The world is thirsty. Our half empty glass means only half full glass to another...

Brian Vastag
for National Geographic News
November 21, 2005


Even as the ice caps melt, global warming threatens to leave a billion people high and dry, says a team of U.S. climate scientists.

If the Earth warms just a degree or two Celsius in coming decades, regions that depend on runoff from mountain snows for drinking water and farming will face shortages, according to a study published in the November 17 issue of the journal Nature.
A companion article supports the claim, showing that mountain runoff has already decreased in some regions of the world.

“We found that, no surprise, less snow falls in a warmer world,” said Timothy Barnett of the Scripps Institute of Oceanography in La Jolla, California. “And what snow there is melts earlier.”

The two factors combine to push peak runoff from summer into spring, when reservoirs are already at capacity.

“The dams get filled earlier in the year, and they can only be filled to a certain level, so there’s still some flood control,” Barnett said.

The result: Much of the early runoff goes to waste, prompting shortages in late summer and autumn.

“It’s like squeezing six months of snowmelt into four,” Barnett said.

A Billion Dry

To develop their climate model, which looks ahead 30 to 40 years, Barnett and Jenny Adam of the University of Washington in Seattle looked at 30 years of global precipitation records.

They mapped the globe into squares and calculated how much precipitation fell in each square as rain and how much as snow. They overlaid that data onto a map of regions that depend on snow for at least 50 percent of their water supply, including the western United States.

“In California, Mother Nature holds the snow for us up in the Sierras,” Barnett said. “It’s basically a massive reservoir.”
Adams then researched manmade reservoirs in the target regions and found that the vast majority do not have the capacity to store the extra, early runoff.

“We were surprised how many places [lacked extra capacity]“, Barnett said. “[Reservoirs] were built on the assumption that ├óÔé¼┬ª water availability throughout the year wouldn’t change.”
In addition to the western United States and Canada, hard-hit regions include parts of Europe, South America west of the Andes, and much of central Asia from northern India across to China and Russia.

About one-sixth of the world’s population├óÔé¼ÔÇØmore than a billion people├óÔé¼ÔÇØinhabit these areas. The regions at risk also account for about a quarter of the world’s economic output.

“What are those people going to do?” Barnett asked. “Just sit there and be thirsty and watch their crops die?”

Less Runoff

Christopher Milly, a hydrologist with the U.S. Geological Survey, said that Barnett and Adam’s model draws on two decades of “really robust” research.

But climate scientists are less confident in predicting how, rather than where, global warming will affect total annual precipitation and river flow.

In a companion article in Nature, Milly used historical data from a dozen climate models to make a composite that accurately predicted changes in 20th century river flow across the globe.

Extending the model into the future, he estimated that by 2050 the western U.S., southern Africa, and areas surrounding the Mediterranean Sea will receive 10 to 30 percent less runoff than they currently do.

“Our contribution has been to show that the models ├óÔé¼┬ª can match observations of trends in water availability,” Milly said of his study.

Add this shortage to a shift in peak runoff from summer to spring, and the potential for crisis looms, warns Barnett.

As an example, he points to the Klamath River in northern California and Oregon. In 2001 the river ran about 25 percent lower than normal, leading to a tussle between conservationists and farmers over the water that remained. A court ruling led to a release of water to save two endangered species of sucker fish.

But in 2002, when the river ran low again, the farmers won and salmon lost. As water was diverted to agriculture, thousands of salmon died, perhaps as much as half of the river’s spawning population, according to the Oregon Natural Resources Council.

More difficult water choices loom, Barnett says.

“The Klamath situation is a harbinger of things to come,” he said. “You can see the whole future sort of happening right there.”

http://www.africanwater.org/drought_water_scarcity.htm

Water scarcity is a more relative concept describing the relationship between demand for water and its availability. The demands may vary considerably between different countries and different regions within a given country depending on the sectoral usage of water. A country with a high industrial demand or which depends on large scale irrigation will therefore be more likely to experience times of scarcity than a country with similar climatic conditions without such demands. Countries such as Rwanda, for example, would be classified by most standards as suffering water shortage but, because of low industrial and irrigation utilisation, would not be classified as water scarce.

Causes of water scarcity

The causes of water scarcity are varied. Some are natural and others are as a result of human activity. The current debate sites the causes as largely deterministic in that scarcity is a result of identifiable cause and effect. However, if water scarcity is the point at which water stress occurs (the point at which various conflicts arise, harvests fail and the like), then there are also less definable sociological and political causes. Many of the causes are inter-related and are not easily distinguished.

Determining water shortage and water scarcity

There are a number of problems related to determining water shortage and water scarcity. In general, national average figures are used which mask annual variability from year to year, seasonal variability and the regional variability within countries.

The Food and Agriculture Organisation (FAO) of the United Nations regards water as a severe constraint on socio-economic development and environmental protection at levels of internal renewable water availability of less than 1 000 m3/capita. At levels of water availability of less than 2000 m3/capita, water is regarded as a potentially serious constraint, and a major problem in drought years. Water scarcity provides a measure of the sensitivity of a given situation to drought. In situations where the average availability of water per capita is low, even slight variations can render whole communities unable to cope and create disaster conditions.

Water scarcity is a relative concept ├óÔé¼ÔÇ£ it is partly a “social construct” in that it is determined both by the availability of water and by consumption patterns. Because of the large number of factors which influence both availability and consumption, the determining of water scarcity will vary widely from country to country and from region to region within a country. Adopting a global figure to indicate water scarcity should therefore be done with great caution. Whilst a threshold such as 1000m3/capita may be useful for purposes of comparison, it should be carefully used because it may understate situations of potentially serious water stress.

Because the concept of water scarcity is a social construct or, put in other terms, a matter of political and economic perception, it may be more useful to describe water scarcity as a particular mix of availability and demand at which water stress occurs, rather than a per capita figure. This means that its determination is more qualitative than quantitative, as the point at which water scarcity occurs may vary widely from one situation to another. In a semi-arid highly industrialized country or in a country where food security is dependent upon the extensive use of irrigation, the aggregated per capita figure at which water becomes sufficiently scarce to cause internal or transboundary conflict may be a lot higher than in a temperate, less highly developed country.

Causes of water scarcity

* Population growth
* Food production
* Climatic change and variability
* Land use
* Water quality
* Water demand
* Sectoral resources and institutional capacity
* Poverty and economic policy
* Legislation and water resource management
* International waters
* Sectoral professional capacity
* Political realities
* Sociological issues

http://en.wikipedia.org/wiki/Water_crisis

Water crisis is a term that has been used by some to refer to the world├óÔé¼Ôäós water resources relative to human demand. The term has been applied to the worldwide water situation by the United Nations and other world organizations.[1][2] Others, for example the Food and Agriculture Organization, claim there is no water crisis.[3] The major aspects of the water crisis are allegedly overall scarcity of usable water[4] and water pollution.

2 billion people have gained access to a safe water source since 1990. [3] The proportion of people in developing countries with access to safe water is calculated to have improved from 30 percent in 1970[5] to 71 percent in 1990, 79 percent in 2000 and 84 percent in 2004, parallel with rising population. This trend is projected to continue. [4]

The Earth has a finite supply of fresh water, stored in aquifers, surface waters and the atmosphere. Sometimes oceans are mistaken for available water, but the amount of energy needed to convert saline water to potable water is prohibitive today, explaining why only a very small fraction of the world’s water supply derives from desalination.[6]

There are several principal manifestations of the water crisis.

* Inadequate access to safe drinking water for about 884 million people[7]
* Inadequate access to water for sanitation and waste disposal for 2.5 billion people[8]
* Groundwater overdrafting (excessive use) leading to diminished agricultural yields[9]
* Overuse and pollution of water resources harming biodiversity
* Regional conflicts over scarce water resources sometimes resulting in warfare

Waterborne diseases and the absence of sanitary domestic water are one of the leading causes of death worldwide. For children under age five, waterborne diseases are the leading cause of death. At any given time, half of the world’s hospital beds are occupied by patients suffering from waterborne diseases.[10] According to the World Bank, 88 percent of all diseases are caused by unsafe drinking water, inadequate sanitation and poor hygiene.[11]

Drought dramatizes the underlying tenuous balance of safe water supply, but it is the imprudent actions of humans that have rendered the human population vulnerable to the devastation of major droughts.

A 2006 United Nations report focuses on issues of governance as the core of the water crisis, saying “There is enough water for everyone” and “Water insufficiency is often due to mismanagement, corruption, lack of appropriate institutions, bureaucratic inertia and a shortage of investment in both human capacity and physical infrastructure”.[12] Official data also shows a clear correlation between access to safe water and GDP per capita.[13]

It has also been claimed, primarily by economists, that the water situation has occurred because of a lack of property rights, government regulations and subsidies in the water sector, causing prices to be too low and consumption too high.[14][15][16]