Full Citation: Williams, A. Park; Seager, Richard; Macalady, Alison K.; Berkelhammer, Max; Crimmins, Michael A.; Swetnam, Thomas W.; Trugman, Anna T.; Buenning, Nikolaus; Noone, David; McDowell, Nate G.; Hryniw, Natalia; Mora, Claudia I.; Rahn, Thom. 2015. Correlations between components of the water balance and burned area reveal new insights for predicting forest fire area in the southwest United States. International Journal of Wildland Fire 24(1):14-26.
External Identifier(s): 10.1071/WF14023 Digital Object Identifier
Location: Southwest United States defined as Arizona, New Mexico and areas of Texas, Oklahoma, Colorado and Utah that lie south of 38.08N, north of 28.58N and west of 100.08W.
Ecosystem types: Forested and non-forested ecosystems
Southwest FireCLIME Keywords: None
FRAMES Keywords: fire danger, area burned, climate variability, warming, water balance, tree mortality, fire danger rating, fire size, fuel moisture, wildfires, climatology, cover, drought, energy, moisture, mortality, precipitation, water, fire management, fuel management, range management

Correlations between components of the water balance and burned area reveal new insights for predicting forest fire area in the southwest United States

A. Park Williams, Richard Seager, Alison K. Macalady, Max Berkelhammer, Michael A. Crimmins, Thomas W. Swetnam, Anna T. Trugman, Nikolaus Buenning, David Noone, Nate G. McDowell, Natalia Hryniw, Claudia I. Mora, Thom Rahn


Summary - what did the authors do and why?

The authors correlated 15 standard climate variables and drought-related metrics, including vapor pressure deficit (VPD), to annual area burned and annual area burned at high severity using data from the Monitoring Trends in Burn Severity dataset (1984 – 2013) in the Southwest. They used Spearman’s rank correlation and Pearson’s correlation analysis to quantify the relationships for comparison.


Publication findings:

The authors found that total area burned in the Southwest has increased since 1984 at a rate of 10.2% per year, and that the rate of increase is greater for forests at higher elevations. Furthermore, March through August VPD, a measure of the ability of the atmosphere to extract moisture from surface vegetation, is more strongly correlated with total area burned and area burned at high severity than temperature alone for the Southwest region. The authors explain that air temperature is commonly correlated with severity, however, it is often used as a proxy for atmospheric water demand as high temperatures in a low-humidity environment cause dry fuel conditions in the Southwest. Extended periods when the value of VPD remains high can directly affect the rate of transpiration or water loss from the foliage and can lead to plant desiccation and mortality causing increased flammability. More importantly, vapor pressure at saturation increases exponentially with increasing temperature, thereby small increases in temperature will exponentially increase VPD, potentially resulting in more frequent drought and increased wildfire risk until fuels become limiting.

Climate and Fire Linkages

March through August VPD, a measure of the ability of the atmosphere to extract moisture from surface vegetation, is more strongly correlated with area burned than temperature alone for the Southwest region.

March through August VPD, a measure of the ability of the atmosphere to extract moisture from surface vegetation, is more strongly correlated with area burned at high severity than temperature alone for the Southwest region.