Water availability and deficits


The distribution of water resources over the complete land mass of Earth is uneven and quite unrelated to population spread or economic development. These facts are very clearly revealed by analysing and comparing the specific water availability for a single period of time for different regions and countries. Specific water availability represents the value of actual per capita renewable water resources and, for every design level, is determined by dividing gross water resources by population number. Here, water resources are assumed to be river runoff originating within a given region plus half the river flow which comes from outside. Thus, what is meant by specific water availability is the residual (after use) per capita quantity of fresh water. Obviously, as population and water consumption grow, the volume of specific water availability decreases.

Specific water availability was obtained for all the natural-economic regions and selected countries for the 1950-2025 period. As expected, this analysis revealed much unevenness in their distribution over the Earth. For instance, the greatest water availability - 170-180 thousand m3 per capita for 1995 - is in the regions of Canada and Alaska and in Oceania while at the same time, in the densely populated areas of Asia, central and southern Europe, and Africa, current water availability falls within 1.2-5.0 thousand m3 per year.

In the north of Africa and on the Arabian peninsula, it is just 0.2-0.3 thousand m3 per year: note that water availability of less than 2 thousand m3 per year per capita is considered to be very low, and less that 1 thousand m3 per year catastrophic. With such low values of water availability, very serious problems arise in population life-support, industrial and agricultural development.




...potential water availability for the Earth's population is decreasing from 12.9 to 7.6 thousand cubic metres per year per person...


To discover more about the water resources deficit facing us in the future, it is very important to analyse the trends and rates of change in specific water availability in relation to socio-economic and physiographic conditions. And indeed, analysis of data from the natural-economic regions of the world shows that the rates of falling water availability depend on both socio-economic development of the countries within a region and on the climatic conditions.

Different approaches for assessing future water availability are required for the very rich and economically well developed countries of the Arabian peninsula. Here, the extent of available water increases constantly due to the intensive use of deep underground waters and desalination of salt and brackish water since there are sufficient funds available to use extremely expensive non-conventional sources of freshwater, inaccessible to the majority of other countries located in similar arid and semi-arid regions.




At the present time, 76% of the total population has a specific water availability of less than 5.0 thousand m3 per year per capita, with 35% having very low or catastrophically low water supplies. This situation will deteriorate further in the beginning of the next century: by 2025 most of the Earth's population will be living under the conditions of low or catastrophically low water supply.




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