Assessing precipitation variations in the Yangtze River Basin during 1979–2019 by vertically integrated moisture flux divergence

Spatiotemporal variations in precipitation are closely related to vertically integrated moisture flux divergence (VIMD), where the extremes further cause natural disasters. Based on precipitation data from 151 meteorological stations in the Yangtze River Basin (YRB) for 1979 to 2019 and the meteorological reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF), this paper studied the spatial and temporal characteristics of precipitation and VIMD and investigated their responsive relationship. The variations in precipitation and VIMD were examined using statistical methods, along with three step ‘staircases’ of terrain clusters dividing the whole basin based on descending altitude from west to the east. The results indicated that (1) the annual precipitation increased at a speed of 6.7 mm/10a during the study period: precipitation in spring, autumn and winter showed increasing trends, especially at the high elevation region (e.g., first step terrain), while a decreasing trend appeared in summer. (2) The VIMD trends in the YRB also varied in space and time, but overall, the summer trend pattern dominated the annual pattern. (3) The spatial distribution of VIMD agreed well with the topography clusters, where the first step terrain was dominated by convergence, and the second and third step terrains were dominated by divergence. (4) The average annual precipitation and seasonal precipitation showed responsive relationship with VIMD in terms of cumulative anomalies. Our results provided information on precipitation variability and revealed the characteristics of water vapor flux distribution as well as improved the understanding of the water transport mechanism in the YRB.