Reliability of water pans in East Africa's semi-arid regions under climate change

Water pans are rainwater harvesting structures formed through ground excavation or natural depression to collect and store surface runoff. They are vital sources of water supply for crops, animals and even for households in many rural arid/semi-arid areas in Africa. However, the reliability of the water pans under increased climate variability is uncertain. Using a water storage simulation tool, we evaluated the reliability of water pans in semi-arid regions Homabay (Kenya) and Arusha (Tanzania) under historical (baseline) and future climate scenarios. In the baseline period (1985-2014), the results show that water pans in Homabay could meet the demand for only 82 days on average annually, with significant interannual variability. The situation of the water pans in Arusha is worse with only 46 days on average meeting the water demand annually. The dry season analysis shows a more severe picture. In the six months dry period (Jan-Feb and Jun-Sep), the water pans in Homabay could meet the demand for only 22 days and in Arusha for only 12 days on average. Under climate change scenarios, the results are mixed with low to moderate impacts. For example, under scenario SSP2-4.5, Homabay’s water pan reliability (annual days meeting demand) decreases slightly (<5%) in both the mid-century (2031-2060) and end-century (2071-2100) periods compared to the baseline. Whereas, in Arusha water pan’s reliability increases slightly (<5%) in the mid-century period and decreases moderately (<10%) in the end-century period compared to the baseline period. In both the baseline and climate change scenarios, the results clearly indicate that substantial enhancement of water pans (in storage capacity and/or numbers) is required to meet water demand for these rural communities in arid/semi-arid regions.