Rwanda’s rainy seasons are shifting towards earlier starts and variable durations

In Rwanda, the characteristics of the rainy seasons are undergoing notable transformations, with direct impacts on agriculture and food security. Between 1983 and 2021, certain regions recorded a significant increase in precipitation and the number of rainy days, particularly around Lake Kivu, in the central temperate highlands, and on the central plateau. During the short rainy season, which runs from September to December, an increase in precipitation and a delay in the end of the season have been observed across the country. These changes suggest that the amount of rain depends more on the number of rainy days during the long season and the end date of the season during the short season.

Projections for the coming decades, up to 2100, reveal contrasting trends depending on climate scenarios. For the long rainy season, which covers March, April, and May, the start of the season is expected to be earlier nationwide. Under an optimistic scenario of reduced emissions, the eastern and western regions and areas around the Congo-Nile divide could see their seasons begin 20 to 40 days earlier, while the center of the country would experience an advance of 0 to 20 days. In a more pessimistic scenario, the advances would be less pronounced but still present, with starts 10 to 30 days earlier depending on the area.

The duration of the rainy seasons is also expected to lengthen, particularly in the central and eastern regions, where an increase of 12 to 24 days is anticipated under the optimistic scenario. In contrast, for the short rainy season, few significant changes are expected in start dates, end dates, or overall duration, except in certain areas where a slight reduction could occur.

The number of rainy days is expected to increase during the long rainy season, with notable rises in the east, around Nyungwe National Park, and in the northwestern regions, where 16 to 24 additional days are anticipated under the optimistic scenario. For the short rainy season, variations would be less pronounced, with localized decreases in the northern highlands and some areas of the southeast.

These climatic changes could have major consequences for Rwandan agriculture, which is highly dependent on rainfall. Longer seasons and an increased number of rainy days could favor long-cycle crops and improve yields in certain regions. Conversely, shortened seasons or delays in the start of the rains could reduce plant growth periods, increasing the risk of food shortages. Farmers will therefore need to adapt their practices, such as adjusting planting dates or choosing more resilient crop varieties, to cope with these changes. Policymakers, for their part, could use these projections to plan adaptation strategies, such as developing irrigation systems or promoting more resilient agricultural techniques.

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Cited Publication

DOI: https://doi.org/10.1007/s44292-026-00084-8

Title: Observed trends and future projections of seasonal rainfall onset, cessation, length, and rainy days in Rwanda

Journal: Discover Atmosphere

Publisher: Springer Science and Business Media LLC

Authors: Ndakize Joseph Sebaziga; Bonfils Safari; Didier Ntwali; Joshua Ndiwa Ngaina