Dominant role of climate in determining spatio-temporal distribution of potential groundwater recharge at a regional scale

Knowledge of spatio-temporal groundwater recharge (GR) is crucial for optimizing regional water management practices. Daily potential GR at 58 sites over the Chinese Loess Plateau (CLP) during 1981-2099 was simulated using the HYDRUS-1D and robust model inputs. The objective was to explore the impacts of soil, vegetation, and climate on potential GR at a regional scale. The median potential GR over the CLP during 1981-2010 was 1.8 cm, accounting for 4.1% of the annual precipitation (P). As dominated by P, the annual potential GR decreased from 18.8 cm (28% of P) at the southeast to 0.0 cm at the northwest. Temporally, consistent low-intensity of GR interspersed with extreme rainfall-induced high GR, being episodic or seasonal depending on sites and years. The lag (average of 5 months) between deep drainage at 3 m depth and rainfall was controlled by climate (i.e., P). From 1981 to 2010, annual potential GR significantly decreased as a result of increased ETp and leaf area index (LAI) over time. A warmer and wetter CLP at the end of this century as predicted by the HadCM3 model may decrease the potential GR because of the increased ETp. This study highlights the dominance of water input factor (P) on the spatial GR and water output factors (ETp and LAI) on the temporal GR. Measures such as water-saving practices and land use optimization should be taken to mitigate climate change effect on groundwater recharge.