Exploring linkages between climate, hydrology and tectonics in the Okavango Delta, Botswana
Anne-Morwenn Pastier, a PhD student in Geosciences at Unversity de Rennes will present the Department of Environmental & Geographical Sciences seminar, with a talk entitled, "Exploring linkages between climate, hydrology and tectonics in the Okavango Delta, Botswana".
The Okavango Delta is an alluvial fan forming an endorheic basin. It is constrained by a seismically active graben, considered as the final extension of the southwestern branch of the East African Rift System since the 70's. The Delta swamps are made of channels, floodplains and islands, and are mainly irrigated through a yearly flood pulse coming from the Angolan highlands. The distribution of the inundated areas thus varies during the year, but also at the inter-annual and decadal time scale. Four processes impact this distribution: tectonics, hydrology, sedimentation and the ecosystem, with different influences in terms of both quality and quantity.
The deformation of the surface in the area, monitored through permanent Africa Array GPS stations, shows in the five past years a horizontal long-term component corresponding to the tectonic deformation, and a seasonal signal associated with the hydrological loading. The latter component is driven by climate variability. Decorrelating these signals provides new insights on the system, and may help to discriminate which of these two processes is the most influent on the variation of the flood distribution. The tectonic deformation rate is revealed to be exclusively strike-slip, in opposition with expected extension. It shows a very low rate of displacement, which, in addition to recent geophysical studies, calls into question the Rifting hypothesis for the area. The hydrological signal shows a great influence of the regional precipitations, and may help, in the near future, to constrain the hydrological model of this basin.