Precipitation and Extreme Heat Projection in Eastern China under CMIP5 Scenarios: the Statistical Downscaling Results

Abstract:

A statistical regression downscaling method was used to project future changes in precipitation and cities’ Extreme Heat over eastern China based on Phase 5 of the Coupled Model Intercomparison Project (CMIP5) scenarios simulated by the second spectral version of the Flexible Global Ocean-Atmosphere-Land System (FGOALS-s2) model. Our validation results show that the downscaled time series agree well with the present observed in terms of both the annual mean and the seasonal cycle. The regression models built from the historical data are then used to generate future projections. The results show that the enhanced land-sea thermal contrast strengthens both the subtropical anticyclone over the western Pacific and the eastern Asian summer monsoon flow under both Representative Concentration Pathway (RCP) 8.5 and 4.5. However, the trend of precipitation in response to warming over the 21st century is different across eastern China under different RCPs. The area to the north of 32°N is likely to experience an increase in annual mean precipitation, while for the area between 23°N and 32°N mean precipitation is projected to decrease slightly over this century under RCP8.5.

The heat wave days in six cities (Beijing, Tianjin, Nanjing, Hangzhou, Fuzhou and Guangzhou) across the eastern China are projected to increase in both frequency and intensity. By the end of the century, all those cities’ TX90 percentiles are projected to be over 55%, with Hangzhou over 80% in summer under RCP8.5. In contrast, those projected heat wave days under RCP4.5 is around 20% less. Percentages of danger Heat Index days under RCP8.5 by 2070–99 are range from 30% in Beijing and Tianjin, up to over 80% for southern China cities (Hangzhou, Fuzhou and Guangzhou), implying that people live in southern China cities will have a much stronger overheat sensation in summer.