Recent Seasonal Variations in Ecosystem Water Use Efficiency in China's Key Tropical-Subtropical Transitional Zones in Response to Climate Change

Understanding the response of terrestrial ecosystem water use efficiency (WUE) to climate change is critical to accurately represent the carbon-water cycle processes. However, how WUE dynamics are evolving under seasonal climate variations and biome-specific characteristics remains still unclear. In this study, we integrated two state-of-the-art retrieval algorithms to estimate gross primary productivity (GPP) and evapotranspiration (ET) from satellite MODIS records. Such metrics served as input to quantify ecosystem WUE, expressed as the ratio of GPP to ET, and explore its dynamics during the dry and wet season from 2001 to 2018 in China's key tropical to subtropical transitional zones, that is, Yunnan Province. Results show large spatial and seasonal variability in WUE over the observational period. During the dry season, the increasing trends in GPP and ET have led to contrasting WUE patterns in forest and non-forest biomes, leading to positive and negative WUE trends, respectively. During the wet season, the declining trends in GPP occurring in combination with opposite trends in ET, have caused decreasing WUE consistently across all biomes except croplands, likely further modulated by human factors. The observed changes in WUE appear primarily driven by variations in air temperature (Ta) and vapor pressure deficit (VPD) during both dry and wet seasons. Overall, these results contribute to a better understanding of the carbon-water interplay in tropical-subtropical transitional zones and provide new insights to improve our capacity to predict the terrestrial ecosystem's response to climate change.

Automated summary

This study investigates the dynamics of terrestrial ecosystem water use efficiency (WUE) in China's tropical to subtropical transitional zones. The results show that WUE exhibits large spatial and seasonal variability, and is primarily influenced by air temperature and vapor pressure deficit.