Increasing trends in high-severity fire in the southwestern USA from 1984 to 2015

In the last three decades, over 4.1 million hectares have burned in Arizona and New Mexico and the largest fires in documented history have occurred in the past two decades. Changes in burn severity over time, however, have not been well documented in forest and woodland ecosystems in the southwestern US. Using remotely sensed burn severity data from 1621 fires (>404 ha), we assessed trends from 1984 to 2015 in Arizona and New Mexico in (1) number of fires and total area burned in all vegetation types; (2) area burned, area of high-severity, and percent of high-severity fire in all forest and woodland areas; and (3) area burned, area of high-severity, and percent of high-severity in seven different grouped forest and woodland vegetation types (Ecological Response Unit [ERU] Fire Regime Types). Number of fires and area burned increased across the Southwest regardless of vegetation type. The significant increasing trends held for area burned, area of high-severity, and percent of high-severity fire in all forest and woodland ecosystems. Area burned and area burned severely increased in all seven ERU Fire Regime Types while percent of high-severity fire increased in two ERUs: Mixed Conifer Frequent Fire and Mixed Conifer with Aspen/Spruce Fir. Managers must face the implications of increasing, uncharacteristic high-severity fire in many ecosystems as climate change and human pressures continue to affect fire regimes.