Westerling et al,2006 Science

Late Snowmelt Years Early Snowmelt Years

1972 - 2003, NPS, USFS & BIA Fires over 1000 acres

Other Large WildfiresHave Not ChangedSubstantially

Since the mid-1980s

Large Forest WildfiresHave Increased ~300%

Forest Fires & Temperature

Correlation: 0.70

Correlation: 0.08

Grass/Shrub Fires and Temperature

Correlation: 0.56

Forest Fires & Timing of Spring

If lilacs bloomIf lilacs bloombefore ~May 20before ~May 20……

Timing of Springsnowmelt in westernstreamflow gauges is a regional signal,

correlated with Forest Wildfire

Most forest firesoccur in years withearly Springs…

… at elevationsaround 7000 feet

Early - Late Oct to May Precip

Early - Late Mar to Aug Temp

largest vulnerable forest area

biggest increasein wildfires

risks least affected bysuppression

less vulnerableto warming

most affected bysuppression

vulnerable

affected bysuppression

Large forest fires increased, but total ignitions did not.