freshwater problem, long before today’s pressures had to be taken into account. Those living in water-short areas or those with seasonal rains tackle their problems by capturing run-off behind dams, and storing or diverting water for agricultural or other uses. As more water is manipulated in this way, the environmental and other limits of this approach have become apparent. Upstream and downstream users of the same resource, in river basins and watersheds, are forced into dispute as populations grow and demands increase. However unevenly distributed, the supplies provided by natural forces are going to have to suffice. New ways of managing water will have to be found in order to maintain quantity and quality and achieve a fair distribution of a substance essential to life on Earth.
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The volume of water in the world never changes, but only 2.5 per cent is fresh. More than two-thirds of fresh water is locked up in polar ice-caps and permanent snow cover. Of the rest, a small proportion is in lakes and streams, and the rest in underground aquifers. Working in tandem, salt and fresh waters power life on Earth by a dynamic and constantly regenerative process. The sun’s heat evaporates water from seas and lakes, and moisture in vegetation is absorbed into the air through evapotranspiration. Once in the atmosphere, water vapour condenses into droplets. Clouds form from which
rain and snow are released. This replenishes rivers and aquifers, enabling them to nourish soil fertility and promote plant growth. The “hydrological cycle” depicts the forces energizing and controlling the movement of water from land, to sea, sky, and back to land. This 20th-century gem of hydrological analysis has had an important influence on ideas of a “global water supply” to be shared among humankind, and the pressures on that supply that today constitute a “global water crisis”. However, it is at the local level – arid, temperate, tropical, mountainous, riverine – that humanity interacts with water, storing, conserving, managing and distributing it. This is also where the impacts of climate change – rising sea levels, changed rainfall patterns – are felt. “Global water”, for all practical purposes, is simply a useful construct.
Global Water
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Water’s Unequal Distribution
The amount of water that falls as rain, filling lakes, rivers, streams and aquifers, is more than enough to meet our needs, but it is unevenly distributed across the Earth. The floodplains of major rivers have water in abundance, and the need to control and deploy water within them helped prompt the birth of civilizations. In arid zones, tropical and frozen, lack of water constrains human settlement and very different societies have emerged. In temperate areas with steady and reliable rainfall, much of which soaks into the ground, it has been relatively easy to manage freshwater flows so as to secure supplies and prevent floods. In water-short areas, and those where storms wreak havoc, water security is more difficult and societies typically poorer. There is also pressure on freshwater resources from population growth, urbanization, and increasingly industrialized lifestyles. In some desert settings, a traditionally well-adapted way of life has given way to water-profligacy – swimming pools, intensive irrigation – beyond the capacity of local renewable resources. In some parts of the world, notably in Asia, the whole year’s rainfall comes in a brief torrential season, complicating agricultural practice. The storage of water and its channelling via hydraulic infrastructure helps redress this problem. But there is a price to be paid by downstream populations, whose fishing or farming economies are jeopardized by major alterations in water pathways and flows.
Brazil
The Amazon region receives nearly 75% of Brazil’s water, but is very lightly populated. The northeast coastal region, where 20% of people live, receives only 2%.
Both China and India face extreme disparities between their share of the world’s water and of its population, prompting China to propose ambitious projects to shift water between major rivers.
North America
All types of aridity zones are to be found in North America, and for millennia its indigenous peoples lived sustainably off the land. As European settlers moved across the country from east to west they also developed technologies that enabled them to survive in some of the harshest environments, but their use of the available water is not always sustainable in the long-term. Las Vegas, sprawling across the Nevada Desert, relies on the waters of the steadily shrinking Lake Mead.
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Ecological degradation
The use of hydraulic engineering to redress the unequal distribution of water is, in many areas of the world, pushed to its ecological limits. The heavy use of irrigation in arid areas can lead to salts leaching to the surface, rendering the soil infertile, as here in Iraq.
Australia
Although Australia appears adequately supplied with water on a per capita basis, most of its inland area is desert, soils are thin and fragile, and the country drought-prone. Industrialized farming practices, including irrigation, have undermined long-term land productivity. Water shortage is becoming acute in certain cities, notably Perth.
Africa
The African continent demonstrates contrasting hydrological conditions: desert and semi-desert dominate the north, while countries through which great rivers flow are water-rich. One-third of Africa’s population – 300 million people – live under conditions of water scarcity but geography and costs limit the prospects for major hydraulic infrastructure.
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3 Water Shortage; 4 Rising Demand; 5 Dwindling Supply; 11 River Basin Stresses R
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Water Shortage
The spectre of water shortage is less a global phenomenon than one threatening particular regions and localities. In areas under-endowed with rainfall or rivers, a combination of ever-increasing demand and, in some cases, less reliable
