Globally, between 12.5 and 14 billion cubic metres of water are available for human use on an annual basis. In 1989, this amount equaled about 9,000 cubic metres per person per year and by 2000 had dropped to around 7,800 cubic metres per person. In 2025 the amount of water per capita is expected to fall to 5,100 cubic metres per person as the world's population grows from 6 billion to over 8 billion.
Click here for a map showing the availability of freshwater in 2000
Even this amount would be enough to meet human needs, if freshwater were evenly distributed. But available freshwater supplies are not distributed evenly around the globe, throughout the seasons, or from year to year. For instance, the Congo River and its tributaries account for about 30 per cent of the entire African continent's annual runoff, but the watershed contains only 10 per cent of Africa's population . Two-thirds of the world's population - around 4 billion people - live in areas receiving only one-quarter of the world's annual rainfall.
Click here for a map showing levels of water stress around the world.
Collecting water, India
© Mark Edwards/Still Pictures
Throughout much of the developing world the freshwater supply comes in the form of seasonal rains. Such rains run off too quickly for efficient use, as during the monsoons in Asia. India, for example, gets 90 per cent of its annual rainfall during the summer monsoon season, which lasts from June to September. For the other eight months the country gets barely a drop.
Pollution of rivers and lakes reduces accessible freshwater supplies. Each year roughly 450 cubic kilometres of wastewater are discharged into rivers, streams and lakes. To dilute and transport this dirty water before it can be used again, another 6,000 cubic kilometres of clean water are needed - an amount equal to about two-thirds of the world's total annual useable fresh water runoff.
The amount of water that people use depends not only on basic needs and how much water is available but also on levels of urbanisation and economic development. Withdrawals of water have grown to meet demand for all types of use - for irrigated agriculture, industry, and municipal (household) purposes. As the world continues to urbanise at rapid rates, the demand for potable water for municipal use is expected to soar, out pacing the capacity of most cities to provide it.
Click here for maps and charts showing the relative proportion of water use by the agricultural, industrial and domestic sectors in 2000.
Population growth and rising demand per capita are creating water shortages in many countries. Globally, the annual population increase of nearly 80 million per year implies an increased demand for freshwater of about 64 billion cubic metres a year - an amount equivalent to the entire annual flow rate of the Rhine River.
A country is said to experience water stress when annual water supplies drop below 1,700 cubic metres per person. When supplies drop below 1,000 cubic metres per person per year, the country faces water scarcity for all or part of the year. These concepts were developed by Swedish hydrologist Malin Falkenmark to gauge current and future water needs and to measure scarcity.
Population Action International (PAI) adapted Falkenmark's concepts to calculate water stress and scarcity in 1995, with an update in 1997 and projections for 2025 and 2050. The results are startling: in 1995, PAI estimated that 31 countries, home to nearly half a billion people, regularly faced either water stress or water scarcity. In 2025, 48 countries containing about 3 billion people will face water shortages. By 2050 the figures will be 54 countries containing 4 billion people, or 40 per cent of the projected world population of 9.4 billion (see Table 1).
Click here for maps showing freshwater scarcity in Africa and the World at large.
The fact that the UN's latest median projection for world population in 2050, is lower, at around 9.1 billion does not significantly alter this scenario.
Still, national level calculations of water availability have serious shortcomings. In a number of countries, the overall access to water on a national level may be above the water stress or scarcity level. But taking a river basin perspective reveals that parts of many water-rich countries are running out of water. On a country-wide basis, for instance, the United States is relatively water-sufficient at 8,838 cubic metres per person per year. Yet the crowded Colorado River Basin has only slightly over 2,000 cubic meters per person per year, and the Rio Grande River Basin registers well within the water scarce category at 621 cubic meters per person per year.
In order to address this shortcoming, the Pilot Analysis of Global Ecosystems, carried out by the World Resources Institute, calculated water availability and population pressures by river basin. Their analysis is even more sobering. This approach indicates that currently 2.3 billion people, or 41 per cent of the world’s population, live in water stressed areas. Of this total, 1.7 billion live in water scarce areas, with less than 1,000 cubic meters per person per year.
According to the PAGE analysis, by 2025, the number of people suffering from water stress or scarcity could swell to 3.5 billion people, or 48 per cent of the world’s projected population. Moreover, 2.4 billion of them are expected to live in water scarce regions.
While projections are not predictions, these figures point to the need for urgent attention to issues of stabilising population growth and using water resources sustainably.
The 20 countries of the Near East and North Africa face the worst prospects. In fact, the Near East "ran out of water" in 1972 in the sense that, since then, the region has withdrawn more water from its rivers and aquifers every year than is being replenished. Currently, for example, Jordan and Yemen withdraw 30 per cent more water from groundwater supplies every year than is replenished, and Israel's annual water use exceeds the renewable supply by 15 per cent. Inevitably, this means that water tables are falling and aquifers are slowly being sucked dry.
(It is a measure of the crisis, that in the early months of 2004 Israel signed a deal with Turkey to ship 50 million cubic metres of water a year, for 20 years,from the river Manavgat in Anatolia, in return for arms).
Africa also faces serious water problems. Currently, some 206 million Africans live in water stressed or water scarce countries. By 2025 the number will rise to about 700 million, as population continues to grow rapidly. Of these, roughly 440 million will live in countries with acute water scarcity (less than 1000 cubic metres per person per year).
If calculations of water stress and water scarcity were made regionally instead of nationally, parts of many other countries would be considered to face shortages. China, for example, has 22 per cent of the world's population but only 7 per cent of all freshwater runoff. China's freshwater supplies have been estimated to be capable of supporting 650 million people on a sustainable basis - only half the country's population. Despite periodic flooding, particularly in the southern part of the country, China faces chronic water shortages in the northern part. (For more about China, see Water Challenge for China).
At the start of the millennium, some 400 of 600 major Chinese cities were suffering from severe water shortages. Of these, 30 cities in northern China, including Beijing, will face long-term shortages severe enough to limit their economic development. Elsewhere, in rapidly growing cities such as in Bangkok, Dhaka, Jakarta, Lagos, Manila, and New Delhi, freshwater is so short that water theft has become widespread.
When water supplies become scarce competition can become intense. Tensions are particularly high in water-short areas where population pressures, urbanisation, and development needs collide to create demand for freshwater beyond nature's available supply. Countries that face tensions over water include Belgium, Poland, Singapore and the United States. In the western United States, for example, farmers demanding more irrigation water for their crops are competing with fast-growing urban areas demanding more water for municipal uses.
Already, China is practising what water expert Sandra Postel calls the "zero sum game of water management" - when authorities increase water supply to one user by taking it away from another. China's Yellow River is a classic example of this. The river is so over-used that, for an average of 70 days a year for the past decade, its waters have dried up before reaching the Bohai Sea. Crops have withered in the once rich delta so that upstream factories and farms could take all the water.
A substantial portion of the total freshwater supply is needed to sustain marshes, rivers, coastal wetlands, and the millions of species they shelter. As humanity withdraws a growing share of all available freshwater, less is available to maintain vital wetland ecosystems. Already, over 20 per cent of the approximately 10,000 freshwater fish species in the world are either endangered, threatened or going extinct.
Click here for a graph showing 'Changes in Freshwater Species Populations'
Healthy natural ecosystems are indispensable regulators of water quality and quantity. Flood plain wetlands, for example, soak up and store water when rivers flood their banks, reducing downstream damage. Wetland ecosystems are economically valuable to humanity. Robert Costanza, director of the Institute of Ecological Economics at the University of Maryland, estimates the global value of wetlands at close to $5 trillion a year based on their value as flood regulators, waste treatment plants, and wildlife habitats, as well as for fisheries production and recreation.
Irrigating rice with shadoof, Bangladesh
© J M McCaud/FAO
The world's 6.3 billion people are already appropriating just over half of all the accessible freshwater contained in rivers, lakes, and underground aquifers. By 2025 humankind's share will be at least 70 per cent - a conservative estimate that reflects the impact of population growth alone. If per capita consumption of water resources continues to rise at its current rate, humankind could be using over 90 per cent of all available freshwater by 2025.
Caught between growing demand for freshwater on one hand and limited and increasingly polluted supplies on the other, many countries face difficult choices. Finding solutions requires responses at local, national, and international levels. Nothing short of a Blue Revolution in water management can prevent the coming crisis.
Community led initiatives to manage water resources better can help urban dwellers gain access to safe, piped water supplies, improved sanitation and public health. Despite considerable efforts in the last two decades, the latest assessment by WHO/UNICEF finds that 2.4 billion people are still without an acceptable means of sanitation, while 1 billion do not have access to clean piped water.
Governments can develop national water management policies that help not only to improve supply but also manage demand better. Key strategies include regulation of water depending on its end use, watershed management, and appropriate pricing - for example, ending inefficient water subsidies that in effect encourage overuse. There are also huge inequities in the amount spent on improving services to the better-off sections of urban society compared to the investments in basic services for the urban poor.
International responses also are important because more than 200 major river systems cross international borders. As long as governments view water problems as national issues, rather than as transboundary issues, conflicts are likely to continue.
International co-operation over sources of freshwater is possible and practicable. In November 1999, for example, Egypt, Ethiopia, and Sudan agreed upon a strategy for "the sustainable development of the Nile water through the equitable exploitation of the river for the common benefit of all the river basin states". If fully implemented, the agreement - which covers all uses of the river, for irrigation, hydropower, drainage, drought and flood control, and pollution prevention - would be a significant breakthrough in a water-short region.
Ultimately, national governments in water-short regions will have to come to terms with acute freshwater shortages and accommodate human needs without over-using and polluting available freshwater resources. This will by necessity require a degree of international co-operation not yet seen in the area of resource management.
World Water Day 2005
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