Detection of nonlinearities in the dependence of burn area on fuel age and climatic variables Suggested running head: Nonlinear dependence on fuel age and climate

Evidence from Los Angeles County in California, USA suggests that the relationships between wildfire burn area and fuel age, temperature, precipitation, and fuel moisture are not linear. Instead, the relationships appear to have thresholds. The data seem to support the notion that fire risk is nearly constant provided various conditions are met: that fuel age and temperature exceed a given threshold, and that fuel moisture and precipitation are sufficiently low. There appears to be little distinction in terms of wildfire risk between conditions that are sufficient for wildfires and those that are extreme.