WATer and Global CHange


Globally, the supply of freshwater far exceeds human requirements. However, it has been estimated that by the end of the 21st century these requirements begin to approach the total available water. Regionally, however, the water demand for agriculture, and domestic and industrial use is approaching, or already exceeds the supply, particularly in Southwestern USA, North Africa and Southeastern Asia. In many of these regions ground water storages are used in unsustainable ways in order to support the current water demand. This will certainly get worse with increasing population and societies changing water demands, a situation exacerbated by the need to maintain river flows for ecological and human services.
In addition, it is well known that there is dramatic influence of climate change on the hydrological cycle. 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, changing water availability and water quality. The deterioration of water quality poses a risk not only to society, but also to ecosystems. Due to their complex character, the assessment of possible changes in these systems is best performed by using modelling tools.
In order to link global water resources change with water quality, WaterGAP (Water  Global Assessment and Prognosis, see also project 'WaterGAP'), a model that calculates water use and availability on global scale, is being further developed to include a water quality module (WorldQual).
The structure of WATCH containing seven work blocks and its cross cutting themes is shown in figure 1.


One of the aims of WATCH is to study the vulnerability of water resources for the 20th and 21st

  • How do different water balance models simulate the water balance over the global domain?
  • How do different water balance models simulate future changes in the water balance due to climate change?

This first international workshop on computing the world water balance was meant to be the first in a series, which has engaged an international community of global modelling experts. Further activities will include not only the Global Hydrological Models (GHMs) but also the Land Surface Hydrology Models (LSHMs) within the Global Climate Models for an enhanced analysis and improvement of modelling the global water balance.

In addition WATCH will provide new insights into the inter-relationships between water, climate change, and the anthropogenic pressures upon global water systems. A global overview of the exposure of society to deteriorating water quality brought on by global-scale changes in climate, population, land use, and human activities will be obtained, leading into the development of a first model of global water quality indicators in which CESR plays a decisive role.
The aim of this new water quality sub-model is to determine chemical fluxes in different pathways which will allow a combination of water quantity with water quality analyses. The simulated key water quality variables have been chosen to indicate the suitability of water for various purposes: household, industrial and agricultural use, as well as for the overall health of the aquatic ecosystem. Thus, the variables in the first phase will include:

  • total dissolved solids (TDS),
  • biochemical oxygen demand (BOD),
  • total coliform bacteria (TC),
  • water temperature (TW), and
  • dissolved oxygen.

In close cooperation with the SCENES project, necessary point source and diffuse loading information was prepared as input data for the in-stream water quality modelling within WATCH.




Februar 2007 − Januar 2011


Joseph Alcamo
Frank Voß


Ellen Kynast