ABSTRACT: Southern Africa relies heavily on precipitation for agricultural purposes; therefore, spatial and temporal changes in precipitation are crucial to identify and understand. The South Indian Ocean Convergence Zone (SIOCZ), a large-scale, austral summer rainfall feature extending across southern Africa into the southwest Indian Ocean, is evaluated in future projections. Using a best-fit algorithm, future projections of the SIOCZ are determined, which indicate a northward shift of approximately 120 km in CMIP5 models under RCP8.5. A dipole pattern of precipitation wetting/drying is evident, where wetting occurs to the north of the climatological axis of maximum rainfall, implying a northward shift of the Inter Tropical Convergence Zone, consistent with the SIOCZ shift. Common drivers responsible for model changes include enhanced warming in the northern Indian Ocean in line with the ‘warmest-get-wetter’ sea surface temperature hypothesis, which impacts circulation by transporting moisture away from the SIOCZ towards the equator. Most CMIP5 models exhibit drying trends over the SIOCZ region, with mechanisms driving uncertainty related to diverse warming trends across models. Empirical orthogonal function patterns of future precipitation changes across CMIP5 models exhibit a pattern much like the SIOCZ, which is related to inter-model changes in future temperature changes. Reductions in model spread are established in SIOCZ projections, whereby model processes of change exhibit agreement, despite differing initial SIOCZ conditions. Therefore, model process convergence and coherence are established with respect to projected changes in the SIOCZ, irrespective of initial climatology biases. Understanding future changes in this feature will help inform decision-making for water and agriculture adaptation planning in southern Africa.

中文翻译：

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评估 CMIP5 模型预测的南印度洋辐合区的未来变化以及相关的不确定性

摘要：南部非洲的农业严重依赖降水；因此，降水的时空变化对于识别和理解至关重要。南印度洋辐合带（SIOCZ）是一个大规模的南方夏季降雨特征，横跨南部非洲延伸至西南印度洋，在未来的预测中将进行评估。使用最佳拟合算法，确定了 SIOCZ 的未来预测，这表明 RCP8.5 下的 CMIP5 模型向北移动了约 120 公里。降水湿润/干燥的偶极模式很明显，其中湿润发生在最大降雨量气候轴以北，这意味着热带辐合带向北移动，与 SIOCZ 移动一致。导致模型变化的常见驱动因素包括北印度洋变暖加剧，这符合“最温暖变得更湿润”的海面温度假说，该假说通过将水分从SIOCZ输送到赤道来影响环流。大多数 CMIP5 模型都表现出 SIOCZ 地区的干燥趋势，其机制驱动了与模型中不同变暖趋势相关的不确定性。CMIP5 模型未来降水变化的经验正交函数模式表现出与 SIOCZ 非常相似的模式，这与未来温度变化的模型间变化有关。SIOCZ 预测中建立了模型分布的减少，尽管初始 SIOCZ 条件不同，但模型变化过程表现出一致性。因此，无论初始气候学偏差如何，模型过程的收敛性和一致性都是针对 SIOCZ 的预计变化而建立的。了解这一特征的未来变化将有助于为南部非洲的水和农业适应规划的决策提供信息。