Assessing development and climate variability impacts on water resources in the Zambezi River basin. Simulating future scenarios of climate and development.

STUDY REGION: : The Zambezi River basin, a transboundary basin supplying vital resources to vast human and environmental systems and subject to radical changes linked to climate and infrastructural development. STUDY FOCUS: : Application of a hydrological model (Pitman) established for 76 sub-basins covering the total basin area of about 1 350 000 km2 to assess the potential impacts of increasing water demand under global warming scenarios (1.5, 2, and 3 degree). NEW HYDROLOGICAL INSIGHTS FOR THE REGION: : The application of the calibrated model to the analysis of different combinations of climate change and water use showed that the relative impacts are quite different across the whole Zambezi River basin. The greatest impacts are found in the areas containing large open water bodies (natural and man-made), that are very sensitive to the multiple effects of increased aridity. The uncertainty in the future simulation results remains hugely dependent upon the source of the climate change data and the change signals given by them. The sample RCM data (6 models) used are representative of many more model outputs, while the spread of possible climate change signals remains quite large. However, the main uncertainties do not invalidate the overall message of possible water resources change that is summarized in a substantial decrease in water availability under all the combined scenarios.