How climate change and fire exclusion drive wildfire regimes at actionable scales

Abstract

Extreme wildfires are increasing in frequency globally, prompting new efforts to mitigate risk. The ecological appropriateness of risk mitigation strategies, however, depends on what factors are driving these increases. While regional syntheses attribute increases in fire activity to both climate change and fuel accumulation through fire exclusion, they have not disaggregated causal drivers at scales where land management is implemented. Recent advances in fire regime modeling can help us understand which drivers dominate at management-relevant scales. We conducted fire regime simulations using historical climate and fire exclusion scenarios across two watersheds in the Inland Northwestern U.S., which occur at different positions along an aridity continuum. In one watershed, climate change was the key driver increasing burn probability and the frequency of large fires; in the other, fire exclusion dominated in some locations. We also demonstrate that some areas become more fuel-limited as fire-season aridity increases due to climate change. Thus, even within watersheds, fuel management must be spatially and temporally explicit to optimize effectiveness. To guide management, we show that spatial estimates of soil aridity (or temporally averaged soil moisture) can provide a relatively simple, first-order indicator of where in a watershed fire regime is climate vs. fuel-limited and where fire regimes are most vulnerable to change.

How does water yield respond to mountain pine beetle infestation in a semiarid forest?

“…We also found that ground/snowpack sublimation decreased when all dead foliage fell to the ground because snowmelt increased with the opening of the canopy. However, this finding differs from that of other studies suggesting that snowpack sublimation can increase with a more open canopy (Biederman et al, 2014;Harpold et al, 2014). The latter can occur because open canopies may allow more snow to reach the ground, which can increase sublimation.…”

Does hot and dry equal more wildfire? Contrasting short‐ and long‐term climate effects on fire in the Sierra Nevada, CA

“…2018) and that the relative effects of climate and previous fire suppression on fire regimes depend on whether the area was historically fuel or flammability limited (Hanan et al. 2021).…”

“…Hanan et al. (2021) propose long‐term average soil moisture as a simple metric to discern whether an area is expected to be fuel or flammability‐limited. Good planning requires understanding the separation of timescales that drive wildfire, both the short‐term and long‐term impacts of climate on vegetation and wildfire and the feedbacks among them.…”

“…2). Some have indicated that fuels may ultimately be more important than the direct impact of climate in some areas (Lenihan et al 2003, Honig and Fulé 2012, Parks et al 2018 and that the relative effects of climate and previous fire suppression on fire regimes depend on whether the area was historically fuel or flammability limited (Hanan et al 2021).…”

“…For example, at higher elevations, increased temperature is predicted to increase productivity (Tague et al 2009) and the effects on fuels will probably differ from those found in this study. Hanan et al (2021) propose long-term average soil moisture as a simple metric to discern whether an area is expected to be fuel or flammability-limited. Good planning requires understanding the separation of timescales that drive wildfire, both the short-term and long-term impacts of climate on vegetation and wildfire and the feedbacks among them.…”