Although there is accumulating evidence of increased fire activity in the western U.S., parsing out the relative contributions of human activity and climate are complicated. Part of the reason is that the region has diverse ecosystems with both historical surface fire and crown fire regimes. This study investigates changes in fire activity on State Responsibility Areas in California over the past 50 years in 5 regions: Pacific Northwest, North-central, Sierra Nevada, Central Coast and Southern California. 
Results/Conclusions

During this time period there has been a 100% change in population density in most regions and a 5-10% increase in mean temperature during the growing season and summer. Area burned has not increased during this 50 year period in most regions, with the notable exception of southern California. In the northern part of the state, fire ignitions and area burned were significantly correlated with population density but in the southern part of the state increased population growth was not correlated with fire activity. In contrast, fire activity was correlated with increased temperature in the southern part of the state but not in the north.