Climate, lightning ignitions, and fire severity in Yosemite National Park, California, USA
The authors examined fire-climate relationships between snowpack accumulation and fire ignition, size, and severity of lightning-ignited fires from 1984 to 2005.
The authors found that the 1 April snow water equivalent (SWE) is correlated with the number of lightning-ignited fires and area burned. High levels of persistent snowpack later into the year decreases the possibility of lightning-ignited fires during the fire season. Conversely, low levels lead to an increase in fire activity earlier in the fire season. The type and duration of winter precipitation greatly affects the fuel moisture conditions of the early fire season, and to a lesser extent, the late fire season as fuels are typically dry regardless of the previous winter’s precipitation. However, the relationship between SWE and area burned was weaker as bottom-up controls were stronger predictors of fire behavior on the landscape. However, they found that fire season length is not directly related to fire severity in that a longer fire season does not necessarily result in more severe fire across the landscape, especially in more drought tolerant ecosystems. Convective instability associated with high temperatures may also lead to increased lightning occurrence and thus increased ignition rates. Should spring SWE decrease, landscape flammability may increase and become more variable.