泛南海地区极端降水的历史分布和未来演变特征

Extreme Precipitation in the South China Sea and Surrounding Areas:Observation and Projection

泛南海地区是全球海—陆—气相互作用最敏感的区域之一,该区域极端降水释放的潜热加热可以调节局地的温度和湿度廓线对大气环流进行调整,进而影响周边地区甚至全球的天气气候。因此,泛南海地区极端降水的时空变化特征及变异机理一直是国内外学者关注的焦点。本文利用观测数据(1951~2014年)和国际耦合模式比较计划第六阶段(CMIP6)两种共享社会经济路径(SSP1-2.6和SSP5-8.5)的统计降尺度数据(2015~2100年),分析了泛南海地区年平均和季节平均的日降水的最大值(RX1day)、连续5日降水的最大值(RX5day)、极端强降水天数(R20)和非常湿润天(R95p)的时空变化特征。RX1day、RX5day、R20和R95p常用于表征极端强降水、持续性强降水、极端强降水的频率和极端累计降雨量的特征。1951~2014年泛南海地区年平均和季节平均的四个极端降水指数的较大值均分布在东南亚、中国东南部以及青藏高原南坡地区,即这些区域不仅是极端强降水发生的区域,也是持续性强降水以及高频极端降水发生的区域。季节平均的极端降水指数特征表现为:东南亚一年四季都极易发生强降水、持续性强降水和高频极端降水;南亚、青藏高原以及东亚的各个极端降水指数在夏季最大,秋季和春季次之,冬季最小。SSP1-2.6和SSP5-8.5情景下2015~2100年泛南海地区年平均和季节平均的四个极端降水指数的空间分布与历史时期相似,且对整个区域而言,各个指数均呈显著增加的趋势。由各个指数在未来三个时段(2016~2035年、2046~2065年和2080~2099年)相比于1995~2014年的百分比变化可知,南亚和青藏高原是泛南海地区未来强降水、持续性强降水以及高频极端降水变化最显著的区域。由此可知,虽然东南亚是历史时期四个极端降水指数的大值区,但该区域各个极端降水指数在未来三个时段的变化没有其他区域明显。此外,以东南亚为例,本文分析了该区域1979~2019年夏季极端降水的形成机理,发现印度洋冷海温异常、热带北大西洋暖海温异常以及热带太平洋和大西洋海温异常是造成东南亚夏季极端降水呈北湿南干、全区一致偏湿和北干南湿的关键因子。

The South China Sea and its surrounding areas are among the most sensitive regions and are characterized by strong sea-land-air interactions.Extreme precipitation patterns over the region have garnered extensive attentions in recent decades,which significantly affects global climate variabilities by providing substantial energy and moisture for global atmospheric circulation.This study utilizes gauge-based gridded data and a statistically downscaled CMIP6(the sixth phase of the international Coupled Model Inter-comparison Project)dataset to systematically investigate the historical and future spatiotemporal characteristics of maximum 1-day precipitation(RX1day),maximum 5-day precipitation(RX5day),very heavy precipitation days(R20),and very wet days(R95p)over this region.The indices RX1day,RX5day,R20,and R95p are commonly used to represent heavy rainfall,persistent heavy rainfall,highfrequency heavy rainfall,and accumulated heavy rainfall,respectively.Our findings reveal that these four indices share a similar spatial pattern from 1951 to 2014 on annual and seasonal time scales.Large values of the indices are recorded over Southeast Asia,Southern China,and the southern part of the Tibetan Plateau.In other words,these regions not only experience heavy rainfall but also exhibit sustained and high-frequency heavy precipitation events.The four indices exhibit large values over Southeast Asia across all seasons.They also exhibit high(low)values over South Asia,the Tibetan Plateau,and East Asia during summer(winter).The projected future patterns of these indices maintain their historical spatial counterparts.Moreover,the four indices averaged over the entire region exhibit increasing trends from 2015 to 2100 under the SSP1-2.6 and SSP5-8.5 scenarios.The percentage changes in the indices from 2016 to 2035,2046 to 2065,and 2080 to 2099 under the two scenarios exhibit a slight decrease in Southeast Asia and East Asia compared with 1995-2014.However,the percentage changes increase over South Asia and the Tibetan Plateau.In addition to these findings,we explore the physical mechanisms associated with extreme precipitation over Southeast Asia.We find that the extreme rainfall patterns observed over Southeast Asia can be attributed to various sea surface temperature anomalies(SSTAs).Cold SSTAs over the Indian Ocean result in dry conditions in the south and wet conditions in the north.Meanwhile,warm SSTAs over the tropical North Atlantic lead to overall wet conditions across Southeast Asia.Finally,SSTAs over the tropical Pacific and Atlantic chang this pattern,with dry conditions in the north and wet conditions in the south.