Response Of Climate During The Meiyu Period Over Yangtze-Huai River Valley To Global Warming

With the global warming,the climate over Yangtze-Huai River Valley?YHRV,110°E–122°E,28°N–34°N?of China tends to be more complicated,which brings more uncertain factors to the climate prediction during the Meiyu period over YHRV.Studying the response of the Meiyu period climate to global warming has a far-reaching significance for understanding the new trends of climate over YHRV,improving the flood season forecast under the new climate background and formulating disaster prevention and mitigation policies.This paper uses the Chinese surface temperature and precipitation daily dataset to analyze the temperature and precipitation changes during the Meiyu period over YHRV in recent decades,and evaluates the Coupled Model Intercomparison Project Phase 5?CMIP5?based on the observations.The mechanism of climate change during the Meiyu period in recent decades and the relationship between climate and sea temperature during the Meiyu period over YHRV are analyzed in depth,and the related mechanism of its change is also discussed.The main conclusions obtained are as follows:?1?Response of observed climate during Meiyu period over YHRV to global warmingUnder the background of global warming,the climate in the Meiyu period over YHRV has also undergone corresponding changes,the temperature has shown a significant increase trend,and the precipitation has also been adjusted accordingly.The precipitation was relatively more in the warm years but less in the cold years.In general,the temperature during the Meiyu period over YHRV in the cold years is low and the precipitation is less.During the warm rainy season,the temperature over YHRV was high and the precipitation has an increase.In terms of spatial distribution,after global warming,the temperature during the Meiyu period over YHRV gradually increases from south to north.The precipitation during the Meiyu period over YHRV generally shows an increasing trend,but only a small reduction in the northern part of the region.?2?Assessment and future forecast of climate change over YHRV simulated by CMIP5 modelsThe ensemble average of 22 CMIP5 models has a good spatial simulation of the average variation trend of the Meiyu period climate over YHRV,which reproduces the climatic distribution characteristics of temperature and precipitation during the Meiyu period over YHRV.It is feasible to estimate the climate of the Meiyu period over YHRV in the future.In the context of further global warming in the future,the average temperature and precipitation during the Meiyu period over YHRV have a further increase,and with the increase in emissions,the spatial heterogeneity of precipitation is also increasing.Under two emission scenarios,the temperature and precipitation during the Meiyu period over YHRV show a significant upward trend comparing with modern times.The increase in temperature is holistic and evenly distributed.The rate of change of the Multi-model Ensemble(0.45?·?10a?^-1)in the RCP8.5 scenario is higher than the RCP4.5 scenario(0.23?·?10a?^-1).By the end of the 21st century,the temperature during the Meiyu period over YHRV under the RCP4.5 scenario has an average temperature increase of 2.20 C relative to modern times.Under the RCP 8.5 scenario,the increase of temperature is more significant,reaching 4.30?.The rate of change of the Multi-model Ensemble under the RSP4.5scenario over YHRV during the Meiyu period(0.72mm·?10a?^-1)is slightly higher than RCP8.5 scenario(0.51mm·?10a?^-1),and the spatial distribution unevenness of precipitation under the RCP 8.5 scenario is also higher than that under the RCP 4.5scenario.With the passage of time,the spatial distribution unevenness of the two discharge scenarios is increasing:while the precipitation in the southern part of YHRV is decreasing,the precipitation in the north has a significantly increase.?3?Discussion of climate change mechanism during Meiyu Period over YHRVThe Asian summer monsoon is the most important circulation system affecting summer precipitation.The 850hPa wind field transports water vapor from the South China Sea and the Bay of Bengal to YHRV,which is directly related to the precipitation during the Meiyu period over YHRV.In the warm years,the weakened South Asian summer monsoon allows water vapor to be transported to the Yangtze River basin,merges the water vapor of the East Asian summer monsoon over YHRV,which together cause the climate over YHRV region to be wet,and vice versa.The water vapor over YHRV is mainly transported by the westerly flow of the South Asian monsoon.The latitudinal transport of the South Asian monsoon is relatively strong in the warm year,when the climate is humid,and vice versa.There is a significant positive correlation between the Meiyu rainfall over YHRV and SST in the equatorial middle-east Pacific Ocean,in which the extreme situation is reflected in the typical El Ni?o and La Ni?a episodes.In the typical El Ni?o affected years,the positive anomalies of SST in the Indian Ocean are in favor of transporting abundant water vapor to south part of YHRV and further beneficial for the Meiyu rainfall there.However,in the typical La Ni?a affected years,the positive anomalies of SST in the western north Pacific Ocean are in favor of the Meiyu rainfall over eastern part of YHRV.The simulations by CMIP5 atmosphere-only models show that the uniform increasing of SST in global can drive an uneven distribution in the Meiyu rainfall over YHRV,in which the rainfall is increased over the eastern part?coastal?but decreased over the western part?interior?of YHRV.Therefore,the anomalies of SST in the western north Pacific Ocean indicate more important to the Meiyu rainfall over YHYV,which could provide some clue to the weather forecast in flood season under a warmer climate.