Effects of climate change on the dynamics of small Sahelian water bodies over the period 1972-2020: a case study in the Logone-Cameroon floodplain (Lake Chad basin)

Studies conducted in recent years in the Lake Chad basin indicate a considerable decrease in the lake's surface area, attributed to rainfall deficits observed across Africa for more than 25 years. However, the dynamics of small water bodies remain poorly understood in other parts of the Chad Basin, where ponds play an important role in socio-economic development. The objective of this study was to characterize the spatio-temporal dynamics (1972-2020) of small water bodies in the Cameroonian part of the Lake Chad basin. The work consisted of assessing meteorological drought and processing and supervised classification of 42 satellite imagery coupled with field data. Standardized Precipitation Index (SPI) values ranged from 2.154 to -2.509, illustrating the uniformity of climatic conditions and a rainfall profile with alternating normal (1972-1979), dry (1980-1997), and wet (1998-2020) periods. These climatic conditions lead to contrasting patterns of flooding and drought during different seasons, contributing to distinct dynamics in water surface areas extracted with an overall accuracy of 98.77% and a Kappa coefficient of 0.97%. Changes in water surface areas between wet and dry periods indicated significant dynamics with a high risk of flooding and very high vulnerability to drought. Correlation coefficients illustrate the relationship between short-term drought (SPI3) and surface water resources. Wet conditions (> 0.3 km²) control water availability in the dry season, but its sustainability depends on the intensity of external inflows and water pumping. Some ponds showed similar average interannual hydrological conditions with corresponding average climatic conditions. Diffuse behaviors indicate complex dynamics that limit water availability in some areas, sometimes leading to local disturbances. These results improve our understanding of how the Sahelian plains function and can provide guidance on post-flood water use in order to ensure water availability, protect communities, and preserve socio-ecosystems in the face of contemporaneous challenges that are sometimes unavoidable.