The area burned by wildfire is synchronous with climate on a regional basis. At this scale, there is a strong relationship with temperature and precipitation patterns. Empirical data demonstrate that in the western US, area burned has increased substantially and this correlates with increased temperature, earlier snowmelt, and increased fuel aridity. Projections of future area burned built on these relationships show a substantial increase under projected climate in the Sierra Nevada Mountains. However, the relationship between climate and area burned neglects the influence of vegetation on area burned. We sought to account for the vegetation feedback in area burned under projected climate by using a forest simulation model. We ran simulations under projected climate from three global climate models across three transects (southern, central, northern) in the Sierra Nevada. At each decadal time-step we used the simulated area burned during the prior decade to estimate a distribution of area burned for the subsequent decade using generalized Pareto distributions of log-area burned (dynamic). We also ran simulations with area burned distributions driven only by projected climate (static).
Results/Conclusions
We found that mean cumulative area burned across all three transects in the absence of the vegetation feedback was 1805 km2 (se = 102.1) by year 2100. When we accounted for the effects of wildfires in the previous decade on vegetation, the mean cumulative area burned was 1545 km2 (se = 83.4) by year 2100. The largest decrease in cumulative area burned under the dynamic scenario occurred in the southern transect (-21.8%), followed by the northern (-14.5%) and central (-9.8%) transects. The larger reductions in area burned for the southern and northern transects resulted in late-century aboveground carbon stocks that were approximately 3% higher for the dynamic simulations. The late-century difference between the dynamic and static simulations was negligible for the central transect. Mean cumulative wildfire emissions decreased by 14.4% across transects, with the largest decrease occurring in the southern transect (21.2%) under the dynamic simulations. Our results demonstrate the importance of accounting for the influence of prior fire events on the vegetation community and how that factor feeds back to limit area burned. Further, our simulations account for the influence of projected climate on forest recovery following wildfire and forest growth and how these system attributes influence area burned.