Drought Conditions

Source: U.S. Drought Monitor

Much-needed precipitation doused Arizona in late February after a record-setting dry beginning to 2011. The storms, however, provided little relief from mounting drought conditions in the Four Corners region of Arizona and New Mexico and did not significantly improve snow pack conditions in most basins in Arizona. The southern tier of both states has experienced less than half of average precipitation since the water year began on October 1 (Figure 1). Precipitation deficits in this area currently range between 3 and 6 inches. Northwest Arizona has been the lone exception to the widespread dry winter, and most of the area’s precipitation fell from a series of storms during a brief period in late December and in February. Drought conditions reflect the dry conditions.  Currently, about 13 percent of Arizona and 33 percent of New Mexico are classified with severe drought, according to the most recent U.S. Drought Monitor. Severe drought has expanded in New Mexico by about 19 percent from March 1; nearly all of New Mexico is classified with at least abnormally dry conditions (Figure 2). Projections of a dry winter, based largely on the La Niña event, have so far been accurate, particularly in the southern regions of both states where La Niña has the strongest impact.

The La Niña event continues to reign across the equatorial Pacific but has begun to weaken. Most forecast models call for a return to neutral conditions by early summer, but chances are greater than 90 percent that La Niña conditions will continue for the next several months (Supplemental Figure 1). Four out of the six previous strong La Niña events carried through the summer and into the following winter, presenting a possibility that this La Niña may continue beyond a single year. Over the next several months, forecasts call for persisting, expanding, and intensifying drought conditions in all of New Mexico and all but the northwest corner of Arizona (Supplemental Figure 2).

Snowpack

Source: National Resources Conservation Service

• Snow water equivalent (SWE) is very low in most mountain ranges in New Mexico and eastern Arizona (left); compared to other La Niña winters, SWE is near near average.
• Nearly all watersheds in the Upper Colorado River Basin show above-average SWE and the upper Rio Grande Basin has near-average SWE (Supplemental Figure 3).
• The most current streamflow forecast suggests a 50 percent chance that inflow to Lake Powell will be about 113 percent of the 1971–2000 average during April–July, or 9 million acre-feet; streamflow in the Little Colorado River is projected to be less than 50 percent of average (Supplemental Figure 4).

Forecast