Home » September 2012 Southwest Climate Outlook
Published September 26, 2012

September Climate Summary

Drought: Monsoon rainfall has brought some improvement to short-term drought conditions across Arizona and western New Mexico, but the entire Southwest continues to experience moderate or more severe drought, mostly due to longer-term deficits in precipitation.

Temperature: An active monsoon in the last 30 days helped lower temperatures in many areas in Arizona. In New Mexico, less copious rain contributed to above-average temperatures.

Precipitation: The monsoon has been a tale of two states. Many parts of Arizona experienced copious rain, while high pressure over New Mexico limited monsoon storms there.

ENSO: Neutral conditions were present again this past month, but a weak El Niño event is still forecast to develop in the next several months.

Climate Forecasts: Temperatures are expected to be slightly above average in coming months in the Southwest. It is unclear if precipitation will be above or below average.

The Bottom Line: Monsoon rains delivered much needed moisture for Arizona in the last three months, but left New Mexico wanting. The near constant presence of high humidity and copious rain in Arizona resulted in above-average precipitation in most of the state and helped improve short-term drought conditions. While all of Arizona is still experiencing moderate or a more extreme drought category, the amount of land classified with severe drought fell from 83 to 32 percent between June 15 and September 12. Precipitation, however, petered out just across the border in New Mexico, and drought conditions there remain more intense and widespread. Currently, about 73 percent of New Mexico is classified with severe drought, and in recent weeks a small sliver of exceptional drought developed in Curry and Roosevelt counties. In both states, longer-term drought impacts such as low water supplies remain widespread. The inflow into Lake Powell, for example, was the third lowest on record for the April and July period, and the combined storage in Lakes Mead and Powell is about 3 million acre-feet lower than one year ago. Also, Elephant Butte Reservoir, which supplies southern New Mexico’s most productive agricultural region, stands at only 5 percent of capacity. Improvement in these longer-term drought impacts is hard to forecast at the moment. An El Niño event, which is forecast to develop in coming months but is expected to be weak and short lived, can bring above-average rain and snow to the southern tier of both states. Also, there is  substantial precipitation variability during El Niño winters. These signs point toward the persistence of drought in the Southwest, but winter forecasts should become clearer in coming months.

 

Warmer Temperatures Pushing Plant Stress to the Extreme

When warmer temperatures like those experienced in recent years combine with periodic drought common to the American Southwest, plants pay the price. Warming that started in the late 1970s in the Southwest has produced fewer cool season freezes, losses in regional snowpack, an earlier onset of spring, and hotter summers. Another impact of regional warming is differential changes to climatic limits on plant growth across seasons and elevations, writes Jeremy Weiss, lead author on a peer-review study recently published in the Journal of Geophysical Research Biogeosciences. In the study, Weiss, a senior research specialist for the department of geosciences at the University of Arizona, and his co-authors compared growing conditions during the two major regional droughts of the 1950s and 2000s, the latter of which occurred during warmer times. Results from the study show that growing conditions during the 2000s drought reached extreme levels, especially for lower and middle elevations from spring through fall. These conditions were in large part spurred by the warmer temperatures, which created a feedback loop that led to drier and even warmer conditions. With global climate models projecting further regional warming in coming decades, the concern is that even more extreme growing conditions could occur during future drought periods.

For more information, visit: http://uanews.org/story/droughts-are-pushing-trees-limit