Enhanced water stress on vegetation productivity with climate warming over the Northern Hemisphere

Water stress is a major environmental factor limiting vegetation productivity, however, large interactions between atmospheric and soil dryness still hinder a complete understanding of the main cause of the widespread drought-related decreased vegetation productivity. In this study, we investigated inter-annual changes in gross primary productivity during 1982 to 1998 and 1998 to 2018 using two independent remote sensing products. We also analyzed the impacts of temperature, soil moisture, and vapor pressure deficit on gross primary productivity trends during 1982 to 1998 and 1998 to 2018 to explore the causes of gross primary productivity declines during recent decades. Results show that gross primary productivity trend during 1998 to 2018 tends to stall after the year 1998 concurrent with a significant enhancement of a positive vapor pressure deficit trend during 1998 to 2018, particularly in forests, grasslands, and warmer regions. In the Northern Hemisphere, whilst increasing vapor pressure deficit plays a dominant role in weakening the gross primary productivity trend from 1998 to 2018, changing soil moisture and temperature also influences the trends as identified in different regional responses. In addition, results from 8 dynamic global vegetation models showed that the dynamic vegetation models fail to capture the inter-annual changes in gross primary productivity, likely due to an overestimation of gross primary productivity responses to soil water.