Hausses soudaines du lac Tanganyika : observations et connaissances locales au nord du lac (Burundi)

Abstract

Lake Tanganyika, one of the oldest and deepest lakes in the world, constitutes a major ecosystem for the riparian populations of Burundi. In recent years, episodes of sudden water level rises have been observed along its northern shores, causing significant ecological and socio-economic impacts. It is with this objective that this study was conducted to explore the knowledge of the local population regarding these phenomena. A survey was carried out in six lakeside localities north of Lake Tanganyika, on the Burundian side (Gatumba, Kajaga, Nyabugete, Kiringi, Nyamugari, and Gitaza). Sixty (60) people living or working near the lake for at least 10 years were surveyed. A mixed-method approach combining a socio-economic survey and analysis of meteorological data for certain parameters from the port of Bujumbura, available for different periods (2020–2025 for some, 2015–2024 for others), was used. According to respondents, the sudden rise of the lake occurs mainly between March and May (cited by 55%) or between October and May (cited by 45%), with the most notable episodes in 2021, 2023, and especially 2024. The perceived causes of these sudden rises are primarily lake squalls, violent winds, waves, and intense rainfall. Identified warning signs include thunder over the lake, black clouds over the lake, strong winds known as ihumba or kasikasi, waves locally called urubangwe, ingunza, igitembagara, unusual animal behavior, and high turbidity of the lake water (isuri). Documented impacts include major consequences such as flooding, temporary population displacement, crop loss, increased fish mortality, phytoplankton blooms (umukombe), and fish abundance. Meteorological data analysis shows a sudden rise in the lake level in 2015, 2020, 2021, and 2022, which can be explained by the heavy rainfall that characterized those years. The local population's adaptation strategies to the sudden lake rise are essentially: temporary relocation, mooring boats on rafts, construction of dikes, erection of physical barriers around houses, planting of reeds, respecting the former lake boundaries, and avoiding construction in flood-prone areas.