Excessive irrigation-driven greening has triggered water shortages and compromised sustainability
Xiaoyao Lu, Minzhong Zou, Gary Gan, Shaozhong Kang
Abstract
Regional greening provides substantial benefits to ecological sustainability in drylands. However, extensive greening, driven by the complex interplay of agronomic practices and climate changes , has profoundly altered terrestrial water storage. Despite its importance, a comprehensive quantification of these impacts in dryland ecosystems remains insufficient. Here, terrestrial water storage changes in the inland arid region of Northwest China are investigated through Gravity Recovery and Climate Experiment (GRACE) mission data combined with a water balance analysis. Machine learning is used to decompose the normalized difference vegetation index (NDVI) by agronomic drivers (irrigated cropland expansion (ICE) and increased nitrogen fertilizer (NFER)) and natural drivers (elevated atmospheric CO 2 (eCO 2 ) and heightened reference evapotranspiration) to quantify the long-term impacts of regional greening (i.e., NDVI increases) on terrestrial water storage anomaly (TWSA). The results show a significant decline in TWSA since the 21st century, and water balance analysis attributed it to persistently high and rising evapotranspiration . Regional greening and heightened reference evapotranspiration , as primary catalysts intensifying regional evapotranspiration, synergistically propelled the depletion of TWSA, with regional greening exhibiting a stronger correlation with TWSA. Further, regional ICE-driven greening has contributed the most to the decline in TWSA, exceeding that of eCO 2 and NFER. The sensitivity of TWSA to ICE-driven greening increased linearly as the regional drought index rose. Effective irrigation and nitrogen fertilizer management have improved crop growth and yields, but also increased evapotranspiration, accelerating the depletion of regional water resources . Ceasing the irrigation expansion will help to combat further decline in TWSA and enhance dryland ecological health.