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Advisor(s)
Abstract(s)
This study provides a novel assessment of trends in rainy season behavior (1981–2020) in West Africa by analyzing highresolution rainfall data from CHIRPS 2.0. Additionally, it presents the frst comprehensive study of rainy season characteristics in Guinea-Bissau, based on an analysis of the country's available observational data, over the same period. The
agronomic method was used to determine the rainfall onset, while the soil water balance was used to calculate the cessation
of the rainy season. The fndings indicate that the onset of the rainy season in West Africa progresses from south to north,
beginning around 8°N in May and advancing to approximately 16°N by July and early August. The cessation of the rainy
season follows an opposite, north-to-south trajectory, typically starting at 16°N in late September or early October and
reaching 8°N by November and early December. This regional pattern is associated with the seasonal movements of the
Intertropical Front. From 1981 to 2020, the onset, cessation, and duration of the rainy season in West Africa have exhibited
signifcant variability. Although statistically signifcant trends are limited, these shifts still afect agricultural planning and
crop planting schedules, underscoring the importance of continuous monitoring. The standard deviation in the onset of the
rainy season ranges from 4 to 55 days, while the cessation shows less variability, spanning between 3 and 21 days. Meanwhile, the number of rainy days varies from 52 in the northern part of the study area to over 200 days in the southern regions.
In Guinea-Bissau, rains typically start between 15–30 June each year, with notable diferences between the northern and
southern parts of the country. The average cessation occurs between the frst and second weeks of November. Evolutionary
trends suggest a slightly delayed onset of rainfall, with more stability in the cessation dates, leading to a slight reduction in
the length of the rainy season.
Description
Keywords
Rainy season West Africa Guinea‑Bissau
Pedagogical Context
Citation
Mendes, O., Correia, E. & Fragoso, M. (2025). Variability and trends of the rainy season in West Africa with a special focus on Guinea-Bissau. Theoretical and Applied Climatology,156, 242. https://doi.org/10.1007/s00704-025-05471-6
Publisher
Springer Nature