Also posted at Climate411.
Sunday's New York Times Magazine had an article aptly titled "The Future is Drying Up", about the threats that climate change and booming populations pose to precious water resources in western states. Usually when we think of water and climate change we think of rising sea levels, but climate change is also causing drops in fresh water supplies.
Most people living in the southwestern U.S. get their water from the Colorado River and California's Central Valley, both of which are fed by winter rains and spring snowmelt. Unfortunately, global warming is not only causing more winter precipitation to fall as rain versus snow, but also is causing the snow that does fall to melt earlier. As a result, in some areas reservoirs will fill earlier in the year and less water will be available over the summer.
The chart below shows changes in the timing of the spring snowmelt over the second half of the 20th century. In many areas, snowpack is starting to melt three weeks earlier than it did 50 years ago.
Timing of Spring Snowmelt Compared to 50 Years Ago
Source: USGS National Streamflow Information Program. Large circles show sites where changes are statistically significant at a 90 percent confidence level.
Scientists warn that, in some areas, mountain snowpack could disappear completely in the coming decades, and this has water managers concerned about future water supply.
In May, scientists reported that global warming is probably already shifting the entire American Southwest toward a drier climate. The author of the New York Times Magazine article asked one of the researchers whether their study meant that the Southwest is looking at a permanent drought. His striking reply: "You can't call it a drought anymore, because it's going over to a drier climate. No one says the Sahara is in drought."
So what can we do? Water conservation is an absolute must. Some water managers believe that with the right choices, we could meet most municipal, agricultural, and ecological water needs with the dwindling supply. But conservation has to go hand-in-hand with a concerted effort to decrease the greenhouse gas emissions that are driving climate change.
Further Reading
-
Climate Change and California Water Resources: A Survey and Summary of the Literature (Section on the Colorado River is relevant to the entire western U.S.)
-
Changes in Streamflow Timing in the Western United States in Recent Decades (Report from the USGS)