Glossary of Key Hydrological Terms

Hydrological (water) cycle: The natural cycle by which water evaporates from oceans and other water bodies, accumulates as water vapor in clouds, and returns to oceans and other water bodies as precipitation. Precipitation over land has two components: runoff and moisture from evapotranspiration.

Nonrenewable water: Water in aquifers and other natural reservoirs that are not recharged by the hydrological cycle or are recharged so slowly that significant withdrawal for human use causes depletion. Fossil aquifers are in this category: They recharge so slowly over centuries that they are, in effect, a nonrenewable resource.

Renewable water: Freshwater that is continuously replenished by the hydrological cycle for withdrawal within reasonable time limits, such as water in rivers, lakes, or reservoirs that fill from precipitation or from runoff. The renewability of a water source depends both on its natural rate of replenishment and the rate at which the water is withdrawn for human use.

Runoff: Water originating as precipitation on land that then runs off the land into rivers, streams, and lakes, eventually reaching the oceans, inland seas, or aquifers, unless it evaporates first. That portion of runoff that can be relied on year after year and easily used by human beings is known as stable runoff.

Water consumption: Use of water that results in its evaporation or transpiration (through plants) or that otherwise makes it unavailable for subsequent human use.

Water withdrawal: Removal of freshwater for human use from any natural source or reservoir, such as a lake, river, or aquifer. If not consumed, the water may return to the environment and can be used again.

Water scarcity: According to a growing consensus among hydrologists, a country faces water scarcity when its annual supply of renewable freshwater is less than 1,000 cubic meters per person. Such countries can expect to experience chronic and widespread shortages of water that hinder their development.

Water stress: A country faces water stress when its annual supply of renewable freshwater is between 1,000 and 1,700 cubic meters per person. Such countries can expect to experience temporary or limited water shortages.

The Coastal Connection

Population patterns. Around the world, people cluster near coasts. Over half of the world's population—about 3.2 billion—occupy a coastal zone 200 kilometers wide. With the exception of India, most of Asia's population is coastal. In China, for example, close to 60% of the population of 1.2 billion live in 12 coastal provinces, along the Yangtze River valley, and in two coastal municipalities—Shanghai and Tianjin. Along China's 18,000 kilometers of continental coastline, population densities average between 110 and 1,600 people per square kilometer.

The population of Latin America and the Caribbean is even more coastal. Among the region's coastal countries, with a total population of around 610 million, a full three-quarters of the population lives within 200 kilometers of the seacoast.

Only in Africa do more people live in the interior of the continent than along or near coastlines. Over the past two decades, however, Africa's coastal cities—centers of trade and commerce—have been growing by 4% a year or more, as millions of people migrate from the interior. Accra, Abidjan, Dakar, Dar es Salaam, Lagos, and other coastal cities have seen their populations soar from in-migration.

In recognition of rapid population growth and increasing water pollution, representatives of Africa's 38 maritime countries met in July 1998 in Maputo, Mozambique, to consider ways to "protect, manage, and value" the continent's coastal environment in the face of limited resources, poor sanitation, and development needs.

Environmental consequences. Population growth, urbanization, and industrialization with little regard for the environment are polluting and depleting coastal and ocean resources. Consider the following trends:

• The world has lost half its coastal wetlands, including mangrove swamps and salt marshes. Over the past century mangrove forests have been decimated: An estimated 25 million hectares have been destroyed or grossly degraded.
• In virtually all inhabited coastal areas, seagrass beds, vital as fish nurseries and feeding areas, are diminishing.
• Coral reefs, the rainforests of the sea, are being pillaged in the name of development. Of the world's 600,000 square kilometers of reefs found in tropical and sub-tropical seas, 70% could be lost within 40 years.
• Coastal and ocean fisheries are in serious decline. According to the UN Food and Agriculture Organization (FAO), in 1995 nearly 70% of the world's marine fish stocks were either fully-to-heavily exploited, overexploited, depleted, or slowly recovering.
• As coastal waters become clogged with raw sewage and agricultural and industrial pollutants, ecosystems begin to unravel.

Source: Adapted from Don Hinrichsen. Coastal Waters of the World: Trends, Threats and Strategies. Washington, D.C., Island Press, 1998 (90).

A Successful Solution:
The Global Guinea Worm Eradication Effort

To locate the areas in which guinea worm disease is endemic, the eradication campaign works closely with local health workers. In Pakistan and Iran cash rewards up to US$850 were offered and publicized widely to help find any remaining guinea worm cases (201). A registry of reports of potential cases was created, and reports were promptly investigated by program staff. Cases found in Pakistan were paid up to US$150 to comply with containment measures, keeping the skin where the worm is emerging wrapped and abstaining from entering water, which prevents the worm from releasing more eggs (156, 191).

School teachers use visual aids and books provided by the eradication program to teach children how to avoid infection, while health educators instruct residents how to strain their drinking water through the cloth filters. In endemic areas water is treated with low concentrations of a nontoxic larvacide, temephos (Abate) (24). These efforts are concentrated in the growing season, when the larvae typically reappear (201) (see Table 2).

In 1997, 19 countries where guinea worm was once endemic were officially certified as free of guinea worm transmission—that is, no cases had been reported for three consecutive years. In the 16 countries of Africa, as well as in India and Yemen, where guinea worm still exists, prevalence is dwindling (201). Sudan, however, still has more than 100,000 cases of guinea worm—an estimated 78% of the world's total cases—largely because civil war makes surveillance difficult (189). Nevertheless, Kenya, although it is highly susceptible to the reintroduction of guinea worm from neighboring Sudan, has reported no cases for several years (201).

Ten years ago guinea worm afflicted millions of people in Africa and Asia. Today, only 10 countries report more than 1,000 cases. In 1989 Ghana reported 180,000 cases but reported only 7,000 in 1994. Recent progress has been even more rapid. For example, in 1992 Niger reported 33,000 cases but reported only about 3,000 in 1996. In 1994 India reported almost 40,000 cases but reported only 9 cases in 1996 (201). If progress continues, guinea worm may soon be a thing of the past.

Wars over Water?

In particular, problems could erupt in a number of areas where freshwater use has already reached or even exceeded natural limits (62, 140). In these areas, mostly in North Africa and the Near East, countries not only face mounting internal competition for limited supplies of freshwater as a result of rapid population growth and escalating demand, but also find themselves squabbling with their neighbors over water rights. For example:

• Water has been at the center of a continuing controversy between Israel and Jordan. In May 1997 a ceremony to create a joint "peace park" on the site where seven Israeli school girls were killed by a Jordanian border guard was canceled after Jordan charged Israel with delaying implementation of a water agreement in the Jordan-Israeli Peace Treaty of 1994. Under the treaty Jordan was to receive an additional 50 million cubic meters of water a year from Israel, mostly from the Yarmuk River, one of the River Jordan's main tributaries. (43). The treaty did not state who would pay for the water and its trans-portation, however. Since the May 1997 "peace park" crisis, Israel has offered to foot half the bill, and the Israeli cabinet has approved a plan to supply Jordan with 50 million cubic meters of water, constituting the second transfer under the treaty.
• Israel already has used its military power to maintain access to the Jordan River. In the early 1960s Israeli soldiers halted a Syrian-Jordanian scheme to divert the river for irrigation. Later, Israel occupied vital sections of the Jordan River's headwaters, thus making sure that most of its flow would be available for Israeli towns and farms (87).
• Egypt has threatened Ethiopia with war if it carries out plans to divert more water from the Blue Nile for agricultural use. The Egyptian government sees this issue as one of life or death (87). Without the Nile's nourishing waters, Egypt could not exist as a nation, since it depends on the Nile for 98% of its freshwater needs.
• The Southeast Anatolia Project in Turkey is one of the largest irrigation and power generation schemes in the Near East (103). This vast complex of dams, canals, and irrigation systems began operating in July 1992. By early in the next century it is expected to divert at least half of the flow of the Euphrates River—some 4 trillion gallons of water a year—into Turkish dams and irrigation canals. This diversion will leave the downstream countries, Syria and Iraq, with less than half of the stable flow they now have access to. Syria also is planning to take some 3.5 trillion gallons out of the Euphrates before it enters Iraq, thus depriving Iraqi farmers of badly needed irrigation water—water that people in the area have had access to for the past 6,000 years (120). The entire region is set for a potentially ruinous conflict over limited water resources.

It can be done, however, as shown by the example of the Chesapeake Bay, North America's largest brackish water estuary. Managing the Chesapeake watershed presents unique and seemingly insurmountable obstacles. Although the Bay itself covers only 2,200 square miles (5,500 square kilometers) and averages just 21 feet deep (6.5 meters), its watershed is vast, sprawling over 64,000 square miles (160,000 square kilometers) through six US states. Moreover, 15 million people live in the watershed, which is one of the most heavily populated areas on the East Coast (22).

By the early 1980s planners were confronted with the con-sequences of decades of accumulated abuse of the water resources in the Chesapeake watershed. Signs of decay were everywhere:

• By 1987 the Bay was receiving about 184,000 metric tons of nitrogen and 74,000 metric tons of phosphorus a year from human and animal wastes and commercial fertilizers.
• The Bay had lost more than half of its natural tidal and nontidal wetlands and 40% of its watershed forests.
• Seagrass beds, which once covered over half the Bay's bottom, amounting to several hundred thousand acres, had been reduced to no more than 34,000 acres (14,000 hectares) by 1984—10% to 20% of their original area.
• Chronic overharvesting, along with mounting pollution and habitat degradation, contributed to the dramatic decline in the Bay's fish and shellfish populations. Commercial catches of rockfish (striped bass) dropped from 2,608 metric tons in 1970 to just 272 metric tons in 1983. The Bay's oyster fishery had plunged catastrophically. From an all-time peak of 20 million bushels in 1884, the oyster harvest declined to just 168,000 bushels in 1992.

A nonprofit membership organization, the Chesapeake Bay Foundation, was one of the key groups urging state governments to take a comprehensive watershed approach to the Bay's environmental problems. After a slow start in the early 1980s, the three key state governments—Maryland, Virginia, and Pennsylvania—with help from the US Environmental Protection Agency (EPA), agreed to launch an ambitious, integrated cleanup program.

In 1987, when the EPA and the governors of the three main watershed states met at a major strategy conference, nothing on this scale had ever been attempted before in the US. The result was the Chesapeake Bay Agreement between the states and the federal government. The agreement provides solid political commitment from all watershed states for a 40% reduction in nutrient loadings to the Bay by the year 2000, using 1985 as the base year. "The year 2000 goal is a permanent cap on emissions of nitrogen and phosphorus," explains William Matuszeski, Director of EPA's Cheasapeake Bay Program in Annapolis, Maryland. It is, in essence, a nondegradation policy for the entire watershed, in which each major tributary of the Chesapeake will reduce nutrient pollution by 40%.

In order to meet such an ambitious target, each state crafted its own pollution reduction strategy, working within the terms of the overall agreement. The Pennsylvania legislature even passed the first nutrient management law in US history. Although neither Maryland or Virginia took binding legislative steps, both states have encouraged farmers in the Chesapeake watershed to adopt "best management practices," which involve low-till or no-till agriculture, along with the reduced use of pesticides and a marked reduction in the appli-cation of chemical fertilizers, one of the main sources of nutrient pollution to the Bay.

The watershed states have made progress in reducing point sources of pollution—effluent from sewage treatment plants and industrial complexes. Maryland, Virginia, Pennsylvania, and the District of Columbia also have passed legislation to ban the use of phosphate detergents. These actions reduced phosphorus pollution to the Bay by 40% between 1985 and 1994.

The main improvement, states Matuszeski, is that "we have halted the increase in nitrogen pollution to the Bay in spite of a growing population." This has been the result of building 3-stage sewage treatment plants around the Bay and decreasing the amount of animal manure and fertilizers seeping into the region's surface waters.

According to the EPA, many farmers in Maryland, Pennsylvania, and Virginia have cut fertilizer use dramatically, and some farmers use no commercial fertilizers at all, relying instead on animal manure and crop residues. The use of pesticides has dropped 20% since 1985. The Bay is not free of problems, as evidenced by the 1997 outbreak of the toxic organism Pfiesteria piscicida, which kills marine life and degrades water quality. Still, Matuszeski thinks that progress in meeting watershed management goals will be faster "once we can get natural ecosystems to start working for us, like wetlands and seagrasses" (90). Progress has been slower than expected, but most trends are in the right direction.