Spatiotemporal Variation Characteristics And Projection Of Heatwaves In Eastern China And Its Adjacent Waters

The eastern part of China has become the world’s fastest growing economy,fastest urbanization process,and most concentrated population.With high-intensity human activities and huge material needs,fishery resources in offshore waters are increasingly depleted and artificial aquaculture is emerging.In the context of global warming,the temperature increase trend in the eastern part of China and its adjacent waters is higher than the global average over the same period,which is a sensitive and significant response area of global climate change.Since the mid-1990s,China’s extreme high temperature events have increased significantly,and marine heatwaves have occurred frequently,bringing huge property losses and serious ecological security risks.This paper adopts a unified definition of heatwaves,based on CMIP6 climate model data,systematically researches on the spatiotemporal characteristics of atmospheric and marine heatwaves in eastern China and its adjacent waters in current and future predictions,and focuses on the physical mechanisms that cause atmospheric-marine heatwaves,and quantitatively evaluates the change in the number of people affected by the atmospherc heatwaves,at last points out the potential ecological risks of the marine heatwaves to the construction of the national marine ranches.The main results are as follows:(1)From a spatial perspective,the areas with high annual average HWT and HWN index values and rapid growth of atmospheric heatwaves are located in the Yangtze River Basin and the Yunnan-Guizhou Plateau;marine heatwaves are mainly distributed in the Sea of Japan,the sea east of Taiwan Island and the northern part of the South China Sea.In terms of time,the HWT,HWDU,and HWN indices of atmospheric heatwaves and marine heatwaves have shown an upward trend,reaching1.8,9.1 days/10 years,0.2,0.6 times/10 years,and 0.2,1.3 days/time/10 years(p<0.01),the rising trend of marine heatwaves is faster than atmospheric heatwaves.The HWI index has obvious inter-annual changes in atmospheric heatwaves and marine heatwaves,but there is no significant trend.Atmospheric heat waves have dominant cycles of 32 a,10a and 5a;marine heatwaves have dominant cycles of 21 a,10a and 3a.Atmospheric heatwaves and marine heatwaves have increased abrupt changes in 1996 and 1998 respectively.(2)In summer,the eastern part of China is warming.The highest temperature increase rate in the Yangtze River Basin and its northern regions generally exceeds0.3℃/10 years,and even reaches 0.5℃/10 years(p<0.01);most of the coastal waters are the warming trend,especially in the coastal areas of China,the warming trend reaches 0.2～0.4℃/10 years(p<0.01).In winter,the western and southeast coastal areas on the land have a significant warming trend,reaching 0.4～0.5℃/10 years and0.3～0.4℃/10 years respectively.Among the offshore waters,the East China Sea and the South China Sea have the most significant warming trends.The East China Sea extending from the Yangtze River estuary to the Taiwan Strait has a warming trend of0.3～0.4℃/10 years(p<0.01).The warm anomaly of sea surface temperature can stimulate the release of latent heat,resulting in a positive anomaly of 500 h Pa geopotential height.Under the control of high pressure,the near-surface weather conditions are clear skies,precipitation decreases,and land temperature increases rapidly.Especially during the rapid decay period of strong El Ni(?)o in summer,the intensity of the subtropical high in the western Pacific Ocean increased and it extended to the west abnormally.At this time,the corresponding high-altitude circulation background where the heat wave occurs is a negative 200 h Pa meridional circulation anomaly and a 500 h Pa geopotential positive anomaly.In addition,the weak wind speed between land and sea and the significant upward trend of atmospheric heat waves at night also provide favorable conditions for the occurrence of heatwaves.(3)From SSP2-4.5 to SSP5-8.5 scenarios,the high-value areas of the atmospheric heatwave HWT index are concentrated in the South China coast,the southwest and the Sichuan Basin;the spatial distribution of HWDU and HWN indices is similar to the HWT index;the high-value areas of the HWI index are concentrated in the central and northern regions.For marine heatwave,the HWT index is distributed in a high-low-high pattern from north to south.The two high value areas are located in the east of the Bohai Sea,the Yellow Sea and the Philippine Islands;the spatial distribution of HWDU index is similar to HWT;the spatial distribution of HWN is opposite to HWT and HWDU.The high-value area is located near the island of Taiwan to the northern South China Sea.Under the SSP2-4.5 scenario,the onshore HWT,HWDU,HWN,and HWI indices have risen to 5.26 days/10 years,0.2days/time/10 years,0.57 times/10 years and 0.07℃/time/10 years(p< 0.01);On the sea,the HWT index shows a quadratic fitting trend with one variavle,and the increasing trends of HWDU and HWI indices reach 27.67 days/time/10 years(p<0.01)and 0.12℃/time/10 years(p<0.01),The HWN index showed a significant decreasing trend,reaching-0.33 times per 10 years(p<0.01).Under the SSP5-8.5 scenario,the development of atmospheric heatwaves is accelerating,while changes in ocean heat waves are slowing down.The four index trends of atmospheric heat wave increased by 3.4 times,4 times,2.4 times and 3 times respectively;the HWDU and HWI indices of ocean heat wave increased by 1.8 times and 2.8 times,respectively,while the trend of decrease of HWN index expanded by 1.8 times.The increase in the HWT index of atmospheric heatwaves is caused by the both increase of the HWDU and HWN indices,but the HWN index changes faster.SSP5-8.5 scenario is 4 times that of SSP2-4.5 scenario and plays a major role;the increase in the HWT index of marine heatwaves is caused by the HWDU index As a result of the increase,the average value increased from 130.6 days/time to 207.4 days/time.That is to say,in the future,the frequency of atmospheric heatwaves in severe areas will increase,while the duration of marine heatwaves in severe areas will prolonged.(4)From 1982 to 2019,the high-value of person-time affected by atmospheric heatwaves in eastern China were mainly located in the North China Plain Yangtze River Delta,and Sichuan Basin,with more than 3 million person-time;most provincial capitals exceed 4 million.The number of people affected by atmospheric heatwaves has increased significantly,reaching 300 million person-time per 10 years(p< 0.01),with an average of 80 million person-time.Before 2040,there is little difference in the number of person-time affected by atmospheric heatwaves under the two different SSP-RCP scenarios,basically around 2 billion person-time;after 2040,the number of person-time affected by atmospheric heatwaves under the SSP5-8.5scenario will increase rapidly,with a peak at 2085,it reached nearly 4.7 billion person-time,with an average of 3.1 billion person-time;under the SSP2-4.5 scenario,the peak occurred around 2076,reaching nearly 3.9 billion person-time,with an average of 2.2 billion person-time.The offshore waters of the Sea of Japan,the Bohai Sea,the Yellow Sea and the East China Sea are the areas with the highest abnormal values of sea surface temperature,generally exceeding 4℃.The vast majority of marine ranching are concentrated in the coastal waters,overlapping with areas with abnormally high sea surface temperatures,and areas with rapid increase in the total number of days and frequency of marine heatwaves.