The impact of seasonal variability and climate change on lake Tanganyika’s hydrodynamics

In this paper, we project future changes in the hydrodynamics of Lake Tanganyika under a high emission scenario using the three-dimensional (3D) version of the Second-generation Louvain-la-Neuve Ice-ocean Model (SLIM 3D) forced by a high-resolution regional climate model. We demonstrate the advantages of 3D simulation compared to 1D vertical models. The model captures the seasonal variability in the lake, with seasonal deep mixing and surfacing of the thermocline. In a simulation of current conditions, the thermocline in the south of the lake moves upward from a depth of 75 m until it reaches the lake surface during August and September. We compare the current conditions with an end-of-the-century simulation under a pessimistic emission scenario (RCP 8.5) showing that surface water temperature increases on average by 3 ± 0.5 °C. Because deeper water warms less, the stratification increases in the upper 150 m of the water column. This temperature-induced stratification reduces mixing and prevents the outcropping of the thermocline, eventually shutting down the ventilation of deep water in the south basin. Our results highlight the extreme changes likely faced by Lake Tanganyika if global greenhouse gas emissions are not curbed.