Assessing the cumulative impact of on-farm reservoirs on modeled surface hydrology

Abstract

On-farm reservoirs (OFRs) are crucial water bodies for meeting global irrigation needs. Farmers use OFRs to store water from precipitation and runoff during the rainy season, which they then use to irrigate their crops during the dry season. Despite their importance to crop irrigation, OFRs can have a cumulative impact on surface hydrology by decreasing flow and peak flow. Nonetheless, there is limited knowledge on the spatial and temporal variability of the OFRs’ impacts. Therefore, to gain an understanding of the cumulative impact of OFRs on surface hydrology, we propose a novel framework that integrates a top-down, data-driven, remote sensing-based algorithm with physically based models, leveraging the latest developments in the Soil Water Assessment Tool+ (SWAT+). We assessed the impact of OFRs in a watershed located in eastern Arkansas, the third most irrigated state in the USA. Our results indicate that the presence of OFRs in the watershed is associated with a decrease in annual flow of 14 %–24 % and a mean reduction in peak flow of 43 %–60 %. In addition, the cumulative impact of the OFRs was not equally distributed across the watershed, varying according to the OFR spatial distribution and their storage capacity. The results of this study and the proposed framework can support water agencies with information on the cumulative impact of OFRs, aiming to support surface water resources management. This is relevant because the number of OFRs is expected to increase globally as a response to climate change under severe drought conditions.