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Worldwide Assessment Of Transboundary Aquifers With A Focus On The African Continent

Congress: 2015
Author(s): Geert-Jan Nijsten, Laura del Val Alonso

Geert-Jan Nijsten
International Groundwater Resources Assessment Centre (IGRAC)

Keyword(s): Sub-theme 12: Transboundary river basins and shared aquifers,

To date there is no complete inventory of transboundary groundwater resources. The Global Environment Facility (GEF) Transboundary Waters Assessment Programme (TWAP) has undertaken the global assessments of the five transboundary water systems: Open oceans, Large marine ecosystems, Rivers, Lakes and Groundwater. The assessment methodologies used have been developed in a preparatory project and are based on indicators and indices, including socioeconomic and governance ones. Each water body to be assessed is described with a summary descriptor, geo-referenced map and a GIS database of attributes. An effort is made to assess the areas at risk and transboundary hot spots. It is expected that the project will assist the GEF set priorities for the allocation of its funds and to make more effective use of its resources for addressing higher priority water bodies [1].

The focus on transboundary groundwater resources only started about a decade ago. Some assessments have been carried out at the national and regional level but at the global scale knowledge was limited to the (approximate) delineation of identified transboundary aquifers. The groundwater component of TWAP which has been executed by UNESCO International Hydrology Programme (UNESCO IHP) is the first global baseline assessment of transboundary groundwater. It considers hydrogeological, environmental, socio-economic, legal and institutional aspects.

In the preparation phase of the project a methodology was developed to describe the aquifers to be assessed in a structured way in terms of key hydrogeological characteristics as well as socio-economical, environmental, legal and institutional characteristics. Based on these key characteristics, twenty indicators have been developed enabling better characterisation and comparison of the transboundary aquifers on a regional or global scale.

Data for the assessment have been collected through an extensive network of national experts, regional organizations and research institutions, who have been mobilised for this worldwide desktop study to compile nationally available knowledge and information for the global assessment. Data were collected through standardised questionnaires in which experts were asked to provide referenced information on the transboundary aquifers aggregated to the level of the national segments. Preliminary results were discussed between the national experts in regional workshops.

At the time of writing of this abstract data collection is in its final phase and data are being processed. The analyses and assessment of the data will take place in the coming months. Results will be presented at the conference / in the final paper explaining the methodology and approach for the worldwide project, followed by an in depth description and assessment of the data collected on the transboundary aquifers of Africa.

All data and information will be centrally processed by IGRAC and uploaded in a web-based information management system for public viewing and use. The information system is a key element in the assessment allowing not only to disseminate the results from the assessment, but also enables future updates of the information.

The project has brought information on existing transboundary aquifers together in a global database. It has also resulted in better delineations of transboundary aquifers which boundaries were previously only known by approximation. Furthermore new transboundary aquifers have been added to the database. The starting point for the assessment was the 2012 Transboundary Aquifers of the World map [2]. This map showed 166 Transboundary Aquifers larger than 5000 km2 (5000 km2 being the lower threshold for inclusion in the TWAP). Now, as a result of TWAP, the number of TBAs larger 5000 km2 included in the global database, has increased to 233. From these 233 aquifers 28% had not yet been included before and for 40% of the TBAs the delineation has been improved compared to the 2012 map.

The global survey by questionnaires resulted in a 40% return rate. National experts from 93 different countries have provided standardised information and references for 207 national segments of transboundary aquifers around the world. In the African continent, where the return rate of questionnaires was 18%, 52% of the transboundary aquifers' delineations were improved.

Figures to be presented in the conference will give an insight into the data collected during the programme and will show results of the TWAP groundwater indicators across transboundary aquifers in Africa. The indicators will provide a regional picture of the current state of transboundary groundwater and will allow comparison between aquifers. As a result, indicators can be used to identify transboundary aquifers requiring action on specific aspects like vulnerability to pollution or overexploitation. Indicators may also be used to highlight the potential for development in certain areas.

It can already be concluded that the participatory approach used in the assessment succeeded to make available groundwater related information which was previously only available at the national or even local level. The systematic and standardised data collection in TWAP has enabled setting up a structured database on transboundary aquifers which will be freely accessible. Futures efforts will be needed to improve the survey and to set up a more elaborate process to evaluate the quality and consistency of the data.

The overall outcome of the programme serves as a tool for comparison of transboundary aquifers at global scale, which is a first step to improve the global knowledge on transboundary aquifers and to monitor the implications of management these important resources. 1. United Nations Environmental Programme, 2011. L. Jeftic, P. Glennie, L. Talaue-McManus, and J. A. Thornton (Eds.). Methodology for the GEF Transboundary Waters Assessment Programme. Volume 1. Methodology for the Assessment of Transboundary Aquifers, Lake Basins, River Basins, Large Marine Ecosystems, and the Open Ocean, UNEP, x+60 pp

2. International Groundwater Resources Assessment Centre, 2012. Transboundary Aquifers of the World 2014. Available at: [Accessed October 30, 2014].

2011 IWRA - International Water Resources Association - - Admin