMs is essential to simulate and understand changes at the global and regional scales. The latest version of the land component of the Norwegian Earth System Model (NorESM), namely the Community Land Model (CLM5), has received substantial new implementations to help simulate the land surface processes in cold environments. At the same time, the behaviour of offline CLM5 simulations and new observational data sets have not been systematically compared over Scandinavian regions. In this study, we run the CLM5 model at relatively high resolution (0.25 degrees) over Scandinavia (including Svalbard) for 15 years between 2002 and 2016. We evaluate the water and energy budget components of CLM5 using several reanalyses and satellite-based observational data sets. In particular, we use monthly model outputs and compare with the satellite retrievals from GRACE, MODIS, AMSR2, and AMSR-E, and reanalysis data sets from ERA5, GLDAS, and MERRA-2. As an additional data source, we use the local‐scale measurements obtained from the Finse Eco-Hydrological Observatory (Finse EcHO) at 1200 m a.s.l, and the high-Arctic research site at Bayelva near Ny-Ålesund, Svalbard. Our investigation is focused on several variables including terrestrial water storage, snow water equivalent, turbulent fluxes, net radiation, and skin temperature. The results indicate that the perceived performance of the land surface model (CLM5) depends strongly on the reference observational data set. Regional discrepancies between data sets, particularly for Svalbard, prompts further investigation of the underlying sources of uncertainty. The results of this evaluation provide a valuable source of information for future studies in the region, particularly in the Land-ATmosphere Interactions in Cold Environments (LATICE) project, which focuses on cold region land surface dynamics, integrating across observational systems, laboratory experiments, field, and modeling efforts. Acknowledgement : This study is conducted under the LATICE strategic research initiative funded by the Faculty of Mathematics and Natural Sciences at the University of Oslo, and the project EMERALD (294948) funded by the Research Council of Norway.

• Falk, Stefanie; Vollsnes, Ane Victoria; Stordal, Frode; Eriksen, Aud Else Berglen & Berntsen, Terje Koren (2020). Surface Ozone in Northern Scandinavia and Implications on Local Vegetation - A Case Study. Full text in Research Archive Show summary

  The Arctic biosphere is subject to comprehensive changes induced by climate change. The highly specialized subartic vegetation will be challenged by both, changing environmental conditions as well as further interference through human activity. Permission of exploitation of natural resources in the Artic is likely to increase the levels of air pollutants which are precursors to ozone. n the course of our project (OzoNorClim: The Double Punch), we had an ozone monitor installed at the Norwegian Institute for Bioeconomic Research (NIBIO) Svanhovd Research Station operated by the Norwegian Institute for Air Research (NILU). In 2018, a long-lasting heatwave accompanied by extensive forest fires across Europe and Scandinavia enhanced surface ozone concentrations by about 2 ppt above the climatological mean in Northern Scandinavia. Ozone sensitive glover species in the ozone garden at Svanhovd showed clear signs of ozone damage in 2018 but not in 2019. We study these two years as example for probable future scenarios in which both heat stress and ozone stress affect vegetation negatively. We look at the corresponding surface ozone concentrations, accumulated ozone dose, and implications on natural and semi-natural vegetation especially in the Pasvik valley in Northern Norway, put these in a larger regional context, and give an outlook on further modelling work.

• Bryn, Anders; Hessen, Dag Olav & Stordal, Frode (2020). Før det bikker over. p. 18–19. Full text in Research Archive
• Vollsnes, Ane Victoria; Falk, Stefanie; Eriksen, Aud Else Berglen; Stordal, Frode; Kauserud, Håvard & Berntsen, Terje Koren [Show all 9 contributors for this article] (2020). The double punch: ozone and climate stresses on vegetation. Full text in Research Archive
• Pirk, Norbert; Ramtvedt, Eirik Næsset; Decker, Sven; Cassiani, Massimo; Burkhart, John & Stordal, Frode [Show all 7 contributors for this article] (2019). Causes of surface energy imbalances of eddy covariance measurements in mountainous terrain. Full text in Research Archive
• Byre, Hanne Eline; Falk, Stefanie; Stordal, Frode & Berntsen, Terje Koren (2019). An Investigation of Source Regions Contributing to the Deposition of Reactive Nitrogen in Arctic and Boreal Areas. Full text in Research Archive Show summary

  Long range atmospheric transport is an important source of reactive nitrogen (Nr) to Boreal and Artic ecosystems. The combined effect of climate change and deposition of reactive nitrogen which is an important nutriant for these systems, have the potential to change the carbon storage in high latitude reservoirs. Furthermore a change in vegetation, will lead to changes in the exchange of energy and humidity between the land surface and the atmosphere. We have conducted several model studies to investigate and quantify the importance and contribution of distinguished source regions to Nr deposition in polar and sub-polar regions in the northern hemisphere. Using a global chemistry transport model, we will assess the following questions: To what extent are emissions from agriculture in South-Asia affecting NOx deposition in the Arctic? What would happen if we shut down the automotive sector in Germany, do we see a reduction in the amount of NOx deposited in Norway?

• Stordal, Frode (2019). Interdisciplinary research in the EMERALD project. Full text in Research Archive
• Stordal, Frode (2019). Vegetation-climate interactions: observations and modelling. Full text in Research Archive
• Falk, Stefanie; Stordal, Frode & Vollsnes, Ane Victoria (2019). Ozon und seine Auswirkungen auf die Vegetation in Nordskandinavien. Full text in Research Archive Show summary

  Ozon ist eines der wichtigsten Spurengasen in der Atmosphäre. Während es uns in Form der Ozonschicht in der Stratosphäre vor schädlicher, kurzwelliger Strahlung schützt, zählt es in der planetaren Grenzschicht zu den überaus schädlichen Reizgasen. Eine Aufnahme einer Dosis von 50 ppm über die Dauer von 30 min gilt für den Menschen als tödlich. Pflanzen nehmen Ozon durch ihre Stoma auf, wo dieses zur Zerstörung von Zellen beiträgt, die der Photosynthese dienen, und letztlich Wachstum und Ertrag reduziert. Die empfindlichen Ökosysteme im Norden Skandinaviens erfahren bereits durch den Klimawandel einen erhöhten Stress. Sollte das Polarmeer dauerhaft eisfrei werden, so würde sich der Schiffsverkehr und damit die Menge der Ozonvorläufersubstanzen drastisch erhöhen. Insbesondere während des Polarsommers ist eine nächtliche Reparatur der entstandenen Ozonschäden gehindert. Wir präsentieren hier einen Überblick über die schädlichen Auswirkungen von Ozon auf Vegetation und erste Studien zu der Entwicklung von Ozonkonzentrationen in Nordskandinavien. Dabei greifen wir sowohl auf Langzeitmessungen als auch Modellsimulationen zurück.

• Stordal, Frode (2019). Our EMERALD planet: Terrestrial ecosystem-climate interactions. Full text in Research Archive
• Stordal, Frode (2019). Ecosystem-climate interactions. Full text in Research Archive
• Stordal, Frode & Vollsnes, Ane Victoria (2019). Eksos har skylden: Ozon på bakken skader avlingene. [Journal]. Apollon. Full text in Research Archive
• Stordal, Frode (2019). Terrestrial ecosystem-climate interactions of our EMERALD planet. Full text in Research Archive
• Stordal, Frode (2019). Improved representation of ecosystem-climate interactions in NorESM. Full text in Research Archive
• Vollsnes, Ane Victoria; Stordal, Frode & Vogt, Yngve (2019). Eksos har skylden: Ozon på bakken skader avlingene. [Journal]. Apollon. Full text in Research Archive
• Vollsnes, Ane Victoria; Stordal, Frode & Bhattacharjee, puja (2019). Ozone pollution from Asia isn't well understood, but may be damaging Arctic plants. [Internet]. www.firstpost.com/tech/science. Full text in Research Archive
• Bryn, Anders; Volden, Inger Kristine; Horvath, Peter; Torma, Michal & Stordal, Frode (2019). Hvor raskt stiger tre- og skoggrensene i Norge? Folkeforskning i praksis. Full text in Research Archive
• Orsolini, Yvan; Guttu, Sigmund; Stordal, Frode & Limpasuvan, Varavut (2019). Impact of Medium-energy Electron Precipitation on Ozone and Middle Atmosphere Dynamics in WACCM Simulations. Full text in Research Archive
• Guttu, Sigmund; Orsolini, Yvan; Stordal, Frode; Limpasuvan, Varavut & Marsh, D. (2019). Impact of medium-energy electron precipitation on ozone and middle atmosphere dynamics in WACCM simulations. Full text in Research Archive
• Yilmaz, Yeliz; Tallaksen, Lena M. & Stordal, Frode (2019). Assessment of the water and energy balance simulations of CTSM using satellite-based observations over Scandinavia. Full text in Research Archive
• Vollsnes, Ane Victoria; Eriksen, Aud Berglen; Falk, Stefanie; Bryn, Anders; Viken, Jeanette & Stordal, Frode (2018). Ozonforurensning. Klima, vegetasjon og matproduksjon. Full text in Research Archive
• Vollsnes, Ane Victoria; Eriksen, Aud Berglen; Büker, Patrick; Kauserud, Håvard; Falk, Stefanie & Stordal, Frode (2018). Ozone stress on sub-Arctic tundra vegetation: ozone exposure experiments with daylength manipulation. Full text in Research Archive
• Vollsnes, Ane Victoria; Eriksen, Aud Berglen; Berntsen, Terje Koren; Kauserud, Håvard; Büker, Patrick & Emberson, Lisa D. [Show all 7 contributors for this article] (2018). The double punch: ozone and climate stresses to sub-Arctic vegetation. Full text in Research Archive
• Karlsson, Per Erik; Pleijel, Håkan; Andersson, Camilla; Bergström, Robert; Engardt, Magnuz & Eriksen, Aud Else Berglen [Show all 13 contributors for this article] (2021). The vulnerability of northern European vegetation to ozone damage in a changing climate An assessment based on current knowledge. IVL Swedish Environmental Research Institute Ltd.. ISSN 9789178832705. Full text in Research Archive

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