A Holistic System Approach to Understanding Underground Water Dynamics in the Loess Tableland: A Case Study of the Dongzhi Loess Tableland in Northwest China

The Loess Plateau in northwest China is one of the most water-scarce areas on Earth. In the loess tableland (LT), the underground water system is the most critical component of terrestrial ecology and the local economy. In this study, a new approach was developed to holistically simulate monthly and yearly underground hydrology in the LT, including the soil water reservoir (SWR) and the groundwater reservoir (GWR). The approach was applied to the Dongzhi Loess Tableland (DLT) to simulate SWR and GWR from 1981 to 2010 to capture the underground water dynamics. The results suggest a strong monthly variability of the SWR, with most time of a year having higher evapotranspiration than the precipitation infiltration, leading to a soil water deficit. The rainy season is the primary period for deep zone recharge, and the water balance of the GWR is generally positive from July to October and negative from November to the following June. In the DLT, The decrease in vertical recharge and increase in human extraction have led to a total groundwater level drawdown of 15.7 m and considerable spring attenuation with an annual ratio of 1.19 % over the past 30 years. If ground water withdraw rate remains the same as since 1981, the GWR will be depleted within approximately 100 years.