Fielding Floods for Flourishing Farms: A Framework for Assessing the Reuse of Small Flood Reservoirs as Irrigation Reservoirs

Due to the increased intensity and frequency of droughts under a warming world, agricultural irrigation demand (AID) is likely to increase in many regions of the world—not just in semi-arid and arid regions, but also in temperate regions. Small reservoirs have often been touted as a decentralized solution to increase water supply resilience, but little research on their potential operating rules exists. In this study, we propose a framework to assess the potential water supply benefit of reusing flood reservoirs as small reservoirs for agricultural irrigation via modeled operation based on hedging rules, using the German state of Baden-Württemberg as an example. Because of their exceptional dryness, the 2018–2020 drought years in Baden-Württemberg can be used as a benchmark for the potential benefit provided by a reservoir to agriculture in its region. Our framework estimated the AID in a 5 km2 region around reservoirs, whose operations were modeled to store smaller flood waves and allow withdrawals for irrigation, while simultaneously maintaining their protection against their design flood. Our results suggest that, operated under best-case scenarios, 20 of the 30 tested reservoirs could have contributed more than 70% of their local AID during the drought years, indicating that the proposed operating rules may be quite suitable for this purpose. ... mehrComparisons with previous work indicate some high-performing reservoirs could also be suitable for streamflow supplementation. This framework for assessing repurposed flood reservoirs could help determine their role in increasing water resiliency in the face of increasing drought frequency in a warming world.