Yeliz Yilmaz

The waters of the Euphrates and Tigris rivers have always been a vital resource in the water-food-energy nexus of the Middle East region. The currently ongoing Southeastern Anatolia Project (GAP) in Turkey aims to increase regional prosperity by optimizing the use of these waters for irrigation and hydropower. Since the beginning of the 1990s, the irrigation schemes and water management infrastructures within the scope of the GAP have caused significant land use and land cover (LULC) change in this semi-arid region. We employed a high resolution regional climate model to simulate the effects of irrigation induced LULC changes on the regional water and energy balances. For this purpose, historical simulations were conducted by using three land cover distributions which reflect the increase in irrigation and water surfaces. Our experiment reveals that water loss through evapotranspiration increases significantly with the areal expansion of irrigation. This increase is driven by the change in partitioning of the available energy at the surface between turbulent heat fluxes. On the one hand, a significant reduction in sensible heat flux causes local cooling by around 0.4 °C and 0.8 °C for the current and future irrigation conditions, respectively. On the other hand, the increase in latent heat flux enhances evapotranspiration and consequently atmospheric water vapor concentration. The moistening of a shallower boundary layer triggers the formation of convective clouds, which increases convective precipitation, most notably during the irrigation months. The enhanced water loss through evapotranspiration has potential to significantly alter the water budget of the GAP region. It seems that the water surplus of the headwaters region may not be enough to meet the water deficit of the GAP region in the future if the planned irrigation schemes are carried out to completion.

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.