| Summary: | The most significant changes in climate, due to the well-known enhanced greenhouse effect, are generally expected to occur at northern high latitudes. Sub-arctic environments, that are dominated by the presence of a seasonal snow cover, may therefore be particularly sensitive to global warming. Due to changes in albedo and the amount of freshwater runoff towards the Arctic Ocean, changes in the hydrological cycle of sub-arctic areas may also provide a feedback to the global climate system. Understanding the hydrological processes operating in sub-arctic environments, and evaluating their sensitivity to climate change, is therefore an essential part of global change research. The main objective of the research presented in this thesis was to assess the sensitivity of the hydrological system of Northern Fennoscandia to human-induced climate changes. Considering the importance of snow coverage, snowmelt and evapotranspiration in sub-arctic hydrology and ecology, special attention was paid to the spatial distribution of these components of the water balance, in addition to river discharge. To achieve this objective, a series of studies was undertaken in the Tana Basin in northernmost Finland and Norway. Central to the approach was a large-scale hydrological model of the study area. Development and application of this model involved four steps: 1 Analysis of the hydrological system of the Tana Basin, at both small and large scales, using field measurements and satellite observations (chapters 2 to 4). 2 Application of an existing water balance model, developed for the River Rhine, to the sub-arctic Tana Basin, and evaluation of the model performance (chapters 5 and 6). 3 Development of physically-based process descriptions of snowmelt and evapotranspiration, that replaced the previous, empirical formulations in the model (chapter 7). 4 Simulation of the hydrological behaviour of the Tana Basin under conditions of climate change, by using this improved model version (chapter 8). The following sections summarise the ...
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