In a dramatic reversal of fortune compared to last year, an unusually dry winter is causing the level of Lake Mead, Nevada, to decline, making water managers increasingly anxious about supplying water to the thirsty Southwest.
The latest U.S. Drought Outlook shows continued dry conditions in the Southwest are likely for the rest of the winter.
During the past three years, the level of Lake Mead has followed a boom and bust cycle, dropping to a record low in 2010 during an intense drought, then recovering during 2011 thanks to record mountain snowfall, and now dropping again in the midst of a dry winter.
According to an article in the Las Vegas Review-Journal, water managers are forecasting the lake level to drop by about 13 feet due to the dry winter so far. As the newspaper reported:
"In December, the U.S. Bureau of Reclamation was predicting a roughly 11-foot rise in Lake Mead over the next year. Now the bureau expects the nation's largest man-made reservoir to shed about 13 feet by January 2013.
One acre-foot equals about 326,000 gallons, which is enough water to supply two average valley homes for one year. At current consumption levels, the 2.45 million acre-foot reduction in Lake Mead's forecast since last month represents enough water to supply the entire Las Vegas Valley for a decade."
During the past 11 years, a particularly dry and warm climate has lingered in Utah, Nevada, Arizona and Southern California, leading to reduced flow along the Colorado River. In fact, scientists have already shown that the stress on the water resources in the Southwest region is consistent with the effects of a warmer climate, and that increased emissions of heat-trapping gases are linked to recent changes in river flows and winter snow pack. Adding to the region's water challenges is the fact that cities that draw water from Lake Mead, such as Las Vegas, have grown in recent years and are further taxing the water supply.
(This Climate Central chart shows how the demand for water from the Colorado River Basin has recently outstripped supply.)