Spatial And Temporal Changes Of Extreme Precipitation In China Based On CMIP6 Model And Its Possible Mechanism

Extreme precipitation events are frequent in China in the context of global warming.Based on the 0.5°×0.5° grid point dataset(V2.0)provided by the National Meteorological Center and 17 climate models from the Coupled Model Intercomparison Project Phase(CMIP6),this study assesses the accuracy of the CMIP6 model using the V2.0precipitation data from 1961-2014,selected and modified the simulation capability of the better Models.The simulation capability of the modified multi-model ensemble(MME)average and individual models are compared for extreme precipitation indices(annual total wet day precipitation(PRCTOT),precipitation intensity(SDII),consecutive dry days(CDD),number of heavy precipitation days(R20mm),5-day maximum precipitation(RX5day),and annual precipitation fraction due to very wet days(R95p)),and the MME is finally selected to represent the model simulation results.The spatial and temporal variability of extreme precipitation in 1961-2014 is analyzed based on the CMIP6 MME.The CMIP6 MME is used to analyze the evolution of extreme precipitation over 1961-2014 and to project the spatial and temporal variability of extreme precipitation in China under the SSP2-4.5 and SSP5-8.5 scenarios,and to further analyze the probability distribution and the range of model uncertainty.Finally,the possible mechanism affecting future extreme precipitation is discussed in terms of four aspects:temperature changes,circulation anomalies,dynamical uplift as well as water vapor transport.The main conclusions are obtained as follows:(1)The ability of the CMIP6 model to simulate daily mean precipitation is assessed by Taylor diagrams,and eight models with correlation coefficients greater than 0.8 are selected.The spatial correlation coefficients between the better model ensemble mean(MME)and measured data for the extreme precipitation index are greater than 0.95 after calibration,and the simulation ability is better than that of individual models.The trend in PRCTOT in China from 1961-2014 is not significant,with SDII,R20 mm,RX5day and R95 p showing a slow upward trend and CDD showing a slow downward trend.(2)The mean PRCTOT,SDII,R20 mm,RX5day,and R95 p in China increase significantly in the 21 st century.under the SSP2-4.5(SSP5-8.5)scenario and increase by21.5%(37.8%),9.3%(18.8%),1.1 d(2.1 d),19.2%(37.6%),and 34.0%(75.9%)in the long-term projection(2081-2100),respectively.The increase is higher under the SSP5-8.5 scenario than under the SSP2-4.5 scenario,suggesting that reducing emissions can largely reduce the risk of increased extreme precipitation in the region.The CDD shows a decrease of 4.2 d(6.3 d),with a spatial dipole-type pattern of shortening in the north and lengthening in the south.It suggests that the drought in northern China will be alleviated in the future without considering the temperature change.(3)Spatial differences in precipitation extremes have become more pronounced in the 21 st century,and precipitation changes tend to be more extreme.The temperature in Northwest China(NWC)and Qinghai-Tibet Plateau(SWC1)increases.PRCTOT,RX5 day and R95 p show an increasing trend,and CDD shows a decreasing trend.This indicates that heavy precipitation is increasing and the duration of dry periods is shortening under the background of climate warming,and that climate warming and precipitation extremes are further intensifying so that water resource distribution in cold and dry areas and ecologically fragile areas will face great risks.The smaller increase in PRCTOT and the larger increases in RX5 day,R20mm and CDD in South China(SC)suggest greater risks of extreme precipitation in densely populated and economically developed areas.In conclusion,the increase in total precipitation is closely related to the increase in extreme precipitation and the shortening of the duration of the dry period.(4)Future extreme precipitation variability increases.The increase in PRCTOT and RX5 day in summer is large and highly variable,with RX5 day in summer showing more pronounced performance and an increased probability of high values,indicating that extreme precipitation is more sensitive to climate warming.The uncertainty in the projection of regional models with large changes is also greater,with a greater range of uncertainty under the SSP5-8.5 scenario.(5)The temperature in China gradually increased in the 21 st century,and extreme precipitation showed an approximately linear relationship with temperature change.The response rates of PRCTOT and R95 p to temperature change are higher,and R95 p in SWC1 is more sensitive to temperature increase,with a response rate of over 14 %/°C.The response rate in the mid-term projection(2041-2060)is greater than in the nearterm(2021-2040)and long-term projection,and the response rate under the SSP2-4.5scenario is greater than under the SSP5-8.5 scenario in this period.(6)The continental thermal low pressure is deepening and the surrounding oceanic high pressure is intensifying in China during summer.The marked contrast in barometric pressure differences leads to a strengthening of southerly airflow in the eastern region,with upper-level northerly winds corresponding to lower-level southerly winds,indicating a strengthening of the East Asian summer monsoon circulation.The strengthening of the East Asian monsoon circulation has led to enhanced water vapor transport in the South China Sea and the Western Pacific.A significant increase in atmospheric precipitable water in the east,with abundant moisture conditions.The deepening and eastward movement of the low-pressure trough from the NEC to the middle and lower reaches of the Yangtze River is conducive to the southward movement of cold air to form a frontal system.The vertical velocity is anomalously negative in the central and western parts of SWC1,NC,SWC2 and SC,showing anomalous upward movement and enhanced convective activity,which favors the formation of extreme precipitation.As a result,total and extreme precipitation in China will intensify in the context of a warming climate,especially in vulnerability areas of climate change,where an increase in extreme precipitation could lead to an increased risk of flooding.