Quantify Urbanization-Induced Precipitation and Runoff Anomalies over the Qinhuai River Basin of China: Sensitivity Experiments with WRF-Hydro

Urbanization-related precipitation and surface runoff changes have been widely investigated, but few studies have directly quantified these changes and their link to urbanization in the hydrological cycle. A two-way dynamically coupled atmospheric–hydrological modeling system, Weather Research and Forecasting (WRF)-Hydro, has been applied in this study to perform the quantification. The offline WRF-Hydro was first calibrated and validated for several flooding events against gauge observed streamflow data, with the Nash–Sutcliffe efficiency reaching 0.9. Compared to the WRF model, WRF-Hydro resolves more detailed rainfall pattern features and reproduces the gauge rainfall with a correlation coefficient of 0.8. Then, the impact of urbanization on hydrometeorological processes was investigated with coupled WRF-Hydro sensitivity simulations over the Qinhuai River basin of China during 2 June–31 July 2015. The results indicate that urbanization enhances regional precipitation, resulting in an indirect increase in surface runoff, overland flow, and streamflow by 16.7, 93.5, and 111.2 mm, respectively; however, the impervious area results in higher surface runoff, overland flow, and streamflow. Moreover, changes in main hydrometeorological processes further impact the atmospheric–terrestrial water budget, resulting in a decrease in terrestrial water storage and an increase (a decrease) in precipitable water storage in the middle (lower) parts of the lower troposphere. These changes are likely associated with the warmer urban environment than rural areas. Increased water vapor and strengthened convective conditions in the middle part of the lower troposphere due to urban warming are advantageous to the formation of precipitation in urban areas, which in turn increases surface runoff, thereby facilitating the water cycle and altering the atmospheric–terrestrial water budget.