Evidence Suggests La Niña Will Return This Winter

Less than 2 percent of the October-July periods since 1895 have been drier than they are currently for all of Texas and many parts of New Mexico. These areas experienced either their driest or second driest October-July periods in the last 117 years. Less than 6 percent of the October-July periods have been drier than current conditions in southeastern Arizona. (Source: Western Regional Climate Center)
Less than 2 percent of the October-July periods since 1895 have been drier than they are currently for all of Texas and many parts of New Mexico. These areas experienced either their driest or second driest October-July periods in the last 117 years. Less than 6 percent of the October-July periods have been drier than current conditions in southeastern Arizona. (Source: Western Regional Climate Center)

Blame it on La Niña.

Pushing the jet stream and the storms it carried north of the region, La Niña played a starring role in a record-dry winter in the Southwest this past year.

The lack of rain and snow led to extensive fires in Arizona and New Mexico, skimpy irrigation allotments and withered vegetation in the spring. Now mounting evidence suggests that after a brief summer hiatus La Niña may be back.

This would not be welcome news for most of the Southwest, and especially those areas mired in extreme and exceptional drought, particularly since the second year in back-to-back La Niña events is often drier than the first.

During the 20 winters since 1950 in which La Niña was present, precipitation has been, on average, below-average across the region. Last winter upheld this dry pattern, as a moderate to strong La Niña event developed in June 2010 and dissipated in April.

At the onset of winter, in the beginning of November, only about 3 percent of Arizona was classified with moderate drought conditions; New Mexico was drought-free. By the beginning of the 2011 monsoon season in mid-June, however, 56 and 99 percent of Arizona and New Mexico, respectively, were in the grips of moderate, if not more severe, drought.

Drought also intensified in nearly every region. By mid-June, nearly 6 and 45 percent of Arizona and New Mexico, respectively, were pegged with the most severe drought category  exceptional drought, which occurs once in every 50 years; about another 13 and 23 percent were classified with extreme drought, which occurs once in every 20 years.
 
With the region desiccated in the lead-up to the summer rains, climatologists at the University of Arizona and National Drought Mitigation Center at the University of Nebraska stated that an average monsoon season would be insufficient to significantly improve drought conditions.

Read more from this August 23 article from UANews at the link below.

Zack Guido, zguido@email.arizona.edu, School of Natural Resources and the Environment, and Mike Crimmins, crimmins@u.arizona.edu, Department of Soil, Water and Environmental Science

Date released: 
Sep 7 2011
Contact: 
Zack Guido