A variable climate, diverse topography and ecosystems, increasing human population, and a rapidly growing and changing economy characterize the West. Scenic landscapes range from the coastal vistas of California to the intimidating deserts of the Southwest to the alpine meadows of the Rocky and Sierra Nevada Mountains. Since 1950, the West has quadrupled its population, expanding urban areas such as Los Angeles, Las Vegas, Salt Lake City, Santa Fe, Albuquerque, Tucson, and Phoenix. Numerous national parks and monuments exist in the West—such as Zion National Park, Arches National Park, Death Valley, Canyonlands, and the Grand Staircase-Escalante National Monument—and attract millions of tourists from around the world. Because of the extreme population growth and development, this region faces multiple stresses such as air quality problems, urbanization, and wildfires. The most significant problem, however, is the availability of water resources. This region includes the characteristically dry Southwest. Water is usually consumed far from where it originates. Competition for water among agricultural, urban, power consumption, recreational, environmental, and other uses are intense, with water supplies already not ample enough in many areas.
Another factor in the West is its variable climate. Historically, it has experienced exceptionally wet and dry periods. During the 20th century, temperatures in the West have risen 2-5°F (1-3°C). The region has also had increases in precipitation, with increases in some areas greater than 50 percent. Some areas, however, such as Arizona, have become drier and experienced more droughts. The length of the snow season has decreased by 16 days from 1951 to the present in California and Nevada. Extreme precipitation events have increased, causing flooding and landslides, such as those in California.
Modeling efforts conducted by the U.S. Global Change Research Program project annual average temperature increases 3-4+°F (2°C) by the 2030s and 8-11°F (4.5-6°C) by the 2090s. The models also project increased precipitation during winter, especially over California, where runoff is projected to double by the 2090s. In these climate scenarios, some areas of the Rocky Mountains are projected to get drier. The models project more extreme wet and dry years.
The future of the West's water resources are of critical concern because they are so sensitive to climate change. The semiarid West is dependent upon a vast system of engineered water storage and transport, such as along the Colorado River, and is governed by complex water rights laws. Much of the water supply comes from snowmelt. The problem with global warming is that snowpacks are expected to decrease, and earlier spring warming will alter the amount and timing of peak flows, upsetting the balance and management of water resources. In some areas, resource managers from the Bureau of Reclamation believe it is likely that current reservoir systems will be inadequate to control earlier spring runoff and maintain supplies for the summer. The situation will become even more critical as populations continue to grow.
In order to adapt to these changes brought on by global warming, improved technology, planting of less water-demanding crops, and other conservation measures will become increasingly important. Transferring water across basins and water users and the integration of surface and groundwater use could also serve as an adaptation strategy for resource managers facing water shortages.
Climate models predict an increase in plant growth, a reduction in desert areas, and a shift toward more woodlands and forests in many parts of the West. They also project an increase in wildfires and a rise in air pollution. Eventually, as CO2 concentrations level off, the fertilization effect would decrease, leading to a decline in forest productivity. A drier climate would also reduce forest productivity.
Ecosystems will also be affected. The diverse topography coupled with landscape fragmentation and other development pressures in the West will probably make it difficult for many species to adapt to climate change by migrating. The U.S. Global Change Research Program believes it is likely that ecosystems such as alpine ecosystems will disappear entirely from some places in the region. They also believe that some species may be able to successfully migrate up mountain slopes to higher elevations. One prominent factor resource managers must consider, however, is that non-native invasive species have already stressed many Western ecosystems and are likely to make adaptation to climate change much more difficult for native species. Global warming is also likely to increase fire frequency. As long as year-to-year variation in precipitation remains high, fire risk is likely to increase, whether the region gets wetter or drier because fuel loads tend to increase in wet years as a result of increased plant productivity and are consumed by fire in dry years.
Tourism, which is a prominent, growing component of the West's economy, is strongly oriented to the outdoors and is extremely sensitive to climate. Higher temperatures will prolong summer season activities such as backpacking but make the winter season activities such as skiing shorter. Changes in the distribution and abundance of vegetation, fish, and wildlife will also affect recreational activities. These effects will cause the tourism industry to become more diversified and force it to provide activities commensurate with the current climate.
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