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Southwest Climate Outlook - June 2003

Date issued: June 27, 2003

A. Summary

Hydrological drought will continue to be a major concern for the Southwest during the upcoming months. The New Mexico Drought Monitor Committee has declared emergency status for most New Mexico river basins, including the Rio Grande and the Pecos. Lake Mead is at its lowest level since July 1969.

Large fires have exploded across Arizona during the past month. Fire danger is above average across all of Arizona and is especially high at elevations lower than 8,500 feet.

New Mexico and Arizona continue to have the poorest range and pasture conditions (relative to state averages) in the United States, due chiefly to long-term soil moisture deficits and high potential for erosion.

Seasonal temperature forecasts indicate increased probabilities of above-average temperatures across Arizona and most of New Mexico for the next year.

There is increased uncertainty in ENSO forecasts. Eastern Pacific Ocean temperatures remain cooler than average; however, the chances of La Niña developing are less than they were one month ago. La Niña often brings warm, dry winter conditions to the Southwest.

Bottom line: Drought will continue in the Southwest during the next several months. The most likely scenario is that summer rainfall will be average to above average, bringing relief to some areas. Neutral-to-cool (La Niña) Pacific Ocean temperatures will persist beyond the summer, resulting in average to somewhat below-average autumn and winter precipitation. Water supply and streamflow will continue to be of concern for the foreseeable future. A mild tropical storm season is expected for the Southwest.

The worst case scenario is that the Southwest summer monsoon will arrive late, prolonging the fire season, and will not produce sufficient moisture to relieve short-term drought. Above-average temperatures will increase evaporation rates, resulting in rangeland degradation, as well as decreases in reservoir and groundwater levels. CLIMAS research shows that summer rainfall has seldom ended severe sustained drought (see END InSight Newsletter, August 2002). In the long-term, La Niña will strengthen and winter precipitation will be well below average, further reducing reservoir and groundwater levels.

The best case scenario is that in the short-term the Southwest will receive abundant summer rainfall and high fire danger will be quickly abated, although severe erosion will be increased by powerful monsoon storms. In the long-term, La Niña conditions will dissipate or El Niño conditions will rebound this fall, bringing above-average fall and winter precipitation. Reservoir and groundwater levels will be maintained at current levels or increase.

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