Prepared for FAO by J.T. Winpenny - Edited to suit this e-mail conference
The nature and scale of the problem
Water scarcity and water stress
[W-1] In popular usage, "scarcity" is a situation where there is insufficient water to satisfy normal requirements. However, this commonsense definition is of little use to policy makers and planners. There are degrees of scarcity - absolute, life-threatening, seasonal, temporary, cyclical, etc. Populations with normally high levels of consumption may experience temporary "scarcity" more keenly than other societies, who are accustomed to using much less water. Scarcity often arises because of socio-economic trends having little to do with basic needs. Defining scarcity for policy-making purposes is very difficult. [W-2] Terms such as water scarcity, shortage and stress are commonly used interchangeably, though have the following specific meanings: 1. water shortage: a dearth, or absolute shortage; low levels of water supply relative to minimum levels necessary for basic needs. Can be measured by annual renewable flows (in cubic metres) per head of population, or its reciprocal, viz. the number of people dependent on each unit of water (e.g. millions of people per cubic kilometre). 2. water scarcity: an imbalance of supply and demand under prevailing institutional arrangements and/or prices; an excess of demand over available supply; a high rate of utilisation compared to available supply, especially if the remaining supply potentials difficult or costly to tap. Because this is a relative concept, it is difficult to capture in single indices. However, current utilisation as a percentage of total available resources can illustrate the scale of the problem and the latitude for policymakers. 3. water stress: the symptoms of water scarcity or shortage, e.g. growing conflict between users and competition for water, declining standards of reliability and service, harvest failures and food insecurity. Difficult to capture in numbers, though a checklist approach is possible (FAO 1995, Ch. 2).
[W-3] One possible starting point is to stipulate a minimum amount of renewable water per head of the population, and to treat countries having less than this as "water short". At levels of internal renewable water availability of less than 1,000 cubic meters per head, FAO regards water as a severe constraint on socio-economic development and environmental protection. It has been estimated that 20 countries will be at or below this level by the year 2000 (FAO, 1995). Most of these are in North Africa and the Middle East. At levels of water availability of less than 2,000 cu.m. per head, water is regarded as a potentially serious constraint, and a major problem in drought years. 40 countries will fall into this category by 2000 (FAO, 1993).
[W-4] The picture changes if account is taken of the level of water use as well as availability. For instance, Tunisia, Algeria, Kenya and Rwanda, all countries with levels of availability of less than 1,000 cu. m., have levels of water use currently below this. Comparing levels of use and availability produces a different, and sometimes surprising, picture of scarcity (Kulshreshtha, 1993). [W-5] Despite these problems of definition and measurement, the concepts of water shortage and scarcity have a hard kernal of reality for many countries. An annual level of renewable supply of 1,000 cu. m. per head is a useful benchmark for comparing countries. The reciprocal of this, viz. the number of people dependent on a given amount of water, may be more vivid and meaningful for certain purposes. For instance, 1,000 cu. m per head is equivalent to 1 million people reliant on a cubic kilometre annually. [W-6] Whatever benchmark level is taken, the precise amount has no absolute significance; scarcity is a relative concept and can occur at any level of supply, depending on demand and other circumstances. A...