The Arid West—Where Water Is Scarce - Unreasonable Expectations

The American pioneers who settled the West knew how precious water was. They had to dig their own wells and haul the water. They watched crops dry up and turn to dust and cattle die from lack of this precious commodity. Today, most people in the United States take a plentiful supply of water for granted because of our many efficient water supply systems. As populations grow, however, particularly in the arid and semiarid West, where the availability of water has been an issue since the earliest settlement days, water supplies are becoming more limited and increasingly vulnerable to drought.

Estimating the Water Supply

Many people base their expectations of "normal" on their experiences when they were younger or what conditions have been like for the past few years. Because of the relatively short human life span, very few people, including water planners, are conscious of the fluctuations in climate across decades or centuries. Some scientists argue that the only real climatic constant is change and that people have invented the idea of "normal weather" for their peace of mind.

Comparison of a region's worst recorded drought (the drought of record) against expectations of water supply can provide a harsh reality check. Urban and agricultural planning would undergo dramatic changes if city, state, and regional planners, managers, and officials operated as if the drought of record would be the next drought. According to the National Drought Mitigation Center (NDMC), droughts of record typically last between three and seven years. For most of the country, the drought of record occurred between the 1930s and 1960s. While the same weather conditions could recur, the effects would almost certainly be different because water-use patterns and population concentrations have shifted substantially since then. These effects can be simulated using economic input/output computer models to determine the effects on society.x

Planning for drought has its limitations. One limitation is that there is no way of knowing if the next drought will be worse than the drought of record. Another is that our climate records do not go back more than 100 to 120 years, while some drought cycles can span several decades or centuries. Scientific research into tree rings (dendochronology) is providing information as to how limited our knowledge really is. For example, the work of Charles Stockton and David D. Meko at the University of Arizona's Laboratory of Tree-Ring Research tells a compelling story about climate history. In January 1983 they reported their findings in the Journal of Climate and Applied Meteorology. Although 1934, 1936, and 1939 were very dry years in the Great Plains, the drought of the 1930s paled in comparison to the droughts of 1860 and 1757, when dry conditions lasted more than three to ten years.

A good portion of California's water supply depends on runoff from precipitation (rain and snow) in the Sierra Nevada Mountains. Scott Stine, a geographer at California State University at Hayward, used carbon dating to study trees growing in lakes, rivers, and swamps. In June 1994 he reported in Nature evidence that for spans of more than a century at a time, the climate was so dry that there was little or no runoff from the Sierra Nevada Mountains. Stine was able to document that past dry spells lasted from 892 to 1112 (220 years) and from 1209 to 1350 (141 years). Stine also found that despite two droughts, the twentieth century was among the wettest in four thousand years.

What Records to Use?

Deciding which of the historic records to use in planning always involves some arbitrary judgments. The effects of these judgments can have far-reaching consequences. A good example is the basis for the 1922 Colorado River Compact, which determines how the river's water is allocated. In 1988 Barbara Brown of the National Center for Atmospheric Research investigated the data used by the U.S. Bureau of Reclamation to establish the allocations and reported her findings in Societal Responses to Regional Climatic Change: Forecasting by Analogy (Michael H. Glantz, editor, Boulder, CO: Westview Press, 1988). She reported that the Bureau used roughly calculated data gathered between 1899 and 1920 to arrive at an estimated average annual flow of 16.4 million acre-feet at Lee's Ferry, a point on the river. An acre-foot (43,560 cubic feet) is a unit of measure that is equivalent to the volume of water it takes to cover an acre to a depth of one foot.

Subsequent climatic record information now shows that theperiodfrom1899to1920wasanunusuallywetperiod in the Colorado Basin. Colorado River flows calculated from tree-ring records for the period reveal that they were the wettest twenty years in the past 450 years. Tree-ring records also show that the flow in the river has been as low as 4.7 million acre-feet per year. The ten-year annual average has been estimated to be 9.7 million acre-feet. Since the 1922 compact, flows in the river have been as low as 6.6 million acre-feet in 1934, with a ten-year annual average lowof12.5millionacre-feetayearfrom1931to1940.

The planners and engineers at the Bureau of Reclamation did not have the climate records and sophisticated technology available to us today. Despite our greater knowledge, drought management continues to be that of response to crisis instead of thoughtful advanced planning. Cities, states, and regions are reluctant to take actions that will anger citizens by restricting growth and access to water use and to raise taxes and increase expenditures to conserve water when the need for the water may not occur for many years. People are naturally optimistic and, even under drought conditions, frequently will not accept the fact that they are in a drought. They continue to reassure themselves that it will rain tomorrow, or that the next year will be a good year, despite the climatic data that show that droughts of record typically occur for two or more years in a row, or that new technology will find a way to solve the problem.