The Hydrology of Northern Eurasia: Uncertainty and Change in the Terrestrial Water and Energy Budgets

Changes in climate during the past century have been particularly pronounced in northern Eurasia, with documented warming in the atmosphere and increasing river discharge into the Arctic Ocean. Understanding and attributing the drivers of these changes has proven difficult because of the sparse observational network, harsh cli- mate, and complex terrain, such as permafrost. This dissertation investigates the uncertainty that exists in the estimates of the water and energy budgets at the land surface and then looks at the effects of climate change on the region's water and energy budgets.;Much of the literature has focused on documenting and explaining the trends rather than understanding the uncertainty that exists in current estimates of the mean hydroclimatology. Through the use of multiple sources of data, this dissertation shows there is significant disparities in the estimates of precipitation, evapotranspiration, runoff, and terrestrial water storage changes. The spread among the various data sets highlights the scientific community's inability to accurately characterize the hydroclimatology of this region, which is problematic because much attention has focused on hydrologic trends using these data sets. A methodology is developed that takes advantage of multiple sources of data and observed discharge to improve estimates of the water budget components.;The next study evaluates the role of winter precipitation and temperature on streamflow trends. Consistent trends are seen in both the in-situ observations and the model. Model experiments show that the interaction of changes in winter precipitation and temperature are causing changes in the snowpack, and the changes in the snowpack drive the modeled annual runoff trends. This leads to concerns for future trends as temperature is expected to continue to warm and winter precipitation is expected to continue to increase.;The third study compares station data and gridded radiation products from re-analysis and remote sensing. On annual time scales, most of the downward shortwave radiation products compare well with long-term station observations, but this agreement breaks down for downward longwave and upward shortwave and longwave radiation. Differences in radiative fluxes are on the order of 15-20 W/m2 on seasonal time scales. The resulting uncertainty in net radiation has implications for climate and hydrologic analyses that seek to understand changes in northern Eurasia's climate and its hydrologic cycle.;The warming of the air temperature has been accompanied by a warming of soil temperatures across northern Eurasia during the twentieth century. Using a land surface model, the final study finds that the soil column across northern Eurasia has accumulated, on average, 10 MJ/m2 between 1930 and 2006 with the majority of the soil heat accumulation occurring after 1980, indicating a change in the soil thermal regime due to an energy balance. Model experiments show that the heat accumulation is due to changes in annual air temperature and the seasonal snowpack: air temperature plays the largest role outside the permafrost zone and a lesser role over the permafrost. These results highlight the role of the land surface in storing heat as well as the vulnerability of the permafrost to degradation.;This dissertation finds that there is large uncertainty in our estimates of the water and energy budgets at the land surface, and therefore uncertainty in our understanding of the processes that drive these estimates. Despite the uncertainty, the drivers of hydrologic change can be isolated in a modeling framework. This dissertation finds that changes in the winter climate play a significant role in the changes in the water and energy cycle in this region.