Meteorological causes of the catastrophic rains of October/November 2019 in equatorial Africa

Abstract The rains of October and November 2019 brought disaster to much of equatorial Africa. In East Africa tremendous rains triggered flooding and landslides in Kenya, causing over 100 deaths and the displacement of some 18,000 people. The situation was exacerbated by an unprecedented locust plague made possible by the intense rains. Floods in the Democratic Republic of the Congo displaced some 40,000 people. The level of the Mono River jumped a meter in four days, producing floods that affected some 50,000 residents of Benin and Togo. This article places the October and November 2019 rainfall extremes in historic context and analyzes the juxtaposition of forcings required to explain these unprecedented hydro-climatic extremes in equatorial Africa. The meteorological factors considered include the Dipole Mode Index, zonal winds over the central Indian Ocean, the Walker circulation, moisture flux and divergence, ENSO and tropical sea-surface temperatures in the Atlantic and Indian Oceans, and zonal circulation. The Dipole Mode Index reached record levels and anomalously high values persisted for five months. This was clearly a major factor in eastern Africa. The impact there was enhanced by increased moisture flux from the Indian Ocean and a marked reduction of the descending branch of the Indian Ocean Walker cell, which strongly controls October–November rainfall. The factors in other regions included extremely warm SSTs in the tropical eastern Atlantic Ocean, the Walker circulation, anomalous moisture flux and flux divergence, and changes in the zonal winds.