SGER: Investigating the Joint Occurrence of Summer Drought and Heat Waves in Climate Change Projections

这是气候变异性和可预测性(CLIVAR)计划试点项目DRICOMP下的一笔赠款，用于耦合模式干旱项目，重点是对干旱的机制进行初步探索，因为它们代表了全球气候模式的输出，并试图评估这些模式在模拟干旱方面的可靠性。夏季干旱经常但并不总是伴随着极端日最高温度或“热浪”，其物理联系是地表能量平衡的变化有利于在干旱期间增加显性加热。虽然气候模型预测一致认为，21世纪地表气温可能会在大多数陆地地区上升(有利于热浪)，但预计的降水变化(因此也包括干旱)存在相当大的不确定性，特别是在区域范围内。这个项目是在最新的气候变化预测中首次看到热浪和干旱同时发生的情况。这些极端情况同时发生的有害后果使这一话题具有极大的实用和科学意义。研究将集中在非洲南部高度脆弱、易发生干旱的地区。研究人员将初步努力解决以下悬而未决的问题：耦合模型再现过去半个世纪联合干旱/热浪的观测统计数据的情况如何？在21世纪的气候预测中，这种共同发生的情况会发生怎样的变化？这种变化在多大程度上与地表通量的变化有关？将考虑以降水量为基础的各种气象干旱指标，以及降水量减去地表蒸发量。气候变暖通常会增加每日极端温度的可能性，预计夏季会加剧地表干燥。由于降水预测不那么明确，这项研究可能会深入了解温度和降水在气候变化预测中热浪和干旱共同发生的相对作用的变化。这些研究的更大影响源于干旱与酷热结合时对粮食生产的影响，这增加了作物的水分损失，并给牲畜带来压力。增进对干旱和热浪综合风险的了解，以及21世纪这种风险的变化，将对农业和粮食分配部门的决策者来说很有价值。

This is a grant under a Climate Variability and Predictability (CLIVAR) Program pilot project called DRICOMP, for the Drought in Coupled Models Project, which focuses on making initial explorations into the mechanisms of drought as they are represented in the output of global climate models and on attempting to assess the reliability of these models in simulating drought.Summer drought is often, but not always, accompanied by periods of extreme daily maximum temperatures or "heat waves", the physical link being that changes in the surface energy balance favor increased sensible heating during drought. While climate model projections agree that 21st century surface air temperatures are likely to increase over most land areas (favoring heat waves), considerable uncertainty surrounds the projected changes of precipitation (and therefore of drought), particularly on regional scales. This project is a first look at the joint occurrence of heat waves and drought in newly available climate change projections. The deleterious consequences of the simultaneous occurrence of these extremes make the topic of great practical, as well as scientific, interest.The research will focus on the highly vulnerable, drought-prone region of southern Africa. The investigators will make initial efforts to address the following open questions: How well do coupled models reproduce the observed statistics of joint drought/heat waves over the last half-century? How does this joint occurrence change in 21st century climate projections? To what extent can any such changes be related to changes in surface fluxes? Various meteorological drought indicators based on precipitation, as well as precipitation minus surface evaporation, will be considered. A warmer climate generally increases the probability of extreme daily temperatures and is expected to intensify surface drying in summer. With precipitation projections less clear, the study may provide insight into changes in the relative roles of temperature and precipitation on the joint occurrence of heat waves and drought in climate change projections.Broader impacts of these studies stem from the impacts on food production of drought when it is coupled with severe heat, which increases water losses from crops and stresses livestock. Improved knowledge of the risk of combined droughts and heat waves, as well as the changes in this risk in the 21st century, will be valuable to decision makers in the agricultural and food distribution sectors.