Abstract
There is a scarcity of long-term groundwater hydrographs from sub-Saharan Africa to investigate groundwater sustainability, processes and controls. This paper presents an analysis of 21 hydrographs from semi-arid South Africa. Hydrographs from 1980 to 2000 were converted to standardised groundwater level indices and rationalised into four types (C1–C4) using hierarchical cluster analysis. Mean hydrographs for each type were cross-correlated with standardised precipitation and streamflow indices. Relationships with the El Niño–Southern Oscillation (ENSO) were also investigated. The four hydrograph types show a transition of autocorrelation over increasing timescales and increasingly subdued responses to rainfall. Type C1 strongly relates to rainfall, responding in most years, whereas C4 notably responds to only a single extreme event in 2000 and has limited relationship with rainfall. Types C2, C3 and C4 have stronger statistical relationships with standardised streamflow than standardised rainfall. C3 and C4 changes are significantly (p < 0.05) correlated to the mean wet season ENSO anomaly, indicating a tendency for substantial or minimal recharge to occur during extreme negative and positive ENSO years, respectively. The range of different hydrograph types, sometimes within only a few kilometres of each other, appears to be a result of abstraction interference and cannot be confidently attributed to variations in climate or hydrogeological setting. It is possible that high groundwater abstraction near C3/C4 sites masks frequent small-scale recharge events observed at C1/C2 sites, resulting in extreme events associated with negative ENSO years being more visible in the time series.
Highlights
Water use in Africa is forecast to dramatically increase (Wada and Bierkens 2014), as more than half of global population growth by 2050 is projected to occur within the sub-Saharan region (UN 2019)
The rarity of such hydrographs has meant assessments of sub-Saharan African water security typically rely on datasets derived from large-scale models (e.g. Döll and Fiedler 2008), with limited validation using field observations (Sood and Smakhtin 2015), or large-scale data reviews (MacDonald et al 2021)
This paper presents an analysis of 21 long-term groundwater hydrographs from two adjacent semi-arid catchments in Limpopo Province, South Africa
Summary
Water use in Africa is forecast to dramatically increase (Wada and Bierkens 2014), as more than half of global population growth by 2050 is projected to occur within the sub-Saharan region (UN 2019). Long-term groundwater hydrographs provide a direct indicator of groundwater abstraction sustainability from a quantitative perspective: allowing assessments of changes in storage, understanding recharge, and linkages to climate and land use change (Cuthbert et al 2019) The rarity of such hydrographs has meant assessments of sub-Saharan African water security typically rely on datasets derived from large-scale models There are examples in the literature of multidecadal African hydrographs which have been used to estimate groundwater recharge and its association with rainfall intensity and climate variability (Kotchoni et al 2019; Owor et al 2009; Sibanda et al 2009; Taylor et al 2013); or changes in storage relating to land use changes (Favreau et al 2009), abstraction and managed aquifer recharge (Murray et al 2018). These studies have only examined hydrograph variation at a limited number of locations: from a single wellfield (Taylor et al 2013) to a limited number of sites spread across an entire country (Kotchoni et al 2019)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
