Conclusions II

It may be a surprising observation, but we find that the general pattern of global water availability does not change much if the problem is considered either on a global scale or for individual regions. First, the extent of surface water used at the expense of groundwater is as much as 15% of total global water withdrawal and approximately the same proportion of water consumption by continents and regions. Second, at least half the underground water used is hydraulically connected to river runoff, in which case groundwater extraction would affect directly the reduction in river runoff. Thus the proposed values for water consumption at the expense of groundwater can be halved. Nevertheless, ignoring groundwater in assessments of water availability dynamics for a number of regions seems to produce a more pessimistic picture than the reality.

All water resources estimates are optimistic because no account is taken of the qualitative depletion of water resources through the ever-increasing pollution of natural waters. This problem is very acute in the industrially developed and densely populated regions where no efficient waste water purification takes place. The major sources of intensive pollution of waterways and water bodies are contaminated industrial and municipal waste water as well as water returning from irrigated areas.

It is estimated that in 1995 the volume of waste water was 326 km3/year in Europe, 431 km3/year in North America, 590 km3/year in Asia and 55 km3/year in Africa. Many countries discharge most of their waste water containing harmful substances into the hydrological system with no preliminary purification. Prime water resources are thus polluted and their subsequent use becomes unsuitable, especially as potable supplies. Every cubic metre of contaminated waste water discharged into water bodies and water courses spoils up to 8 to 10 cubic metres of pure water. This means that most parts of the world are already facing the threat of catastrophic qualitative depletion of water resources.

The reliability of predictions for 2010-2025 requires special attention. Such estimates certainly take on board trends observed during past decades but to a considerable extent they are based on long-term demographic and global economic development forecasts expressed in GNP values. Some additional errors can arise, especially for arid and semi-arid regions, because no account is made of the expected anthropogenic global climate change due to increasing atmospheric carbon dioxide and other greenhouse gases.

24.JPG (16773 bytes)

Forecasts of future populations, industry and thermal power generation growth are usually given for different socio-economic development variables. This information is used to predict water withdrawal and water availability. The values obtained for 2025 are ą10-15% for those regions with predominantly developed countries and ą20-25% for the regions with a predominance of developing countries.

More reliable and detailed water availability values for the future can be obtained but they will need to consider river runoff variability over a long period, to include data on groundwater resources plus the dynamics of resource quantity and quality under both a static climate and anthropogenic global climate change.

To solve this problem, it will be vital to achieve close co-operation between scientists from different countries and international organisations dealing with the problems of hydrology, climatology, and the complex use and protection of water resources.