Contribution of Remote Sensing to the Analysis of the Drying Process of Lake Tanma under Strong Climate Variability

Climate variability represents one of the most severe threats to lacustrine ecosystems worldwide, leading to water loss in nearly half of the world’s lakes and reservoirs. On the one hand, this variability is associated with drought conditions, manifested by a decline in precipitation. On the other hand, it is linked to rising temperatures, which enhance evaporation rates at lake surfaces.

In Senegal, a Sahelian country, the prolonged drought period of the 1970s led to the desiccation of several water bodies, including Lake Tanma. In this context, the present study contributes to a better understanding of the drying process of Lake Tanma under climate variability conditions, using remote sensing techniques. Lake Tanma is located in Thiès region, approximately 70 km from Dakar.

To achieve this objective, Landsat Earth observation products were used at the beginning and end of each decade between 1984 and 2024. The time series consists of multispectral images acquired in October, corresponding to the end of the rainy season in Senegal. This choice ensures the capture of the lake’s maximum water extent, thereby minimizing seasonal fluctuations. All data were acquired and processed using the Google Earth Engine platform. The Modified Normalized Difference Water Index (MNDWI) was computed for the entire time series to accurately delineate and characterize water-covered surfaces.

The results reveal a highly variable evolution of the inundated surface area of Lake Tanma, with a variation coefficient of 57.8%. The largest flooded area was observed in 1984, covering 969.33 ha, while the smallest extent was recorded in 2024, with only 76.18 ha. Analysis of intra-decadal variations shows a slight decrease (7%) in the flooded surface, between 1984 and 1989. In contrast, subsequent decades exhibit a marked and progressive regression of the lake’s water surface, reaching 21% during the 2000–2009 decade, 61% during 2010–2019, and up to 89% over the 2020–2024 period.

These decrease trends highlight the influence of hydro-climatic parameters, particularly precipitation and evaporation, which constitute the primary drivers of lake recharge and desiccation. Consequently, further investigation, of hydro-climatic factors, namely rainfall and temperature, is required, to better understand the drying process of Lake Tanma and to assess the impacts of hydro-climatic variability on its long-term dynamics.