Spatial-temporal variabilities of the contrasting hydrometeorological extremes and the impacts on vegetation growth over the Yangtze River basin

This research aimed to determine the temporal and spatial variations of the hydrometeorological extremes, and their impacts on vegetation across the Yangtze River basin (YRB). First, a meteorological reanalysis dataset with high spatial and temporal resolution from 1982 to 2015 was used to identify and analyze the annual variation trends of the extreme drought (Dry-PRE or Dry-VPD) and extreme wetness (Wet-PRE or Wet-VPD), based on precipitation and vapor pressure deficit (VPD), respectively. Subsequently, the responses and sensitivities of vegetation growth (indicated by normalized difference vegetation index, NDVI) to the hydrometeorological extremes were explored. The results showed that the frequencies of Dry-VPD, Wet-PRE and Dry-PRE generally increased while that of Wet-VPD decreased during the study period. Particularly, Dry-VPD increased significantly in the upstream and downstream of the YRB after 1998. The vegetation across the YRB was more sensitive to extreme drought (mainly with a negative correlation) than extreme wetness. Moreover, the vegetation growth in the upstream was sensitive to Dry-VPD, while that in the midstream and downstream was sensitive to Dry-PRE. To summarize, this study found that extreme drought was on the rise across YRB. Different from the general notion that precipitation limits vegetation growth, our study indicates that vegetation in the upper reach of the YRB is more negatively impacted by atmospheric drought.