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February 01, 2011 / Vol. 1 / Issue 3 / Drought Tracker / A Publication by CLIMAS
Dry conditions have reigned in the last 30 days after a brief soggy period in late December and despite a small front moving through the region at the end of January. In January, nearly all of Arizona and New Mexico received less than 5 percent of the historical average. The scant recent rainfall has lowered total precipitation since the water year began on October 1, and many regions have received less than 75 percent of average precipitation since October 1 (Figure 1). Some areas have been particularly dry, including Roswell, New Mexico, where no rain has fallen in the last 90 days, and El Paso, Texas, which has only experienced one meager event in this period (Supplemental Figures 1–2). However, areas to the north such as Las Vegas, Nevada, and Cedar City, Utah, have been wetter than average, largely because of late December storms (Supplemental Figures 3–4). Also, most of the Upper Colorado River Basin has above-average snowpacks, which bodes well for producing above-average spring streamflows. This north-south precipitation divide suggests the brunt of the La Niña impacts will be felt in southern regions. Currently, 60 percent of Arizona and 95 percent of New Mexico have abnormally dry conditions or worse (Figure 2). The southern regions are the hardest hit by parched conditions. Severe drought conditions have developed in this area and now span about 11 and 4 percent of New Mexico and Arizona, respectively. The influence of the moderate to strong La Niña event so far this winter has upheld the historical pattern of below-average precipitation in the Southwest, and more dry weather is expected.
The La Niña event remains moderate to strong. Because a large pool of cold water continues to exist below the surface in the eastern tropical Pacific, forecasts indicate a 98 percent chance that La Niña will persist through March, and chances remain above 65 percent through May. As a result, drought forecasts call for continuing, expanding, and intensifying drought conditions in the southern half of Arizona and nearly all of New Mexico (Supplemental Figure 5).
Source: National Resources Conservation Service
- Above-average temperatures and below-average precipitation in the high country have contributed to below-average snow water content (SWC) in snowpacks (at left); SWC at many sites are below the 1971—2000 average (Supplemental Figures 6–10).
- Most snow telemetry stations in the Upper Colorado River Basin (not shown) measure above-average SWC; the upper Rio Grande basin has received near-average SWC.
- Early streamflow predictions call for above-average spring flows in the Upper Colorado River Basin; as of January 15, there was a 50 percent chance that inflow into Lake Powell will be 117 percent of average (Supplemental Figure 11).
- The February–April precipitation outlook suggests greater than a 50 percent chance for drier-than-average conditions in most of Arizona and western New Mexico (at right); chances for above-average precipitation are less than 17 percent.
- Dry conditions also are forecasted for the March–May period, in large part because of the high likelihood that La Niña will persist through this period.
- About 70 percent of the La Niña events between 1950 and 2008 contributed to precipitation totals between 0.4 and 2.8 inches below the February–April average in Arizona and western New Mexico (Supplemental Figure 12).
- The La Niña event maintained its moderate to strong strength during January. Cold water beneath the sea surface in the eastern tropical Pacific suggests the event will persist at least for a few more months.
- Most of the precipitation since the water year began on October 1 has fallen in a few events in December. Despite this, most of the Southwest has experienced less than 75 percent of rain and snow since October 1. In the last 30 days, precipitation has measured less than 5 percent of the January average.
- Severe drought conditions have developed in southern Arizona and New Mexico; forecasts call for drought to persist, expand, and intensify in most of Arizona and nearly all of New Mexico.
- Below-average spring streamflows are projected for most basins in Arizona and New Mexico. Streamflow forecasts, however, are less reliable in the beginning of the year than as the date approaches April 1.
- Arizona and New Mexico have greater than a 35 percent chance of experiencing an extremely dry February–April; the historical average for extreme dry risk in this period is 20 percent (Supplemental Figure 13).
- Water management and projections of above-average inflow to Lake Powell likely will spare major metropolitan areas in Arizona from water supply shortages stemming from short-term drought conditions caused by La Niña. Similarly, adequate storage in Navajo Reservoir guarantees that Albuquerque, New Mexico, will receive its full water allotment from the Colorado River.
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):