Evaluating the effects of topography and land use change on hydrological signatures: a comparative study of two adjacent watersheds

Abstract

Watershed hydrological processes are significantly influenced by land use and land cover change (LULCC) and characteristics such as topography. In economically advanced regions, coordinating land use planning and water resource management is essential for mitigating flood risks and ensuring sustainable development. This study compares the effects of terrain slope and urbanization-driven LULCC on hydrological processes in two adjacent subtropical watersheds but with distinct terrain and land cover in the Greater Bay Area (GBA) of China. We developed an integrated surface-subsurface hydrological model (ISSHM) using the Simulator for Hydrologic Unstructured Domains (SHUD) and calibrated it with data from river and groundwater monitoring stations. The calibrated model simulated hydrological processes, including surface runoff, subsurface flow, evapotranspiration (ET), and infiltration, to quantify water movement (measured in meters) and assess the impacts of slope and LULCC. Results show that slope impacts hydrological processes differently based on watershed characteristics. In mountainous areas, there are consistent high correlations between slope and annual surface runoff, infiltration, and subsurface flow across all watersheds. However, at lower elevations, the hydrological responses of steeper watersheds correlate weakly with local slope. Urbanization, marked by increased impervious surfaces, significantly raises annual surface runoff and decreases infiltration and ET, especially in steeper watersheds. In flatter watersheds, the rise in surface runoff is proportionally less than the increase in impervious areas, indicating a buffering capacity against urbanization. However, this buffering capacity diminishes with increasing annual rainfall intensity. Overall, the ISSHM provides robust analysis of LULCC effects on watershed hydrology across scales, enabling predictive approaches to optimizing urban management for sustainable development in growing cities.</p