长江中下游平原2022年高温干旱复合型极端事件的影响因子分析

基于ERA5和ERA5-LAND再分析资料,利用水量平衡分解法,将净降水量(降水量减蒸发量,P-E)的变化分解为热动力贡献、热力学贡献和涡动贡献,分析了2022年发生在长江中下游平原的极端干旱事件的机理和演变过程,并将其与2013年同样发生在长江中下游的高温干旱事件进行对比分析。净降水量分析表明,2022年长江中下游平原汛期前期(5—6月)干旱主要由降水量减小导致,水量平衡分解分析显示,湍流涡动与平均环流变化的贡献是早期干旱的主要因子;中期(7—8月)的高温增强了地表蒸散发,尤其是裸土蒸发的增强,加剧了干旱程度,水量平衡分解显示,表征温度升高引起的水汽含量变化的热力贡献对干旱加剧的贡献最大;后期(9—10月)高温进一步引发平均环流变化导致的热动力贡献延长了干旱持续时间。而2013年的高温干旱为高温引发的热力学贡献主导,持续事件短,干旱程度弱。本文对2022年发生在长江中下游平原的高温干旱复合型极端事件的发展和演变过程的剖析,可为湿润区极端高温干旱事件的预测预警提供参考。

Analysis of influencing factors of heatwave and drought compound extreme events in 2022 in the middle-lower Yangtze Plain

Drought poses a significant threat to economic and agricultural development,impacting physical health and daily life.With global warming,heatwaves,and droughts,extreme events are occurring with increasing frequency,exacerbating disaster risks.The middle-lower Yangtze Plain,one of China''s most densely populated,economically developed,urbanized regions,experienced the most severe heatwave and drought-compound extreme event since 1961 in 2022.This event significantly impacted energy supply,agricultural production,and the ecosystem.This study analyzes precipitation and evaporation characteristics during the flood season from 2000 to 2022,exploring the mechanism and evolution of the 2022 extreme drought event in the middle-lower Yangtze Plain.A comparison with the high-temperature and drought events in 2013 provides a deeper understanding of the relationship between high temperatures and extreme drought in this region.The hydrological drought index,net precipitation(precipitation minus evapotranspiration,P-E) is used to analyze the drought conditions.Using ERA5 and ERA5-LAND reanalysis data,changes in P-E are decomposed into dynamic,thermodynamic,and transient eddy componentsby analyzing the moisture flux budget.Surface temperature during the 2022 flood season increased by nearly 1 ℃ compared to the 20-year average(2000—2019),with temperatures rising over 2 ℃ from July to August.Precipitation during the flood season decreased by 37％ and by 45％ from July to August,respectively,compared to the average for the same period.Net precipitation analysis indicates that the drought was primarily caused by decreased precipitation in the early flood season(May—June) of 2022.Moisture flux budget decomposition shows that changes in transient eddy and mean circulation were major contributorsto the early drought.In the mid-period(July—August),high temperatures enhanced surface evapotranspiration,especially in bare soil,worsening the drought.The thermodynamic contributionfrom increased specific humidity,driven by temperature rise,was the greatest factorin drought intensification.In the later period(September-October),high temperatures further altered the average circulation,with the dynamic component extending the drought duration.In contrast,the 2013 high-temperature and drought event was initially dominated by thermodynamic contributions,with mean circulation and transient eddy changes intensifying the mid-period droughtand only thermodynamic contributions remaining later,resulting in shorter duration and weaker drought severity.This analysis of the 2022 heatwave and drought compound extreme event development and evolution in the middle-lower Yangtze Plain provides a reference for predicting and warning about high-temperature and drought extreme events in humid areas.In-depth research on these development and evolution events can improve regional drought event prediction and duration forecasting.