Implications of Climate Change and Socio-Economic Development on Future States of Global Freshwater Resources
Frank Voß, University of Kassel, Germany

There are many uncertainties in our understanding of the current water cycle and how it will develop in the future. Changes in the hydrological cycle induced by global warming may affect society more than any other changes, e.g. with regard to flood and drought risks and/or changing water availability. Globally, the supply of freshwater far exceeds human requirements. However, in many countries current levels of water use are unsustainable, with systems vulnerable to collapse from even small changes in water availability. In these regions water availability and water demands are already heavily outbalanced due to natural and socio-economic variability. Continuing population growth, economic development and climate change further increase the number of people living in areas with severe water stress, a situation exacerbated by the need to maintain river flows for ecological services.
Scientifically-based assessments of potential impacts on water resources provide a basis for the society to adapt to these changes. Although the focus of such assessments has tended to be climate change, socio-economic changes do also have a significant impact on water availability across the main use sectors, i.e. domestic, manufacturing, energy and agricultural. To improve understanding of the complex interactions of the climate system, ecosystems and human interventions scenarios are being developed and implemented. They reveal not only implications on climate change but also on environment and society and span a variety of different pathways.

Estimates of future global freshwater resources require integrated assessment tools which combine both, the simulation of water availability and its dependency on climatic conditions as well as the modelling of water use impaired by social and economic changes. For this purpose we developed and applied the integrated model WaterGAP. WaterGAP (Water - Global Assessment and Prognosis; Alcamo et al. 2003, Döll et al. 2003) is a global water model that combines geographical explicit computations of water availability and water withdrawals on river basin scale with a spatial resolution of 0.5°x0.5° grid cell size.

In impact assessments uncertainty derives from a number of sources including model uncertainties, the assumptions about scenario parameters especially those affecting alternative socio-economic development pathways, the magnitude of error propagation through integrated modelling systems and uncertainties in the underlying datasets. Herein we will concentrate on data uncertainty for both socio-economic and climate development. We will make use of different bias-corrected climate input data sets as provided by the EU-WATCH project combined with different socio-economic driving forces. Finally, water stress is used as an indicator to estimate future impacts of climate and socio-economic changes on water resources in different regions of the World.

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