Controls on Southern African Wet Season Timing under Climate Change

气候变化下南部非洲雨季时间的控制

• 批准号: 2439048
• 金额: --
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2439048
• 关键词: Controls; Southern; African; Wet; Season

Southern Africa's economy, rural population and economic development are highly dependent on rainfall, which varies significantly on intraseasonal to multidecadal timescales (Cook and Reason, 2004; Tadross, Hewitson and Usman, 2005; Conway et al., 2015). The region is also very vulnerable to climate-related risks, such as drought and flooding, and climate change, yet has limited ability to prepare or react to these due to the socio-economic status of the subcontinent (Dunning, Black and Allan, 2018). This research aims to understand why and how the Southern African rainfall season becomes later under climate change, and what role the CAB has in this process. The DPhil will be done through the paper route, so the objectives and methods are separated into three separate papers.The first paper will focus on understanding what key process(es) cause CAB breakdown, both in reanalysis data, historical GCM simulations and higher resolution models. This is because a better understanding of the causation of CAB breakdown will enable better understanding of the influence it may have on rain belt movement under climate change. Firstly, three reanalysis datasets - ERA-5, ERA-Interim and MERRA2 - will be analysed to understand how CAB breakdown occurs and what atmospheric processes are involved. CAB locations will be identified using the method of Howard and Washington (2019), and the data fields of relative humidity, specific humidity, surface winds, temperature and atmospheric pressure will be used. The analysis will then be repeated in the historical simulations of a large group of CMIP6 models, to enable comparison with the reanalysis results to see how well the models are capturing CAB breakdown characteristics and the process of breakdown. Thirdly, the key process(es) will be evaluated in high resolution regional models, to see if they can reveal the characteristics of these processes in more detail.The next research focus and paper of this DPhil will be an evaluation of how the key process(es) influencing CAB breakdown occur in climate change simulations of CMIP6 models, and what influence this has on rain belt timing. This will test in what way(s) the CAB breakdown is connected to the delayed movement of the rain belt under climate change. To begin, rain belt characteristics and their timing will be calculated for both historical and future CMIP6 model runs, in order to see how the timing of the rain belt changes. The next step is to separate the models into those with the greatest and smaller rain belt timing changes, and evaluate the key process(es) in CAB breakdown in each of them. This will likely require an evaluation of relative humidity, moisture, surface winds, pressure, and temperature data fields. This paper will use RCP8.5/SSP585 in the future climate simulations in to maximize any signal of change.As work on the DPhil begins, the scope and focus of the third paper is likely to shift, depending on the interesting discoveries found in papers 1 and 2. However, two ideas for this paper include evaluating CAB breakdown key processes in idealized experiments, or assessing the sensitivity of rain belt timing changes to greenhouse gas emissions. It is likely to be difficult to find a clear causality in the second paper due to the great variety of models in the CMIP6 ensemble, so idealized experiments between the CAB breakdown key processes and rain belt timing under climate change could clarify the relationships between these variables. The latter idea would be a more policy-focused paper, investigating the climatic requirements of Southern African crops and when these are no longer met under different SSP emissions scenarios in CMIP6 models.

南部非洲的经济、农村人口和经济发展高度依赖降雨量，而降雨量在季节内到数十年的时间尺度上变化很大（Cook和Reason，2004年; Tadross、Hewitson和Usman，2005年; Conway等人，2015年）的报告。该地区也非常容易受到干旱和洪水以及气候变化等气候相关风险的影响，但由于次大陆的社会经济地位，该地区准备或应对这些风险的能力有限（Dunning，Black和Allan，2018）。这项研究的目的是了解为什么以及如何南部非洲的雨季在气候变化下变得更晚，以及CAB在这一过程中发挥了什么作用。哲学博士论文将通过论文途径完成，因此目标和方法分为三篇独立的论文。第一篇论文将重点了解导致CAB崩溃的关键过程，无论是在再分析数据、历史GCM模拟还是更高分辨率的模型中。这是因为更好地了解CAB崩溃的原因将有助于更好地了解它可能对气候变化下的雨带运动产生的影响。首先，将分析ERA-5、ERA-Interim和MERRA 2三个再分析数据集，以了解CAB崩溃是如何发生的，以及涉及哪些大气过程。将使用霍华德和华盛顿（2019）的方法确定CAB位置，并将使用相对湿度、比湿度、地面风、温度和大气压力的数据字段。然后将在大量CMIP 6模型的历史模拟中重复分析，以便与再分析结果进行比较，以了解模型捕获CAB故障特征和故障过程的情况。第三，关键过程（es）将在高分辨率的区域模式进行评估，看看他们是否可以揭示这些过程的特征更详细。下一个研究重点和论文的这个博士论文将是评估的关键过程（es）如何影响CAB崩溃发生在气候变化模拟的CMIP 6模式，这对雨带的时间有什么影响。这将测试CAB故障与气候变化下雨带延迟移动的联系方式。开始时，将计算CMIP 6模式历史和未来运行的雨带特征及其时间，以了解雨带的时间如何变化。下一步是将模型分成雨带时间变化最大和最小的模型，并评估每个模型中CAB故障的关键过程。这可能需要对相对湿度、湿度、表面风、压力和温度数据场进行评估。本文将在未来的气候模拟中使用RCP8.5/SSP 585，以最大限度地提高任何变化信号。随着DPhil工作的开始，第三篇论文的范围和重点可能会发生变化，这取决于论文1和2中发现的有趣发现。然而，本文的两个想法，包括评估CAB故障的关键过程中理想化的实验，或评估的敏感性雨带的时间变化的温室气体排放。由于CMIP 6集合中的模式种类繁多，在第二篇论文中可能很难找到明确的因果关系，因此气候变化下CAB分解关键过程和雨带时间之间的理想化实验可以澄清这些变量之间的关系。后一个想法将是一个更注重政策的文件，调查南部非洲作物的气候要求，当这些不再满足不同的SSP排放情景下CMIP 6模型。