Synergistic changes in precipitation and soil water use efficiency and their driving mechanisms of terrestrial ecosystems in China

Soil water use efficiency (SWUE) and precipitation use efficiency (PUE) are paramount indicators in examining the coupling mechanism of carbon and water cycles in terrestrial vegetation ecosystems. However, the mechanisms influencing variations in PUE and SWUE warrant further investigation due to existing research gaps. The gross primary productivity (GPP) and net primary productivity (NPP) in China were simulated using the TL-LUE model and improved CASA model, respectively. PUE and SWUE were then calculated in conjunction with precipitation and soil water data. A further investigation was conducted on the joint evolutionary patterns of PUE and SWUE. The impact of factors such as climate change, vegetation variation, carbon dioxide emission, and human activities on PUE and SWUE was separately identified using partial derivatives and elasticity coefficients. The results suggest an insignificant downward in PUE and a significant upward trend in SWUE in China from the period of 2000-2018. Notably, drought mitigation in the arid zone led to a steeper decrease in PUE compared to humid, sub-humid and semi-arid zones. Drought mitigation resulted in a decrease of SWUE in arid zones, yet an increase in humid, sub-humid and semi-arid zones. The correlations between vegetation change and precipitation and PUE or SWUE, respectively, were predominantly influenced by changes in drought conditions. NPP and precipitation collectively dominated the alterations in PUE, contributing 41.55% and -58.45%, respectively. However, GPP exerted a more substantial influence on SWUE compared to precipitation, with notable contributions of 93.93% and -6.07%, respectively. The contributions to PUE from climate variation, human activities, vegetation change and carbon dioxide were -57%, 30%, 12% and -1%, respectively. Simultaneously, the contributions to SWUE from these same factors appeared as 20%, 63%, 16% and 1%, respectively. This study intends to augment the comprehension of the influence exerted by global climate change and human activities on the correlation between carbon and water in terrestrial vegetation ecosystems.