Seasonal variation in the precipitation recharge coefficient for the Ordos Plateau, Northwest China

The precipitation recharge coefficient (PRC) is an important parameter for regional water resource evaluations and groundwater numerical simulations. This parameter has evident seasonal variations due to seasonal differences of climatic and vegetation, especially in cold arid regions. While the annual mean value and spatial variability of PRC are reported commonly, fewer studies have focused on seasonal variations of PRC. Understanding seasonal variations of PRC is important for accurately assessing groundwater resources and interpreting the effect of vegetation and climate change on groundwater recharge. This study identifies and quantifies seasonal variations of PRC based on water-table fluctuation and hydrogen and oxygen stable isotopes (using an end-number mixing model) in the Ordos Plateau of Northwest China. The results show that PRCs in the cold season (October-March) are more than twice as high as in the warm season (April-September). The freeze-and-thaw processes of seasonally frozen soil lead to a lag in groundwater recharge processes as a response to precipitation infiltration, which should be considered when using PRC to evaluate groundwater recharge. The deep water mixing and the effect of the amount of precipitation on isotopic composition should be taken into consideration when the isotopic method is used to estimate PRC.