Collision of population growth and wildfires in California

Background/Question/Methods

It is widely accepted that anthropogenic global warming will be a major driver of future fire regimes in the Western US, however, in some highly fire-prone regions climate signals account for relatively little fire activity.  More direct human impacts have long been implicated as a major driver of historical changes in area burned throughout many parts of California. Humans not only account for the vast majority of ignitions throughout the state, but they have greatly altered the temporal and spatial distribution of ignitions in ways that produce increasingly disastrous fires.  In some subregions humans account for nearly 99% of all area burned.  Beyond projections of future fire activity under climate change, predictions of future fire regimes need to account for the impact of rapidly expanding populations to be of any value for planning appropriate responses. 

Results/Conclusions

Models projecting spatial and temporal patterns of population growth and land-use conversion, when coupled with fire and climate models,  show us how to identify where, when, or how thresholds in population growth can lead to tipping points at which catastrophic alterations in ecosystem processes may occur.   Some regions may be particularly vulnerable to this collision of population growth and wildfire, such that human-driven changes override the effects of climate.   Understanding where and when these conflicts could occur may provide an opportunity to plan accordingly. While it is widely believed there are engineering solutions to this problem through enhanced fire hazard forecasting, more intensified vegetation management, better fire prediction and fire response time, our studies fail to support that conclusion. We believe a doubling of population size expected in the 21^st century will dramatically alter fire regimes resulting in highly altered ecosystems in California. Population growth will not just increase numbers of ignitions, but change the temporal and spatial distribution of  ignitions in ways that increase the size of Santa Ana wind driven fires. The future scenario for the regions shows accelerated population growth pushing these fire-prone ecosystems beyond their threshold of tolerance and rapidly change landscape dynamics.