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Wildfires in the Western U.S. Are on the Rise, Posing Threats to Drinking Water

A flash flood carries sediment and debris toward the Rio Grande from forestlands burned by the 2011 Las Conchas fire in the Jemez Mountains of northern New Mexico. Photo credit: John Floyd Pecos.
A flash flood carries sediment and debris toward the Rio Grande from forestlands burned by the 2011 Las Conchas fire in the Jemez Mountains of northern New Mexico. Photo credit: John Floyd Pecos.

When the Las Conchas Fire scorched some 151,000 acres of northern New Mexico in 2011, it wasn’t just the direct fire damage that was cause for worry.
 
Striking as it did in the midst of a persistent drought, but just before summer “monsoon” rains, the Las Conchas – the largest blaze in New Mexico’s recorded history – set in motion the one-two-three punch of drought, fire and flood that much of the western United States has seen all-too frequently in recent years.
 
As the intense rains pounded burned-out watersheds, peak floods poured through the Jemez Mountain canyons pushing tree trunks, boulders and tons of blackened soil down to the valleys below.   Soon after, to avoid the high costs of de-clogging equipment and treating sediment-laden river water, the Albuquerque drinking water utility cut its intake from the Rio Grande by half – and tapped more groundwater to make up the deficit.
 
With new research showing that fires in the western United States are getting larger and more frequent, water managers need to mitigate the impacts of fire in their source watersheds, as well as prepare for the consequences.
 
In a study published online in the journal Geophysical Research Letters, Philip E. Dennison of the University of Utah and colleagues analyzed a database of large wildfires (those greater than 1,000 acres, or 405 hectares) in the western United States over the period 1984-2011 and found a significant increase in the number of large fires and/or the area covered by such fires.
 
Specifically, in the region stretching from Nebraska to California, the number of large wildfires increased by a rate of seven per year over the 28 years of study, and the total area burned by these fires increased at a rate of nearly 90,000 acres a year – an area the size of Las Vegas.
 
“We looked at the probability that increases of this magnitude could be random, and in each case it was less than one percent,” Dennison said.
For their analysis, Dennison and his team used satellite data from the Monitoring Trends in Burn Severity Project, which is supported by the US Forest Service and the US Geological Survey.
 
The team also found a correlation between increased fire activity and increased drought severity.
 
Those regions expected to be most affected by climate changes, especially more intense droughts, showed the greatest increase in fire activity, including the Rocky Mountains, the Arizona-New Mexico mountains, the southwestern desert region, and western Texas.
 
A satellite image of the 2011 Las Conchas Fire in New Mexico

A satellite image of the 2011 Las Conchas Fire in New Mexico shows the 150,874 acres burned in magenta and the unburned areas in green. Credit: Philip Dennison/MTBS.

For water managers, the new research is a clarion call to begin action now to safeguard water supplies originating in watersheds prone to fire. 
 
Fires are natural and beneficial to forested watersheds.  But for many decades, firefighters focused on protecting people and property have squelched even small fires that would do the important work of cleansing the forest floor and thinning trees to healthy densities.
 
As a result, many forests have accumulated an excess of  “fuel,” so when a fire ignites– whether from a natural cause, such as a lightening strike or a human one, such as a campfire – the forest is primed to burn rapidly, increasing the potential for a mega-fire like Las Conchas.  Drought only adds to the favorable fire conditions.
 
Partly in response to the damage wildfires have inflicted downstream, a few pioneering water suppliers are taking a proactive approach to addressing wildfires’ costs and risks to drinking water sources.
 
After the 2002 Hayman Fire, Denver Water faced a reservoir cleanup and infrastructure repair bill upwards of $30 million. Rather than pay such a steep price over and over again, Denver Water is investing $16.5 million to match the Forest Service’s investment in thinning ponderosa pine stands, cutting trees killed by pine beetle infestations, and generally rehabilitating the watershed critical to Denver’s water supply.
 
Likewise, Santa Fe, New Mexico, has embarked on watershed protection measures to safeguard against wildfires in the Santa Fe National Forest (SFNF).  In partnership with the Nature Conservancy and the US Forest Service, Santa Fe has established a water fund to help pay for restoration efforts in the 17,520 acres of the forested watershed that supplies about 40 percent of the city’s drinking water. (Some 88% of that forestland is in the SFNF, and half of that is located in the Pecos Wilderness, where forest thinning is not allowed.)
 
Such partnerships between municipalities and the Forest Service would seem to offer great potential to mitigate the risks of fire to downstream water supplies while simultaneously reducing the costs of both fire-fighting and water treatment.
 
Collectively, the national forests are part of more than 3,000 municipal watersheds that supply 60 million Americans with drinking water.
 
The Nature Conservancy, building on its watershed protection work in Latin American, has also been instrumental in forming the Rio Grande Water Fund in New Mexico.  The fund aims to generate sustainable financing for a 10-30 year program of large-scale watershed restoration to avoid more impacts like those caused by the Las Conchas Fire.
 
Recognizing that adequate supplies of clean water are critical to the health of the local economy, a number of businesses – including Lowe’s, PNM (the state’s largest electricity provider) and Wells Fargo – are contributing to the water fund.
 
With wildfire activity increasing across the western United States, more partnerships like these to proactively improve watershed health are a crucial line of defense to safeguard our drinking water.

 

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