Historical climate change impacts on the water balance and storage capacity of agricultural reservoirs in small ungauged watersheds

Abstract

Study region: Agricultural reservoirs are the principal source of irrigation supplies for sustaining rice production and play a critical role in the water resource management of South Korea. Study focus: We comprehensively evaluated the performance of 400 major agricultural reservoirs, spread throughout the country, as a function of climate change during 1973–2017 considering the constituents of reservoir water balance, such as watershed runoff, irrigation water demand, and evaporation loss. New hydrological insights: Based on the trend analysis during the 45-year study period, the reservoir inflows remained higher than the irrigation water demands because of the gradually increasing annual rainfall. Most reservoirs had enough storage capacities; their resilience gradually declined particularly during the last 15 years. The northern and northeastern region reservoirs had acceptable resilience whereas the reservoirs in the western and southwestern inland and coastal regions showed insufficient resilience. Reservoirs received sufficient inflows but the residence time of the excess inflow has to be increased to suffice the peak irrigation demands in the coming cropping season. Study outcomes could help prioritize the reservoirs requiring immediate rehabilitation located in the central and southwest regions with high failure risks. Results suggested that a reservoir with a watershed-irrigated area ratio > 5 would have a better chance of coping with future climate change threats.

Keywords

• Agricultural reservoirs
• Water balance
• Reliable storage capacity
• Recharge index
• Water deficit index