Les pluies extrêmes sont des aléas météorologiques qui causent beaucoup de dégâts matériels et de nombreuses pertes en vies humaines. L'estimation des pluies extrêmes est donc d'un grand intérêt pour anticiper des catastrophes, telles que des inondations, et ainsi permettre un aménagement réfléchi du territoire. La présente étude se propose, à travers l'approche des valeurs supérieures à un seuil, d'analyser la distribution de probabilité des pluies extrêmes de la Côte d'Ivoire. Pour ce faire, les séries de dépassements d'un seuil de 44 postes pluviométriques ont été analysées sur la période 1942-2002. Les analyses statistiques mettent en évidence des seuils optimaux d'estimation des pluies journalières extrêmes compris entre 32 mm et 55 mm. La majorité (34) des séries de pluies journalières supérieures à un seuil sont bien ajustées par la loi de PARETO généralisée, avec un paramètre de forme (k) significativement négatif. L'incertitude liée au paramètre de forme (k) est très importante et augmente avec le seuil d'estimation. Par ailleurs, l'analyse spatiale des pluies journalières centennales et décennales montre que les plus fortes valeurs se trouvent surtout sur le littoral (entre les latitudes 4˚30' et 5˚30' Nord), dans la zone montagneuse à l'extrême ouest, et au centre-ouest.

This study analyzes, at local and regional scales, the rainfall variability across the Agneby watershed at the Agboville outlet over the period 1950–2013. Daily rainfall data from 14 rain gauges are used. The methods used are based, firstly, on the rainfall index which aims to characterize the inter-annual and decadal variability of rainfall and, secondly, on the moving average to determine the dynamics of the mean seasonal cycle of the precipitations. Furthermore, the Pettitt test and the Hubert segmentation are applied to detect change-point in the rainfall series. At the basin scale, analysis of rainfall signals composites has shown that the rainfall deficit was more pronounced after the leap of monsoon. Dry years were characterized by an early monsoon demise which is remarkable after 1968. Moreover, the years after 1969 presented a shift of the peaks in precipitation for about 12 days. These peaks were reached early. The rainfall signal showed that the rainfall deficit for the period after 1968, relatively to the period before, was 10% in June against 36% in October for the average rainfall in the Agneby basin. At the local scale, the deficit of the peaks depends on the location. These rainfall deficits were 23% against 36.3% in June for the Agboville and Bongouanou rain gauges, respectively.

Aghien lagoon is a source of fresh water outskirts of Abidjan city in the south of Côte d'Ivoire. For a better understanding of its functioning, we proposed to estimate its main tributaries (Bété and Djibi) soil loss during 2016 and 2017 as part of our research activities in the lagoon watershed in order to evaluate its vulnerability face to soil loss. The methodological approach is based on USLE (Universal Soil Loss Equation) incorporated into GIS (Geographic Information Systems). This equation takes into account five key factors: the erosivity of rainfall, the soil erodibility, the topographic factor integrating slope length and steepness, the cover-management factor and the support practice factor. The combination of these factors made it possible to obtain soil loss maps of the lagoon main tributaries. The analysis of them revealed that soil loss varying mostly between 0 and 250 t ha⁻¹ yr⁻¹ in 2016 and 2017. With regard to the two years, the vulnerability of the lagoon face to soil loss is “low” category. In fact, the soil loss class ranging from 0 to 20 t ha⁻¹ yr⁻¹ occupies more than 60 % of the two sub-basins area in 2016. This trend increased in 2017 with equivalent of 71 % of the area. On the over hand, the “very high” vulnerability ranging from 250 to 1050 t ha⁻¹ yr⁻¹, occupied in 2016, only 0.01 % of the area. In 2017, this category of vulnerability increased in intensity, occupying 0.05 % of it. Ultimately, the increasing observed in 2016 and 2017 seems to be related to annual rainfall of respectively 1553 and 2198 mm. The case study of Aghien lagoon, soil loss vulnerability can be improved by taking account a long time series of rainfall and land use data.