1. Identifying Transboundary Aquifer hotspots in the SADC-region.
Geert-Jan Nijsten
Karen G. Villholth

2. Transboundary Aquifers in SADC
35 known TBAs in SADC
25 TBAs fully in SADC
Non-SADC countries: Gabon, Congo, Central Africa Republic, Uganda, Rwanda, Burundi, Kenya
Majority of TBAs shared by 2 countries only
Nearly 70 million people living on top of SADC TBAs  compares to 25% of SADC population. Combining this with facts presented by speakers in the morning: High groundwater dependence, high storage capacity, relatively high productivity and the importance of TBAs to the development and livehoods of the SADC population is clear!
But strangely little is known Assessed TBAs: in progress Monitored: 1+ 1 in progress  example from RSA how few monitoring points there are in TBAs
Governed: 2 + 2
So there is plenty of work to be done, but how to prioritise this work?  defining hotspots may help. But what is a TBA hotspot? N
IGRAC, UNESCO-IHP (2015), Nijsten, et al. (2018)

3. TBA hotspots Thematic approach1 2 3
SADC 4
What is a hotspot? There is no widely agreed definition for TBA hotspots yet.
First of all it is important to acknowledge TBAs as complex systems in diverse socio-economic, environmental and hydro-geological settings and under increasing pressure. So there is more to a TBA then only hydro-geology!
Back to the definitions:
TBA hotspots will typically have significant potential for future development and/or face early signs of pressures from present development. TBA hotspots can furthermore be characterized as TBAs with incipient ground-based knowledge, or knowledge bias in terms of inter-disciplinary approaches and/or geographic coverage.
Colvin et al., 2012
Villholth et al. (2011)
Urbanization (1)
Groundwater dependent eco-systems (2)
Transfrontier conservation areas (3)
Groundwater quality (4)
Villholth et al. (2011)

4. TBA hotspots Indicator based approach
Transboundary Waters Assessment Program (TWAP):
20 indicators, of which 9 where also modelled.
5 hotspots under future conditions based on:
Groundwater development stress &
Humand dependency on groundwater
TWAP hotspots:
TBA-CUs under medium to very high groundwater development stress (> 20%) and a dependency on groundwater of >40% in 2030 and/or 2050 (3 TBAs)
TBA-CUs under medium to very high groundwater development stress (> 20%) and a dependency on groundwater of <40% in 2030 and/or 2050 (4 TBAs; partially the same)
IN TOTAL 5
TWAP challenges: Lack of data and quality of data. Also difficult to see the forest for the trees  therefore looking for a more simple, but still structured approach, requiring less data:
UNESCO-IHP, UNEP (2016), Riedel and Doll (2015)

5. TBA hotspots Indicator based approach - simplified
Groundwater development stress
Groundwater quality (natural / antropogenic)
Current state
Risks / hotspots
High current risk
High future risk
Human dependency on groundwater
Vulnerability to climate change
Vulnerability to pollution
Future development
Ecosystem dependency on groundwater
Transboundary legal & institutional framework
IGRAC, UNESCO-IHP (2016)

6. Thank you Geert-Jan Nijsten: geert-jan.nijsten@un-igrac.org
Karen Villholth:

7. References
Colvin, C., Maherry, A., Roberts, W. and Le Maitre, D., (2012?) Mapping aquifer-dependent ecosystems at the SADC Scale: Methods and results. Poster presentation.
IGRAC, UNESCO-IHP, Transboundary aquifers of the world [map]. 15 Scale 1: , edition IGRAC, Delft, Netherlands.
IGRAC, UNESCO-IHP, IGRAC GGIS: TWAP Groundwater data and information portal. Data from UNESCO-IHP, UNEP, Transboundary Aquifers and Groundwater Systems of Small Island Developing States: Status and Trends. Transboundary Waters Assessment Programme TWAP. Online, URL:
IGRAC, UNESCO-IHP (2016) TWAP groundwater additional analyses (unpublished)
Nijsten, G., Christelis, G., Villholth, K.G., Braune, E., Gaye, C.B., (2018 in press) Transboundary aquifers of Africa: Review of the current state of knowledge and progress towards sustainable development and management
Riedel, C., Döll, P., Global-scale modeling and quantification of indicators for assessing transboundary aquifers. In: GEF Transboundary Waters Assessment Programme (TWAP). Frankfurt.
SADC (?)
UNESCO-IHP, UNEP, Transboundary aquifers and groundwater systems of small island developing states: status and trends. Transboundary Waters Assessment Programme TWAP. UNEP, Nairobi.
Villholth, K., Tøttrup, C., Stendel, M., Maherry, A., Claassen, M., Chikozho, C., Colvin, C. (2011) SADC Regional Groundwater Drought Vulnerability Mapping