Change in groundwater drought and its consequence for vegetation in the Middle Reaches of the Yellow River Basin

Abstract

【Background and Objective】 Groundwater is a vital resource in the Middle Reaches of the Yellow River basin, crucial for maintaining soil and water ecological functions. However, its depletion due to insufficient supply and excessive consumption has led to groundwater drought. Amidst the increasing demand for groundwater in the region, uncertainties persist regarding its ability to meet ecological and consumption demand. Evaluating groundwater drought is hence imperative to ensure sustainable development of the region. This study aims to assess the spatiotemporal evolution in groundwater drought and its consequence for vegetation growth. 【Method】 This study was based on the GRACE/GRACE-FO data and GLDAS data measured from April 2002 to December 2021 in the Middle Reaches of the Yellow River Basin, from which we analyzed the groundwater storage anomaly and estimated the standardized groundwater drought index (SGDI). The spatiotemporal variation in groundwater drought was calculated using the run theory, the modified Mann-Kendall trend test, and the Spearman correlation analysis. The impact of vegetation on groundwater drought and its determinants was analyzed using detrended NDVI. 【Result】 ① Temporally, terrestrial water storage anomaly, surface water storage anomaly and groundwater storage anomaly in the basin changed at the rates of -0.022 mm/d, 0.005 mm/d, and -0.027 mm/d, respectively. Spatially, terrestrial water storage anomaly and groundwater storage anomaly were distributed unevenly in the basin. ② Temporal variation in groundwater drought in the basin had been in increase, with a total of 65 months occurring drought during the studied period, including six severe droughts and fourteen extreme droughts. Between 2016 and 2021, there were multiple consecutive groundwater droughts, including severe and extreme droughts after 2018. The most extreme drought from 2002 to 2021 was in October 2021. The Theil-Sen slope of SGDI in the basin was -4.10×10-4/d, which passed the MMK trend test, indicating there is a significant increasing trend of groundwater drought in the future. ③ In October 2021, the proportion of drought-affected areas in the basin were 95.81%, in which 64.66% were extreme drought. The Theil-Sen slope of SGDI varied spatially in the range of -0.014 to 0.007 per month. The groundwater drought in the north and east of the basin had increased significantly, with areas reaching 63.02% and drought tendency increasing from the southwest to the northeast. ④ The driving effect of vegetation changes on groundwater drought is not significant. 【Conclusion】 Groundwater drought in the Middle Reaches of the Yellow River Basin has intensified, characterized by an expanded drought areas, increased drought events, and a significant upward trend in drought. Groundwater drought did not result in a significant impact on vegetation. These findings underscore the urgent need to protect groundwater resource and mitigate its adverse impact on ecology and socio-economic development of the region.

Keywords

• grace
• groundwater drought index
• temporal and spatial changes
• cause analysis
• middle reaches of the yellow river basin