| Summary: | The Arctic is considered to be particularly sensitive to global climate change. Global warming will seriously affect the components of the water balance in northern regions and changes in precipitation and temperature have immediate as well as long term effects on river systems. The main goal of this thesis was to assess the potential impact of climate change on the water balance and river discharge in the (sub)arctic Usa basin, East-European Russia on an annual, monthly and 5-daily basis. This enables the evaluation of 1) annual changes in the amount of river flow, 2) variations in timing and magnitude of discharge in various seasons, and 3) short-term responses in discharge to extreme events. To achieve these objectives a model is created with a monthly resolution for runoff simulation on seasonal scale (USAFLOW-1 and USAFLOW-2) and a model with a 5-daily resolution for the assessment of weekly runoff (USAFLOW-V). The models make optimal use of the available input data, have a model structure in which relevant processes are more adequately represented, and use parameters that are believed to be valid under present-day and future climate change conditions. The high sensitivity of the Arctic implies that impact of climate change and related environmental changes on river discharge can be considerable. The study shows that discharge in the Usa basin is highly sensitive to changes in precipitation and temperature. The effect of precipitation change is present throughout the year, while temperature changes affect discharge only in seasons when temperature fluctuates around the freezing point (April and October). Discharge is rather insensitive to changes in vegetation and permafrost. The impact study shows that annual discharge increases with up to 40% due to global warming. In case of a temperature increase of more than 8°C the (sub)arctic nival regime may give way to a pluvial discharge regime. The effects of climate change may be nonlinear and snowmelt runoff either increases or decreases depending on the amount ...
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