Spatial and Temporal Trends in Extreme Rainfall in a Transition Zone: Case of the Marahoué Catchment

The Marahoué catchment area in west-central Côte d'Ivoire is an area of high agricultural activity. Like other regions of the country, the Marahoué region has experienced alternating wet and dry periods, making it difficult to manage water resources in the river systems within it. (N’Guessan et al., 2017) Numerous studies have addressed future changes in hydroclimatic extremes using a variety of approaches. However, trends in extreme precipitation intensities remain less well known, especially for design precipitation intensities used in stormwater infrastructure design. Hence the importance of identifying flood and low-water extremes in the Marahoué catchment in Côte d'Ivoire. Given their importance, trends in the series of extremes were studied using the modified Mann Kendall test. Trends were studied for various short-term rainfall durations at eight stations. Spatial distribution using the IDW interpolation method enabled climate indices to be distributed over the Marahoué basin. Spatial analysis of precipitation indices over four decades shows a trend towards an intensification of extreme events (Rx1day and Rx5day), accompanied by a decrease in prolonged drought periods (CDD, R10 and R20). Temporal analysis of extreme rainfall indices reveals a variety of trends depending on the station and type of index. However, most of the trends obtained are insignificant. The use of decades makes it easy to update intensity-duration-frequency curves, and is more practical and understandable for engineers. The results of this study underline the importance of monitoring climate change through localized analyses and approaches, and of adapting water resource management strategies to better cope with the growing risks associated with extreme rainfall.