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March 01, 2011 / Vol. 1 / Issue 4 / Drought Tracker / A Publication by CLIMAS
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).
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).
- The precipitation outlook for March–May suggests a 40–50 percent chance for drier-than-average conditions in nearly all of Arizona and New Mexico (right); chances for above-average precipitation are less than 27 percent.
- Dry conditions also are forecasted with a 40–50 percent chance for below-average precipitation for the April–June period in New Mexico; odds are slightly less in Arizona.
- About 60–80 percent of the La Niña events between 1950 and 2008 contributed to precipitation totals between 0.4 and 1.2 inches below the March–May average in Arizona and New Mexico (Supplemental Figure 5).
- Expanding drought conditions are based on forecasts for below-average precipitation and above-average temperatures. These stem in part from the La Niña event and decreasing precipitation trends in the spring months caused by longer-term climate changes.
- The La Niña event weakened, but forecasts suggest the event will persist at least for a few more months.
- January was the driest on record in New Mexico and the second driest in Arizona (Supplemental Figure 6).
- The past 30 days have been very dry in much of Arizona and New Mexico, particularly in the southern tier of both states where precipitation has been less than 50 percent of average (Supplemental Figure 7).
- Most of New Mexico and Arizona have at least a 40 and 30 percent chance, respectively, of experiencing an extremely dry March–May, in which conditions are similar to the driest 20 March–May periods in the last 100 years (Supplemental Figure 8).
- Natural climate variability other than La Niña also influences the region’s climate. Negative phases of the Arctic Oscillation often cause below-average winter temperatures (Supplemental Figures 9–10).
- If dry conditions continue, the risks of an active wildfire season, lower spring streamflows, and poor range conditions will increase.
Precipitation Analysis (National Weather Service Advanced Hydrologic Prediction Service):
Drought Status (National Integrated Drought Information System):
Snowpack Conditions (National Resources Conservation Service):
Precipitation Outlooks (NOAA–Climate Predictions Service):