Precipitation

The October–September 2010 water year was mixed across Arizona and New Mexico (Figures 1a–b). Most locations received within 3 inches of their normal precipitation, including northern and south-central Arizona and the western half of New Mexico. The regions that experienced below-average precipitation ranged between 50 to 100 percent of average precipitation, while the wetter areas received 110 to 200 percent of average. The wetter-than-average conditions were generally related to the winter precipitation, which had an El Niño pattern. Winter storms took a southerly track across the eastern Pacific Ocean, picking up subtropical moisture as they moved across Southern California, Arizona, and New Mexico. However, winter was not uniformly wet, as the El Niño frequently had little moisture. Also, many of the storms missed the Colorado Plateau just above the Mogollon Rim. Instead, the storms dumped most of the precipitation on the White Mountains of eastern Arizona and left little precipitation to fall on western New Mexico. Eastern New Mexico fared much better during the winter in part because moisture moved westward across Texas. Typically, cold winter storms have relatively uniform precipitation, with deeper snowfall at the highest elevations. During many of the 2010 winter storms, the lower elevations of Arizona received no precipitation, leading to larger-than-average variability in precipitation with elevation. Table 1 shows that most cities had a drier-than-average water year, but not nearly as dry as the 2009 water year.

Spring and early summer were relatively dry, but the monsoon did bring near-average precipitation to southeastern Arizona and southeastern New Mexico. Higher elevations in both states benefitted more from the monsoon than the southern deserts.  The lower Colorado River basin was very dry all summer and received most of its rain during the winter storms. While the 2010 water year was relatively dry in many locations, it was significantly wetter than 2009, when precipitation deficits ranged from 2 to 9 inches and only Yuma was wetter than average (due to a tropical storm). Water year 2010 had a few extreme precipitation events, an anticipated result of regional warming.

Click figures to enlarge.

Table 1. Water Year 2009 precipitation values (in inches) for select cities.

City	WY 2010 Precip.	Average WY Precip.	2010 Departure from Avg.	2009 Departure from Avg.
Phoenix, AZ	7.88	8.29	-0.41	-4.05
Tucson, AZ	10.69	12.17	-1.48	-5.66
Douglas, AZ	13.08	13.76	-0.68	-8.03
Albquerque, NM	9.31	9.47	-0.16	-2.24
Winslow, NM	5.72	8.03	-2.31	-4.66
Flagstaff, AZ	23.71	22.91	+0.80	-9.53
Yuma, AZ	4.41	3.05	+1.36	+2.14
El Paso, TX	8.35	9.43	-1.08	-2.17

Notes: