Intermittent heavy rainfall over an eleven day period (11–21 January 2013) led to devastating floods over parts of South Africa and southern Mozambique, with regions within the Limpopo River Basin (LRB) being the worst affected. Previous observational work, based on an Eulerian analysis and low resolution data, indicated that moisture emanating from anomalously warm waters off the Angolan coast played a very important role in the evolution of this heavy rainfall event. However, there has been some debate about this moisture source and the general synoptic settings of the event that produced the heavy rainfall in the LRB. In this study, an analysis of the event using WRF model (12 km resolution) simulations, reanalyses, SAWS synoptic maps and NASA satellite images indicated that a tropical low was largely responsible for the floods which occurred over the LRB, particularly between 17 and 21 January. Moisture sources and transport are determined using the HYSPLIT model forced with WRF output and reveal a new perspective on the complex evolution of the event. During the early parts of the event, there were two core moisture source regions: i) a continental source with moisture being supplied from the Congo Basin region and, ii) a local oceanic region with moisture originating from the Agulhas Current and the Mozambique Channel. As the event progressed, the dominant moisture input was from parts of the South Indian Ocean including off the coast of Tanzania/Mozambique and to the east of Madagascar. Two days showed a moisture contribution from the tropical South Atlantic Ocean. A WRF sensitivity study with the observed warm SST anomaly off Angola replaced by climatological SST there indicated a reduction of moisture from the tropical South East Atlantic Ocean in the beginning and towards the end of the event, when there was some of the heaviest rainfall over the LRB, thereby reinforcing the suggestion that there was also some moisture being sourced from the tropical South East Atlantic during part of the observed event. When calculated over the entire 11–21 January 2013 event, there were four moisture sources, the largest contribution of which was from the Agulhas Current/Mozambique Channel and the South Indian Ocean, accounting for 53% of the moisture, followed by the continental source (25%). The tropical western Indian Ocean had the third largest contribution, at 17%, and the midlatitude South Atlantic Ocean (5%) contributed the least.

为期 11 天（2013 年 1 月 11 日至 21 日）的间歇性强降雨导致南非部分地区和莫桑比克南部发生毁灭性洪水，林波波河流域 (LRB) 内的地区受灾最严重。先前基于欧拉分析和低分辨率数据的观测工作表明，来自安哥拉海岸异常温暖水域的水分在这次强降雨事件的演变过程中发挥了非常重要的作用。然而，关于这一水分来源和在 LRB 中产生强降雨的事件的一般天气背景存在一些争论。在这项研究中，使用 WRF 模型（12 公里分辨率）模拟、重新分析、SAWS 天气图和 NASA 卫星图像表明，热带低气压是造成 LRB 上空洪水的主要原因，尤其是 1 月 17 日至 21 日之间。水分来源和传输是使用 HYSPLIT 模型与 WRF 输出强制确定的，并揭示了事件复杂演变的新视角。在事件的早期阶段，有两个核心水分源区：i) 大陆源，水分来自刚果盆地地区，ii) 局部海洋区域，水分来自阿古拉斯海流和莫桑比克海峡。随着事件的进展，主要水分输入来自南印度洋的部分地区，包括坦桑尼亚/莫桑比克海岸和马达加斯加以东。两天显示来自热带南大西洋的水分贡献。一项 WRF 敏感性研究，在安哥拉附近观测到的温暖海温异常被气候海温替代，表明在事件开始和接近结束时热带东南大西洋的水分减少，当时有一些最严重的降雨LRB，从而加强了在部分观测事件期间也有一些水分来自热带东南大西洋的建议。在整个 2013 年 1 月 11-21 日事件计算时，有四个水分源，其中贡献最大的是厄加勒斯海流/莫桑比克海峡和南印度洋，占水分的 53%，其次是大陆源(25%)。