Abstract
Southern California is a biodiversity hotspot and home to over 23 million people. Over recent decades the annual wildfire area in the coastal southern California region has not significantly changed. Yet how fire regime will respond to future anthropogenic climate change remains an important question. Here, we estimate wildfire probability in southern California at station scale and daily resolution using random forest algorithms and downscaled earth system model simulations. We project that large fire days will increase from 36 days/year during 1970–1999 to 58 days/year under moderate greenhouse gas emission scenario (RCP4.5) and 71 days/year by 2070–2099 under a high emission scenario (RCP8.5). The large fire season will be more intense and have an earlier onset and delayed end. Our findings suggest that despite the lack of a contemporary trend in fire regime, projected greenhouse gas emissions will substantially increase the fire danger in southern California by 2099.
Highlights
Southern California is a biodiversity hotspot and home to over 23 million people
To address the above questions, we statistically model the relationship between daily climate and the probability of large (> 40 hectares) wildfires at the local scale in the coastal southern California area (CSCA)
We estimate the change in large fire occurrence in response to changes in climate from historical (1950–2005) and future (2006–2099) simulations from an ensemble of earth system models (ESMs) of the 5th phase of the Coupled Model Intercomparison Project (CMIP5)
Summary
Southern California is a biodiversity hotspot and home to over 23 million people. Over recent decades the annual wildfire area in the coastal southern California region has not significantly changed. In the CSCA, there has been no significant trend in the annual or seasonal total burned area over the past five decades, possibly due to a combination of high interannual variability in climate, reduced ignitions, improved fire suppression, and land cover change[5]. The interaction of climate change and continuously present human ignition sources may be responsible for the increase in large fires, i.e., climate change leads to faster drying of fuels and increased large fire risk in areas where human ignitions are prevalent[15,23,24] This hypothesis is supported by the fact that a recent increase in large fire frequency occurred when humanignited fires decreased in the CSCA21,23. Climate-model projections of continued warming, increased VPD, and frequency of extreme fire-danger days raise questions as to whether an increasing trend of large fire occurrence in the CSCA will develop and persist in the future[5,22]
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