Integrating hydrologic modeling and land use projections for evaluation of hydrologic response and regional water supply impacts in semi-arid environments

Semi-arid environments are generally more sensitive to urbanization than humid regions in terms of both hydrologic modifications and water resources sustainability. The current study integrates hydrologic modeling and land use projections to predict long-term impacts of urbanization on hydrologic behavior and water supply in semi-arid regions. The study focuses on the Upper Santa Clara River basin in northern Los Angeles County, CA, USA, which is undergoing rapid and extensive development. The semi-distributed Hydrologic Simulation Program Fortran (HSPF) model is parameterized with land use, soil, and channel characteristics of the study watershed. Model parameters related to hydrologic processes are calibrated at the daily time step using various spatial configurations of precipitation and parameters. Potential urbanization scenarios are generated on the basis of a regional development plan. The calibrated (and validated) model is run under the proposed development scenarios for a 10 year period. Results reveal that increasing development increases total annual runoff and wet season flows, while decreases are observed in existing baseflow and groundwater recharge during both dry and wet seasons. As development increases, medium-sized storms increase in both peak flow and overall volume, while low and high flow events (extremes) appear less affected. Urbanization is also shown to decrease natural recharge and, when considered at the regional scale, may result in a loss of critical water supply to Southern California. The current study provides a coupled framework for a decision support tool that can guide efforts involved in regional urban development planning and water supply management.