Drought

Arizona and New Mexico were in good shape, drought-wise, at the beginning of the 2011 water year thanks to a wet winter and decent monsoon. Those rainy conditions were not to last. On October 1, 2010, moderate or more severe drought covered only 19 percent of Arizona, and New Mexico was drought free. By November 16, drought conditions in Arizona decreased, blanketing a mere 7 percent of the state (Figure 4a). A few very strong and wet early-season winter storms pounded northwest Arizona in December, causing flooding and shrinking the short-term drought conditions that were present in this region.

But while the rains fell, a moderate to strong La Niña event was building, ultimately casting a dry winter shadow over the region. The La Niña, which began to form in the summer 2010 and peaked in February 2011, pushed most storms north of Arizona and New Mexico for much of the remainder of the winter and early spring. A few areas, including northern Arizona, received enough precipitation to  keep local drought conditions at bay, but drought spread and intensified elsewhere. Some stations in far southeast Arizona and southern New Mexico observed no precipitation between October and March. Most of Arizona and almost all of New Mexico were experiencing at least moderate drought by late spring; extreme and exceptional drought, which are droughts that occur, on average, once in every 20 and 50 years, respectively, covered much of New Mexico (Figures 4b–c). During intense monsoon rainfall in August and September, some localized areas flooded, bringing some drought relief, particularly in southeast Arizona (Figure 4d). Overall, however, the region experienced below-average summer rainfall, and severe to exceptional drought remained entrenched at the end of the water year.
 

Click figures to enlarge.