A multi-pronged analysis of global water resources indicates the supply of clean freshwater for use by humans and natural ecosystems is shrinking by the year, according to a University of Colorado at Boulder researcher.
Associate Professor Kenneth Strzepek of the civil, architectural and environmental engineering department said the analysis indicates one-third of the world聮s population is currently living in regions that are classified as "water stressed." And, as the human population grows, more water will be needed for irrigation, livestock, industry and to sustain natural ecosystems.
"It is estimated under a 聭business as usual聮 scenario that by the year 2025, almost one-half of the population will be living in water-stressed regions," he said.
Strzepek and his colleagues have used sophisticated computer models and geographical information systems to look at river basins around the world and identify those that are the most stressed. Some of the "hot spots" include China聮s Yellow River basin, Africa聮s Zambeze River basin, the Syr Darya and Amu Darya River basins leading to Russia聮s Aral Sea and the Colorado River basin.
His research is part of a background analysis for the World Water Commission聮s "World Water Vision for the 21st Century" report. The commission is a government and privately funded organization seeking global solutions to water problems.
He said socioeconomics, geography, politics and the environment all need to be factored in to develop sound policy decisions. "We are using a broad-brush approach here, but major water-policy decisions require analysis and input from a wide number of disciplines."
Strzepek gave an invited talk on the subject at the annual fall meeting of the American Geophysical Union held Dec. 13 to Dec. 17 in San Francisco. He has been working on the project with CU graduates Alyssa Holt of the Stockholm Environmental Institute and Jeff Bandy of the University of Leuven in Belgium.
The modeling tools have allowed Strzepek and his colleagues to look at the vegetation, soils and climate from the headwaters to the mouths of the world聮s major river systems in 25 mile-square chunks to model runoff and streamflow. They also have been able to use past temperature and precipitation data to reconstruct runoff and streamflow data for major river basins going back 100 years.
While reservoirs have long been used to change the distribution of river flows, evaporation can result in losses up to 25 percent of a river聮s annual flow in arid and semi-arid years. Today, 70 percent of the world聮s freshwater withdrawn by humans is used to irrigate crops, he said. Unfortunately, much of the irrigation water takes up pesticides, herbicides and salts from cropland soil and returns to the river system, polluting the water and adversely affecting humans and the environment.
"In the Nile Delta in Egypt, water quality is a major problem for human and agricultural use due to upstream pollution from agricultural, industrial and municipal uses," Strzepek said. "Similar situations are found in other river systems like the Indus River in Pakistan and the Yellow River in China."
A sustainable water supply is determined by the nature of a river basin聮s hydrology and storage capacity. While more dams provide more water for humans, they cause environmental impacts, he said. Researchers factoring in some knowledge of aquatic ecosystems have set a goal that no more than 40 percent of a river basin聮s water should be diverted for human use in order for the environment to be adequately protected, he said.
"In the Colorado River basin, however, 100 percent of the water is used," Strzepek said. While the average flow in the basin is 15 million acre-feet per year, only 1.5 million acre feet is delivered annually to Mexico and only a trickle remains as the Colorado River enters the Gulf of California in Mexico.
Strzepek said that developing sustainable water policy requires experts to gain input from "stakeholders" in the river basins regarding their own cultural and social values on sustainability. "In developing countries, especially in arid and semi-arid regions, this means involving women more in the water-management decision process. They are the primary water-gatherers and often bear the heaviest load in agricultural labor," he said.
"The goal of the World Water Commission is to make water everybody聮s business in the 21st century and to see that the needs of nature and humans are met as we pursue the task of sustainable economic growth," Strzepek said.