Water Harvesting: climate change adaptation measure in the arid Khartoum?

Climate change has influenced the magnitude and the distribution of rainfall, where some regions may receive more rainfall while others may become drier (IPCC, 2007). Episodes of flooding and drought, according to the World Water Council (2010), have already been observed and are expected to become more apparent in the coming decades. Being located within the arid belt, the urban areas of Khartoum State, the capital of Sudan, experience erratic and intense rainfall during the short rainy season and dryness and heat throughout the dry season throughout the rest of the year. Rainstorms with a short duration have become more frequent in the area since the last two decades, e.g. 1994, 1998, 2001, 2003, 2007, and 2009, resulted in cities inundation. From another hand, a study by Elagib (2010a) has proved the existence of the Urban Heat Island (UHI) phenomenon in the city of Khartoum, where the highest warming rate is registered for the hot season and is more than twice that for a rural surrounding. Therefore, the present study has investigated the potential of rainwater harvesting in the urban area of Khartoum State, represented by Khartoum city center, as runoff water management and drought mitigation tool during the wet and dry seasons, respectively. In other words, to change the dominant concept of the immediate drainage of runoff water to its retention within the area for later beneficial utilization. The characteristics of the drainage system were examined using ArcGIS platform revealing that the drainage system covers about 42% of the city center area (6 km 2 ) with total capacity of 24000 m 3 . Daily rainfall data for 32 years was used to calculate the probability and the return period of the rainfall, as well as the potential runoff. The Natural Resources Conservation Services method provided by the United States Department of Agriculture (US-NRCS) was implemented to calculate the potential runoff that could be generated from a certain rainfall. Accordingly, the curve number (CN) was determined corresponding to the land use/land cover and the hydrologic soil group (HSG). The weighted curve number is found to be 94%, indicating dominant imperviousness. Consequently, runoff volume that equals the drainage