Potential keys to evaluate climate-induced changes on hydrogeology and biogeochemistry in northern Botswana and Namibia

Groundwater is a critical primary resource in most of Southern Africa due to a low annual precipitation and limited surface water alternatives. Furthermore, a poor understanding of how groundwater systems function and evolve in time and space may also lead to unsustainable abstraction practices and hence to a depletion of an otherwise renewable resource. This study aims to characterize the Linyanti and Kwando hydrologic systems (surface water and underlying aquifers) in the Caprivi strip and the Chobe enclave by: 1. Evaluating groundwater-surface water interactions that constitute recharge and discharge between the two systems over the course of several seasons. 2. Determining the importance of seasonal flooding for in-situ groundwater recharge. 3. Quantifying the mean residence time of groundwater recharge within the aquifer. 4. Determining the source of the water used by the trees and quantifying their periodical growth. 5. Outlining the roles of soils in the regulation of water resources. 6. Tracking how local vegetation registers changes in hydrologic conditions and projecting those interpretations to paleoclimate interpretations via dendrochronology. The objectives will be achieved through long-term seasonal sampling of the groundwater, surface water and precipitation for geochemical and isotopic analysis of the water as well as monitoring water table fluctuations coupled with remote sensing data. A variety of soils will also be sampled and characterized. The vegetative cover and local conditions will be determined, and trees will be sampled seasonally and compared with waters to calibrate the behavior of vegetation toward water availability and thus also reconstruct the climatic history via an isotopic-dendrochronological approach. This will aid in determining the vulnerability of the hydrologic system and related ecosystem functioning to potential changes in climate.