No abstract

Overexploitation of groundwater (GW) in the North China Plain (NCP) since the 1960s has many environmental consequences. However, mechanistic understanding of this perturbation 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 spatiotemporal 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 impacts of GW pumping and irrigation on the ground surface temperature (GST). Results show 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, leading to increases in the spatiotemporal 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 0.01 and 10 m, the 0.5-m/yr increase of WTD simulated by the model due to pumping can continue to increase the regional averaged WTD and hence, perturb GST for about 20 years after GW pumping began in the NCP, before WTD exceeds 10 m. The variations of GST are expected to increase faster initially and gradually slow down due to the nonlinear behaviors of GST with WTD. The findings from this study in the NCP may also have implications for other regions with GW depletion. Key Points:• Effects of groundwater pumping on GST in the North China Plain are investigated using an integrated hydrologic model • Groundwater pumping increases the spatiotemporal variability of GST and results in hotter summers and colder winters • The effect of groundwater pumping on GST may last for 20 years, with a stronger effect in the beginning due to nonlinear response Supporting Information:• Supporting Information S1

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.