Changes in seasonal and diurnal precipitation types during summer over the upper reaches of the Yangtze River Basin in the middle twenty-first century (2020-2050) as projected by RegCM4 forced by two CMIP5 global climate models

摘要

Changes in summer and diurnal precipitation in the upper reaches of the Yangtze River Basin (UYRB) in the middle of the twenty-first century were estimated by RegCM4 with a resolution of 50 km under two representative concentration pathway scenarios. ERA-Interim, CSIRO-MK3.6.0 and MPI-ESM-MR were used as the initial and lateral boundary conditions, and two observation data sets (CN05.1 and CRU) were used to evaluate the precipitation performance. RegCM4 captured the spatial characteristics of summer precipitation in the UYRB during the reference period. Compared with the two observational data sets, the three groups of downscaling results underestimated the precipitation in the eastern part of the basin by 20% and overestimated that in the west by more than 80%. In the middle of the twenty-first century, the total precipitation (TPR) in the UYRB varied significantly from east to west. The multiyear average TPR in the eastern plains was projected to significantly decrease, while it significantly increased in the western mountains. As a major contributor to the TPR in the UYRB, convective precipitation (CPR) differed between the eastern and western regions, especially at night. The TPR changes in the east (decrease) and west (increase) were projected to be strongest in the afternoon. The probability of high-intensity precipitation in the central and western areas will increase, implying a potential increase in the risk of flooding in these areas. The diametric changes in the TPR between the east and west may further exacerbate the spatial heterogeneity of water resources, resulting in large impacts to surface hydrological processes. The spatial variations in precipitation were mainly due to the variation in precipitation mechanisms between the western mountainous area and the eastern basin, while the changes in water vapour transport and atmospheric stability also played a role.