Charity Kgotlaebonywe / Earth & Environmental Sciences / Faculty Mentor: Ricardo Sanchez-Murillo
This study applied isoscapes to assess the spatial and temporal distribution of water sources in Gaborone’s tap water system during two contrasting ENSO years. A total of 399 tap water samples were collected over four seasonal campaigns (Winter 2022–Summer 2023/24), alongside rainfall (N=88), weekly tap water (N=42), and reservoir water (N=48). Cluster analysis and the MixSIAR model identified isotope patterns and quantified seasonal source contributions. The results revealed significant seasonal variations in δ18O and d-excess, with winter seasons showing more depleted and variable signatures than summer. Cluster analysis identified four groups, reflecting spatial differences across the city and seasonal shifts in water sources. MixSIAR modeling estimated that Dikgatlhong Dam was the primary water source (46.2% ± 18.8%), followed by Gaborone Dam (17.5% ± 11.9%) and Bokaa Dam (15.6% ± 10.4%). Groundwater contributed 11.1% ± 6.4%, while Letsibogo Dam had the lowest contribution (9.6% ± 7.6%). These findings underscore the dynamic nature of Gaborone’s water system, which is influenced by ENSO conditions and strategic use of reservoirs and groundwater. This study also provides a methodological framework for analyzing urban water systems in semi-arid regions, aiding water management in rapidly growing cities in Africa and the Global South.
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