Watersheds
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Dan Neary
Southwest Watershed Science Team
Rocky Mountain Research Station
2500 S. Pine Knoll Lane
Flagstaff, AZ 86001

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Managing Arid and Semi-Arid Watersheds

History of the Arizona Watershed Program

The main focus of the Arizona Watershed Program (AWP), a joint initiative of the Arizona Water Resources Committee and the State Land Department, was to work with the USDA Forest Service, their cooperators, and others to obtain and extrapolate research findings on water yield improvement to large-scale watershed management practices designed to increase water yields by manipulating vegetative cover.

Need for Water

One situation that conditioned and circumscribed people's behavior throughout Arizona and the Southwestern United States was the perennial shortage of water. The expected but variable supplies of surface water have long since been appropriated. Electricity and electric pumps enabled access to previously unavailable groundwater sources, while the favorable climate resulted in an increase in agriculture and urbanization. 

As a consequence, nearly all of the increased water supplied to this rapidly growing area is pumped from underground basins. This increase in pumping has caused a steady decline in regional water tables, which has affected local economies. Many acres that formerly supported agriculture have been abandoned, converted to housing developments, or switched to an alternate source of water, such as the Central Arizona Project (CAP) water that became available in the late 1980s.

However, the water situation, especially in the heavily populated areas, has had little affect on people's use of water, except for the farmer. Within any user group (household, municipal, commercial, industrial, or agriculture), the willingness to pay for water varies significantly depending on the benefits obtained from its use.

Water uses by various crops and user groups
Water uses by various crops and user groups

For example, as the price of water increases, the quantity demanded by various users changes because of differences in their ability to purchase water. Household users have the highest willingness to pay and one of the lowest quantities demanded (about 2 to 3 acre-ft/acre/yr assuming 4 families per acre). On the other hand, the willingness of farmers to pay is far less than any other user. However, their crops require much more water (5 and 6 acre-ft/acre/yr to grow cotton and alfalfa, respectively). To put this in perspective, the native desert around Phoenix uses about 0.5 acre-ft/acre/yr.

When the cost of water sufficiently reduces the farmer's income, he is forced to stop farming and either abandons or sells his land to a developer who provides what many homeowners desire: artificial lakes, golf courses, pools, and green lawns. Conversion of water previously used for agriculture (5 or 6 times that used by a household), therefore, has the potential to sustain growth of municipalities and industry for some years into the future.

Barring conversion of saline water, additional importation of outside water, advancements in rainmaking, and rigorous conservation measures, regional residents must rely on the variable surface and diminishing groundwater supplies. In response to this situation, the initial direction of research in the arid and semi-arid Southwest focused on investigating the potentials for increasing water yields from forests, woodlands, and shrublands of the region through vegetative manipulations.

Arizona Watershed Program

The University of Arizona was commissioned in 1955 to investigate the potential for increasing water yield from the state's forest and rangelands. Numerous watersheds were instrumented with various climatic and hydrologic measuring equipment by the USDA Forest Service, and its cooperators, in the late 1950s and throughout the 1960s to study the effects of vegetative clearings, thinnings, and conversions on water yields under controlled, experimental conditions.

These watersheds formed a research network, called the Arizona Watershed Program, for public agencies and private groups interested in obtaining more water for future economic growth while maintaining the state's watersheds in good condition. This collaborative program was the focus of watershed research in Arizona through the 1960s, 1970s, and into the early 1980s.

For more on water in the Central Arizona Highlands and the Arizona Watershed Program, see Historical Perspective on Water in the Arizona Highlands and More Water for Arizona (Fox, et al., 2000).

Reference

Barr, G.W. 1956. Recovering rainfall: More water for irrigation, Part I. Arizona Watershed Program. Cooperating: Arizona State Land Department, Water Division of the Salt River Users' Association, University of Arizona. 33 p.

Fox, K.M., P.F. Ffolliott, M.B. Baker, Jr., and L.F. DeBano. 2000. More water for Arizona: A history of the Arizona Watershed Program and the Arizona Water Resources Committee. Primer Publishers, Phoenix, Arizona. 118 pp.