Climate Change Of Precipitation Diurnal Cycle Across The Eastern Tibetan Plateau-Sichuan Basin-Middle And Lower Yangtze River Reaches

The eastern Tibetan Plateau-Sichuan Basin-middle and lower Yangtze River reaches are China’s most distinctive areas of precipitation diurnal cycle. From the perspective of climate change, this study explores the precipitation diurnal cycle across this region, recognizes the impact of global warming on structural changes of precipitation in this region. Firstly, applicability in hourly-scale precipitation analysis across the eastern Tibetan plateau-Sichuan basin-middle and lower Yangtze River reaches are evaluated by using the hourly rain-gauge data from June to September during 1969-2008. Secondly, the relationship between the diurnal cycle of precipitation and climate change in this region is discussed by using the surface observation data of meteorological elements at the same period. Finally, using the ERA-Interim reanalysis data provided by ECMWF the Weather Research and Forecasting (WRF) model is used to perform the regional climate simulation and to improve the model simulation performance. The main conclusions are as follows:(1) The southeast of Tibetan Plateau region, Sichuan Basin region and the south of the Yangtze River region were selected as the key areas. The peak time of precipitation is found mostly in the middle of the night in the southeast of Tibetan Plateau region and early morning in the Sichuan Basin region and afternoon in the south of the Yangtze River region. In the southeast of Tibetan Plateau region, the precipitation and the intensity of precipitation are smaller; the frequency of precipitation is larger than the other regions. The precipitation mainly concentrated in the night until the early morning in this region. As time goes by, the large precipitation region has a growth trend. The precipitation and the intensity of precipitation in the Sichuan Basin region are larger than the southeast of Tibetan Plateau region. In the Sichuan Basin region, the precipitation mainly concentrated in the middle of the night to the morning, the precipitation and the frequency of precipitation peak reduced with the time. There are two precipitation peaks coexist in the south of the Yangtze River region, one is in the morning, and the other is in the afternoon. The intensity of precipitation is largest in the three regions, but the frequency of precipitation is smallest. The precipitation and the frequency of precipitation have an increasing trend until the 1990s, but have reduced after the 2000s.(2) The interannual variability of temperature was more consistent in the study area, while the interannual variability of the diurnal range of temperature showed a different characteristic. There is a good negative correlation between the precipitation peak and the diurnal range of temperature. In the year that the diurnal range of temperature decreased, while the peak of precipitation increased. On the contrary, the peak of precipitation decreased while the diurnal range of temperature increased. The precipitation has a good positive correlation with the relative humidity in these three regions, but there is a difference with other elements. The precipitation has a positive correlation with temperature and 0 cm ground temperature in the southeast of the Tibetan plateau region, while has a negative correlation in the Sichuan Basin region. Daily variation of precipitation has a good negative correlation with daily variation of temperature in the south of the Yangtze River region.(3) Within 27°～35° region, the precipitation and temperature were simulated by WRF model, in which the appropriate parameterization scheme was selected. The actual spatial distribution and magnitude of hourly precipitation and the frequency of precipitation are consistent with the simulated. The simulated intensity of precipitation is not consistent with the observation. The model can simulate the precipitation diurnal cycles in the three key areas basically. The sensitivity test of greenhouse gas concentrations and surface albedo were made to investigate the responses of precipitation diurnal cycle across the eastern Tibetan plateau-Sichuan basin-middle and lower Yangtze River reaches to global warming. With the increase of greenhouse gas concentrations, the diurnal range of temperature in southeastern Tibetan Plateau decreases while the peak of precipitation increases; the diurnal range of temperature in Sichuan Basin region increases while the precipitation peak reduces; the diurnal range of temperature in the south of the Yangtze River decreases while the peak of precipitation increases. With the increase of surface albedo, the diurnal range of temperature is reduced in most regions.