Effects of water table dynamics on regional climate: A case study over east Asian monsoon area

Groundwater is an important component of the hydrologic cycle, and its anomaly will result in variations of soil moisture, water, and energy balances between the land surface and atmosphere, which ultimately influence climate. In this study, we implement a groundwater model into the regional climate model RegCM3, which is called RegCM3_GW, and investigate the effects of water table dynamics on regional climate. Numerical experiments by RegCM3_GW and RegCM3 over the east Asian monsoon area show that incorporating the water table dynamics into the regional climate model reduces the systematic biases of the simulated precipitation by 38.5% and 39.8% over semiarid and humid regions, respectively, and increases the bias slightly by 5.6% over semihumid regions. To seek the reasons for the differences of simulated precipitation, we analyze the atmospheric water vapor budget and the local water cycle among the water table, soil moisture, evapotranspiration (ET), and convective precipitation. It is found that the top and root zone soil layers become wetter and enhance the bare soil evaporation but do not always increase the transpiration. Because of the variations of each ET's component, the obvious enhancements of ET occur in semiarid regions and contribute to more instable profiles of pseudoequivalent potential temperature. The atmospheric moisture budget analysis indicates that the recycling rate and precipitation efficiency increase greatly over semiarid regions, which presents a local aquifer-atmosphere feedback, while the variations of atmospheric water vapor transport control the development of precipitation over semihumid and humid regions. Therefore, the effects of water table dynamics on regional climate consist of the local aquifer-atmosphere interaction and the changes of circulation originated from ambient aquifer-atmosphere interaction, and the latter factor plays an important role in the monsoon area. Sensitivity of the results to a change in convection parameterization is also explored.