Drought is here despite demands for more water
August 27, 2004
Don’t look now, but the Tahoe-Truckee region and much of Nevada are suffering from an extended drought. After five years of below-normal precipitation and above-average temperatures, Lake Tahoe is projected to drop below its rim in September, cutting off flow to the Truckee River. The Carson River is expected to reach an all-time low flow in September. In much of Nevada, springs and creeks are drying up, and wildlife and fisheries are being monitored. In Carson City, ground water levels are falling and wells are producing 15 percent less than normal.Folk singer Joni Mitchell said it best when she sang “We go ’round and ’round in a circle game.” For those of us who call the West home, our relationship with water is a roller coaster ride of boom and bust. The weather almanac may indicate daily, monthly and seasonal “averages” for temperature and precipitation, but in reality the Far West is a region of microclimates that experience extended dry spells broken by flooding rains and dramatic snowfalls. With a combined population approaching 40 million in California and Nevada, the demands on the region’s water supply has never been greater. Each drought period will bring tighter water restrictions, and every wet season will be hailed as total salvation. Considering the explosive population growth projections for the West, weather and Sierra snowpack conditions will be front-page news for many years to come.
For snow-hungry skiers and boarders as well as parched farmers and ranchers, the same weather conditions that create glorious sunshine can become a stubborn curse. Life in the arid West has always tilted on the edge, climatically, as well as socially and geographically. Now that another summer has passed, the eyes of skiers, boarders, and hydrologists will begin to focus on the outlook for the approaching winter. Due to severe drought conditions in eastern California and Nevada, this upcoming winter season will be critical in helping to alleviate low water conditions in our regional reservoirs, lakes and streams. Rising sea surface temperatures in the tropical waters of the eastern and central Pacific Ocean indicate the early stages of El Niño (ENSO – El Niño Southern Oscillation), an episodic climate event that can influence global weather patterns. ENSO events occur on an irregular cycle from two to seven years, and last from less than a year to as long as three years. ENSO events can have a profound effect on California’s winter weather. Although it’s too soon to determine how the jet stream will react to this weak-to-moderate phase of El Niño, the National Weather Service Climate Prediction Center is forecasting a wetter than average rainy season for central and southern California and Nevada. Temperatures are also expected to be above normal.
Another factor that may influence this winter’s storm track, and possibly for years to come, is the Pacific Decadal Oscillation, or PDO. The PDO is often described as a long-lived El Niño-like pattern – in the 20th century major PDO eras persisted for 20 to 30 years. University of Washington fisheries scientist Steven Hare coined the term in 1996 to describe an oscillation in Northern Pacific sea surface temperatures that he noticed while researching connections between Alaskan salmon production cycles and Pacific climate. In parallel with the ENSO phenomenon, the extreme phases of the PDO have been classified as being either warm or cool, as defined by ocean temperature anomalies in the Pacific Ocean. These long-term changes in the location of cold and warm water masses in the Pacific can affect the position of high and low pressure systems, and alter the storm-steering jet stream by forcing it further north. Climatologists are already warning residents in arid Southern California to prepare for drier conditions over the next two decades. In contrast to El Niño events, which are concentrated over the tropics and have their greatest influence there, with only secondary signatures in the North Pacific, the PDO has its greatest impact on the Pacific Basin and western North American climate. Many scientists believe that the warm PDO that dominated from 1977 to about 1998 is possibly reversing to cool conditions. That would be good news for powder hounds in the West. Cool phase PDOs reigned from 1890 to 1924, and again from 1947 to 1976, time periods that include many of the snowiest winters on record in the Sierra Nevada.
Research by California climate expert, Daniel Cayan of the Scripps Institution of Oceanography, indicates that PDO-related temperature and precipitation patterns are strongly expressed in above average regional snowpack and stream flow anomalies, especially in the western United States. Historically, cool phase PDOs seem to produce cooler temperatures and increased precipitation in Northwestern North America, vital components for pumping up the snowpack and replenishing water supplies. A 20- to 30-year stretch of a cool phase PDO might be just what the doctor ordered to help turn around the drought. We’re going to need all the help we can get. The overall Western snowpack has declined 11 percent since the 1970s, with some of the largest declines reported in Northern California. According to a recent projection about global warming impacts in California, the most optimistic computer models predicted that the Sierra Nevada snowpack could decline by 30 to 70 percent over the next century. So pray for snow and the PDO.Mark McLaughlin’s column, “Weather Window,” appears monthly in the Sierra Sun. His award-winning books, “Western Train Adventures: The Good, the Bad & the Ugly” and “Sierra Stories: Trues Tales of Tahoe, Vol. 1 & 2” are available at local bookstores. Mark, a Carnelian Bay resident, can be reached at firstname.lastname@example.org.