Rafael Chavez Garcia Silva1, Jenny Grönwall2, Hans van der Kwast3, Kerstin Danert4, Jan Willem Foppen3
1. Helmholtz UFZ
2. Stockholm International Water Institute
3. IHE Delft
4. Ask for Water GmbH
(a) Purpose or objectives and status of study or research hypothesis
The objective of this research is to present a method and estimates for the Urban population Using Groundwater obtained via Self-supply (UUGS) for the entire African continent (without islands).
(b) Key issue(s) or problem(s) addressed
Self-supply of groundwater for domestic use in urban sub-Saharan Africa (SSA) is common, but the extent to which it is practiced is unknown. Self-supply is critical for those that are left out of the public network coverage, for those who are inadequately served, and/or for those who chose to go off-grid.
(c) Methodology or approach used
We developed a GIS-based methodology to estimate both maximum UUGS and likely UUGS.
Maximum UUGS (GM) was estimated only by considering the physical groundwater potential
Likely UUGS (GL) was estimated by considering the groundwater potential as well as limiting factors, including: proximity to surface water, groundwater use restrictions and proxies we developed: socioeconomic status and access to public water supply.
The proxy socioeconomic distribution assumes that, low income areas depend on springs and hand-dug wells- controlled by groundwater depths. While middle- and high-income status areas can also access private boreholes- affected by aquifer productivity. It is developed by mapping spatial concentrations of luxury amenities and green areas available in OpenStreetMap. For the public water supply network proxy, we assumed, that newer urban developments will be less likely to have public water infrastructure, and therefore more likely depend on self-supplied groundwater. Based on time dependent urban boundaries, areas newer than a certain threshold were assumed to have absent or unreliable public water supply.
To validate our results, we compared GL with the survey data from the ‘Performance Monitoring and Accountability 2020 project’ (PMA) for seven cities in SSA
(d) Results and conclusions derived from the project
Given the distribution of hydrogeological conditions, we estimated that 79% of the total urban population of mainland Africa could potentially use groundwater to meet their domestic needs.
We compared the PMA surveys with the three ranges of likely use we calculated. Four out of the seven cities were closest to the survey values in the case of high likelihood estimations.
Earlier studies estimated that more than 30% of the urban population depends on wells, boreholes or springs as their principal source of drinking water. Based on our expanded method, we arrive at a slightly higher figure in the order of 32% (~150 million inhabitants).
(e) Implications of the project relevant to selected conference theme, theory and/or practice
This research makes use of available open datasets and technology to develop a novel GIS based methodology to determine the urban population using self-supply groundwater for domestic use can be determined. These approaches are essential to inform policy and practice, and to influence public investment to ensure water access in rapid growing urban areas.