Models utilized by the Intergovernmental Panel on Climate Change indicate a striking trend toward increasing aridity in the Southwest United States. Two landmark articles published in Science magazine have emphasized the critical future consequences of this trend. Data from 59 National Weather Service stations distributed across the region west of the continental divide and south of the 41stparallel (the northern border of Colorado and northeastern Utah), including 36 stations in the Upper Colorado River Basin and lower Southwest, show that annual and winter precipitation increased over the 60-year period 1950-2010, although the record is impoverished by the deletion of precipitation data in 2005-09 for 18 of the 21 stations in southern Arizona. For western

California and central and eastern Arizona, the 1999-2009 drought was the most severe of the past 60 years. For the region surrounding central and eastern Arizona, 1999-2009 was seven percent wetter than 1950-60. Regional contrasts were particularly pronounced in 2005-09. For the Colorado River water supply and high demand areas in the lower interior Southwest, 2005-09 was exceptionally dry. Average annual precipitation along the Little Colorado River and the Las Vegas-Phoenix-Tucson growth corridor was 25 percent below the 60-year average. Average annual precipitation in western California in 2005-09 was eight percent below the 60-year average. For the 31 weather stations surrounding central and eastern Arizona and the Las Vegas-Phoenix-Tucson corridor, average annual precipitation in 2005-09 was less than one percent below the 60-year average. The 112-foot decline in the elevation of Lake Mead from 2000 through 2010 was due primarily to the addition of nearly two million more water consumers in the Phoenix-Tucson “Sun Corridor” and southern Nevada and the simultaneous emergence of water banking. By promoting water lavish urban landscapes and manipulating evaporation data in metropolitan Phoenix particularly, Arizona has gained as many seats in the U. S. House of Representatives since 1950 as Colorado, New Mexico, and Nevada combined. Recent Arizona legislation documents state government’s opposition to any mandatory water conservation measures.


Earth Sciences | Environmental Indicators and Impact Assessment | Geography | Geology | Natural Resources and Conservation

Map_WeatherStations.pdf (284 kB)
Southwest United States weather stations

Table 1.doc (27 kB)
Missing months precipitation data

Table 2.doc (24 kB)
Average annual precipitation

Table 3.doc (24 kB)
Average annual precipitation, interior

Table 4.doc (24 kB)
Precipitation comparison

Table 5.doc (24 kB)
Winter precipitation

Table 6.doc (24 kB)
Summer, Fall precipitation