Abstract
Climate and weather have long been noted as playing key roles in wildfire activity, and global warming is expected to exacerbate fire impacts on natural and urban ecosystems. Predicting future fire regimes requires an understanding of how temperature and precipitation interact to control fire activity. Inevitably this requires historical analyses that relate annual burning to climate variation. Fuel structure plays a critical role in determining which climatic parameters are most influential on fire activity, and here, by focusing on the diversity of ecosystems in California, we illustrate some principles that need to be recognized in predicting future fire regimes. Spatial scale of analysis is important in that large heterogeneous landscapes may not fully capture accurate relationships between climate and fires. Within climatically homogeneous subregions, montane forested landscapes show strong relationships between annual fluctuations in temperature and precipitation with area burned; however, this is strongly seasonal dependent; e.g., winter temperatures have very little or no effect but spring and summer temperatures are critical. Climate models that predict future seasonal temperature changes are needed to improve fire regime projections. Climate does not appear to be a major determinant of fire activity on all landscapes. Lower elevations and lower latitudes show little or no increase in fire activity with hotter and drier conditions. On these landscapes climate is not usually limiting to fires but these vegetation types are ignition-limited. Moreover, because they are closely juxtaposed with human habitations, fire regimes are more strongly controlled by other direct anthropogenic impacts. Predicting future fire regimes is not rocket science; it is far more complicated than that. Climate change is not relevant to some landscapes, but where climate is relevant, the relationship will change due to direct climate effects on vegetation trajectories, as well as by feedback processes of fire effects on vegetation distribution, plus policy changes in how we manage ecosystems.
Highlights
Wildfires are globally widespread and affect both ecosystem processes and distribution patterns of flora and fauna [1,2,3]
In our studies of fire-climate relationships in California we have investigated these relationships within climatically homogeneous divisions as defined by NOAA [33], focusing on the main fire-prone landscapes in the state
Drought plays a key role in driving fire regimes and annual precipitation is a primary driver of drought variability [39]
Summary
Wildfires are globally widespread and affect both ecosystem processes and distribution patterns of flora and fauna [1,2,3]. Higher temperatures during spring and summer, correlated with early snow melt, will reduce moisture of both live fuels and dead surface fuels by increasing evaporative demands will reduce moisture of both live fuels and dead surface fuels by increasing evaporative demands during the dry season Distinguishing between these two processes is difficult with the Westerling study [6] as it reports only the timing of peak river flow in associated watersheds as a surrogate for snowpack melt-off date, and by implication spring temperature. Keeley and Syphard [4] found a negative correlation between spring snowpack depth and area burned in Sierra Nevada forests, but doubted there was a causal relationship since the climate variables most strongly tied to snowpack melt-off were not parameters most strongly affecting area burned They hypothesized that high spring temperatures did result in early melt of the snowpack, fires were more strongly controlled by direct effects of spring and summer temperatures on live and dead fuel moisture. Here we focus on more direct and local climate drivers of fire activity
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