Land use/cover changes and subsequent water budget imbalance exacerbate soil aridification in the farming-pastoral ecotone of northern China

Understanding the impact of human activities on changes in surface dryness/wetness is crucial for the sustainable development of terrestrial ecosystems. The farming-pastoral ecotone of northern China (FPENC) is experiencing obvious soil aridification under ongoing climate change. The impacts of human activities on cropland and grassland vary. However, how human activities affect soil aridification in terms of cropland and grassland remains unclear. To fill this knowledge gap, this impact mechanism based on the remote sensing retrieval of aridification index and the construction of water budget mismatch index(WMI) is quantified in this study. The results demonstrate a strong spatial consistency between the WMI and the trend of soil aridification. In particular, the trend of soil aridification in the west-central and northeastern areas remained unmitigated where the WMI was less than one. This was due to a more dramatic increase in evapotranspiration (ET) (+64.7 mm) compared to precipitation after subtracting runoff (Pi) (+53.9 mm) in the decade between 2001 and 2019. Under the same climatic conditions, croplands had higher crop evapotranspiration and lower soil water storage capacities (WSC) than grasslands, resulting in the aridification intensity of croplands being 1.3 times greater than that of grasslands. Moreover, irrigation exacerbated the depletion of regional groundwater and intensified soil aridification in adjacent drylands and grasslands within a radius of at least 2000 m. These findings provide a scientific foundation for comprehending the mechanism of aridification, developing ecological restoration strategies, and promoting regional sustainable development in the FPENC.