Originally Published: August 27, 2007 9:51 p.m.
PRESCOTT - Citizens logging precipitation with free rain gauges are helping Arizona climate research, an expert told people at a Prescott meeting Monday.
Mike Crimmins, a University of Arizona climate specialist, talked about Arizona's seasons during the second meeting of Yavapai County's Local Drought Impact Group Monday. The group previously met in Cottonwood, so Monday it met on this side of Mingus Mountain to recruit more volunteers.
And for the second time, the Yavapai County crowd, with more than 50 people in attendance, pleasantly surprised speakers.
The state called for local governments to organize the groups, and it is giving away free professional-grade rain
gauges at their meetings.
The state wants people to send their precipitation information to the program's rainlog.org website, especially since monsoon rains can be so variable over small regions.
"This has been real helpful to me," Crimmins said of the rain logs in relation to his research that includes rain variability.
The Local Drought Impact Group for Yavapai County also is recruiting volunteers for its sub-groups that are focusing on drought monitoring, a drought preparation plan and education/outreach. More information is available from Crystal Frost at 776-4507.
Crimmins provided a detailed PowerPoint presentation about the monsoon and Arizona weather in general, noting that this state has some unique weather characteristics.
"Arizona is in a very unique spot, and it has a unique climate because of its geography," Crimmins said.
It's unique because it has two rainy seasons from two sources, he explained. The winter rainy season gets its precipitation out of the Northwest when it can get over the Sierras, while the summer monsoon comes out of the subtropical South.
Not many states outside of the gulf region get
subtropical moisture, he said.
Yavapai County is unique too, because it experiences a noticeable effect from both of these seasons, Crimmins said. And it has highly variable precipitation because of its varied terrain.
Parts of mostly southeastern Arizona get more than half of their annual precipitation during the monsoon months of July through September, Crimmins said, and surprisingly, so does a small portion of Yavapai County.
The winter rainy season is more important to Arizona's long-term groundwater resources than the summer, because those rains tend to be less intense and soak into the ground instead of running downstream. Winter storms also are more likely to produce snow that percolates into the ground instead of running downstream.
However, with climate change, the state is seeing less snow and more rain during the winter lately. Prescott is no exception.
Higher temperatures that are coming with climate change also translate into less precipitation, Crimmins noted.
Arizona is at 30 degrees north latitude, where high-pressure systems that produce sunny weather tend to form, Crimmins said.
New research suggests that the Bermuda high-pressure system is getting stronger and moving farther to the north, and "That has huge implications for Arizona," Crimmins said.
This winter could produce disappointing precipitation as the monsoon is doing, because of the periodic La Niña effect, Crimmins said. That means the jet stream could drop down here to encourage precipitation only a few times this winter.
August, which historically produces the most rain of any month, has been disappointing so far.
The remnants of Hurricane Dean didn't bring much rainfall to the area, although it still was producing widespread clouds early this week, Crimmins said.
He recalled record flooding from the remnants of Hurricane Octave in 1983.