Year: 2025
Type: article
Abstract: . Equatorial East Africa (EEA) experiences strong intraseasonal precipitation variations; developing understanding of the processes that drive these variations can improve predictability and help local populations be better prepared for extremes. Previous research has highlighted anomalous westerly moisture transport from the Congo basin as an important driver of enhanced precipitation in EEA. Here, we have developed the first spatially unconstrained, objective framework to detect what we refer to as westerly moisture transport events (WMTEs) in ERA5 reanalysis data from 1980 to 2022, revealing new insights into the drivers of these westerlies and their impact on EEA precipitation. We show that over EEA, WMTEs were most common in January and February between about 5° S and 15° S, where there were typically 4–6 WMTE days per month, with each individual event persisting for around 2–4 days. During the March to May wet season in EEA, there were on average around 1–2 WMTE days per month. Using a precipitation attribution algorithm, we estimate that WMTEs were associated with up to 60 % of precipitation during January and February in Tanzania, and up to 20 % of precipitation during March–May to the East of Lake Victoria. Consistent with previous work, we found that WMTEs were more likely during phases 2–4 of the Madden-Julian oscillation (MJO). We expand on previous case-study based investigations by showing that the presence of a tropical cyclone anywhere in the south-west Indian Ocean makes WMTEs up to three times more likely, even during inactive or unfavourable phases of the MJO. This work builds on previous studies of the westerly wind feature by providing an objective framework to describe EEA westerlies and joins previous work in highlighting the complex nature of the interactions between different features of tropical meteorology that drive these short timescale variations.
Source: Weather and Climate Dynamics
Authors: Robert Peal, Emily Collier
Institution: Universität Innsbruck
Language: English
Subfield: Global and Planetary Change
Field: Environmental Science
Domain: Physical Sciences
SDG: Climate action
Open Access status: diamond
OpenAlex ID: W4415987337