Response of vegetation phenology to soil moisture dynamics in the Mongolian Plateau

Soil moisture (SM) plays a paramount role in maintaining plant growth. However, the understanding of the influences of SM dynamics on vegetation phenology is still insufficient. This is especially true for the arid and semi-arid regions, where moisture is the main limiting factor for vegetation growth. Therefore, by selecting the typical arid and semi-arid Mongolian Plateau as the study region, we evaluated the dynamics of SM and drought characterized by the standardized soil moisture index (SSMI) from 1982 to 2019 based on SM product derived from the fifth generation of the European Center for Medium-Range Weather Forecasts Interim Re-Analysis (ERA5). Their impacts on vegetation phenological indices, including the start of the growing season (SOS), the end of the growing season (EOS), and the length of the growing season (LOS), were further investigated. Our results showed that SM in the growing season had experienced a significant negative trend accompanying with the increment of SM droughts. A significantly abrupt change of SM occurred around 2000. The influences of SM on vegetation phenology displayed strong seasonal variations and weakened with soil depths. Except for some alpine areas in northwestern and southeastern parts and areas with artificial plantations, negative correlations between spring SM and SOS were generally found in the Mongolian Plateau, indicating that a decreasing SM was not conductive to an earlier SOS. Most plain areas showed a positive correlation between summer SM and EOS, while the relationship became stronger in autumn. Summer SM also had a strong control on prolonging the growing season. Furthermore, vegetation phenology was sensitive to drought, with a higher sensitivity in the EOS. Our findings have derived a better understanding on the effects of climate change, but also provided vital references to maintain sustainable development of ecosystems for the Mongolian Plateau and other arid and semi-arid regions worldwide.