Evaluating the Impacts of Urbanization and Climate Change on Streamflow by Comparing Two Neighboring Basins in Texas

Urbanization is an important driver of environmental problems. Severe urban flooding resulting from increased impervious area threatens resident security, household assets, and infrastructure integrity. However, the impacts of urbanization are generally intertwined with those from climate change, and cannot be separated easily. To systematically quantify the individual and combined impacts of urbanization and climate change on streamflow, we applied a paired catchments approach to two adjacent river basins in south-central Texas—the San Antonio River Basin (SARB) with fast urbanization and the Guadalupe River Basin (GRB) with no significant land cover change. The integrated, physically-based distributed hydrologic model — Distributed Hydrology Soil Vegetation Model — was set up with a 200-meter spatial resolution and 3-hourly time step to simulate the streamflow over both basins. The model is first calibrated (2000–2011) and validated (1966–2011). We then conduct the simulations using multiple scenarios: (1) the fixed 1970 land cover condition, (2) 1970–2011 time-varying land cover conditions, (3) continuous land cover maps with different extreme climate conditions, and (4) varied urban land cover maps with the scaled observed precipitations. The simulated streamflow results were then analyzed via the change point detection method and the elasticity test. The results show that (1) the change of monthly maximum streamflow (i.e., MMS) pattern is mainly contributed by the changing precipitation when there is little urbanization; (2) the abrupt change of MMS pattern for the SARB is mainly contributed by the urbanization in the San Antonio City area; and (3) the elasticity values of MMS to precipitation range from 1.5 to 3.0 for the SARB