Drying Versus Wettening of the East African Climate

该项目考虑了3月至5月“长雨季”期间东非降水量的变化，文献中对这一季节的关注少于对10月至12月“短雨季”的关注。 虽然短雨季有更强的年际变化和更强的联系厄尔尼诺现象，长期降雨经历了1999-2009年和1980-1998年期间的下降。降雨量的这种十年趋势与印度洋SST的增加有关，而SST的增加又归因于人为气候变化。 然而，耦合模式相互比较项目第3版（CMIP 3）的气候变化模拟显示，一个强有力的预测是，东非将在21世纪变得更加湿润。 驱动长时间降雨的气候过程及其年际变率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。该研究分为三项任务：1）确定与观测到的东非季节性降雨变率及其最近下降有关的大尺度和区域尺度大气和海洋表面温度（SST）异常模式的主要特征; 2）利用气候模型模拟和理想化气候模型实验来辨别观测到的特征和变化的主要驱动因素;（3）在CMIP 5试验中确定与21世纪东非长降雨量变化相关的气候模式预测中的动力学和热力学过程，并将结果与CMIP 3试验分析中发现的结果进行对比。东非是地球仪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量变化的可能性对该区域的发展至关重要。 该奖项下的工作将与饥荒预警系统网络和红十字国际联合会等组织密切相关，这两个组织都与方案执行机构的所在机构有着密切的联系。 因此，这项工作除了具有科学价值外，还具有重要的广泛影响。

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.