Water use in the world: present situation/future needs

To reliably assess in detail future water resources and present water availability, it is insufficient to rely simply on volume data and natural variations in river runoff. It is also necessary to take into account changes due to human activities. During recent decades natural variations in river runoff and quantitative and qualitative characteristics of renewable water resources have been much affected by a whole complexity of anthropogenic impacts. They include those related directly to water intake from river systems for irrigation, industrial and domestic water use. They also include reservoir runoff control, river basin landuse change such as afforestation and deforestation, field management, urbanisation, and drainage. All these factors differently affect the total volumes of water resources,
river runoff regime and water quality.

To estimate the true role of all anthropogenic factors is likely to be problematic. However, we should not overlook those factors transforming the surface of river catchments. Such factors may exert major effects on the runoff of small and middle-sized rivers, and on monthly and extreme river runoff characteristics rather than annual values, as well as on water quality. Under certain physiographic conditions these kinds of human activities can even promote an increase in renewable water resources simply by decreasing the total evaporation loss from basins.

However, estimation of global anthropogenic effects on water resources is based, primarily, on a consideration of the role of those factors related to direct water intake from water bodies and reservoir runoff control. These factors, causing unilateral decrease in surface and groundwater runoff, are widely distributed, most intensively developed and able to exert a pronounced effect on water resources in large regions.

Speaking of man's impact on water resources, it is impossible to avoid touching upon an acute modern problem, the problem of global warming due to increasing carbon dioxide concentration in the atmosphere and strengthening of the 'greenhouse' effect. An expected rise in air temperature and change in precipitation could not help but affect the values of renewable water resources and the character of their economic use. However, an insignificant anthropogenic global climate change recorded for recent decades is more or less reflected in observation-based estimates of water resources and water consumption variations.

As to calculations for the future, it has to be said that the global warming forecasts for most regions so far available are very contradictory, particularly with regard to expected changes in precipitation. They are, therefore, unusable for obtaining anywhere near certain estimates of water resources and water consumption. In addition, according to the recent assessments for the future, the most serious anthropogenic changes in global climate are not to be expected until after 2030-40.

Thus, a quantitative estimation of global water resources for past years and for the decades to come was based on water use for public and domestic needs, industrial production, and agriculture (irrigation). Water losses occurring during reservoir construction were also taken into account. All the estimations for the future have been made ignoring potential anthropogenic global climate change, i.e. they are for a stationary climatic situation.