East Africa water pans at risk due to climate variability and change

Water pans are rainwater harvesting structures formed through ground excavation or natural depression to collect and store surface runoff. They supply water for crop and animal production in rural (semi-)arid areas. The ability of these structures to meet the community water demand have been hampered by recent droughts and floods. However, limited research reveals the ability of water pans to harvest and store water in changing climate. Here we evaluated the ability of water pans in Homabay-Kenya and Arusha-Tanzania to meet at least 90% of water demand under current and future climate conditions. A water pan storage simulation program was developed to estimate the storage and duration the water pans were able to meet the required demand. We found that water pans in Homabay supplied the set demand for a duration of 82 days per annum during the baseline period. They were projected to increase the supply by 15 and 12 days respectively in the mid and end century period, under high emission. In Arusha, the pans served for 46 days in the current period with a projected 5 days increase and ‐13 days decrease during mid and end century periods. No water pan except water pan 1 in Homabay was projected to meet over 90% water demand lasting for over two months in the mid and end century periods under high emission scenarios. Therefore, understanding how temperature and precipitation influence the performance of water pans, can inform the future scenarios of water availability, which can have significant economic impacts.