Can land use/land cover optimization improve the environmental flow guarantee in regulated basins?

Abstract

Land use/land cover (LULC) change is an important driver of changes in hydrologic processes in watersheds. Many studies have focused on the disruptive effects of human activity-induced urban sprawl and increased impervious surfaces on river runoff and environmental flow (e-flow), and little has been reported on whether LULC changes can improve e-flow security. Therefore, we proposed a hypothesis on whether LULC optimization can improve the e-flow guarantee using the Shayinghe River watershed as an example. To test the hypothesis, we evaluated the runoff response and e-flow security status of seven LULC scenarios (four historical scenarios and three possible optimization scenarios) by constructing the Soil and Water Assessment Tool (SWAT) model to establish the statistical relationship between a single LULC type and the e-flow guarantee rate (EGR) and e-flow deviation rate (EDR) and screened the best land optimization scenario for the Shayinghe River watershed. The results showed that: (1) forest land and grassland have positive effects on EGR, and LULC optimization can counteract the risk of dry season e-flow security caused by urban expansion and increased construction land to a certain extent; (2) construction land was the most active LULC type and inhibited the dry season flow and EGR of rivers, leading to moderate changes in the hydrological process of Shayinghe River; (3) the Grain for Green Project was the best LULC optimization scenario for the Shayinghe River basin, which converts 1342 km2 of cultivated land in the western part of the basin to forest land, resulting in the highest dry season EGR increases of 3.23 % and 2.26 % in Zhoukou and Fuyang, respectively. Our study proposes a relatively simple and easily replicable approach in other watersheds, providing a new reference for rational LULC planning and environmental flow protection in highly regulated watersheds.