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Transboundary Aquifers and Groundwater Systems of Small Island Developing States: Status and Trends

UNESCO-IHP led the execution of the global Assessment of Transboundary Aquifers and Small Island Developing States (SIDS) Groundwater Systems. The TWAP Groundwater Assessment was carried out jointly with a network of partners at national, regional and international level.
Volume one, presents the first comprehensive indicator-based global assessment of status and trends in 199 transboundary aquifers and 46 groundwater systems of Small Island Developing States. It was prepared by UNESCO-IHP and UNESCO International Groundwater Assessment Center (IGRAC) in partnership with the Simon Fraser University (Canada) and Frankfurt Goethe University (Germany). The overall objectives of the Groundwater Component of TWAP are to:

(i) Provide a description of the present conditions of transboundary aquifers (TBA) with areal extent >5000km2, and aquifers in Small Island Developing States (SIDS) that will enable the GEF IW Focal Area to determine priority aquifers/regions for resources allocation; and

(ii) Bring the major issues, concerns and hotspots of these transboundary aquifer systems and SIDS aquifers to the global attention and catalyse action.

The results of the TWAP Groundwater assessment have provided elements to help the GEF and other interested parties to find answers to, amongst others, the following questions:

(a) What human and ecosystem uses of the water resources are currently affected or impaired (use conflicts, depletion, and degradation)?

(b) How will water conditions and uses develop during the next decades? Global change is likely to produce increased pressures during the next decades, such as higher water demands for food security/irrigation and domestic use, more intensive use of fertilizers and nitrogen, and increasing seawater intrusion in coastal zones;

(c) Where will all these problems be occurring? Increasing droughts or floods are observed in some areas and have been projected through modelling - these projections need to be incorporated and summarized in the assessment.

(d) Which international groundwater systems are likely to prevent, buffer or mitigate water related problems under increasing stresses during the coming decades?

A major element in the TWAP Groundwater Component is the information management. To facilitate storage, retrieval and visualization of results and underlying data, a dedicated information management system (IMS) has been developed. Final results and underlying data from the TBA and SIDS subcomponent have been uploaded to the IMS database. These data can be visualized as maps in the IMS-viewer. Results and underlying data can be downloaded in excel format. The transboundary aquifer and SIDS information sheets are also available for download (pdf-format). The TWAP Groundwater Information Management System and its underlying database will facilitate the periodic update of the inventory and characterization as well as monitoring of trends and impacts.


Key Messages : Transboundary Aquifers

1 – Groundwater is still largely untapped resource.

Worldwide, the majority of transboundary aquifers with surface expression greater than 5000 km2 are located outside regions highly affected by groundwater development stress, and show very low depletion rates of less than 2 mm/yr. in most regions of the world. Human dependency on transboundary groundwater is still generally low to very low in 193 out of the total 258 TBA national segments analyzed.

It is hence possible to draw the conclusion that large amounts of groundwater resources are still potentially available for development in transboundary groundwater basins and aquifer systems. When considering that this assessment, largely based on modelling, has necessarily not taken into consideration the vertical dimension of aquifers, i.e.: the existence and thickness of multilayered systems and deep seated aquifers, the quantity of these still unexploited reserves becomes very large indeed.

2 Areas of high groundwater development stress are presently limited, but will more than double between now and 2050.

The number of TBAs suffering from medium to very high groundwater development stress resulting from combinations of high human dependency, low renewable groundwater per capita, and high extraction/recharge ratios, is rather limited. Under the worst-case climate and irrigation scenario, the national segments of transboundary aquifers showing high risk of groundwater stress are expected to increase between now and 2050 from 20 to 58. New hotspots, largely driven by population pressure, are projected to develop mainly in Sub-Saharan Africa, China and Mexico. The highest future groundwater development stress values as well as the largest increases of groundwater development stress of up to 40 percentage points are projected for TBAs located in Botswana, the Middle East and North Africa region, South Asia, Uzbekistan, and Yucatán. For the future, eight new TBA-CUs with economic groundwater stress are projected, all of them in West or East Africa.

3Alarming lack of modern data and of governance frameworks.

The assessment has evidenced an alarming lack of knowledge and modern data on groundwater in general, and TBAs in particular. It is a fact that without the help of modelling this assessment would not have been possible. The information received through the widely distributed questionnaires –notwithstanding the highly appreciated efforts of hundreds of national and regional experts - unquestionably reflects the lack of quantitative, modern standardized data on many key groundwater parameters, and the generalized limited knowledge of the subsurface and its water resources.

The lack of adequate groundwater governance at the global, regional and local levels hinders the achievement of groundwater resources management goals such as resource sustainability, water security, economic development, and equitable access to benefits from water and conservation of ecosystems. This statement is even more valid when applied to transboundary groundwater. The assessment has in fact confirmed that governance and institutional frameworks for TBAs are absent, with few albeit notable exceptions.


Key Messages: Groundwater systems in Small Island Developing States

1 - Many island states are facing dramatic choices

The situation that emerges from the assessment calls for immediate attention. In the absence of coordinated, sustained remedial national and international action Low-lying islands in the Pacific, highly dependent on scarce, polluted and growingly saline groundwater resources, and impacted by climatic variability and change, are facing dramatic choices. In many other islands, degradation of groundwater quality and growing demands are posing short-medium term threats to human health, and impairing the provision of ecosystem services of great economic relevance.

2 - Water scarcity, pollution and high human dependency threaten sustainability

Population Density appears to be the main driver of water stress in all but one of the 43 representative islands object of the assessment. This reflects in the high number of islands (71%) at risk of water scarcity with a peak of 91% for low-lying islands. Risk due to groundwater anthropogenic pollution affects 73% of all islands, compounded in many cases by seawater intrusion and by natural salinization.  High human groundwater dependency represents a risk factor in 10% of the Caribbean and Atlantic/Indian Ocean islands, and 72% of the Pacific islands for which data was available. This marked difference among regions likely reflects differences in the availability of alternative water resources, either surface water or seawater desalinization (e.g.: Bahamas), and/or different stages of socio-economic development.

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