Response Of Rainy Season In China To Global Warming And Its Possible Mechanism

The climate in China exhibits significant annual cycle characteristics.Global warming not only affects the annual cycle of temperature,but also affects the rainy season in China via the influence of monsoonal circulation.The understanding of the response and mechanisms of rainy season in China to global warming not only provides scientific basis for dealing with global warming,but also has important scientific significance for improving climate prediction skills.Based on the daily data of Chinese stations,CN05.1 data,atmospheric reanalysis data,etc.since 1961,this paper discusses the trends of the East Asian Monsoon(EAM),rainy season in China,circulation,the impact of surface air temperature(SAT)and sea surface temperature(SST)in key areas,reveals the trend of warming and wetting in China,and compares the rainy season in China,circulation,SAT and SST between warm-wet and warm-dry annual-mean backgrounds,as well as extreme years.The main conclusions obtained are as follows:(1)The dominant mode of annual average temperature and precipitation in China shows a significant increasing trend with interannual scale fluctuations.All regions in China have a warming trend in temperature,while the increasing trend of precipitation is mainly located in the Three Rivers Source and Northwest China.Since 1999,the regions with significant warming in China have decreased,but the regions with significant increasing precipitation have increased.Of which,the temperature increase in spring is the largest,and the precipitation increase in summer and early autumn is the largest,mainly located in the eastern region of China.Since 1999,there has been a significant warm-wet trend in northern China,including the Three Rivers Source,Hetao,and Northeast China.Extreme warm-wet climates are more likely to occur after 1999.(2)The annual cycle of EAM has significantly adjusted in 22 years around 1999.The East Asian summer monsoon(EASM)shows a linear trend of early onset,delayed withdrawal,and longer duration.In warm-dry years,the onset and withdrawal of the EASM advance,and the duration becomes longer.In warm-wet years,the onset and withdrawal of the EASM postpone,and the duration increases.In extreme cold-wet and warm-wet years,the onset of the EASM postpone.The maximum value of the East Asian monsoon index(EAMI)is smaller,and withdrawal postpone in cold-wet years.The onset of the EASM in extreme warm-dry years is advanced,and the maximum value of EAMI in cold-dry and warm-dry years is larger.(3)The onset,withdrawal,and duration of the rainy season in China have also shown significant adjustments,but there are spatial differences.The main manifestation is that the rainy season has early onset,delayed withdrawal,and longer duration in the Three Rivers Source and Hetao areas.In warm-dry years,the onset of the rainy season is postponed,and the duration decreases.In warm-wet years,the onset of the rainy season is advanced,and the withdrawal is postponed,and the duration increases.The phenomenon of prolonged duration of rainy seasons is more obvious in extreme warmwet years,mainly contributed by the early onset of the rainy season.The phenomenon of shortening duration of rainy seasons is more obvious in extreme cold-wet years,which is jointly influenced by the onset and withdrawal.The changes during extreme cold-dry years are relatively small compared to other situations.Under extreme warmdry years,the duration of the Qinghai Tibet Plateau,the southwest,as well as the middle and upper reaches of the Yangtze River becomes longer,while the duration of other regions becomes shorter,which is jointly affected by the onset and withdrawal.(4)The circulation and thermal factors that affect the changes of the EASM and the changes of rainy season in China are significantly different.The warming SAT around Lake Baikal with enhanced upper-level anticyclone in April are the key factor to the onset advance of the EASM and the rainy season in China.The warming of the northwest Pacific Ocean SST in October with enhanced subtropical anticyclone in the northwest Pacific are the key factors leading to the withdrawal delay of the EASM and the longer rainy season in northern China.The Northwest Pacific subtropical high is a key factor determining the occurrence of warm-dry and warm-wet climates in China.When the SST in the Indian Ocean and the ocean continent is abnormally warming,the enhanced subtropical high in the northwest Pacific and the accompanying southwest airflow transport water vapor for China.With the abnormally anticyclone circulation over Lake Baikal,the precipitation in China increases abnormally,which is conducive to a warm-wet climate.When the SST is cooler or has smaller warming,the West Pacific Ocean will not produce abnormally anticyclonic circulation,which will weaken the southwest monsoon and water vapor transport.Even though there is also an anticyclone circulation near Lake Baikal,the precipitation in most areas of China will decrease,forming a warm-dry climate.Under extreme cold-wet years,the Pacific SST shows El Ni?o characteristics.At this time,there is a weak anticyclone circulation near the South China Sea,and there are regional differences in significant precipitation changes in China.Under extreme warm-dry years,the Pacific SST exhibits La Nina characteristics.while under extreme cold-dry years,the Indian Ocean and western Pacific Ocean are significantly colder.Under extreme warm-dry and cold-dry years,there are less precipitation across the country.Under extreme warm-wet years,the Indian Ocean and the Pacific Ocean are significantly warming,and the abnormally anticyclone circulation in the western Pacific Ocean transports water vapor for China,resulting in a larger precipitation in China.