Global-scale modeling and quantification of indicators for assessing transboundary aquifers (Transboundary Waters Assessment Programme)

Groundwater is an important freshwater resource and accounts for about 25% of the water withdrawn worldwide and for about 40% of the global consumptive water use (the fraction of withdrawn water that is lost to the atmosphere through evapotranspiration). Many of the aquifers used by humans extend over political state borders requiring international conventions and agreements as a basis for sustainable water resource management.

The Transboundary Waters Assessment Programme (TWAP) is aimed at generating the first global assessment of all transboundary waters, including groundwater, and at establishing a network of partners as an institutional basis for future periodic assessments of transboundary waters. The TWAP Groundwater Component is executed by UNESCO’s International Hydrological Programme (IHP) and deals with transboundary aquifers (TBA) as well as groundwater systems of Small Island Developing States (SIDS) (UNESCO-IHP Methodology Report 2012). Besides groundwater basins, the TWAP project covers the following interconnected water system types: river basins, lake basins, Large Marine Ecosystems (LME’s), and open oceans.

The University of Frankfurt will contribute to the TWAP Groundwater Component by simulating, in a globally-consistent manner, groundwater resources and use for the identified TBA using the global water availability and use model WaterGAP. The focus of the work will be the computation of quantity-related groundwater stress indicators under present and future conditions. To this end, climate and water use scenarios for 2030 and 2050 will be applied that are consistent among all TWAP water systems. In order to generate best estimates of indicator values, new regional data collected mainly through regional expert networks will be implemented and an improved model version of WaterGAP will be developed.

Keywords: transboundary aquifers, groundwater stress indicators, climate change, water use scenarios, global hydrological model, WaterGAP

Participants: Claudia Riedel, Petra Döll

Duration: until December 2014

Executing organization: UNESCO-IHP

Funding entity: Global Environment Facility (GEF)

Contact: C.Riedel(at)


More information about TWAP can be found at