Nonlinear hydrological responses to intermediate development pathways in semi-arid watersheds

Hydrological vulnerability in semi-arid watersheds is increasingly shaped by coupled climate and land-use change, yet the relative importance of runoff and sediment dynamics remains unclear. Here, we develop an integrated socio-hydrological framework that combines SWAT modeling, CA–Markov land-use projections, and CMIP6-based Shared Socioeconomic Pathways (SSPs) to quantify runoff, sediment yield, and vulnerability at the sub-watershed scale. Across 16 sub-watersheds and two future periods (2021–2040; 2041–2052), simulations reveal pronounced spatial heterogeneity in runoff responses, whereas Sediment yield increased by approximately 15–30% relative to the baseline period under all evaluated scenarios. This divergence indicates a systematic decoupling of runoff and sediment dynamics, with sediment emerging as a more sensitive indicator of watershed degradation. Notably, the intermediate SSP2-4.5 pathway produces more consistent hydrological responses across sub-watersheds than SSP5-8.5, highlighting nonlinear relationships between development trajectories and hydrological risk. A spatially explicit Integrated Vulnerability Index incorporating dynamic adaptive capacity identifies persistent vulnerability hotspots in central and downstream sub-watersheds. These findings demonstrate that moderate development pathways can induce disproportionate hydrological stress and underscore the importance of sediment-focused, transferable frameworks for climate adaptation in semi-arid regions.