Contrasting Changes in Rainy Season Length, Rainfall Frequency, and Intensity Across Eastern Africa

Interannual rainfall variability presents critical challenges across eastern Africa. However, studies often focus on trends in seasonal rainfall totals, overlooking the intraseasonal characteristics that directly affect societal livelihoods. Our analysis of daily rainfall from the Climate Hazards Group Infrared Precipitation with Stations (CHIRPS) dataset (1982–2023) reveals significant and contrasting shifts across the region. In northern East Africa, the rainy season has lengthened by over a month and become wetter due to a higher frequency of rainy days. Similarly, the season in southern East Africa has lengthened by three weeks and become wetter, primarily due to rising rainfall intensity. Over the bimodal eastern Horn of Africa, the trends diverge sharply: the boreal spring "long rains" have shortened by up to a month and become drier with fewer rainy days, with intensity increasing in the southeast but decreasing in the northeast. Conversely, the boreal fall "short rains" have become longer and wetter in the northeast, while shortening and becoming drier in the southeast. Crucially, for both the long and short rains, changes in the number of rainy days are the primary factor determining seasonal totals; even where intensity has increased, it often fails to offset the decline caused by fewer rain events. These findings underscore the need for climate adaptation strategies to specifically account for sub-regional shifts in rainfall frequency and intensity. Longer dry periods between rainfall events may produce stress not represented by seasonal totals, while more intense rainfall may offer opportunities for water storage and infiltration.