Simulation Evaluation And Future Projection Of Regional Heavy Rain Events In China Based On RegCM4 Dynamic Downscaling

Based on the Regional Climate Model Version 4(Reg CM4)simulations(named Cd R,Ed R,Hd R,and Md R,respectively)dynamically downscaling from four global climate models(CSIRO-Mk3.6.0?EC-EARTH?Had GEM2-ES and MPI-ESM-MR))as well as the observed high-resolution grid dataset CN05.1,the regional rainstorm events that occurred in China were identified by use of the “tracing” objective method.The basic characteristics of regional rainstorm events in China were analyzed.The fidelity of the Reg CM4 downscalings in simulating the climate features of regional rainstorm events in China was evaluated.And future changes in the regional rainstorm events that occurred in China by the middle and late of the 21 st century under RCP4.5 scenario are projected.The main conclusions are as follows.(1)Analyses of the observations revealed that the climatologically spatial distribution of accumulative frequency,duration and rainfall amount of regional rainstorm events are similar.The areas severely affected by regional rainstorm events in China are mainly in the middle and lower reaches of the Yangtze River,Jiangnan Area,Huanan Area,Sichuan-Shaanxi border.There was no significant trend in the frequency of regional rainstorm events in China from1961 to 2016,but duration,average rainfall amount,average extent and comprehensive intensity of regional rainstorm events in China show an obvious upward trend consistently from 1961 to 2016,especially after the early 1990 s.(2)The simulation evaluation indicated that the four Reg CM4 simulations and their ensemble(MME)can reasonably capture the observed annual cycles and climate mean values of the frequency,duration,average rainfall amount,average extent,and comprehensive intensity of regional rainstorm events average in China.The simulations can also well reproduce the probability of indices of regional rainstorm events in different bands and the climatologically spatial distribution of accumulative frequency,duration and rainfall amount of regional rainstorm events in the observation.The spatial correlations of the simulations with the observation are all above 0.9 and the root-mean-square errors are generally below 0.4.However,the frequency of regional rainstorm events simulated by the model is slightly less,which is mainly due to the underestimation of moderate regional rainstorm events.The duration and average rainfall amount of the simulation are slightly higher,while the average extent is slightly smaller.In terms of comprehensive intensity,except for HDR,all the other simulations,especially MDR,were overestimated.In terms of frequency distribution characteristics and spatial distribution,CDR performance is lower than other simulations.The relative errors of the frequency,duration,average rainfall amount,average extent,and comprehensive intensity of the ensemble(MME)were 13%,2%,-11% and 3%,respectively.This study lays a foundation for the projection of regional rainstorm events in China.(3)The projection of ensemble mean of the four Reg CM4 simulations under RCP4.5scenario indicates that the frequency,duration,average rainfall amount,average extent,and comprehensive intensity of regional rainstorm events show varying degrees of upward trend from 2006 to 2098.Compared with the period 1986-2005,the climatological spatial distribution of projected frequency,duration and cumulative intensity display a large-scale increase in the middle(2046-2065)and late(2079-2098)of the 21 st century.Besides,in the middle and late of the 21 st century,the proportion of indices of regional rainstorm events increases from January to April and from October to December and decreases from May to September.And the occurrence frequencies of all indices in the "small value region" decrease,while the occurrence frequency of events in the "medium value region" and "great increase" increase in the middle and late of the 21 st century decreases.According to the results of deviation ratio of the ensemble,for the climatologically spatial distribution of accumulative frequency,duration and rainfall amount of regional rainstorm events,the reliability is higher in the central and southern China and the northeast part of China with the ratio greater than 1,while the reliability of the prediction in the other areas is lower in the regions with regional rainstorm events.