Assessing hydroclimate response to land use/cover change using coupled atmospheric-hydrological models

Modeling techniques provide a straightforward means to dissect regional hydroclimate in response to changes in land use conditions. This study uses the Weather Research and Forecasting Model (WRF) and WRF-Hydrological modeling system (WRF-Hydro), driven by survey-based land use data in 1995 and 2015, to assess how central Taiwan’s hydroclimate responds to land use/cover change. We first run WRF-Hydro with observed rainfall as meteorological forcing to ensure reasonable runoff simulation, and then select ten cases under weak synoptic forcings in July and August in recent decades for the simulation under two land use conditions. The WRF-only simulation (i.e., uncoupled with WRF-Hydro) can reveal significant changes in heat fluxes and surface variables due to land use/cover change, including sensible and latent heat fluxes, 2-m temperature and specific humidity, and precipitation over the hotspots of urbanization or downwind areas. Coupling WRF with WRF-Hydro discloses varied runoff characteristics subject to land use/cover change: a general increase in average peak flow (~ 4.3%) and total runoff volume (~ 5.0%) accompanied by less definite time-to-peak flow, indicating a synergistic but sometimes competitive relationship between the pure hydrologic/hydraulic perspective and land–atmosphere interactions. By taking the difference between the uncoupled and coupled simulations, we verify that surface pressure, precipitation, and soil moisture are more sensitive to a better depiction of terrestrial hydrological processes; differences in the spatial variances of soil moisture can be as high as two orders of magnitude. Our findings highlight the importance of more comprehensive model physics in regional hydroclimate modeling.