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2010 Water Year in Review

Published October 26, 2010

The 2010 Water Year in Review offers a summary of the information presented in the Southwest Climate Outlook during the 2010 water year, which began October 1, 2009, and ended September 30, 2010. This review provides an overview of precipitation, temperature, reservoir levels, drought, wildfire, and El Niño–Southern Oscillation (ENSO) conditions.

In general, the 2010 water year was marked by a wet winter, a dip in drought conditions, and the influence of both El Niño and La Niña events. In the beginning of the water year, drought conditions covered all of Arizona, reflecting the record-dry 2009 monsoon season. Drought relief finally came in January, as a cavalcade of soppy winter storms rolled into the region. By May 18, less than 37 percent of the state was classified as having some drought conditions. By the end of the winter, many regions had received above-average precipitation. The wet winter was in part due to an El Niño event, which helped pull the westerly jet stream south and over the Southwest and resulted in a higher frequency of Pacific Ocean storms drifting into the region.

The El Niño event peaked in the winter, followed by a rapid transition to a La Niña. This quick switch likely influenced the summer monsoon season, which was characterized by a late start, a one-month wet period, and a relatively early departure. While many regions experienced near-average rainfall for the monsoon season, there were notable dry areas, including the Colorado River Corridor in western Arizona.

The following highlights present in more detail the evolution and characteristics of the 2010 water year.

Top 5 headlines of the water year

  1. Lake Mead water elevation approaches 1,075 Lake Mead’s water levels declined by 10 feet during the 2010 water year, inching to within 9 feet of the 1,075 elevation line that will trigger water rationing in the Lower Colorado River Basin. However, joint management of Lakes Powell and Mead stipulate extra water releases from Lake Powell to Lake Mead if that threshold is breached. An extra pulse of about 3 million acre-feet (MAF) is likely in 2011, increasing the water level in Lake Mead by about 30 feet and temporarily delaying water rationing.

  2. Copious winter rains drenched the Southwest Arizona received about 140 percent of the 1971–2000 average between November and March, while New Mexico received about 110 percent of average. Precipitation was most intense between mid-January and mid-February, when a series of storms set precipitation records for single day and multi-day accumulations in many watersheds.

  3. Mercurial El Niño–Southern Oscillation Sea surface temperatures in the tropical Pacific Ocean waffled between moderate El Niño conditions and moderate La Niña conditions. The El Niño event began in the summer of 2009, peaked in December, and then rapidly transitioned into a La Niña event in the spring of 2010.

  4. Monsoon a one-month wonder The dry start and end to the 2010 monsoon season sandwiched frequent and intense rains in July. The monsoon arrived about two weeks late. Storms finally exploded in many parts of the region in mid-July, and the one-month spurt was enough to deliver near-average rainfall totals to many parts of the Southwest.

  5. Warm Summer Summer was warmer than average over Arizona and New Mexico due to a short monsoon that had high humidity and nighttime cloudiness but relatively few precipitation events. The lack of cooling rainfall helped to increase average temperatures, which exceeded long-term averages in both states during the summer. September was the second warmest on record in both Phoenix and Tucson.