Lena Merete Tallaksen

Fleig, A. K., Tallaksen, L.M., Hisdal, H. and Hannah, D. M. (2010) Regional hydrological drought in north-western Europe: linking a new Regional Drought Area Index with weather types (2010). Hydrological Processes, 24 (in press).

Fleig A.K., Tallaksen, L.M., Hisdal H., Stahl K., Hannah D.M. (2010) Inter-comparison of weather and circulation type classifications for hydrological drought development. Physics and Chemistry of the Earth, 35, 507-515.

Gudmundsson, L., Tallaksen, L.M. & Stahl, K. (2010) Spatial cross-correlation patterns of European low, mean and high flows. Hydrological Processes, 24 (in press).

Hannah, D.M., Demuth, S., Van Lanen, H.A.J., Looser, U., Prudhomme, C., Rees, G., Stahl, K. & Tallaksen, L.M. (2010) Large-scale river flow archives: importance, current status and future needs. Commentary, Hydrological Processes, 24 (in press).

Kingston, D.G., Fleig, A.K., Tallaksen, L.M. & Hannah, D.M. (2010) Sea surface temperature and atmospheric linkages to British summer streamflow drought. In: Global Change: Facing Risks and Threats to Water Resources (Proc. of the Sixth World FRIEND Conf., Fez, Morocco, October 2010), IAHS Publ.340, 598-604.

Laaha, G., Saquet, E., Hisdal, H., Kroll, C.N., van Lanen, H.A.J., Tallaksen, L.M. & Woods, R. (2010) FRIEND’s contribution to the PUB Benchmark Assessment Report on low flow estimation. In: Global Change: Facing Risks and Threats to Water Resources (Proc. of the Sixth World FRIEND Conf., Fez, Morocco, October 2010), IAHS Publ.340, 54-60.

Stahl, K., Hisdal, H., Hannaford, J., Tallaksen, L.M., van Lanen, H. A. J., Sauquet, E., Demuth, S., Fendekova, M., and Jódar, J. (2010) Streamflow trends in Europe: evidence from a dataset of near-natural catchments, Hydrol. Earth Syst. Sci. Discuss., 7, 5769-5804.

Stahl, K. & Tallaksen, L.M. (2010) RCM simulated and observed hydrological drought: a comparison of the 1976 and 2003 events in Europe (2010). In: Global Change: Facing Risks and Threats to Water Resources (Proc. of the Sixth World FRIEND Conf., Fez, Morocco, October 2010), IAHS Publ.340, 150-156.

Lettenmaier, D.P. with contribution from Tallaksen, L.M. and 20 others (2009) Changes in the global water cycle (Chapter 11). In: World Water Assessment Programme. 2009. The United Nations World Water Development Report 3: Water in a Changing World. Paris: UNESCO, and London: Earthscan.

Stewart, B. with contribution from Tallaksen, L.M. and 24 others (2009) Evolving hazards – and emerging opportunities (Chapter 12). In: World Water Assessment Programme. 2009. The United Nations World Water Development Report 3: Water in a Changing World. Paris: UNESCO, and London: Earthscan.

Tallaksen, L.M., Hisdal, H. & van Lanen, H.A.J. (2009) Space-time modeling of catchment scale drought characteristics. J. Hydrol., 375, 363-372.

Tallaksen, L.M. & Hewa, G.A. (2009) Extreme value analysis. In: A. Gustard & S. Demuth (Eds) Manual on Low-flow Estimation and Prediction. Operational Hydrology Report No. 50, WMO-No. 1029, 57-70.

Tallaksen, L.M. & van Lanen, H.A.J. (2004) (Eds) Hydrological Drought – Processes and Estimation Methods for Streamflow and Groundwater. Developments in Water Sciences 48. Elsevier B.V., the Netherlands, 580p.

Hisdal, H. & Tallaksen, L.M. (2003) Estimation of regional meteorological and hydrological drought characteristics. J. Hydrol., 281(3), 230-247.

Hisdal, H., Stahl, K., Tallaksen, L.M. & Demuth, S. (2001) Have streamflow droughts in Europe become more severe or frequent? Int. J. Climatol., 21, 317-333.

Tallaksen, L.M., Madsen, H. & Clausen, B. (1997) On the definition and modelling of streamflow drought duration and deficit volume. Hydrol. Sci. J., 42(1), 15-33.

Tallaksen, L.M., Schunselaar, S. & Veen, R. van (1996) Comparative model estimates of interception loss in a coniferous forest stand. Nordic Hydrol., 27(3), 143-160.

Tallaksen, L.M. (1995) A review of baseflow recession analysis. J. Hydrol. 165, 349-370.

• Horvath, Peter; Tang, Hui; Halvorsen, Rune; Stordal, Frode; Tallaksen, Lena M.; Berntsen, Terje Koren & Bryn, Anders (2021). Improving the representation of high-latitude vegetation distribution in dynamic global vegetation models. Biogeosciences.  ISSN 1726-4170.  18, s 95- 112 . doi: 10.5194/bg-18-95-2021 Fulltekst i vitenarkiv. Vis sammendrag

  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.

• Bakke, Sigrid Jørgensen; Ionita, Monica & Tallaksen, Lena M. (2020). The 2018 northern European hydrological drought and itsdrivers in a historical perspective. Hydrology and Earth System Sciences.  ISSN 1027-5606.  24, s 5621- 5653 . doi: 10.5194/hess-24-5621-2020 Fulltekst i vitenarkiv.
• Bhattarai, Bikas Chandra; Burkhart, John; Tallaksen, Lena M.; Xu, Chong-Yu & Matt, Felix Nikolaus (2020). Evaluation of global forcing datasets for hydropower inflow simulation in Nepal. Hydrology Research.  ISSN 1998-9563.  51(2), s 202- 225 . doi: 10.2166/nh.2020.079 Fulltekst i vitenarkiv.
• Stoelzle, Michael; Schuetz, Tobias; Weiler, Markus; Stahl, Kerstin & Tallaksen, Lena M. (2020). Beyond binary baseflow separation: a delayed-flow index for multiple streamflow contributions. Hydrology and Earth System Sciences.  ISSN 1027-5606.  24(2), s 849- 867 . doi: 10.5194/hess-24-849-2020 Fulltekst i vitenarkiv.
• Tijdeman, E.; Stahl, K & Tallaksen, Lena M. (2020). Drought Characteristics Derived Based on the Standardized Streamflow Index: A Large Sample Comparison for Parametric and Nonparametric Methods. Water Resources Research.  ISSN 0043-1397.  56(10) . doi: 10.1029/2019WR026315 Fulltekst i vitenarkiv.
• Brunner, Manuela I & Tallaksen, Lena M. (2019). Proneness of European Catchments to Multiyear Streamflow Droughts. Water Resources Research.  ISSN 0043-1397.  55(11), s 8881- 8894 . doi: 10.1029/2019WR025903
• Erlandsen, Helene B.; Tallaksen, Lena M. & Kristiansen, Jørn (2019). Merits of novel high-resolution estimates and existing long-term estimates of humidity and incident radiation in a complex domain. Earth System Science Data.  ISSN 1866-3508.  11(2), s 797- 821 . doi: 10.5194/essd-11-797-2019 Fulltekst i vitenarkiv.
• Hegdahl, Trine Jahr; Engeland, Kolbjørn; Steinsland, Ingelin & Tallaksen, Lena M. (2019). Streamflow forecast sensitivity to air temperature forecast calibration for 139 Norwegian catchments. Hydrology and Earth System Sciences.  ISSN 1027-5606.  23(2), s 723- 739 . doi: 10.5194/hess-23-723-2019 Fulltekst i vitenarkiv.
• 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), s 547- 560 . doi: 10.1111/avsc.12451 Vis sammendrag

  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.

• 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), s 6995- 7016 . doi: 10.1175/JCLI-D-18-0529.1 Fulltekst i vitenarkiv.
• Rizzi, Jonathan; Nilsen, Irene Brox; Stagge, James Howard; Gisnås, Kjersti Gleditsch & Tallaksen, Lena M. (2018). Five decades of warming: impacts on snow cover in Norway. Hydrology Research.  ISSN 1998-9563.  49(3), s 670- 688 . doi: 10.2166/nh.2017.051 Vis sammendrag

  Northern latitudes are experiencing faster warming than other regions in the world, which is partly explained by the snow albedo feedback. In Norway, mean temperatures have been increasing since the 1990s, with 2014 being the warmest year on record, 2.2 °C above normal (1961–1990). At the same time, a concurrent reduction in the land area covered by snow has been reported. In this study, we present a detailed spatial and temporal (monthly and seasonal) analysis of trends and changes in snow indices based on a high resolution (1 km) gridded hydro-meteorological dataset for Norway (seNorge). During the period 1961–2010, snow cover extent (SCE) was found to decrease, notably at the end of the snow season, with a corresponding decrease in snow water equivalent except at high elevations. SCE for all Norway decreased by more than 20,000 km2 (6% of the land area) between the periods 1961–1990 and 1981–2010, mainly north of 63° N. Overall, air temperature increased in all seasons, with the highest increase in spring (particularly in April) and winter. Mean monthly air temperatures were significantly correlated with the monthly SCE, suggesting a positive land–atmosphere feedback enhancing warming in winter and spring.

• Devoli, Graziella; Jørandli, L.; Engeland, Kolbjørn & Tallaksen, Lena M. (2017). Large-Scale Synoptic Weather Types and Precipitation Responsible for Landslides in Southern Norway., In Matjaž Mikoš; Nicola Casagli; Yueping Yin & Kyoji Sassa (ed.),  Advancing Culture of Living with Landslides: Volume 4 Diversity of Landslide Forms.  Springer Publishing Company.  ISBN 978-3-319-53485-5.  17.  s 159 - 167
• Erlandsen, Helene B.; Haddeland, Ingjerd; Tallaksen, Lena M. & Kristiansen, Jørn (2017). The sensitivity of the terrestrial surface energy and water balance estimates in the WRF model to lower surface boundary representations: a South Norway case study.. Journal of Hydrometeorology.  ISSN 1525-755X.  18(1), s 265- 284 . doi: 10.1175/JHM-D-15-0146.1 Fulltekst i vitenarkiv.
• Ionita, Monica; Tallaksen, Lena M.; Kingston, Daniel; Stagge, James Howard; Laaha, Gregor; van Lanen, Henny, A.J.; Scholz, Patrick; Chelcea, Silvia M. & Haslinger, Klaus (2017). The European 2015 drought from a climatological perspective. Hydrology and Earth System Sciences.  ISSN 1027-5606.  21(3), s 1397- 1419 . doi: 10.5194/hess-21-1397-2017
• Laaha, Gregor; Gauster, Tobias; Tallaksen, Lena M.; Vidal, Jean-Philippe; Stahl, Kerstin; Prudhomme, Christel; Heudorfer, Benedikt; Vlnas, Radek; Ionita, Monica; van Lanen, Henny, A.J.; Adler, Mary-Jeanne; Caillouet, Laurie; Delus, Clair; Fendekova, Miriam; Gailliez, Sébastien; Hannaford, Jamie; Kingston, Daniel; Van Loon, Anne F.; Mediero, Luis; Osuch, Marzena; Romanowicz, Renata; Sauquet, Eric; Stagge, James Howard & Wong, Wai Kim (2017). The European 2015 drought from a hydrological perspective. Hydrology and Earth System Sciences.  ISSN 1027-5606.  21(6), s 3001- 3024 . doi: 10.5194/hess-21-3001-2017 Fulltekst i vitenarkiv.
• Nilsen, Irene Brox; Stagge, James Howard & Tallaksen, Lena M. (2017). A probabilistic approach for attributing temperature changes to synoptic type frequency. International Journal of Climatology.  ISSN 0899-8418.  37(6), s 2990- 3002 . doi: 10.1002/joc.4894 Vis sammendrag

  To understand the cause of regional temperature change, it is common to separate the temperature change signal into changes in atmospheric synoptic circulation and other factors, so-called within-type changes. In this study, we suggest a novel probabilistic approach that allows detection of months and regions where temperature changes can mainly be attributed to changes in synoptic circulation and where within-type changes also play a role. By combining resampling with a Monte Carlo test, we assess the likelihood that the observed warming can be explained by synoptic circulation changes alone. This method is applicable for any variable, and in any region of the world. We applied it to an example case using gridded WATCH Forcing Data ERA-Interim (WFDEI) temperature data and synoptic types derived from the SynopVis Grosswetterlagen catalogue (1981–2010). For this European example, the most widespread warming was found in summer, with up to 60% of the land area experiencing signicant warming during August, notably in Eastern and Northern Europe. In spring and autumn, this area was reduced to 10–30%. In December and January, only about 5% of the land area experienced signicant warming, most pronounced in northern Scandinavia. The probabilistic approach revealed that changes in synoptic circulation c ould not account for all the observed (WFDEI) warming, with the exception of regions in southeastern Europe in February and Western Europe in May. Signicant warming in other months and regions, such as the large-scale warming in April, June, July, August, and November, must also be caused by other factors. Within-type changes were conrmed for the Black Sea region in November, where the magnitude of a widespread temperature trend was strongest. This European example contributes to an improved understanding of the causes of recent temperature change by assessing the relative role of synoptic circulation changes and within-type changes on regional-scale warming.

• Rydsaa, Johanne Hope; Stordal, Frode; Bryn, Anders & Tallaksen, Lena M. (2017). Effects of shrub and tree cover increase on the near-surface atmosphere in northern Fennoscandia. Biogeosciences.  ISSN 1726-4170.  14(18), s 4209- 4227 . doi: 10.5194/bg-14-4209-2017 Fulltekst i vitenarkiv.
• Stagge, James Howard; Kingston, Daniel G.; Tallaksen, Lena M. & Hannah, David M. (2017). Observed drought indices show increasing divergence across Europe. Scientific Reports.  ISSN 2045-2322.  7(1) . doi: 10.1038/s41598-017-14283-2 Fulltekst i vitenarkiv.
• van Lanen, Henny, A.J.; Laaha, Gregor; Kingston, Daniel; Gauster, Tobias; Ionita, Monica; Vidal, Jean-Philippe; Vlnas, Radek; Tallaksen, Lena M.; Stahl, Kerstin; Hannaford, Jamie; Delus, Claire; Fendekova, Miriam; Mediero, Luis; Prudhomme, Christel; Rets, Ekaterina; Romanowicz, Renata J.; Gailliez, Sébastien; Wong, Wai Kwok; Adler, Mary-Jeanne; Blauhut, Veit; Caillouet, Laurie; Chelcea, Silvia; Frolova, Natalia; Gudmundsson, Lukas; Hanel, Martin; Haslinger, Klaus; Kireeva, Maria; Osuch, Marzena; Sauquet, Eric; Stagge, James Howard & Van Loon, Anne F. (2016). Hydrology needed to manage droughts: the 2015 European case. Hydrological Processes.  ISSN 0885-6087.  30(17), s 3097- 3104 . doi: 10.1002/hyp.10838 Fulltekst i vitenarkiv.
• Blauhut, Veit; Stahl, Kerstin; Stagge, James Howard; Tallaksen, Lena M.; Stefano, Lucia De & Vogt, Jürgen V. (2016). Estimating drought risk across Europe from reported drought impacts, drought indices, and vulnerability factors. Hydrology and Earth System Sciences.  ISSN 1027-5606.  20(7), s 2779- 2800 . doi: 10.5194/hess-20-2779-2016
• Hegdahl, Trine Jahr; Tallaksen, Lena M.; Engeland, Kolbjørn; Burkhart, John & Xu, Chong-Yu (2016). Discharge sensitivity to snowmelt parameterization: A case study for Upper Beas basin in Himachal Pradesh, India. Hydrology Research.  ISSN 1998-9563.  47(4), s 683- 700 . doi: 10.2166/nh.2016.047
• Stagge, James Howard; Tallaksen, Lena M.; Gudmundsson, Lukas; Van Loon, Anne F. & Stahl, Kerstin (2016). Response to comment on 'Candidate Distributions for Climatological Drought Indices (SPI and SPEI)'. International Journal of Climatology.  ISSN 0899-8418.  36(4), s 2132- 2138 . doi: 10.1002/joc.4564
• Stahl, Kerstin; Kohn, Irene; Blauhut, Veit; Urquijo, Julia; De Stefano, Lucia; Acacio, Vanda; Dias, Susana; Stagge, James Howard; Tallaksen, Lena M.; Kampragou, Eleni; Van Loon, Anne F.; Barker, Lucy J; Melsen, Lieke A; Bifulco, Carlo; Musolino, Dario; De Carli, Alessandro; Massarutto, Antonio; Assimacopoulos, Dionysis & Van Lanen, Henny A. J. (2016). Impacts of European drought events: Insights from an international database of text-based reports. Natural hazards and earth system sciences.  ISSN 1561-8633.  16(3), s 801- 819 . doi: 10.5194/nhess-16-801-2016
• Van Loon, Anne F.; Gleeson, Tom; Clark, Julian; Van Dijk, Albert I. J. M.; Stahl, Kerstin; Hannaford, Jamie; Baldassarre, Giuliano Di; Teuling, Adriaan J.; Tallaksen, Lena M.; Uijlenhoet, Remko; Hannah, David M.; Sheffield, Justin; Svoboda, Mark; Verbeiren, Boud; Wagener, Thorsten; Rangecroft, Sally; Wanders, Niko & van Lanen, Henny, A.J. (2016). Drought in the Antropocene. Nature Geoscience.  ISSN 1752-0894.  9(2), s 89- 91 . doi: 10.1038/ngeo2646
• Van Loon, Anne F.; Stahl, Kerstin; Di Baldassarre, Giuliano; Clark, Julian; Rangecroft, Sally; Wanders, Niko; Gleeson, Tom; Van Dijk, Albert I. J. M.; Tallaksen, Lena M.; Hannaford, Jamie; Uijlenhoet, Remko; Teuling, Adriaan J.; Hannah, David M.; Sheffield, Justin; Svoboda, Mark; Verbeiren, Boud; Wagener, Thorsten & Van Lanen, Henny A. J. (2016). Drought in a human-modified world: Reframing drought definitions, understanding, and analysis approaches. Hydrology and Earth System Sciences.  ISSN 1027-5606.  20(9), s 3631- 3650 . doi: 10.5194/hess-20-3631-2016
• Bartholomeus, Ruud; Stagge, James Howard; Tallaksen, Lena M. & Witte, J.P.M. (2015). Sensitivity of potential evaporation estimates to 100 years of climate variability. Hydrology and Earth System Sciences.  ISSN 1027-5606.  19(2), s 997- 1014 . doi: 10.5194/hess-19-997-2015
• Fleig, Anne Kristina; Tallaksen, Lena M.; James, Philip; Hisdal, Hege & Stahl, Kerstin (2015). Attribution of European precipitation and temperature trends to changes in synoptic circulation. Hydrology and Earth System Sciences.  ISSN 1027-5606.  19(7), s 3093- 3107 . doi: 10.5194/hess-19-3093-2015
• Kingston, Daniel; Stagge, James Howard; Tallaksen, Lena M. & Hannah, David M. (2015). European-scale drought: Understanding connections between atmospheric circulation and meteorological drought indices. Journal of Climate.  ISSN 0894-8755.  28(2), s 505- 516 . doi: 10.1175/JCLI-D-14-00001.1
• Li, Hong; Xu, Chong-Yu; Beldring, Stein; Tallaksen, Lena M. & Jain, Sharad K. (2015). Water Resources Under Climate Change in Himalayan Basins. Water resources management.  ISSN 0920-4741.  30(2), s 843- 859 . doi: 10.1007/s11269-015-1194-5
• Ngongondo, Cosmo; Xu, Chong-Yu; Tallaksen, Lena M. & Alemaw, B. (2015). Observed and simulated changes in the water balance components over Malawi, during 1971-2000. Quaternary International.  ISSN 1040-6182.  369, s 7- 16 . doi: 10.1016/j.quaint.2014.06.028
• Rydsaa, Johanne Hope; Stordal, Frode & Tallaksen, Lena M. (2015). Sensitivity of the regional European boreal climate to changes in surface properties resulting from structural vegetation perturbations. Biogeosciences.  ISSN 1726-4170.  12(10), s 3071- 3087 . doi: 10.5194/bg-12-3071-2015
• Stagge, James Howard; Kohn, Irene; Tallaksen, Lena M. & Stahl, Kerstin (2015). Modeling drought impact occurrence based on meteorological drought indices in Europe. Journal of Hydrology.  ISSN 0022-1694.  530, s 37- 50 . doi: 10.1016/j.jhydrol.2015.09.039
• Stagge, James Howard; Tallaksen, Lena M.; Gudmundsson, Lukas; Van Loon, Anne F. & Stahl, Kerstin (2015). Candidate Distributions for Climatological Drought Indices (SPI and SPEI). International Journal of Climatology.  ISSN 0899-8418.  35(13), s 4027- 4040 . doi: 10.1002/joc.4267
• Stahl, Kerstin; Kohn, I.; De Stefano, L.; Tallaksen, Lena M.; Rego, F.C.; Seneviratne, S.I.; Andreu, J. & van Lanen, Henny, A.J. (2015). An impact perspective on pan-European drought sensitivity, In Joaquin Andreu Alvarez; Abel Solera; Javier Paredes-Arquiola; David Haro-Monteagudo & Henny van Lanen (ed.),  Drought: research and science-policy interfacing.  CRC Press.  ISBN 978-1-138-02779-4.  Chapter 48.  s 329 - 334
• Tallaksen, Lena M.; Stagge, James Howard; Stahl, Kerstin; Gudmundsson, Lukas; Orth, Rene; Seneviratne, Sonia I.; Van Loon, Anne F. & van Lanen, Henny, A.J. (2015). Characteristics and drivers of drought in Europe—a summary of the DROUGHT-R&SPI project, In Joaquin Andreu Alvarez; Abel Solera; Javier Paredes-Arquiola; David Haro-Monteagudo & Henny van Lanen (ed.),  Drought: research and science-policy interfacing.  CRC Press.  ISBN 978-1-138-02779-4.  Chapter 2.  s 15 - 21
• van Lanen, Henny, A.J.; Tallaksen, Lena M.; Assimacopoulos, Dionysis; Stahl, Kerstin; Wolters, Wouter; Andreu, Joaquin; Seneviratne, Sonia I.; De Stefano, Lucia; Seidl, Irmi; Rego, Francisco Castro; Massarutto, Antonio & Garnier, Emmanuel (2015). Fostering Drought Research and Science-Policy Interfacing: Achievements of the DROUGHT-R&SPI project, In Joaquin Andreu Alvarez; Abel Solera; Javier Paredes-Arquiola; David Haro-Monteagudo & Henny van Lanen (ed.),  Drought: research and science-policy interfacing.  CRC Press.  ISBN 978-1-138-02779-4.  Introduction.  s 3 - 12
• Ngongondo, Cosmo; Tallaksen, Lena M. & Xu, Chong-Yu (2014). Growing season length and rainfall extremes analysis in Malawi. IAHS-AISH publication.  ISSN 0144-7815.  363, s 361- 366
• Nilsen, Irene Brox; Fleig, Anne K.; Tallaksen, Lena M. & Hisdal, Hege (2014). Recent trends in monthly temperature and precipitation patterns in Europe. IAHS-AISH publication.  ISSN 0144-7815.  363, s 132- 137
• Stagge, James Howard; Tallaksen, Lena M.; Xu, Chong-Yu & van Lanen, Henny, A.J. (2014). Standardized precipitation-evapotranspiration index (SPEI): Sensitivity to potential evapotranspiration model and parameters. IAHS-AISH publication.  ISSN 0144-7815.  363, s 367- 373
• Stahl, Kerstin; Vidal, J.P.; Hannaford, J.; Prudhomme, C.; Laaha, G. & Tallaksen, Lena M. (2014). Synthesizing changes in low flows from observations and models across scales. IAHS-AISH publication.  ISSN 0144-7815.  363, s 30- 35
• Tallaksen, Lena M. & Stahl, Kerstin (2014). Spatial and temporal patterns of large-scale droughts in Europe: Model dispersion and performance. Geophysical Research Letters.  ISSN 0094-8276.  41(2), s 429- 434 . doi: 10.1002/2013GL058573
• Van Lanen, H.A.J.; Demuth, Siegfried; Daniell, Trevor; Hannah, David M.; Laaha, Gregor; Mahé, Gil & Tallaksen, Lena M. (2014). Over 25 years of FRIEND-Water: an overview.. IAHS-AISH publication.  ISSN 0144-7815.  363, s 1- 7
• Hannaford, J.; Buys, G.; Stahl, Kerstin & Tallaksen, Lena M. (2013). The influence of decadal-scale variability on trends in long European streamflow records. Hydrology and Earth System Sciences.  ISSN 1027-5606.  17(7), s 2717- 2733 . doi: 10.5194/hess-17-2717-2013
• Kingston, Daniel; Fleig, Anne K.; Tallaksen, Lena M. & Hannah, David M. (2013). Ocean-Atmosphere Forcing of Summer Streamflow Drought in Great Britain. Journal of Hydrometeorology.  ISSN 1525-755X.  14(1), s 331- 344 . doi: 10.1175/JHM-D-11-0100.1
• Laaha, Gregor; Demuth, Siegfried; Hisdal, Hege; Kroll, C.N.; van Lanen, Henny, A.J.; Nester, T.; Rogger, M.; Sauquet, E.; Tallaksen, Lena M.; Woods, R.A. & Young, A. (2013). Prediction of low flows in ungauged basins, In Günter Blöschl; Murugesu Sivapalan; Thorsten Wagener; Alberto Viglione & Hubert Savenije (ed.),  Runoff Prediction in Ungauged Basins, Synthesis across Processes, Places and Scales,.  Cambridge University Press.  ISBN 978-1-107-02818-0.  Chapter 8.  s 163 - 188
• Ngongondo, Cosmo S Abdul; Xu, Chong-Yu; Tallaksen, Lena M. & Alemaw, Berhanu (2013). Evaluation of the FAO Penman-Montheith, Priestley-Taylor and Hargreaves models for estimating reference evapotranspiration in southern Malawi. Nordic Hydrology.  ISSN 0029-1277.  44(4), s 706- 722 . doi: 10.2166/nh.2012.224
• van Lanen, Henny, A.J.; Wanders, N.; Tallaksen, Lena M. & Loon, Anne van (2013). Hydrological drought across the world: impact of climate and physical catchment structure. Hydrology and Earth System Sciences.  ISSN 1027-5606.  17(5), s 1715- 1732 . doi: 10.5194/hess-17-1715-2013
• Gudmundsson, Lukas; Tallaksen, Lena M.; Stahl, Kerstin; Dumont, E.; Clark, D.B.; Hagemann, S.; Bertrand, N.; Gerten, D.; Hanasaki, N.; Heinke, J.; Voss, F. & Koirala, S. (2012). Comparing Large-Scale Hydrological Model Simulations to Observed Runoff Percentiles in Europe. Journal of Hydrometeorology.  ISSN 1525-755X.  13(2), s 604- 620 . doi: 10.1175/JHM-D-11-083.1
• Gudmundsson, Lukas; Wagener, Thorsten; Tallaksen, Lena M. & Engeland, Kolbjørn (2012). Evaluation of nine large-scale hydrological models with respect to the seasonal runoff climatology in Europe. Water Resources Research.  ISSN 0043-1397.  48(11) . doi: 10.1029/2011WR010911 Vis sammendrag

  Large-scale hydrological models, simulating the terrestrial water cycle on continental and global scales, are fundamental for many studies in earth system sciences. However, due to imperfect knowledge of real world systems, the models cannot be expected to capture all aspects of large-scale hydrology equally well. To gain insights in the strengths and shortcomings of nine large-scale hydrological models, we assessed their ability to capture the mean annual runoff cycle. Unlike most other studies that rely on discharge observations from continental scale river basins, our study is based on observed runoff from a large number of small, near-natural catchments in Europe. We evaluated the models’ ability to capture the average magnitude, the amplitude, as well as the timing of the mean annual runoff cycle. Our study revealed large uncertainties when modeling runoff from these small catchments. We identified large differences in model performance, however, the ensemble mean (mean of all model simulations) yielded rather robust predictions. Model performance varied systematically with climatic conditions and was best in regions with little influence of snow. In cold regions, many models exhibited low correlations between observed and simulated mean annual cycles, which can be associated with shortcomings in simulating the timing of snow accumulation and melt. Local (grid cell) scale differences between observed and simulated runoff can be large and local biases often exceeded 100%. These local uncertainties are contrasted by a relatively good regional average performance, ultimately reflecting the purpose of the models, i.e., to capture regional hydroclimatology.

• Stahl, Kerstin; Tallaksen, Lena M.; Hannaford, J. & van Lanen, Henny, H.A.J. (2012). Filling the white space on maps of European runoff trends: estimates from a multi-model ensemble. Hydrology and Earth System Sciences.  ISSN 1027-5606.  16(7), s 2035- 2047 . doi: 10.5194/hess-16-2035-2012
• Fleig, Anne Kristina; Tallaksen, Lena M.; Hisdal, Hege & Hannah, David M. (2011). Regional hydrological drought in north-western Europe: linking a new Regional Drought Area Index with weather types. Hydrological Processes.  ISSN 0885-6087.  25(7), s 1163- 1179 . doi: 10.1002/hyp.7644
• Gudmundsson, Lukas; Tallaksen, Lena M.; Stahl, Kerstin & Fleig, Anne Kristina (2011). Low-frequency variability of European runoff. Hydrology and Earth System Sciences.  ISSN 1027-5606.  15(9), s 2853- 2869 . doi: 10.5194/hess-15-2853-2011
• Stahl, Kerstin; Tallaksen, Lena M.; Gudmundsson, Lukas & Christensen, Jens H. (2011). Streamflow Data from Small Basins: A Challenging Test to High-Resolution Regional Climate Modeling. Journal of Hydrometeorology.  ISSN 1525-755X.  12(5), s 900- 912 . doi: 10.1175/2011JHM1356.1
• Gudmundsson, Lukas; Tallaksen, Lena M. & Stahl, Kerstin (2011). Spatial cross-correlation patterns of European low, mean and high flows. Hydrological Processes.  ISSN 0885-6087.  25(7), s 1034- 1045 . doi: 10.1002/hyp.7807
• Harding, R.; Best, M.; Blyth, E.; Hagemann, S.; Kabat, P.; Tallaksen, Lena M.; Warnaars, T.; Wiberg, D.; Weedon, G.P.; van Lanen, Henny, A.J.; Ludwig, F. & Haddeland, I. (2011). Current knowledge of the terrestrial Global Water Cycle. Journal of Hydrometeorology.  ISSN 1525-755X.  12(6), s 1149- 1156 . doi: 10.1175/JHM-D-11-024.1
• Harding, Richard; Best, Martin; Blyth, Eleanor; Hagemann, Stefan; Kabat, Pavel; Tallaksen, Lena M.; Warnaars, Tanya; Wiberg, David; Weedon, Graham P; van Lanen, Henny; Ludwig, Fulco & Haddeland, Ingjerd (2011). WATCH: Current Knowledge of the Terrestrial Global Water Cycle. Journal of Hydrometeorology.  ISSN 1525-755X.  12(6), s 1149- 1156 . doi: 10.1175/JHM-D-11-024.1
• Morawietz, Martin; Xu, Chong-Yu; Gottschalk, Lars & Tallaksen, Lena M. (2011). Systematic evaluation of autoregressive error models as post-processors for a probabilistic streamflow forecast system. Journal of Hydrology.  ISSN 0022-1694.  407(1-4), s 58- 72 . doi: 10.1016/j.jhydrol.2011.07.007
• Ngongondo, Cosmo S Abdul; Xu, Chong-Yu; Tallaksen, Lena M.; Alemaw, Berhanu & Chirwa, Tobias (2011). Regional frequency analysis of rainfall extremes in Southern Malawi using the index rainfall and L-moments approaches. Stochastic environmental research and risk assessment (Print).  ISSN 1436-3240.  25(7), s 939- 955 . doi: 10.1007/s00477-011-0480-x
• Staudinger, M.; Stahl, Kerstin; Seibert, J.; Clark, M.P. & Tallaksen, Lena M. (2011). Comparison of hydrological model structures based on recession and low flow simulations. Hydrology and Earth System Sciences.  ISSN 1027-5606.  15, s 3447- 3459 . doi: 10.5194/hess-15-3447-2011
• Fleig, Anne Kristina; Tallaksen, Lena M.; Hisdal, Hege; Stahl, Kerstin & Hannah, David M. (2010). Inter-comparison of weather and circulation type classifications for hydrological drought development. Physics and Chemistry of the Earth.  ISSN 1474-7065.  35(9-12), s 507- 515 . doi: 10.1016/j.pce.2009.11.005
• Hannah, D.M.; Demuth, S.; van Lanen, Henny, A.J.; Looser, U.; Prudhomme, C.; Rees, G.; Stahl, Kerstin & Tallaksen, Lena M. (2010). A review of the status, research opportunities and future of large-scale river flow archives. IAHS-AISH publication.  ISSN 0144-7815.  340, s 584- 590
• Kingston, Daniel; Fleig, Anne K.; Tallaksen, Lena M. & Hannah, David M. (2010). North Atlantic sea surface temperature, atmospheric circulation and summer drought in Great Britain. IAHS-AISH publication.  ISSN 0144-7815.  340, s 598- 604

Se alle arbeider i Cristin

• Keetz, Lasse Torben; Bryn, Anders; Horvath, Peter; Skarpaas, Olav; Tallaksen, Lena M. & Zliobaite, Indre (2021). Using machine learning to model the distribution of Vegetation Types across Norway.
• 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.
• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Filhol, Simon Vincent P; Stordal, Frode & Tallaksen, Lena M. (2020). Scandinavian snow cover phenology from MODIS, CLM, and reanalyses.
• 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. Vis sammendrag

  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.

• Yilmaz, Yeliz; Tallaksen, Lena M. & Stordal, Frode (2020). Hydroclimatological evaluation of CLM5 simulations using multiple data sources for land-atmosphere interaction studies over Scandinavia. Vis sammendrag

  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.

• Pirk, Norbert; Ramtvedt, Eirik Næsset; Decker, Sven; Cassiani, Massimo; Burkhart, John; Stordal, Frode & Tallaksen, Lena M. (2019). Causes of surface energy imbalances of eddy covariance measurements in mountainous terrain.
• Silantyeva, Olga; Burkhart, John; Tallaksen, Lena M.; Helset, Sigbjørn & Skavhaug, Ola (2019). Shyft - Hydrologic Forecasting Toolbox: current state and future work.
• Silantyeva, Olga; Tallaksen, Lena M. & Burkhart, John (2019). Understanding terrain topography impact on snowmelt at catchment scale.
• Silantyeva, Olga; Tallaksen, Lena M.; Burkhart, John; Skavhaug, Ola & Helset, Sigbjørn (2019). Analysis on the added value of accounting for slope/aspect and shading effects in hydrologic simulations.
• Yilmaz, Yeliz; Tallaksen, Lena M. & Stordal, Frode (2019). Assessment of the water and energy balance simulations of CTSM using satellite-based observations over Scandinavia.
• Haugnes, Gunhild M.; Tallaksen, Lena M.; Vogt, Rolf David; Storelvmo, Trude; Hessen, Dag Olav; Stordal, Frode; Lefevre, Sjannie; Kääb, Andreas & Uggerud, Einar (2018, 27. august). Klimaforskerne tar temperaturen på tropesommeren. [Tidsskrift].  Titan.uio.no.
• Burkhart, John; Decker, Sven; Filhol, Simon; Hulth, John; Nesje, Atle; Schuler, Thomas; Sobolowski, Stefan Pieter & Tallaksen, Lena M. (2017). Development of the Finse Alpine Research Station towards a platform for multi-disciplinary research on Land-Atmosphere Interaction in Cold Environments (LATICE).
• Nilsen, Irene Brox; Tallaksen, Lena M. & Stordal, Frode (2017). Potential feedbacks between snow cover, soil moisture and surface energy fluxes in Southern Norway. Vis sammendrag

  At high latitudes, the snow season has become shorter during the past decades because snowmelt is highly sensitive to a warmer climate. Snowmelt influences the energy balance by changing the albedo and the partitioning between latent and sensible heat fluxes. It further influences the water balance by changing the runoff and soil moisture. In a previous study, we identified southern Norway as a region where significant temperature changes in summer could potentially be explained by land-atmosphere interactions. In this study we hypothesise that changes in snow cover would influence the summer surface fluxes in the succeeding weeks or months. The exceptionally warm summer of 2014 was chosen as a test bed. In Norway, evapotranspiration is not soil moisture limited, but energy limited, under normal conditions. During warm summers, however, such as in 2014, evapotranspiration can be restricted by the available soil moisture. Using the Weather Research and Forecasting (WRF) model we replace the initial ground conditions for 2014 with conditions representative of a snow-poor spring and a snow-rich spring. WRF was coupled to Noah-MP at 3 km horizontal resolution in the inner domain, and the simulations covered mid-May through September 2014. Boundary conditions used to force WRF were taken from the Era-Interim reanalysis. Snow, runoff, soil moisture and soil temperature observational data were provided by the Norwegian Water Resources and Energy Directorate for validation. The validation shows generally good agreement with observations. Preliminary results show that the reduced snowpack, hereafter “sim1” increased the air temperature by up to 5 K and the surface temperature by up to 10 K in areas affected by snow changes. The increased snowpack, hereafter “sim2”, decreased the air and surface temperature by the same amount. These are weekly mean values for the first eight simulation weeks from mid May. Because of the higher net energy available (∼ 100 Wm-2) in sim 1, both the evapotranspiration and sensible heat fluxes increased. In sim 2, they decreased because of lower net energy. The ground heat flux decreased in sim1 (and increased in sim2). Large increases were seen in runoff, both surface and underground runoff, during the first weeks of sim2 (from mid May), but the timing of snowmelt was only slightly affected. This study contributes to a greater understanding of land-atmosphere interactions in a wet, temperate climate, in particular the role of snow cover (and snowmelt) and its feedback to the atmosphere.

• Rydsaa, Johanne Hope; Stordal, Frode; Bryn, Anders & Tallaksen, Lena M. (2017). Effects of shrub cover changes on the near surface atmosphere in northern Fennoscandia: A model study..
• Burkhart, John; Schuler, Thomas; Tallaksen, Lena M.; Filhol, Simon; Hulth, John & Decker, Sven (2016). Snow model validation in Norway at the Land Atmosphere Interaction in Cold Environments (LATICE) Finse site.
• Holter, Øystein Gullvåg; Liestøl, Knut; Tallaksen, Lena M. & Kristensen, Solveig (2016). Universitetene er sterkt konkurransedrevet. I dette løpet taper kvinnene. Kronikk Aftenposten 7.3.2016 http://www.aftenposten.no/meninger/kronikker/Kronikk-Universitetene-er-sterk t-konkurransedrevet-I-dette-lopet-taper-kvinnene-8380246.html. Aftenposten (morgenutg. : trykt utg.).  ISSN 0804-3116.
• Nilsen, Irene Brox; Stagge, James Howard & Tallaksen, Lena M. (2016). A probabilistic approach to attribute warming to changes in atmospheric circulation. Vis sammendrag

  Europe has been warming over the past decades, especially in southern Europe in summer and northern Europe in winter. To understand the causes of regional warming, it is common to separate the temperature change signal into changes in atmospheric circulation (or dynamic causes) and other factors, so-called within-type changes (or thermodynamic causes). For example, increasing temperatures due to greenhouse gases may alter the position and strength of the polar jet stream, thus causing a change in the atmospheric circulation signal. On the other hand, warming may be entirely independent of circulation, occurring as a general increase in surface temperature. With the aim to detect regions and time of the year in Europe in which recent warming can either be explained by changes in atmospheric circulation or by within-type changes, we suggest a novel probabilistic approach to calculate the circulation-induced trend, the part of the temperature trend that is induced by changes in atmospheric circulation. Through the use of resampling, in combination with a Monte Carlo test, we assessed the likelihood that the observed temperature trend can be explained entirely by changes in atmospheric circulation frequency. The temperature data originate from the gridded 0.5◦ Watch Forcing Data Era-Interim (WFDEI), and cover the period 1981–2010. The SynopVis Grosswetterlagen catalogue of circulation types was used to detect circulation-induced trends in the same time period. We analysed trends on the monthly time scale to reveal short-term responses, such as those related to snow or greening. The most wide-spread observed warming was found in summer, with up to 60% of the European land area experiencing a significant warming trend during August, most notable in eastern and northern Europe. In spring and autumn, the percent area with significant temperature increases reduced to 10–30%. In December and January, only 5% of the land area experienced significant warming, most pronounced in northern Scandinavia. The probabilistic approach revealed that changes in atmospheric circulation could not account for all the observed warming. Regions where the observed trend likely can be explained entirely by changes in atmospheric circulation include western Europe in May, eastern Europe in August and Scandinavia in September. In most of the regions and months experiencing significant trends, however, warming must be caused by other factors as well; such within-type changes potentially driven by feedbacks between the land surface and atmosphere. For two cases where the magnitude of the temperature trend was strongest, northern Scandinavia in December and in the Black Sea region in November, circulation types warmed over time. This confirms the role of within-type change, i.e., that circulation types changed their properties over time. This study provides an important contribution toward improved understanding of the causes of synoptic-scale temperature change in Europe, more specifically, the relative role of circulation-induced changes and within-type changes.

• Engeland, Kolbjørn; Tallaksen, Lena M.; Bakken, Tor Haakon & Killingtveit, Ånund (2015). Water footprint of hydro power in Norway. Vis sammendrag

  The IPCC Special Report on Renewable Energy (IPCC, 2012) assesses the potential for renewable energy sources to replace fossil-based fuels and benchmarks the technologies with respect to a set of criteria, including their water footprint measured as m3/MWh. While most of the renewable technologies show a typical range of 1-5 m3/MWh, the very sparse data on hydropower range from a minimum of 0.04 to a maximum of 209 m3/MWh. More recent studies on water footprint from hydropower indicate that the water consumption rates could go even far beyond the numbers published by IPCC (2012). The methodological approach behind these numbers are, however, criticized as it appears over-simplistic and several issues need to be defined and clarified in order to present the ’true picture’ of the water footprint of hydropower. Despite this, the rather high numbers for hydropower may imply a reputational risk for the sector and also be a direct investment risk in new projects if hydropower is considered a "large-scale water consumer". Estimation of water footprint has two important components (i) definition of water footprint (including system boundaries), and (ii) estimation of evaporation, which is assumed to constitute the main water loss from hydropower. Here we will mainly address the second topic and have chosen to use a water footprint definition based on net evapotranspiration from reservoirs. Thus, we need estimates of evapotranspiration from the land surface prior to inundation and the evaporation from the reservoir after it has been filled up. The primary objective of the study is to estimate water footprint of hydropower in Norway and in particular to answer the following questions: (i) How does different environmental variables influence water footprint estimation in Norway?, and in particular (ii) What is the total/specific water footprint from Norwegian hydropower production? To answer these questions we tested how environmental variables like climate and vegetation characteristics influence the estimated net evaporation and water footprint estimates by systematically varying their values. The water footprint was estimated for a subset of hydropower complex for which GIS data sets with land use prior to construction of reservoirs were available. The presentation will focus on the differences in evaporation from reservoirs and evapotranspiration from various land surfaces.

• Nilsen, Irene Brox; Tallaksen, Lena M. & Stagge, James Howard (2015). A probabilistic method of calculating circulation-induced trends. Vis sammendrag

  The water cycle in Europe has changed substantially over the past three decades. Increasing runoff is observed during winter and at northern latitudes in particular. Spring and summer months, as well as southern latitudes, are facing drier conditions. To understand what is driving large-scale changes in runoff, we look into changes in precipitation and temperature and link these to changes in atmospheric circulation. Previous studies have used the method of trend ratios (Cahynová and Huth, 2009) to attribute precipitation and temperature trends to changes in the frequency of circulation types. A trend ratio is the ratio of hypothetical trend, i.e., the trend that would result due to changes in circulation type frequency only, to the observed trend. However, the method of trend ratios has two drawbacks. First, if the observed trend is small, division by a very low value results in a meaningless trend ratio and thus requires a cut-off value to keep the trend ratio within meaningful boundaries. Second, the method does not allow a comparison of the observed trend to the spread of possible outcomes, because the method of hypothetical trends is based on a deterministic model. We propose a new, more robust method for detecting the importance of circulation-induced changes in explaining the observed trends, which has the benefit of being a non-parametric statistical test that assesses the entire range of hypothetical trends. Instead of creating a hypothetical series by replacing the observation on a given day with the long-term climatic mean of a certain month and circulation type (as in the existing trend ratio method), the new approach replaces the observation on a given day with a random sample from the distribution of the variable for the given month and circulation type. The method introduces the possibility to assign a rejection rate, thus allowing statistical significance to be assessed. We apply the method on time series of precipitation and temperature from the gridded 0.5 degree WFDEI dataset, covering Europe (40-65N, 10W-30E). The SynopVis Grosswetterlagen catalogue of circulation types for the time period 1981-2010, the same period as the climatic data, is used. The new approach is used to map in which regions and months changes in atmospheric circulation is the dominating factor controlling changes in precipitation and temperature in Europe.

• Stahl, Kerstin; Kohn, I.; De Stefano, L.; Tallaksen, Lena M.; Rego, F.C.; Seneviratne, S.I.; Andreu, J. & van Lanen, Henny, A.J. (2015). An impact perspective on pan-European drought sensitivity.
• Tallaksen, Lena M.; Stagge, James Howard; Stahl, Kerstin; Gudmundsson, Lukas; Orth, Rene; Seneviratne, Sonja; Van Loon, Anne F. & van Lanen, Henny, A.J. (2015). Characteristics and drivers of drought in Europe – a summary of the DROUGHT-R&SPI project.
• van Lanen, Henny, A.J.; Tallaksen, Lena M.; Assimacopoulos, Dionysis; Stahl, Kerstin; Wolters, Wouter; Andreu, Joaquin; Seneviratne, Sonia I.; De Stefano, Lucia; Seidl, Irmi; Rego, Francisco Castro; Massarutto, Antonio & Garnier, Emmanuel (2015). Fostering Drought Research and Science-Policy Interfacing: Achievements of the DROUGHT-R&SPI project.
• Nilsen, Irene Brox; Tallaksen, Lena M.; Hisdal, Hege & Fleig, Anne Kristina (2014). Regional precipitation and temperature trend patterns in Europe (presentasjon av Paper I: Recent trends in monthly temperature and precipitation patterns in Europe).
• Nilsen, Irene Brox & Tallaksen, Lena M. (2014). Temperature changes in Norway: Recent increases in WFDEI validated against interpolated observations. Vis sammendrag

  Increased global temperatures have been observed during the past decades, and trends are expected to be greatest at high latitudes because of the polar amplification. Polar amplification may be caused by feedbacks between the atmosphere and the surface, such as the ice–albedo feedback: when increased temperatures cause increased snow melting, areas with a lower albedo are exposed and more radiation is absorbed. Thus, the temperature increase is enhanced. In a previous study, we analysed precipitation and temperature trends for the period 1979–2009 using gridded, bias-corrected re-analysis data from the WATCH Forcing Data Era-Interim (WFDEI). The data used consisted of daily temperature and precipitation data from 1 January 1979 to 31 December 2009 (31 years) and covered 34◦ –72◦ N and 13◦ W–32◦ E with a spatial resolution of 0.5◦ × 0.5◦ . Temperature and precipitation trends covering all of Europe were mapped using the Theil-Sen slope as a robust trend estimator. We found the greatest warming in Europe in the northernmost parts of Norway during December and January. The temperature trends for certain months and regions were as high as 8 ◦ C. In this study, monthly temperature trends from WFDEI will be compared with and validated against a daily interpolated dataset for Norway (presented at www.seNorge.no). This dataset has a spatial resolution of 1 × 1 km and covers mainland Norway. Residual kriging is applied to the data to ensure stationarity and remove bias. The daily data will be aggregated to the monthly time scale and monthly temperature trends will be calculated using the Theil-Sen slope for the period 1979–2009. The results will be compared visually with the WFDEI trends covering Norway. In addition, the distribution of trends as well as the fraction of positive and negative trends in the two datasets will be compared.

• Tallaksen, Lena M. & Nilsen, Irene Brox (2014). Norge er i gjennomsnitt blitt mer enn to grader varmere fra 1979 til 2009. Aftenposten Vitenskap.  ISSN 2464-3033. Vis sammendrag

  Den største oppvarmingen finner vi om vinteren, med hele fem grader i januar. Har vi kunnskapen og beredskapen til å møte konsekvensene?

• Stagge, James Howard; Tallaksen, Lena M.; Kohn, Irene; Stahl, Kerstin & Loon, Anne van (2013). A European Drought Reference Database: Design and Online Implementation.
• Gudmundsson, Lukas; Tallaksen, Lena M. & Stahl, Kerstin (2011). Projected changes in future runoff variability - a multi model analysis using the A2 emission scenario. WATCH Technical Report. 49.
• Hannah, David M.; Demuth, Siegfried; van Lanen, Henny; Looser, Ulrich; Prudhomme, Christel; Rees, Gwyn; Stahl, Kerstin & Tallaksen, Lena M. (2011). Large-scale river flow archives: importance, current status and future needs. Hydrological Processes.  ISSN 0885-6087.  25(7), s 1191- 1200 . doi: 10.1002/hyp.7794
• Stahl, Kerstin; Tallaksen, Lena M.; Hannaford, J. & van Lanen, Henny, A.J. (2011). Abflusstrends in Europa: Vergleich eines Multi-Modell-Experiments mit Beobachtungen.
• Tallaksen, Lena M.; Stahl, Kerstin & Wong, G. (2011). Space-time characteristics of large-scale droughts in Europe derived from streamflow observations and WATCH multi-model simulations. WATCH Technical Report. 48.
• Fleig, Anne Kristina; James, Paul; Hagemann, Stefan & Tallaksen, Lena M. (2010). Weather type frequencies in ECHAM5/MPI-OM simulations for the 20th and 21st century and an application to hydrological drought.
• Gudmundsson, Lukas; Tallaksen, Lena M.; Stahl, Kerstin & Fleig, Anne Kristina (2010). Low-frequency Variability of European Runoff.
• Fleig, Anne K.; James, Paul; Hagemann, Stefan & Tallaksen, Lena M. (2010). Circulation type frequencies in GCM simulations and an application to hydrological drought.
• Fleig, Anne K.; Kingston, Daniel G.; Tallaksen, Lena M. & Hannah, David M. (2010). Ocean-atmosphere conditions associated with hydrological drought in Britain.
• Fleig, Anne K.; Tallaksen, Lena M.; Hisdal, Hege & Hannah, David M. (2010). Regional hydrological drought in north-western Europe and associated weather types.
• Fox Maule, C.; Svendsen, S.H.; Thejll, P.; Cristensen, J.H.; Tallaksen, Lena M. & van Lanen, Henny, A.J. (2010). Applying the Palmer Drought Severity Index to regional climate models.
• Gudmundsson, Lukas; Tallaksen, Lena M. & Stahl, Kerstin (2010). Large-scale patterns of wetness and drought of European streamflow on inter-annual to decadal time scales.
• Gudmundsson, Lukas; Wagener, Thorsten; Tallaksen, Lena M. & Engeland, Kolbjørn (2010). Evaluation of a multi-model ensemble to observed spatially distributed runoff.

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