Distribution of small seasonal reservoirs in semi-arid regions and associated evaporative losses

Abstract

To support the increasing demand of a growing population for freshwater, small-sized (<0.1km2) water reservoirs are necessary in areas with limited infrastructure, especially in water-stressed regions having seasonal and variable precipitation. Seasonal storage in small reservoirs is often overlooked in present inventories. Accordingly, we assessed the current state in semi-arid regions using highly resolved Sentinel-2 satellite imagery. Globally, about 3 million small reservoirs are in operation in semi-arid regions having a total water surface area of 17 800km2 and seasonal storage of 37km3, supporting 15% of the world’s population in semi-arid regions. Estimated upper-bound of evaporative losses represent 38% (14km3) of storage during dry season. The study estimates the evaporation suppression using floating covers and lays foundation to assess the feasibility of this technical solution to increase water savings.