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

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. 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...more