Southwestern Streams

Southwestern streams originating in high mountains are fed by snowpack and often flow throughout the year because of this summertime water source. There are also an abundance of intermittent or ephemeral southwestern streams that flow only in spring or during heavy rains. At lower altitudes these streams flow through desert and steppe habitats with very low rainfall, and are often the only water source across large landscapes. The stream corridors harbor plants, such as native cottonwood and willows that are unable to survive in the dryer surrounding uplands.

Benefits for Humans and Wildlife

The value of western streams is so great that it is essentially incalculable. Just their importance for supplying drinking water to major cities—such as Phoenix, Las Vegas, and Los Angeles—is huge. They also supply essential irrigation water for large-scale farming, especially during the summer growing period when temperatures are high and snowpack melt becomes the primary source of water.

Western streams provide critical in stream flows that nurture diverse ecosystems and wildlife, without which the ecology of the Southwest would be radically different. The diversity and productivity of western streams are important for many Native American tribes. For example, the Lower Colorado River is vital to the Cocopah Tribe for subsistence, cultural, economic, and recreational activities.

Whether permanent or intermittent, western streams are important recreational areas throughout the southwest, with both the permanent and higher altitude streams supporting recreational fishing. The stream habitats are used extensively by migratory birds during nesting and migration, as well as a variety of other wildlife including beaver and deer.

Threats from Climate Change

The threat to western streams from climate change is extensive. As a result of rising winter temperatures reducing the winter accumulation of snowpack in western mountains, the amount of available spring and summer melt-water is declining.

An equally significant threat is that spring temperatures are arriving as much as three to four weeks earlier than in the past, also reducing the amount of water available in the summer and fall. With only a 1.5 degree Fahrenheit increase in average global temperature, the Colorado River may shrink to its lowest level in at least 500 years. This is expected to occur within the lifetime of children born now, even with immediate reductions in greenhouse gas emissions. Lake Mead, a major reservoir on the Colorado River, is less than half full and could run dry by 2020. Increased severity of droughts and flood events from climate change will also affect water supply and water quality.

The decline of water availability caused by climate change will exacerbate an already severe shortage of water in many areas of the Southwest. Water prices will likely sky-rocket as growing water demand conflicts with declining water availability. Mandatory water restrictions will likely affect people’s daily lives and the economic survival of irrigated croplands. These water wars may leave fish and wildlife last in line.

Conservation Investments

Addressing exacerbated water shortages brought on by climate change will require a diversity of approaches. Considerable investment will be needed to reduce water demand by assisting homes, businesses, and agriculture in developing new water conservation strategies and low water use technologies.

Stream corridors should be restored to natural conditions wherever possible to maintain optimal water flows and habitat for fish and wildlife. Restoration of native plant species along southwestern streams is vital for wildlife survival and diversity. Ensuring base flows and restoring natural flood flows is also critical to preserving natural stream habitat processes. On the Lower Colorado River alone, riparian and river flow restoration has a price tag of more than $250 million.