Global Warming and 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 o