Assessing the Impacts of Climate Change on River Basin Management: A New Method with Application to the Nile River
Tidwell, Amy C.
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A framework is developed for the assessment of climate change impacts on water resources systems. The applied techniques include: quantifying global climate model (GCM) skill over a range of time scales; developing future climate scenarios based on GCM data that are found to skillfully represent the observed climate over an historical baseline period; and using the climate scenarios together with hydrologic and water resources models to make assessments of the potential impacts and implications of climate change on water resources systems. A statistical analysis of GCM skill in East Africa shows that temperature is well represented in the GCMs at monthly to annual time scales. Precipitation is found to be much less reliable in the models and shows skill in fewer seasons and nodes than temperature. Eight climate scenarios, stemming from three global climate models and two atmospheric emissions scenarios, project temperature increases between 2 and 5 ° Celsius by the year 2080. Precipitation projections vary widely across models as well as regionally. The scenarios project changes in precipitation from -38% to +42%. The climate change impact methodology is applied to the Nile River Basin. It is shown that, in spite of widely varying precipitation projections, the major sub-basins of the Nile River will experience decreases in watershed runoff under all eight climate scenarios. Detailed water resources models are employed to assess the system wide response to the climate-induced hydrologic changes. The assessments indicate that water supply deficits will emerge by 2030 and continue to grow in frequency and magnitude by 2080. Additional impacts include reservoir depletion and reduced hydropower generation. An assessment of the river system response to basin development projects, including additional water storage and wetlands water conservation, indicates that adverse climate impacts may be mitigated for 30 to 40 years. The assessments demonstrate the relevance of climate change considerations to water resources management and the development of water policy.