Combined Impacts of Warm Central Equatorial Pacific Sea Surface Temperatures and Anthropogenic Warming on the 2019 Severe Drought in East China

Abstract

A severe drought occurred in East China (EC) from August to October 2019 against a background of long-term significant warming and caused widespread impacts on agriculture and society, emphasizing the urgent need to understand the mechanism responsible for this drought and its linkage to global warming. Our results show that the warm central equatorial Pacific (CEP) sea surface temperature (SST) and anthropogenic warming were possibly responsible for this drought event. The warm CEP SST anomaly resulted in an anomalous cyclone over the western North Pacific, where enhanced northerly winds in the northwestern sector led to decreased water vapor transport from the South China Sea and enhanced descending air motion, preventing local convection and favoring a precipitation deficiency over EC. Model simulations in the Community Earth System Model Large Ensemble Project confirmed the physical connection between the warm CEP SST anomaly and the drought in EC. The extremely warm CEP SST from August to October 2019, which was largely the result of natural internal variability, played a crucial role in the simultaneous severe drought in EC. The model simulations showed that anthropogenic warming has greatly increased the frequency of extreme droughts in EC. They indicated an approximate twofold increase in extremely low rainfall events, high temperature events, and concurrently dry and hot events analogous to the event in 2019. Therefore, the persistent severe drought over EC in 2019 can be attributed to the combined impacts of warm CEP SST and anthropogenic warming.

摘要

2019年,长江中下游地区在显著增暖背景下遭遇严重的伏秋连旱,给农业生产和人民生活造成较大影响,导致该极端干旱事件产生的机制及其与全球变暖之间的联系亟待研究。本文的分析结果表明,赤道中太平洋暖海温和人类活动导致的全球变暖对该事件均有重要贡献。中太平洋暖海温异常导致西北太平洋出现气旋性环流异常,其西北侧的北风异常减弱了源自南海的水汽输送,增强了长江中下游地区的下沉运动,抑制局地对流,导致降水稀少。CESM-LE计划(Community Earth System Model Large Ensemble Project)的模式模拟结果验证了赤道中太平洋暖海温异常与长江中下游地区干旱之间的物理联系。赤道中太平洋极端暖海温异常作为气候系统内部变率,对2019年长江中下游地区的伏秋连旱具有重要贡献;同时,人类活动引起的全球变暖显著增加了类似2019年长江中下游地区极端干旱事件的发生概率。基于CESM-LE计划的模式模拟结果,全球变暖使类似2019年长江中下游地区的极端少雨、高温和热干旱事件的发生概率大约增加了2倍。