Following is a discussion of various strategies for increasing water supplies in the Tucson Basin. A few obviously require a large-scale investment of funds and other resources; others can be done by individuals in their homes and communities. A few appear doable; others seem far-fetched.

Import Water From Outside the Basin

CAP has not been the only project designed to import water from outside the basin to increase Tucson’s water supplies. Its distinction is that it was the only such project to be built. Over the years, other strategies have been proposed to bring water here from elsewhere. One scheme offered in the 1970s would have brought water from the Yukon, through Canada to the Great Lakes and ultimately to the Southwest. Another heroic scheme would have imported water from the Pacific Northwest to California and Arizona. Both strategies were found to be excessively costly, not to mention being unacceptable to people in the Northwest and Canada.

The City of Tucson tried a much less ambitious scheme in the 1960s when it purchased land with water rights north of Benson along the San Pedro River, with the intent of building a pipeline to Tucson. A lack of funds and a questionable supply of water, coupled with opposition from residents, stopped this project, and Tucson sold the land. Another effort to capture San Pedro water was the Charleston Dam, originally part of the CAP system. This, too, was defeated when Cochise County residents opposed the idea.

Other ideas for obtaining additional water include desalinating seawater, either along the Gulf of California or near San Diego and piping it to Arizona. A fanciful proposal in the 1980s suggested towing icebergs from Antarctica to the California coast and piping the melted water to Arizona. Neither of these projects appeared feasible or cost-effective.

Capture Floodwater

To many people, allowing flood water to drain out of the basin represents a lost resource. Heavy rain showers occur occasionally in the desert, filling arroyos and river beds with abundant and vigorously flowing water. Capturing more of this flow could augment our supplies, whether used directly or recharged. With Tucson riverbeds seeming to offer promising sites, Tucson water history during the twentieth century includes various references to plans for capturing runoff. At times, suitable locations to capture and control mountain runoff have been proposed. Tucsonans looked to the dams along the Salt River as models, but the Santa Cruz River and its tributaries offered no comparable sites suitable for large storage dams. Studies are underway to determine whether other methods such as inflatable dams can be effective. (See Chapter 4 for a discussion of this topic.)

Vegetation Management

In the 1960s and 1970s, removing vegetation along watersheds was considered a promising way to increase water supplies for cities. This strategy was based on the fact that vegetation uses water that otherwise could be put to human uses. Some experiments were conducted; chains, cables and chemicals were used to remove chaparral and piñon-juniper forests. Ponderosa and mixed conifer forests were harvested. While initial results often showed an increase in streamflow, long-terms results were not conclusive. Grasses often took over areas denuded of trees, using about as much water as did the trees. Where vegetation did not have a chance to regrow before heavy rains, erosion took away topsoil.

Some people have advocated removing cottonwoods along rivers such as the San Pedro because of the water they use, but the results would be mixed at best. Some gains would be offset by the loss of shade to cool the water and reduce evaporation and by the loss of a root system to help hold soil in place. The increased importance that people place on riparian vegetation for habitat and recreation further advises caution when considering vegetation management practices. This approach to increasing water supplies has generally fallen out of favor in Arizona.

Weather Modification

Advocates of weather modification look to the clouds as a source of water to augment current supplies. Arizona’s interest in weather modification evolved over time, from early cloud seeding experiments to the adoption of sophisticated computer modeling techniques that simulate climatological phenomena and test weather modification premises. The evolution reflects a change in attitudes, from an optimistic expectation of immediate results to a more cautious, even skeptical regard about the potential of weather modification.

Clouds consist of small water droplets that, despite below-freezing temperatures, remain liquid. The water’s purity and the lack of foreign particles in the atmosphere prevent the droplets from freezing. These “supercooled droplets” form supercooled clouds. As temperatures decrease, the droplets form ice crystals around small atmospheric particles such as dust. Cloud seeding introduces additional particles or nuclei into the atmosphere, causing more ice crystals to form. Silver iodide compounds or dry ice are the usual cloud seeding agents. Aircraft or ground-based generators introduce the agents into the atmosphere. The ice particles grow and attract nearby water vapor and droplets. The enlarged ice particles eventually fall as snow. Clouds which form over mountainous areas are preferable for seeding because they last longer, and weather modification experiments can be more readily arranged.

A number of legal, social and environmental issues would have to be resolved before weather modification could be used on a large scale, even if it proves to be effective. Who is liable for damages from floods or other weather events resulting from weather modification? How are the rights of those who want rain to be reconciled with the rights of those who prefer sunshine? What if precipitation increases in a basin in which cloud seeding occurred but decreased during the same period in another basin? Has the latter basin been wrongfully deprived of its precipitation?