The Whitewater-Baldy blaze has now burned more than 350 square miles of the Gila National Forest and Gila Wilderness, a rugged gem of a landscape and the headwaters of the Gila River, a tributary to the Colorado.

 

The two biggest fires on record in the state have occurred in back-to-back years, 2011 and 2012.  Last year’s big burn, the Las Conchas, raged through 245 square miles of northern New Mexico, threatening Los Alamos National Laboratory and, weeks later, Cochiti Pueblo, as monsoonal rains created debris-laden flash floods down mountain canyons.

 

Much of the West has dried out after years of below-normal rains.  The U.S. Drought Monitor now registers severe drought for large swaths of Arizona, Colorado, New Mexico, Nevada, and Utah.  More fire is likely ahead this summer.

 

While fire is a natural phenomenon and essential to long-term ecological health, it is posing increased risks due to unnatural fuel build-up, prolonged droughts and more people living in harm’s way.  Whitewater-Baldy, which apparently formed when two fires sparked by lightning merged into one, has burned with less intensity than others in part because forest managers have prescribed smaller burns in the Gila National Forest.

 

That deep droughts fuel fire risk is no surprise. Less known, though, is that extensive fires like Whitewater Baldy can worsen water stress years down the road, because as the burned forests rebound, the young plants and trees demand more water as they grow.

 

It’s a feedback that could make adapting to our warming, water-stressed world even more difficult.   And if the results of Australian scientists’ investigation into this phenomenon prove to hold widely, the ramifications could be huge.

Following fires in 2003 that burned some 2.5 million acres of forest and grazing land in southeastern Australia, the Murray Darling Basin Commission (now the Murray Darling Basin Authority) and the government of the state of Victoria commissioned a group of scientists to study the fires’ impact not only on water quality, but water quantity, as well.  2003 happened to be the year the Murray River, the main artery sustaining Australian agriculture, failed to reach the sea for the first time, and the decade of drought that came to be called the Big Dry was in full swing.

 

Scientists have long known that forest fires affect water yield.  For the initial 5-10 years after a big fire, water supply typically increases, because the dead trees are no longer transpiring water, which leaves more to run off across the landscape.  But as the forest regenerates, the new vegetation consumes more water as it rapidly grows.  The maximum impact of diminished flow typically occurs around 15-25 years after the fire.

 

What’s surprising about the Australian study is the magnitude of the estimated impact. The team looked at twelve catchments that drain to the Murray River and modeled the river flows expected twenty years after the fire (year 2023) and compared them with the average flow conditions in the twenty years prior to the fire.

Eight catchments showed more than 15 percent reductions in flow; five showed more than 25 percent reductions.  During summer, the height of farmers’ demand for irrigation water, reductions 20-years post-fire were even more dramatic, with two-thirds of the catchments showing flow reductions of one-third or more.

 

More extensive fire – a potent risk in its own right – is clearly a serious added stressor on our water supplies.   And these fire impacts will occur on top of those from anticipated warming and intensified drought due to climate change.

 

In planning our water future, whether in the Murray, the Colorado, the Rio Grande or any other major river basin where drought and fire are likely to conspire to diminish future water supplies, it would serve us well to assess these impacts and take them into account to get a more realistic picture of just how much water is likely to be available down the line – and to plan, prepare and adapt accordingly.