Monitoring groundwater drought risks in major agricultural regions of China: A combined perspective of GRACE- and groundbased obervations and modeling

With the challenges of cliamte change and increasing food demand, North China has produced more than 65% of cereal productions of China, and is of great importance in food security. However, North China is facing with significant ecological degradation subsequent to water withdrawal for irrigation. As a result, lots of rivers run drying-up and groundwater table declined fast in the past several decades. There is a observed positive precipitation trend in past 2 decades over North China, and most rivers' flow has been measured increasing, accompanied with vegeration revigorous, i.e. increase in vegetatoin cover.  Under this background of climate and land cover change, we find groundwater continued to subject overpumping and has played a key role to support the gain of food production and vegetation restoration during this period. In this study, we will present the results in detail to use combined method of ground-based and GRACE observations to screening up groundwater drought risk under the increasing precipitation or wetting background. Using some machine learning algoriths, we extropolated the GRACE observed Terrestiral Water Storage (TWSA) and Groundwater Storage (GWSA) back to 1960s, and proposed a groundwater drought index (GDI) to investigate the groundwater drough characteristics under the effects of climate change and human exploitation. And we found that in major basins across North China, such as Tarim River Basin, Yellow River Basin, Hai River Basin, and Songhua River Basin, groundwater experienced more frequent and severe drought in recent 20 years, than it was in the past 4 decades before 2000. This is mainly caused by agricultural withdrawal and vegetation restoration. And in future, groundwater would be likely encounter with more severe drought threats.