Anomalous circulation patterns associated with 2011 heavy rainfall over northern Tanzania

The socio-economic impacts of floods calls for improved understanding of flood drivers. While the large-scale circulation anomalies associated with rainfall anomalies is a well-studied, the interaction of the phases of the Indian Ocean Dipole and the El Nino Southern Oscillation with rainfall anomalies over Tanzania is comparatively less understood. This paper fills this knowledge gap by studying the circulation anomalies associated with heavy rainfall events over northern Tanzania during the 2011 October-December season. A total number of 28 heavy rainfall events were observed, whereby 8, 11, and 9 events are recorded during October, November, and December, respectively. Bukoba is the only region that experienced more heavy rainfall events during each month of the study. Analysis of circulation anomalies reveals that heavy rainfall events are significantly related to moisture flux convergence that was transported through the northeasterly, southeasterly, and westerly pathways. The remarkable active upward motion that is conducive for heavy rainfall events also occurs over northern Tanzania. The moisture flux in October and November was under the influence of the cyclonic circulation over the south-central Indian Ocean and Indian Ocean Dipole. In December, westerly from the Congo basin forest play a significant role in enhancing the moisture flux. The results demonstrate the interplay between Indian Ocean Dipole and westerly in modulating moisture flux over northern Tanzania at a sub-seasonal time scale. The current study offers useful angles of contribution in understanding the mechanism controlling the country's weather, therefore improving forecasting accuracy.