By Bethany Conway
Arizona-Sonora News Service
(Wednesday, 24 November 2010) - An unwanted visitor has made her way to the border region, and it's not your irate aunt here to put a damper on the holidays.
Continuing this winter and into the spring, a moderate-to-strong La Niña is predicted to reign across most of the United States. This natural cycle, brought about by cooler temperatures in the equatorial Pacific Ocean, has historically meant lower-than-average precipitation for the Southwest.
"The Pacific jet stream is weaker and it's pushed a little north, so the winter storms that form in the Pacific Ocean get pulled north of us and we are drier," said Zack Guido, associate staff scientist with Climate Assessment for the Southwest (CLIMAS), a program housed at the University of Arizona Institute for the Environment.
La Niña could mean bad news for parts of Arizona and northern Mexico, where most of the last 10 years have been dry, leaving water levels dangerously low.
In an effort to "improve the region's ability to respond sufficiently and appropriately to climatic events and climate changes," CLIMAS will debut the La Niña Drought Tracker the first week of December. The monthly online publication will provide information on current and future drought conditions to ranchers, water managers, wildlife managers and others who could be affected by La Niña's outcome.
"The major impact of the La Niña will likely be the expansion of drought," Guido said.
According to the National Oceanic and Atmospheric Administration, the exacerbation of drought conditions will also put Southwest states at risk of having above-normal wildfire conditions in the coming months.
But just like any climate prediction, its occurrence and severity are a toss-up.
"It's a gamble because these are statistics, and it doesn't always hold," Guido said. "But by and large it holds, and it is less of a gamble in La Niña years than El Niño years."
El Niño, sometimes called La Niña's sibling rival, is characterized by warmer ocean temperatures in the tropical Pacific Ocean and generally brings more rain to the Southwest region. Data from the National Weather Service, a division of the NOAA, shows that the last time El Niño made its mark was from May 2009 through March 2010.
The National Weather Service has already reported that La Niña conditions across the tropical Pacific Ocean stayed strong during October and early November and are expected to hold through the end of the year.
The La Niña Drought Tracker will incorporate these climate signals as a way of informing people about future conditions. Data will come from large organization such as the National Weather Service, the Climate Predictions Center, Department of Agriculture and the National Integrated Drought Information Systems.
Climatologists in Arizona and members of the University of Arizona College of Agriculture and Life Sciences Cooperative Extension Program will also contribute.
Dino DeSimone of the U.S. Department of Agriculture Natural Resources Conservancy Center in Phoenix will also put the publication to use.
As Arizona's water supply specialist, DeSimone focuses on streamflow forecasting. By monitoring stations and focal points around the state, using both manual snow surveys and automated snow telemetry, DeSimone helps water managers prepare for what La Niña might have in store.
"This helps people know what to expect in terms of runoff and total acre-feet (of water) to expect in the reservoirs," he said. "During these La Niña periods, you have the reservoirs drying up, and you have less water for irrigation so there definitely needs to be some planning ahead."
But not everyone is worried.
"(Forecasts) give you a good indication of what could happen, but I have seen exceptions to the rule," said Doug Mason, general manager of the San Carlos Irrigation and Drainage District. In his area of eastern Arizona, San Carlos Lake was nearly empty in January 2010, threatening fish and agriculture.
Across the state in Yuma, where farmers are well under way with the planting and harvesting of winter crops, John Boelts, president of the Yuma County Farm Bureau, said, "They predicted a La Niña last year, and we didn't get a La Niña at all."
Boelts said that in some ways Yuma farmers are actually counting on La Niña's arrival.
"We are kind of an oddity in agriculture because we have easier days without rain," he said, adding that the rains tend to foul up fields and result in unwanted frost. "Snowpack in the Colorado Rockies is what we rely on in the spring to refill the reservoir and the system."
Boelts said he hopes the northward swing of arctic storms will mean more snow over the Rockies, resulting in a higher streamflow come spring.
But that, too, is a gamble. Currently, the National Weather Service is predicting "equal chances of above-, near- or below-normal temperatures and precipitation" for the central United States.
"Some years the storm track can be way north and then the upper Colorado River Basin will also lose out," said Gregg Garfin, a UA climatologist. "Other years it will fly north of Arizona and hit Utah and Wyoming and Colorado and everything will be just fine. It is a little dicey to try to predict what will happen, but all of the water managers are kind of on the edge of their seats."
How this scenario plays out will have a major impact on the replenishment of reservoirs for irrigation and domestic water supply.
In the meantime, there is another factor for which farmers in Yuma and stakeholders all over the state should prepare – higher-than-average temperatures.
Regardless of what brings on the extreme heat – be it global warming or natural weather patterns – higher-than-average temperatures are predicted to be a major factor in the region's water supply.
"We are seeing, in the last 30 to 50 years, a pretty clear trend of increasing temperatures, and that will make the land drier in and of itself regardless of what precipitation does," Guido said.
And drier land not only increases the risk of fire but also can impact the survival of wildlife.
Less freestanding water and less forage growth can affect fawn survival among the endangered Sonoran pronghorn, said Duane Aubuchon of the Arizona Game and Fish Department.
Lack of forage and water can also impact ranchers who may need to invest in additional food sources for their herds.
Garfin said drier weather could even make it tough for migrants who sometimes depend on the same water catchment areas as wildlife.
For members of CLIMAS, the Drought Tracker is one example of increasing stakeholders' adaptive capacity and ability to cope with repeated weather events. Guido said CLIMAS will continue to release the two-page publication throughout the entirety of La Niña.
"We suspect that, in the beginning, it won't be as impactful because the drought impact hasn't intensified," Guido said. "But let's pretend that in February we have had three consecutive months of very dry conditions."
That's when the publication could be extremely useful, he added.
"We are hoping that drought conditions don't get too severe, but we want to be prepared in case they are," he said.
No comments:
Post a Comment