中国高温、干旱及其复合事件的研究进展和展望

Research progress and prospect on the drought,heatwave,and compound drought and heatwave events in China

摘要:

干旱是全球最主要、影响最严重的气象灾害之一。随着全球变暖,干旱更易与高温同时发生,干旱与高温的正反馈过程导致极端事件持续更久、强度更强,形成高温干旱复合极端事件,对农业、生态环境等造成更为严重的影响。本文通过对中国高温、干旱及其复合事件研究进展的回顾,总结了中国高温、干旱及其复合事件的变化事实,并对影响中国高温、干旱的关键因子及物理机制进行了梳理;指出了当前研究存在的不足,并提出系统研究海温-陆面-海冰-大气多因子、多过程协同影响中国复合高温干旱事件的必要性;最后,对当前高温干旱的预测现状进行了简要回顾,指出在系统认识复合高温干旱事件发生发展机制的基础上,亟须发展动力-统计相结合的方法,以提升其预测水平。

Abstract:

Drought,as one of the leading and most severe meteorological disasters globally,occurs frequently in China.Between 2001 and 2020,approximately 48％ of the crop area affected by meteorological disasters in China were due to drought (Li et al.,2021).Heatwaves are believed to be increasing under global warming,while droughts exhibit more regionalized patterns.The simultaneous occurrence of drought and heatwave has become more frequent,mainly due to increase in high temperature events driven by global warming.High temperature and soil moisture deficit can reinforce each other,likely leading to more frequent,longer-lasting,and stronger extreme events,known as compound drought and heatwave events (CDHEs).CDHEs have more severe and persistent impact on agriculture and ecological environment through the positive feedback between drought and high temperature.This work provides a brief review of research progress on drought,heatwave,and CDHE events in China.First,the various definitions of drought,heatwave,and CDHE are summarized.The influencing factors,including sea surface temperature (SST) and sea ice,land surface conditions,atmospheric circulation patterns,and the underlying physical processes,are then reviewed.
Northeast China (NEC) is a typical region where drought,heatwave,and CDHE events often occur.Previous studies have identified several factors that influence these events in NEC.As an example,we integrate the effects of sea-land-ice-air system on NEC drought,heatwave,and CDHE events based on prior research,constructing a simplified physical framework.The key mechanisms can be briefly depicted as follows:
Local anomalous anticyclone plays a central role in drought,heatwave,and CDHE events.These local circulation anomalies can be induced by Rossby wave train in the upper atmosphere,which are influenced by climate variations in the upstream,including the North Atlantic Oscillation (NAO),Atlantic Multidecadal Oscillation (AMO),North Atlantic SST,polar sea ice,and soil temperature in Central Asia.Additionally,phenomena like El Niño and Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) can significantly affect the drought,heatwave,CDHE events in NEC.
Despite the identification of several local,regional,remote natural climate systems contributing to drought,heatwave,CDHE events in China,a comprehensive understanding of the synergistic physical and dynamical mechanisms behind these events remains lacking.These processes are complicated by the interplay between regional SST,sea ice,land surface conditions,and atmospheric dynamics.In addition to natural climate systems,anthropogenic activity are proposed to significantly drive the increasing frequency and intensity of drought,heatwave,CDHE events in China.However,the relative contribution of natural climate variation and anthropogenic forcing remain unclear and require further investigation.
Although the impact of drought,heatwave,CDHE events is growing rapidly,predictive skills remain limited.Numerical weather forecast based on state-of-the-art models have a skill horizon of only about one week.These limitations arise from our incomplete understanding of the underlying physical processes and the imperfect representation of the real world by current numerical models.The first step in improving prediction skills is to systematically enhance our understanding of the physical processes driving extreme climate events.Developing effective dynamical-statistical methods,including deep-learning techniques,is essential for improving the predictability of drought,heatwave,CDHE events over various timescales,addressing the urgent need to prevent disasters and reduce damages under global warming.