By Frederic Wagner, Utah State University

The Rocky Mountain/Great Basin region is the second largest of the assessment regions. Extending 15°of longitude and 17°of latitude, and covering parts of nine large western states, it is exceeded in size only by Alaska. As a result, there is a diversity of subregional climates in the region: at the northwest extreme precipitation is largely winter, frontal moisture; toward the southeast, there is a significant shift toward summer, monsoonal rain. This geographic gradient is complicated by hundreds of separate mountain ranges and basins with their own elevational gradients and local microclimates. Nevada alone has 160 mountain ranges.

We have subdivided the region into three Great Basin and five Rocky Mountain subregions, and analyzed their climate records for the past 100 years. Adjacent subregions exhibit different climate patterns, and there were no consistent patterns in any of the climate parameters across all subregions (with the exception of a tendency toward rising minimum temperatures, increased precipitation and increased streamflow in the northern portion of the region).

This spatial variability seriously complicates assessment because of the difficulty of devising reasonable scenarios for considering consequences across the region. It is unlikely that any single climatic change will occur over the entire region, and the climate models do not yet have the resolution to provide subregional detail in their predictions. We convened a September 1998 focus group meeting of climatologists and hydrologists to produce a limited set of reasonable scenarios for the region. The result was a wide range of opinions, however, with no consensus, suggesting that a wide range of possibilities needs to be considered.

Because of its aridity, water availability is a critical issue for the Rocky Mountain/Great Basin region. Some 90 percent of human water use in the region comes from surface water, three fourths of which is produced each year by melting of winter snowpacks on its mountain ranges. In February 1999, we surveyed water managers in the region about the current stresses on water resources and likely current problems associated with climate change. Later that month, we convened a focus group meeting of water managers employed at local, state and national levels, and specialists in western water law, policy and economics. A clear signal emerged that the managers' major concerns are coping with the variability in western water resources created by climate fluctuations. Their longer-term concerns focus on the population growth in the region and the shift in demand, with primary use moving from traditional uses by agriculture to municipal and industrial needs. Climate-change effects are not very high on the attention screens of water resource managers at present compared to concerns about climate fluctuations.

However, were climate change to occur, decline in winter precipitation would reduce water resources that are already oversubscribed. The region's population growth is the most rapidly increasing of any region in the nation, and demand for water resources is likely to increase as this growth continues. Increase in winter precipitation would ease any shortage, but could exacerbate flood-control problems. With agriculture using 75-80 percent of water allocations in the West, it is looked upon as a buffer to absorb rising municipal and industrial needs.

Rising temperatures could shorten snowpack seasons by delaying the autumnal change from rainfall to snow, and advancing spring snowmelt. The result could be a change in seasonal run-off schedules that might or might not coincide with power, municipal and agricultural withdrawals; the changes might also alter the availability of water for aquatic ecosystems and recreational use, especially through protracted summer run-off seasons. A shortened snowpack season could also place at risk many ski businesses that must have a minimum number of skiing days to operate profitably.

Because western ecosystems are substantially water limited, the regional assessment will closely examine the potential effects of both precipitation increase and decrease. A particular concern will be the effects on fire frequencies. Dry years in the mountains make the montane forests more fire prone, but the shrub steppe less so. Wet years in the shrub steppe enhance growth of herbaceous understories, increase ground fuels, and increase fires that convert native, perennial vegetation to monotypes of exotic annuals. Other ecological effects to be analyzed are changes in plant community composition, vulnerability to invasion by non-native plant species, and effects on threatened and endangered species, especially stream and wetland organisms.

One sector that is closely adjusted to current climate patterns is the livestock industry, which pays fees to graze its animals on the 75-80 percent of the region that is public land. Ranchers typically operate from privately owned home ranches where they may or may not have significant acreage of irrigated forage crops, move animals to national forest ranges in the mountains in summer, and to low-elevation U.S. Bureau of Land Management lands in winter. Depending on the native rangelands available to an operator and the productivity of the natural vegetation, it may be necessary to provide seasonal, supplemental forage, either produced on the home ranch or purchased on the open market.

Thus, by depending on forage produced by the natural vegetation, and on supplements for which prices vary according to weather conditions, the industry is closely attuned to the vagaries of weather. Because it operates on a thin profit margin, the livestock industry would be significantly affected by climate change. Decline in precipitation would eliminate profitability for many ranchers. Increases in precipitation and temperatures could enhance forage production and grazing-season lengths on natural vegetation. Both would reduce costs and increase profitability.

The next stage in the regional assessment is to hold additional focus group meetings with those sectors most likely to be affected by climate change: tourism (with special attention to the skiing industry), cultivated agriculture, livestock industry and natural ecosystems.

For more information, contact:

Frederic Wagner, Utah State University; phone: (435)797-2852; email: fwagner@cc.usu.edu.