Effects of Wildfires on Landscape Evolution in Southern California

Julia Rogers

GE154

6 May 2015

Why study wildfires?

From Westerling et al. 2006

Bedrock of Southern California

From Jennings et al. 1977

Vegetation CommunitiesChaparral Systems

• Rely on fires as part of their

natural cycles

• 90% of annual rainfall

between November and

April

• Dry Ravel

• Debris flows are common

after fires

Sonoran Desert

• Large portion of the

landscape

• Frequently burned

• Low-intensity fires

• Little effect on

landscape evolutionFrom http://www.resecol.wur.nl/gest/privateGEST/North%20America/Dry%20site/Landscape%20&%20vegetation/2005_02032008_South_America_30382.JPG

From http://www.azfirescape.org/sites/azfirescape.org/files/dsc00738.jpg

Mass Wasting• Debris flows

range from small

to large

• Wildfires increase

likelihood of a

slope to fail

• 2009 Station FireFrom Cannon et al., 2009

Fluvial Transport

• Indirect effect from

mass wasting

• Erosion of larger

materials

• Change in depth

and course

From http://geologycafe.com/images/arroyo_seco2.jpg

Soils and Water Repellency

Water repellency is

created by:

1. Heat of the fire

2. Quantity of

organic matter in

the ecosystem

Causes less water to

be absorbed and

more runoff

From DeBano 1981

Chemistry of the Substrates• Increase in pH due

to the ash

• High levels of

certain metals

including lead,

zinc, chromium,

and copper

From http://www.iarc.uaf.edu/sites/default/files/fig1.jpg

Citations

DeBano, L. F.: 1981. Water repellent soils: a state-of-the-art (Vol. 46). US Department of

Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station.

Cannon, S. H., Boldt, E. M., Laber, J. L., Kean, J. W., and D.M. Staley: 2011. Rainfall

intensity–duration thresholds for postfire debris-flow emergency-response planning.

Natural Hazards, 59(1), p. 209-236.

Jennings, C.W., Strand, R.G., and Rogers, T.H: 1977. Geologic map of California. California

Division of Mines and Geology.

Westerling, A. L., Hidalgo, H. G., Cayan, D. R., and T.W. Swetnam: 2006. Warming and

earlier spring increase western US forest wildfire activity. Science, 313(5789), p.

940-943.

Questions?