黄土高原区域尺度地下水补给特征及其对退耕还林还草工程的响应

区域尺度地下水补给是地下水资源可持续开发和管理的关键科学问题，探明其季节性与年度变化规律是预测环境变化对地下水资源影响的前提。当前相关研究在时空尺度上多为十年至千年尺度和点尺度，难以准确评估退耕还林还草工程等土地利用/覆盖变化对年尺度、大区域地下水补给的影响。本项目拟结合田间试验与数值模拟，以GRACE重力卫星、全球陆地数据同化系统（GLDAS）和多种环境示踪等新技术为研究手段，1）探究黄土高原区域尺度地下水补给机理；2）厘清黄土高原大尺度土壤水分动态并评估GLDAS在该地区的适用性；3）开发并验证推算区域地下水补给量的新方法-根区以下储水量波动法；4）确定退耕还林还草工程核心区域近20年的地下水补给量及其特征，揭示该工程对区域地下水补给的影响。本项目将形成一套年尺度、大区域推算地下水补给量的新方法，为黄土高原生态工程可持续建设提供科学参考和决策依据，并为全球地下水补给研究提供借鉴。

Regional groundwater recharge is a critical scientific issue for sustainable groundwater resource development and management, and understanding its seasonality and inter-annual variability is a prerequisite for predicting the effects of environmental changes on groundwater resource. However, most of the previous studies are limited to the point spatial scale and decades to millennia temporal scales. As such, these deficiencies hinder our ability to accurately evaluate the effects of land use/cover changes, such as the Grain for Green Project (GGP), on groundwater recharge at annual and regional scales. In this project, we will conduct both in-situ field monitoring and numerical simulations, coupled with a series of new techniques, such as: GRACE, GLDAS, and various environmental tracers, to accomplish the objectives: (1) to investigate the regional scale groundwater recharge mechanisms on the Loess Plateau of China (LPC); (2) to clarify the large-scale soil moisture dynamic on the LPC and evaluate the applicability of GLDAS on the LPC; (3) to develop and verify a new method, the below root zone groundwater reserve fluctuation method, for calculating the regional groundwater recharge; and (4) to determine the groundwater recharge and its characteristic in the core area of GGP in the past 20 years and to reveal the effects of GGP on groundwater recharge at the regional scale. This project will produce a set of new methods that can calculate the annual and large-scale groundwater recharge, provide theoretical basis for the sustainable development of GGP on the LPC, and promote the groundwater recharge research in the world.