The National Assessment The Arid and Semi-Arid Western United States Broadly defined as all of Arizona, New Mexico, Nevada, and Utah plus the arid and semi-arid regions of California, Colorado, Idaho, Oregon, Montana, and Wyoming, this vast region is dominated by public lands. Three workshops--focused on the Southwest, Great Basin/Rocky Mountains, and California--are building networks of people and organizations. This western region contains major metropolitan centers and is among the most urbanized in the country (Utah, for example, is the sixth most urbanized state in the nation). The region's economy is a mixture of ranching, dryland and irrigated agriculture, tourism, retail, manufacturing, and high technology industry. In the left photo, the extent of Grinnell Glacier at Glacier National Park is recorded in 1910, while the right photo shows the significantly reduced glacier in 1997. Left photo by Kiser, from GNP archives, right photo by Fagre. With some of the highest population growth rates in the country (Phoenix and Las Vegas, for example), the region's demand for resources, particularly water, is increasing--water use could exceed sustainable supply. Changes in patterns of land use accompanying the growth in population are stressing natural ecosystems and adding to regional air pollution. Climate extremes are characteristic of the region; moderate to severe floods and droughts affect portions of the Southwest every year. Changes in climate and climate variability will likely have a significant impact on this region. Studies that have reconstructed the climate history of the southwestern U.S. reveal a complex and cyclical nature of floods and droughts that includes the El Niño-Southern Oscillation. Various climate scenarios for the region are plausible. For example, if summer rains increase in the Great Basin, the productivity of native vegetation would increase, shrub-steppe grasses would increase, and livestock grazing would improve. The increase in flammable vegetation, however, could result in more frequent and intense fires resulting in land degradation and a loss of biodiversity. If winter precipitation decreases, the consequences for the ski industry and downstream water uses could be significant. (This information was taken from the Southwest climate impact workshop report.) U.S. Department of the Interior U.S. Geological Survey This page is <http://esp.cr.usgs.gov/info/assessment/southwest.html> Maintained by Randy Schumann Last modified Friday, 23-Feb-2007 16:20:43 MST