Asia Faces a Growing Threat From Intraseasonal Compound Weather Whiplash.

The sudden swings between drought/heat and pluvial could cause adverse impacts far surpassing the sum of their individual effect. We propose a concept of intraseasonal "compound whiplash event" (CWE) to investigate sudden swings between wet and the compounding warm‐dry events and their changes under climate change. We find that global warming would likely escalate the compound whiplash frequency to two to three and half times (two to three times) by the end of the 21st century under the business‐as‐usual scenario (mitigated scenario). The growing threat of CWE not only stems from the increasing occurrence but also from its intensified severity and extended spatial coverage. Among all sub‐regions, East Asian summer monsoon (EASM) region would expect the largest intensification. The resulting population exposure would soar two‐to‐three‐fold over Asia. Populous regions such as North India and EASM region might face a much worse situation than the western China where population is sparse and projected to decline. Moreover, the seasonality of swings with opposite directions would further split as a response to the skewed Asian monsoon annual cycle, leading to more frequent heat‐drought to pluvial swings in spring, and more opposite‐direction swings in autumn, disrupting cultivation and water management convention. Plain Language Summary: Either drought/heat or pluvial already causes adverse impacts on ecosystem and human society. The swing between these extremes could escalate their impact to the next level, far beyond their simple addition. Though some studies have investigated weather whiplash on longer time scales, such as months to years, intraseasonal whiplashes on an event basis are rarely explored. Hence, we propose a concept of "compound whiplash event" to investigate the intraseasonal alternation between warm‐dry and wet conditions and their potential changes in a warmer future climate. We find that global warming not only leads to one‐to‐two and half times more compound weather whiplashes by the end of 21st century under the business‐as‐usual scenario, but also intensifies their severity and extends their extent. Within Asia, East Asian summer monsoon region will likely face the largest increase. As a result, the population exposed to the compound weather whiplash would double or even triple, especially in the populous regions with further population growth. In addition, with skewed Asian monsoon annual cycle, the seasonality of swings expects a coherent shift, that is, more heat‐drought swings in spring and more opposite‐direction swings in autumn, potentially posing more disruption in agricultural and water management activities. Key Points: Intraseasonal compound weather whiplash in Asia is introduced and defined using a 3D event‐based approachCompound weather whiplash is projected to triple with intensified severity and shifted seasonality by the end of the 21st centurySouthern and eastern Asia will see the most increase in population exposure while population decline tempers the increase elsewhere [ABSTRACT FROM AUTHOR]