Multiscale Assessment of the Impacts of Climate Change on Water Resources in Tanzania

In the context of changing climate, this study assessed the impacts of the global warming on water resources in Tanzania for the mid-21^st century. Climate projections from six global circulation models under the most extreme emission scenario (RCP 8.5) were used as inputs to the Soil and Water Assessment Tool (SWAT) to examine the impacts. The results were analyzed both at spatial (country-level, watershed-level and subbasin-level) and temporal (annual and seasonal) scales concerning potential and actual evapotranspiration, surface runoff, water yield, and soil moisture. At the country-level, the results showed 0.8 to 27.4%, increase in annual precipitation, which led to a general increase in evapotranspiration (-2.2 to 7.3%), surface runoff (12.6 to 94.1%), water yield (7.5 to 73.4%) and soil moisture (2.9 to 20.7%). Watershed-level analysis showed 2.4 to 31.5%, -2.6 to 6.8%, 18.4 to 159.7%, and 3.2 to 22.8% change in average precipitation, evapotranspiration, surface runoff and soil moisture, respectively. While no distinct spatial trend was identified for evapotranspiration and surface runoff, soil moisture was projected to increase in the majority of the areas during both the wet and dry seasons. Probability analysis at the subbasin-level showed that less than 15% of the area, during the wet season,  experiencing decline in precipitation, soil moisture, potential and actual evapotranspiration, surface runoff and water yield, while less than 86% of the country experiencing decline during the dry season. Overall, the climate change was found to create a more favorable condition for agricultural production during the wet season by increasing the supply of water, but in the dry season, less favorable conditions were projected.