Wildland Fire Today and in the Coming Decades: What Might We Expect? Scott Stephens ESPM - Division of Forest Science University of California, Berkeley Berkeley, CA. USA

Wildland Fires Function of: Ignitions Fuel loads (vegetation types) Fuel moisture content Weather Topography

United States Averaged 100,000 fires/year Annual acreage burned 3,300,000 acres (range 1,000,000 – 6,500,000 acres) Nationally about 50% or fires from people, 50% from lightning Approximately 52% of annual area burned by lightning fires

Past Fire Occurrence Sensitive to Climate Giant sequoia fire history (Swetnam 1993) Groves experienced fire every 2-3 years during warm period between (medieval warming period) Compared to every 3-8 years between and when climate was cooler (little ice age) Expect fire regime changes with GCC

Lightning Very common ignition source worldwide Approximately 100 strikes/second worldwide Lightning is a function of cloud dynamics highly correlated with the height of convection clouds This may change in response to Global Climate Change

Lightning in 2 X CO 2 NASA Scientists used a General Circulation Model (GCM) (Price and Rind, 1991, 1994) Results suggest a 26% increase in the number of lightning strikes, addition of 2 million strikes/day worldwide This is independent of temperature or precipitation changes

Lightning Episodic in nature Today up to 1000 strikes can occur in a weekend in 1 or 2 western states Dry storms can ignite hundreds of fires Huge problem for initial attack not enough resources for all fires Larger problem with increased CO 2, higher initial attack budgets in the future?

Canadian Fire Severity Index Seasonal severity rating (SSR) Daily estimate of the control difficulty of a potential fire Derived from potential fire intensity (flame length) Similar to our National Fire Danger Rating System (United States)

Increases in Potential Fire Behavior Canadian GCM estimates over 30% increase in Seasonal Severity Rating in south-east US and Alaska (Flannigan et al. 2000) Increase of approximately 10% in the western United States

Changes in Fire Regime Climate change could effect fire regimes before changes in vegetation occurred In fire prone ecosystems, fire may be the main vehicle of vegetation change. Could occur over a few decades with higher frequency fires Extension of fire season, especially in areas with snow pack (2-3 weeks)

Fire Season Season of fire occurrence can have a profound effect on flora and fauna – everything else equal (intensity, frequency, size) Today, majority of fires in California occur in the dormant season

Fire Season Change in California with GCC Sierra San Pedro Martir Mountains Northern Baja California, Mexico Mediterranean climate Annual precipitation averages 70 cm (28 inches) Similar to east-side Sierra Nevada

Sierra San Pedro Martir Mountains Within the California floristic province unique to Northern Baja California 26% of seasonal precipitation occurs in the summer 10-15% in the eastern Sierra Nevada

Sierra Nevada vs. Sierra San Pedro Martir Same floristic province, similar vegetation Similar soil parent materials Very different past and current fire season Sierra Nevada fall (10-15% summer) SSPM growing season (24% summer) Some models predict more summer rain in CA., major shift in fire season

Uncertainty in Predictions Difficulty in predicting disturbances Fire, insects, disease, drought Added complexity with prediction of climate change Recent research gives some possibilities Still have only a basic understanding of climate change and wildland fire

Conclusions Need more research in this area High amount of uncertainty Possible feedback mechanism Global Climate Change increases wildfire This would produce even more CO 2 which may increase rate of GCC

Desired Future Conditions May be best to manage for resilient ecosystems instead of pre-historic conditions lower densities, lower fuel loads Pre-historic conditions may not be the appropriate choice with GCC