A comprehensive index for stream depletion in coupled human-water systems

Intensive land use and land cover (LULC) change along with the gradually increasing effects of climate change have made streams both hydrologically and ecologically vulnerable to depletion. Since stream depletion has a direct impact on human and ecological water use with socioeconomic and ecological consequences, it is imperative to manage streams to keep them in a healthy state. In this study, we developed a stream depletion potential index (SDPI) based on the concept of a coupled human-water system (CHWS) operating at simultaneous, interacting scales, and we tested its applicability to watersheds across South Korea. Eight indicators - precipitation, dry days, effective basin area, stream water usage, return flow, groundwater usage, impervious area, and environmental flow supplied by dams - were identified as the key variables for the SDPI. We adopted the Structural Equation Model (SEM) to estimate the weights of the identified indicators based on their causal relationships. Furthermore, we applied three different weighting schemes for urban, rural, and intermediate areas to make the index more effective and applicable to watershed LULC. The spatial distribution of the SDPI results indicated that the western Han River, the central and southern Nak-Dong River and some parts of the southwestern region of the Korean peninsula are prone to stream depletion from several different causes. The SDPI, by predicting changing streamflow characteristics, can be used by policy makers and stakeholders to determine a safe yield for both human and environmental stream use without causing a long-term decline of water availability.