Estimation of groundwater recharge by chloride mass balance (CMB) method in a typical semiarid climate of China

Chloride mass balance (CMB) method for unsaturated zones was applied to estimate groundwater recharge in northwestern Shaanxi Province, where the climate is typically semiarid and water use depends largely on groundwater resources. Based on three different chloride profiles, similar recharge estimations of 49.6mm/yr, 47.2mm/yr and 45.9/yr, representing 12.5%, 12.6% and 11.6% of MAP (mean annual precipitation) respectively, are achieved. The results are consistent with recharge estimates by the same method in similar regions globally. In addition, the recharge rates from this study are lower than that by other methods in this region such as empirical method, Darcyan method and CMB for saturated zones method. The difference in spatial scales and uncertainties associated with the method of CMB for unsaturated zones itself may be responsible for it.