Investigation of the 2016 March to May extreme rainfall over Rwanda

Abstract

This paper investigates the features of extreme rainfalls and associated floods during March to May (MAM) season in 2016 over Rwanda and the atmospheric circulation influencing these rainfalls. All stations over the study area received above the average rainfall during MAM (long rain) season in 2016. Among all the months in this season, the rainiest month was April when most parts of the country received highest amounts of rainfall (≥ 180 mm). The presence of anomalous high pressure over the southwestern Indian Ocean, with the help of intense Mascarene high, advected warm moist air through southeasterly winds toward the study area. During this rainy season, the study area was characterized by convergence (divergence) in the lower (upper) troposphere, implying ascending (descending) motion. The ascending moist air at lower level enhanced convection and hence enhanced rainfall over Rwanda. This is associated with more convective activities over central Indian Ocean, and central to eastern Pacific Ocean due to vertical stretching. Moreover, the heavy rainfall events occurred in 2016 are strongly connected to Indian Ocean Dipole Modoki and El Nino due to observed above normal Sea Surface Temperature anomalies over the central Indian Ocean and central to eastern Pacific Ocean, respectively.