California has one of the most extreme latitudinal and elevational ranges of any western state in the continental US. Thus, not surprisingly this highly fire-prone landscape has radically different fire regimes from north to south and from low to high elevation. Understanding how future fire regimes may change in response to warming and other global changes is a challenge. One approach is to investigate historical patterns of fire activity in response to wide annual variations in climate. California has two written databases that extend back to the early 1900s and we utilized these to investigate how seasonal patterns of PRISM climate data affected annual fire activity in forested and non-forested landscapes throughout the state.
Results/Conclusions
Landscapes differed markedly in the relationship of climate to fire activity. Strong fire-climate signals were evident on many forested landscapes in the central and northern part of the state but were weak or non-existent on non-forested landscapes, particularly in the southern half of the state. The relationship of fire activity in forests was unrelated to average annual temperature variation, in part because winter and autumn temperatures were not correlated with fire activity. However, variation in spring and summer temperatures were strongly associated with fire activity. Annual variations in climate signals during any season were unrelated to fire activity on most low elevation foothill and valley habitats, and throughout the southern half of the state. On these latter landscapes it is hypothesized that in most years climate is suitable for large fire events but their occurrence is more a function of other anthropogenic impacts. Global changes beyond just climate need to be considered in understanding future fire regimes in California.