Future Precipitation Projections over Central and Southern Africa and the Adjacent Indian Ocean: What Causes the Changes and the Uncertainty?
Future Precipitation Projections over Central and Southern Africa and the Adjacent Indian Ocean: What Causes the Changes and the Uncertainty?
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DOI：
10.1175/jcli-d-17-0311.1
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发表时间：
2018-05
影响因子：
4.9
通讯作者：
M. Lazenby;M. Todd;R. Chadwick;Yi Wang
中科院分区：
文献类型：
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作者：
M. Lazenby;M. Todd;R. Chadwick;Yi Wang
区域尺度未来降水预测对于气候变化适应活动至关重要。因此，量化预计的变化和相关的不确定性并理解负责的模型流程非常重要。本文讨论了南部非洲和邻近印度洋的这些挑战，重点关注当地的雨季。二十一世纪末的降水预测表明 CMIP5 多模式平均值中存在明显的偶极模式。偶极子表明未来最大降雨量气候轴北（南）的湿润（干燥），意味着ITCZ和南印度洋辐合带向北移动，这与简单的“湿变湿”模式并不相符。这种模式在南半球初夏最为明显，表明南部非洲大部分地区的雨季较晚且较短。使用分解方法，我们确定了预测变化的偶极子模式背后的物理机制以及相关的模型间不确定性。预测的偶极子模式很大程度上与指示对流位置变化的动态分量相关。在印度洋上空，ITCZ 明显的北移可能反映了印度洋上空南北海温梯度变化的响应，与“最暖变湿”机制一致。陆地上的亚热带干燥相对强烈，特别是在雨季初期。这与对流位置的动态变化有关，这可能与南印度洋的区域海温结构以及相对湿度的热力学下降有关。讨论了理解和预测中潜在的不确定性的影响。
Future projections of precipitation at regional scales are vital to inform climate change adaptation activities. Therefore, is it important to quantify projected changes and associated uncertainty, and understand model processes responsible. This paper addresses these challenges for southern Africa and the adjacent Indian Ocean focusing on the local wet season. Precipitation projections for the end of the twenty-first century indicate a pronounced dipole pattern in the CMIP5 multimodel mean. The dipole indicates future wetting (drying) to the north (south) of the climatological axis of maximum rainfall, implying a northward shift of the ITCZ and south Indian Ocean convergence zone that is not consistent with a simple “wet get wetter” pattern. This pattern is most pronounced in early austral summer, suggesting a later and shorter wet season over much of southern Africa. Using a decomposition method we determine physical mechanisms underlying this dipole pattern of projected change, and the associated intermodel uncertainty. The projected dipole pattern is largely associated with the dynamical component of change indicative of shifts in the location of convection. Over the Indian Ocean, this apparent northward shift in the ITCZ may reflect the response to changes in the north–south SST gradient over the Indian Ocean, consistent with a “warmest get wetter” mechanism. Over land subtropical drying is relatively robust, particularly in the early wet season. This has contributions from dynamical shifts in the location of convection, which may be related to regional SST structures in the southern Indian Ocean, and the thermodynamic decline in relative humidity. Implications for understanding and potentially constraining uncertainty in projections are discussed.