Chen Yang , Hong-Yi Li, Yilin Fang, Chixiao Cui, Tianye Wang, Chunmiao Zheng, L. Ruby Leung, Reed Maxwell, You-Kuan Zhang, Xiaofan Yang

Over-exploitation of groundwater (GW) in the North China Plain (NCP) since the 1960s has many environmental consequences. However, understanding of the dominant mechanisms remains limited, particularly at the regional scale. In this study, the coupled ParFlow.CLM model representing subsurface and land-surface processes and their interactions was applied in the NCP at high spatio-temporal resolutions. The model was validated using the water and energy fluxes reported in previous studies and from the JRA-55 reanalysis. Numerical experiments were designed to examine the relative impacts of GW pumping and irrigation on the ground surface temperature (GST). Results showed significant effects of GW pumping on GST in the NCP. Generally, the subsurface acts as a buffer to temporal variations in heat fluxes at the land-surface, but long-term pumping can gradually weaken this buffer, resulting in increases in the spatio-temporal variability of GST, as exemplified by hotter summers and colder winters. Considering that changes of water table depth (WTD) can significantly affect land surface heat fluxes when WTD ranges roughly between 1–10 m, the 0.5 m/year increase of WTD simulated by the model due to pumping can continue to increase the average WTD and hence, GST, for about 20 years from the pre-pumping WTD in the NCP, before the WTD exceeds 10 m. The increase of GST is expected to be faster initially and gradually slow down due to the nonlinear increase of GST with WTD. The findings from this study in the NCP may also have implications for other regions with GW depletion.