Long-term drought likely, study says
Trying to decipher weather patterns is a little bit like taking apart one of those Russian dolls – each time you open one, you find a smaller doll inside. Most researchers acknowledge that year-to-year fluctuations in climate may be part of a larger pattern. El Nio and La Nia cycles have been widely reported, so that even very non-scientific minds understand the connections between shifts in Pacific Ocean water temperatures and precipitation in the Western United States.Researchers with the U.S. Geological Survey (USGS) now say there may be an even larger dynamic in play – the Pacific Decadal Oscillation (PDO) – which may set the tone for climatic cycles that last for 20 to 30 years. In a recent fact sheet, "Precipitation History of the Colorado Plateau Region, 1900-2000," USGS researchers conclude there is evidence showing that the region has – as of 1998 – entered into a long-term drought pattern similar to one that affected the Southwest between 1942 and 1977."Recent trends in southwest precipitation and the PDO suggest that climate of the region may become drier for the next 2-3 decades in a pattern that could resemble the drought of 1942-1977," the report concludes.But don’t mothball your skis just yet. The research suggests that less of the total precipitation in the region will fall as snow, but a larger share could come during extreme weather events.According to the USGS fact sheet, changes in the PDO trigger sharp transitions from one climate regime to another on the Colorado Plateau. During the 20th century, a wet regime prevailed between 1900-1941, a drought from 1942-1977, and a wet regime from 1978 – 1998. Cool phases of the PDO are associated with the droughts, while warm phases are associated with wet periods.The early part of the most recent drought regime (1942-1977) has been recognized as a drought at least in parts of the region – particularly in New Mexico, where some researchers characterized the period as the most severe drought in the past 400 years. The first five years of the 20th century was the culmination of an 11-year drought in the Southwest that began in 1893.Changes in precipitation on the Colorado Plateau are linked with events in the tropical and northern Pacific Ocean, with "periods of unusually wet or dry weather resulting from interrelated global-scale fluctuations of sea-surface temperature, atmospheric pressure, and atmospheric circulation patterns"In plain English, that means when certain parts of the Pacific cool off, the weather dries up. And vice-versa, warmer ocean temperatures can bring higher-than-average precipitation to the region.