Thread by @PatrickTBrown31

We have a paper out today in @Nature on the role that human-caused climate change is playing in changes in extreme wildfire behavior, at the daily timescale, in California.

nature.com/articles/s4158…

Many previous studies have looked at the influence of climate change on wildfires in California, the US West, and around the world. However, most previous studies have focused on *conditions conducive* to wildfires rather than characteristics of wildfires themselves.

This is exemplified by the relevant statement in the latest Intergovernmental Panel on Climate Change (IPCC) report, which is an assertion about weather conditions conducive to wildfires.

Another example of this would be the recent findings from the @WWAttribution on wildfires in Canada this year, which focused on weather conditions, not wildfire characteristics themselves.

https://twitter.com/WWAttribution/status/1694085556760633777

Also, when climate change studies *do* look directly at characteristics of wildfire activity, these tend to be of rather low resolution in space and time: usually area burned accumulated over large regions and entire years.

Our study makes progress on both of these fronts: We investigate the impact of climate change directly on wildfire behavior, and we do this at high resolution: daily timescale at the level of individual fires.

We use a “storyline approach” where the day-to-day weather conditions associated with historical fires are placed in differing background climatological temperatures and aridity conditions.

We used machine learning to quantify the relationship between temperature and wildfire behavior empirically directly from the data itself so that there were not any built-in assumptions about relationships between temperature/aridity and fire behavior.

One of our study's key findings was that the background climatological warming had very different impacts on different historical fires depending on whether or not that warming had pushed conditions over certain critical thresholds of temperature and aridity.

In some cases, warming’s impact on fire behavior was nonexistent (or even negative), and in others it had a huge impact – e.g., increasing the risk of extreme growth in daily burned area by more than a factor of 5.

For example, warming since the Industrial Revolution increased the risk of extreme growth by only 6% for the Carr Fire but by 40% for the North Complex Fire (averaged over their lifetimes).

This means that we should pay closest attention to the places and times of the year that historically have experienced conditions just on the moist side of these thresholds but which are being pushed over these thresholds onto the dry side more frequently by background warming.

This research looked at the effect of warming in isolation but warming is just one of many important influences on wildfires with others being changes in human ignition patterns and changes in land use and vegetation/fuels.

In the current phase of the research, we are looking at the simultaneous effect of future climate change concurrent with hazardous fuel reduction treatments (mechanical thinning and prescribed burning), which are endorsed by the US Wildfire crisis strategy.

We have an experimental, operational version of the model running here:

(still under development and working out several kinks)met.sjsu.edu/weather/wirc-p…

In these simulations, the forecasted weather conditions of the next several days are placed in different combinations of background climate and vegetation states so that the predicted fire danger can be compared.

One thing to note is that the difference between aggressive emissions reductions (RCP2.6) & delayed/tempered emissions reductions (RCP4.5) is very small in 2050. Thus, emissions policies do not have much leverage on wildfire activity until well into the 2nd half of the century.

So, while emissions reductions are important for the long term, if we are interested in reducing wildfire danger in the next several decades, we have to look to more direct solutions.

The good news is that preliminary results indicate that fuel characteristics have huge leverage on wildfire danger, and thus, hazardous fuel reductions have the potential to more than offset the increase in wildfire danger from warming.

Overall, we hope this research can serve as a foundation for many other practical applications to help mitigate wildfire danger including:

1) Where to prioritize hazardous fuel reduction treatments (mechanical thinning and prescribed burning)
2) When and where utilities should Intentionally de-energize power lines
3) Where utilities should prioritize undergrounding powerlines

4) Where advanced monitoring networks should be installed
5) When and where public awareness campaigns on ignition reduction should be focused

6) Where public awareness campaigns on wildfire preparedness should be focused
7) When and where firefighting resources like firefighters, bulldozers, and helicopters should be deployed

The paper is here:

Brown, P. T., H. Hanley, A. Mahesh, C. Reed, S. J. Strenfel, S. J. Davis, A. K. Kochanski, C. B. Clements (2023) Climate warming increases extreme daily wildfire growth risk in California. Nature, doi: 10.1038/s41586-023-06444-3nature.com/articles/s4158…

Full-text access to view only version: rdcu.be/dkMyN