Long-term Stream Flow Impact Of Wild Fires In Mediterranean Shrubland Ecosystems

In Southern California, chaparral ecosystems dominate the local mountains. These ecosystem have a fire return interval under natural conditions of 40 to 60 years. Fire is an integral process to these ecosystems fostering germination and regular changes in vegetation. Inhabitants of Southern California depend on chaparral catchments for upwards of 1/3 of their water supply through rainfall in the mountains and recharge to regional aquifers at the mountain front. There is ample evidence in the literature to support the idea that soon after a wild fire, runoff increases. However, the long-term effects of burns that cover greater than 50 percent of a watershed have been investigated to a lesser degree. The aim of this paper is to begin preliminary investigation of the long-term effects of large wildfires. The results after examination of two sets of paired watersheds so far show very little impact after 3 to 5 years, with flows returning to a statistically insignificant difference within that time period. Three other watersheds preliminarily chosen for this study showed little impact from fire due to evidence of long term precipitation variability and its impact on annual stream flow. This result clearly shows that not all variables were accounted for in this study and that long term data (> 100 years) may be needed in some situations to demonstrate what the effects of fire are on annual stream flow.