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2012 Water Year in Review

Published October 24, 2012

The 2012 Water Year in Review is a summary of the information presented in the Southwest Climate Outlook between October 1, 2011, and September 30, 2012. The water year is a standard period of measurement used in hydrology because the natural seasonal ground recharge and discharge cycles are more aligned with the October–September period than the calendar year due to precipitation and evaporation patterns. This review highlights precipitation, temperature, reservoir levels, drought, wildfire, and El Niño-Southern Oscillation (ENSO) conditions over this 12-month period.

Heat and drought defined the water year, smothering the Midwest, in particular, during the spring and early summer. Temperatures during the water year were among the top five warmest on record in 39 of the 48 contiguous states, ranking as the 19th and fifth warmest on record in Arizona and New Mexico, respectively, out of 117 years. These conditions conspired with scant precipitation to cause many of the nation’s fertile farmlands to wilt.

Warmer-than-average temperatures and below-average precipitation across nearly all of Arizona and New Mexico characterized the water year. Consequently, moderate or more severe drought covers almost the entire Southwest and drought conditions are now more widespread, though less intense, than they were at the beginning of the water year. The fact that drought has persisted in many parts of the Southwest during the last two years is not surprising given the occurrence of a La Niña event during back-to-back winters; La Niña conditions often deflect winter storms north of the Southwest. It was also a relatively dry winter in the headwaters of the Colorado River and Rio Grande in Colorado, where scant rain and snow contributed to storage declines in many reservoirs on these rivers. Dry conditions also set the stage for wildland fires in the Southwest. Although this water year’s fire season did not surpass the record number of acres burned last year, New Mexico’s largest wildland fire on record—the Whitewater-Baldy Complex fire—tore across 298,000 acres in the west-central part of the state in and around the Gila National Forest, nearly doubling the size of the state’s previously largest fire.

Top 5 headlines of the water year

1 Back-to-back La Niña Events  A La Niña event re-emerged in September 2011, marking the second consecutive winter in which a La Niña influenced weather in the Southwest. The statewide November 2011–April 2012 precipitation for Arizona was 66 percent of average, while New Mexico fared slightly better, recording 91 percent of average.

2 Widespread but less intense drought  Moderate drought now covers nearly 100 percent of Arizona and New Mexico, an increase of about 30 and 4 percent, respectively, since the water year began on October 1. Although drought has expanded, it has become less severe. Extreme or exceptional drought covered about 6 percent of Arizona on October 2, down from about 15 percent one year ago, and less than 1 percent of New Mexico, a decrease of about 34 percent from one year ago.

3 Monsoon: A tale of two states  The position of the subtropical high pressure area allowed moist air to waft into Arizona. Southern areas of the state and the Mogollon Rim benefited the most, receiving above-average rainfall totaling 6.5 to 9.5 inches between July and September. The position of the high, however, limited rain in New Mexico and nearly all of the state received below-average rainfall.

4 Elephant Butte Reservoir nearly empty  Winter rain and snow in the Upper Rio Grande Basin in Colorado, from which most of the water flowing in the Rio Grande originates, was below average for the fifth time in the last 10 years. Consequently, Elephant Butte Reservoir, which provides irrigation water to New Mexico’s most productive agricultural region, stood at less than 5 percent of capacity and water available to farmers is now completely exhausted.

5 Colorado River streamflows tank  Combined storage in Lakes Mead and Powell stood at 54 percent of capacity as of September 1, which is 7 percent lower than it was one year ago. Based on preliminary data, flow into Lake Powell for October 2011 to September 2012 was 5 million acre-feet (maf), or about 46 percent of average, making it the lowest inflow volume since 2002. Also, inflow between April and July was 2.06 maf, or 29 percent of average, which was the third smallest April to July volume since the closure of Glen Canyon Dam in 1963.