Assessing climate vulnerability in the Southwest U.S
How will ecosystems in the Southwest respond to warmer, drier conditions? The most arid region of the United States—the Southwest—is expected to become even warmer and drier in the future as the climate changes, according to several global climate models. This region is particularly vulnerable to climate change because it is the southernmost edge of the range for several temperate ecosystem types.
In 2019 and 2020, fires carried by the invasive red brome burned hundreds of thousands
of acres of Sonoran desert scrub and resulted in some of the biggest fires in Arizona history.
To effectively respond and adapt to the threat of climate change, the Forest Service and its partners need to understand how vulnerable ecosystems in this region are and how they are likely to change over time. The Southwest is not a homogenous landscape and some ecosystems may be more vulnerable than others, so assessments at subregional scales are needed.
Rocky Mountain Research Station researchers and other Forest Service Scientists have responded to this need. Several RMRS scientists and collaborators developed GTR 309, which synthesized vulnerability assessment methods, summarized current knowledge, and identified information gaps.RMRS researcher Megan Friggens has also developed a vulnerability assessment tool called FireCLIME, which scores ecosystems based on how they are likely to respond to changes in climate and fire regimes. It can also assess how effectively different treatments can mitigate the impacts of these changes. FireCLIME has been used in several National Forests, including the Santa Fe and Lincoln National Forests in New Mexico. Finally, Region 3 Forest Service ecologist Jack Triepke modelled vulnerability on all lands in the Southwest at the subregional scales relevant to resource managers. This study divided the landscape into 26 “Ecological Response Units” based on vegetation type. It then determined vulnerability for each unit by comparing predictions of certain climate variables in 2090 to their pre-1990 range.
The Southwest is likely to experience more extreme climate change than other regions. Only about 6 percent of the Southwest will remain within its historic range of variability by 2090. Ecosystems at the edge of their range (like sagebrush shrubland) and at high elevations (like bristlecone pines) are more vulnerable. Assessment tools like FireCLIME can also be used to identify the specific ways different management strategies might or might not reduce vulnerability. Managers can use this information to develop adaptation strategies for particular vegetation types and ecosystems.