Is heavy rainfall the new norm? What caused the heavy rains in October - December 2019?


By Emmah Mwangi, Maurine Ambani, Mark Arango, Halima Saado Abdillahi

1.0 Abstract

March-April-May (MAM) and October-November-December (OND) are the two significant rainy seasons in Kenya and East Africa at large. The two seasons are influenced by the movement of the rain belt and overhead sun northwards and southwards. In addition, the scientific evidence is indicating that it is much easier to forecast expected seasonal rainfall over the East African Region in the October-November-December (OND) season several months in advance as compared to the MAM season.

The Indian Ocean Dipole (IOD) plays a critical role in driving the OND seasonal rainfall over the East Africa Region. Positive IOD signifies the warmer ocean waters near the East African Coast, which enhances the rise of warm moist air leading to more cloud formation inland, resulting in higher than normal rains being received in East Africa, including Kenya.

The OND 2019 seasonal rains were linked to a positive Indian Ocean Dipole (IOD). This confirms the reason for the normal rainfall that was recorded in several weather stations in Kenya during OND 2019 that recorded the highest IOD index ever observed.

The impact associated with the normal OND 2019 rains stresses the need for all disaster risk management actors to embrace the Early Warning Early Action concept to curb losses. These include loss of life and destruction of properties. The scientific community should not only predict accurately the occurrence of a positive IOD but also its magnitude.