Water and Population
WATER AND POPULATION
Fresh water is essential for human survival and for most human activities. The human body depends on a daily throughflow of drinking water. Unless that water is safe, people get ill; this is a problem of enormous dimensions because an estimated 1.1 billion persons are still without safe water supply and over 2.4 billion do not have safe sanitation. Water also is fundamental for productive activities in society, especially to produce the food people eat. Water precipitating over land is partitioned at the ground: Some evaporates directly; some infiltrates into the soil, is picked up by plant roots, and vaporizes; and the rest recharges rivers and aquifers. In the early twenty-first century an average of some 1,200 cubic meters of water is consumed (evaporated) annually per person, about 50 times the amount an average person uses in the household.
Predicament of Countries with Rapidly Growing Populations
Food production problems tend to be significant in regions that have monsoon climates with a short rainy season and a long dry season, an atmosphere in which rainwater evaporates rapidly, large variability in rainwater both interannually (recurrent drought years) and in the rainy season (large risk of dry spells hurting growing plants), and vulnerable soils that easily degrade into crushed and eroded lands. The difficulties of coping with these complex problems, most of which are unknown in the temperate zone, have left large regions of the world in poverty and with undernutrition. The problems are particularly significant in southern Asia and sub-Saharan Africa. However, it was in regions with such climatic challenges that agrarian civilization emerged.
Using human ingenuity, riverine populations developed intricate irrigation systems to protect growing crops from deficiencies in rainfall. In the contemporary world agricultural development presents the greatest difficulties in regions where rivers are absent, carry water only during heavy rains, or are shared with other countries so that the water supply is contingent on international agreements.
Irrigated areas should be able to produce much more food than most currently do by turning to less wasteful methods of irrigation. However, food production in most countries is heavily dependent on rain-fed agriculture. Large-scale upgrading of rainfed agriculture is needed to forestall recurrent crop failures and food shortages in those regions as their populations rise. Fortunately, there is enough rainfall for much better yields: Rainfall now wasted through flood flows and evaporation could be caught and put to productive use. The problem thus is not so much lack of rainfall as lack of soil infiltrability and inadequate plant uptake capacity caused by dry spell damage. Better soil conservation methods can raise the level of soil infiltration, and better harvesting of local water runoff can improve the ability of plants to absorb soil water.
Figure 1 shows current similarities and differences in the water resources predicaments of different clusters of regions. Moving up the vertical scale is equivalent to mobilizing more of the streamflow to make it accessible for withdrawal for household use, productive activities, and irrigation. Because a certain amount has to remain in rivers to protect aquatic ecosystems and fisheries, there is a ceiling beyond which no more water can be put to use except through the reuse of upstream wastewater. Countries and regions find themselves in different situations. As long as it is still possible to mobilize more, increased water demands can be met through supply management, provided expertise, labor power, and financial resources will allow the necessary infrastructures to be built. Countries that are already close to their "water ceilings" have to change their water management policies and promote water-saving approaches (demand management).
The effect of larger population size, and thus indirectly of population growth, can be traced in the figure by moving out along the horizontal scale, which shows the level of "water crowding": the number of persons per flow unit. Higher values of this measure indicate more people polluting every unit of water flow and imply increasing proneness
to disputes. In such situations water pollution abatement becomes essential, as does dispute mitigation, supported by legislation, mediation, flexible institutions, and public participation in order to secure social acceptance of the remedial action that is decided on. It is evident that with high levels of water crowding, efforts to curtail population growth are called for because the population-supporting capacity of the existing water resources is being exhausted. Solutions that could support an even larger population include reliance on imported food and nonconventional means of expanding water availability, such as desalination, water importation in tankers (or in towed plastic megabags), and water transfers through pipelines and canals from countries with better water resources.
Shift in Thinking
In the increasingly precarious conditions created by continued population growth in water-short regions political leaders are expected to guide their countries safely toward water security, food security, and environmental security. The task of constructing safe water supply and sanitation systems remains fundamental. In addition, the situation calls for a broadening of perspectives to encompass pollution abatement so that the available water stays usable, food imports to compensate for shortfalls in food self-reliance, income-generating activities to pay for that food, dispute risk minimization in a climate of increasing water crowding, and preparedness for recurrent droughts and floods linked to variability in rainfall.
Among experts on water resources, attention is moving away from seeing current streamflow as a stable resource and toward seeing rainfall as the original resource. This resource is partitioned between evaporation, linked especially to biomass production in forests, grasslands, wetlands, and croplands, and the surplus that is feeding the rivers and aquifers and is used for societal purposes. In tropical regions changes in land use may alter the streamflow considerably. Large-scale deforestation may increase the streamflow and/or raise the water table (causing damage from salination, as it did in Australia); largescale forest plantations may reduce the streamflow (as in South Africa, where such plantations are considered a streamflow-reducing activity and require special permits). These linkages make land use decisions water management decisions. As a consequence, the currently recommended long-term route is integration of land and water management as part of a catchment-based ecological approach.
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