Drying Versus Wettening of the East African Climate

该项目考虑了3月至5月“长雨”季节东非降水的变化，与10月至12月的“短雨”相比，这一季节在文献中受到的关注较少。虽然短雨季节的年际变异性更强，与厄尔尼诺现象的联系也更强，但在1999-2009年和1980-1998年期间，长雨经历了下降。降雨量的这种十年趋势与印度洋海温上升有关，而海温上升又归因于人为气候变化。然而，来自耦合模式比较项目第三版(CMIP3)的气候变化模拟显示，东非在21世纪将变得更加潮湿。驱动长降雨的气候过程及其年际变化尚未得到很好的了解，更好地了解这些过程有助于确定模型预测是否可信，以及哪些因素导致长期模型预测和短期观测趋势之间的二分法。这项研究分为三个任务：1)确定与东非地区观测到的季节性降水变率及其近期下降有关的大尺度和区域尺度大气和海面温度(SST)异常模式的关键特征；2)利用气候模式模拟和理想化气候模式实验来识别观测特征和变化的主要驱动因素；3)在CMIP5实验中确定与21世纪东非长雨降水变化有关的气候模式预测中的动力和热力学过程，并将结果与CMIP3实验分析中发现的结果进行对比。东非是全球粮食最不安全的地区之一，更好地了解干旱的原因和未来降雨变化的可能性可能对该地区的发展发挥关键作用。这一奖项下的工作将与饥荒预警系统网络(FEWSNET)和红十字国际联合会(红十字国际联合会)等组织高度相关，这两个组织都与私营部门主管机构有密切联系。因此，这项工作除了具有科学价值外，还具有重要的更广泛的影响。

This project considers changes in East African precipitation during the March to May "long rains" season, which has received less attention in the literature than the October to December "short rains". While the short rains season has stronger interannual variability and stronger links to El Nino, the long rains have experienced a decline between the periods 1999-2009 and 1980-1998. This decadal trend in rainfall has been linked to increasing SST in the Indian Ocean, which in turn has been attributed to anthropogenic climate change. However, climate change simulations from the Coupled Model Intercomparison Project version 3 (CMIP3) show a robust projection that East Africa will become wetter over the 21st century. The climate processes which drive the long rains and their interannual variability are not well understood, and a better understanding of these processes could help to determine whether the model projections are credible, and what factors lead to the dichotomy between long-term model projections and the shorter-term observed trend. The research is divided into three tasks: 1) Identifying the key features of the anomalous large- and regional-scale atmospheric and sea surface temperature (SST) patterns that are linked to observed seasonal rainfall variability and its recent decline in East Africa; 2) Employing climate model simulations and idealized climate model experiments to discern the main drivers of the observed features and changes; and 3) Identifying dynamical and thermodynamical processes in climate model projections associated with changes in long rains precipitation in East Africa during the twenty-first century in the CMIP5 experiments, contrasting results with those found in analysis of CMIP3 experiments.East Africa is one of the most food-insecure regions of the globe, and a better understanding of the causes of drought and the likelihood of future rainfall change could play a critical role for the development of the region. Work under this award will be highly relevant to organizations including the Famine Early Warning Systems Network (FEWSNET) and the International Federation of the Red Cross (IFRC), both of which have close ties to the PIs' home institution. The work thus has important broader impacts in addition to its scientific merit.