IRA FLATOW: This is Science Friday. I’m Ira Flatow. Last year, California saw a record-breaking wildfire season. Nearly 10,000 fires scorched over 4 million acres in the state. The wildfire season usually peaks during the late summer, but there are indicators that scientists look for to get an idea about the upcoming season. And my next guest is here to talk about that. Craig Clements is a professor and director at the Wildfire Interdisciplinary Research Center at San Jose State University in California. Welcome to Science Friday.

CRAIG CLEMENTS: Thanks for having me.

IRA FLATOW: Now, I understand that your group has a couple of field sites looking at a shrub called– what? What’s the shrub called?

CRAIG CLEMENTS: It’s chemise. It’s a common shrub in California. And so we use that to sample what those shrubs are– how they’re responding to the climate and the precipitation from the previous winter.

IRA FLATOW: And what’s so good about this shrub?

CRAIG CLEMENTS: Well, it’s because it’s so common across the state. And it’s an indicator of what the fuel moistures are of other shrubs. So basically, it was selected just because it’s from Northern California to Southern California, from the Sierra Nevada all the way to the coast range.

IRA FLATOW: What does that– I have to stop you for a second and explain to us what fuel moisture is and why you measure that.

CRAIG CLEMENTS: Yeah, so fuel moisture content is the amount of water in the plant.

IRA FLATOW: And what have you observed about the vegetation this year?

CRAIG CLEMENTS: Well, because of the low precipitation we had this last winter, our fuel moistures, mostly across the state, particularly in Northern California, are below normal. And so that’s indicative of what we can maybe think about this summer. Generally, April, we have the highest fuel moisture content of the season. And what happened April 1, when we went up to the site, I was actually training the scientists on how to clip fuels, because it’s usually very easy in April because there’s new growth. And the new growth is bright yellow, bright green, and you can really determine where that is versus what we call old growth, which is the plant that’s from last year.

And we went up there in April. We didn’t have any new growth. And so that was quite surprising.

Eventually, April 15, we had new growth, so just a couple weeks later. But that new growth moisture content wasn’t as high as it was. So fuels just– they didn’t get the moisture. The soil moisture is really low. So that’s why they’re stressed out and struggling.

IRA FLATOW: And so how much water is in those living plants? What can it tell you?

CRAIG CLEMENTS: It can tell us their flammability. So as you probably know, if you try to start a campfire, you always try to find the most dry kindling and the most dry logs. If you’ve ever tried to start a campfire with wet logs, it doesn’t work very well. And so that’s the same thing with a wildfire. If the fuels are wet, if they have a lot of moisture content, then it’s harder for them to burn.

IRA FLATOW: Wow, so how could this impact the fire season in California this year?

CRAIG CLEMENTS: Well, typically, our peak fire season is in August and then in fall, when we have a lot of what we call offshore wind events, our Santa Ana winds and the Diablo winds in Northern California. And so that coincides with the minimum in fuel moisture content of these plants.

So we’re starting off at a deficit already. And so that’s the problem. We could have larger fires earlier in the season than we typically would expect.

And we’re already seeing grass fires take off in early May, when we usually get those late May, June. And we had a red flag warning already for Northern California. So we’re already getting into fire season.

IRA FLATOW: So this portends for a pretty bad fire season again, if I’m reading you correctly.

CRAIG CLEMENTS: It could be. I mean, obviously, we have to have the ignitions. Without the ignition, we don’t have a fire. But if we do have an ignition, it is anticipated these fires could get quite large quickly.

IRA FLATOW: There are lots of other variables that go into determining how the fire season will go. Can you give us an idea of what other indicators you will be watching for?

CRAIG CLEMENTS: One thing that we’re looking at, and one of our researchers at our center has produced a kind of preliminary model based off some previous research that was published showing that maximum daytime summer temperatures are an indicator for large fire growth. So we can look, actually– we can try to predict what we expect the summer season to be. Is it going to be slightly warmer? Is it going to be slightly cooler? And if that’s the case, we can kind of say, well, it looks like it might be more normal.

So our indications show that we could expect a just slightly above-normal summer in terms of area growth of fires, how large the fire is going to get. But that just depends on how the weather pans out. And one thing about wildfires is that their size and their behavior is a function of the fuels they’re burning, the atmospheric conditions, and whether the terrain’s very steep and complex and there’s a lot of topography.

IRA FLATOW: We’ve always heard in years before, when we’ve talked about the future of California wildfires– we’ve always looked backwards a bit about the snowpack from the season before in the wintertime. How much effect is that having this year, and was it a good year for snow? And will that affect the fire season?

CRAIG CLEMENTS: It was not a good year for snow. We had a very low snowpack. I think April 1, we were around 38% to 40% of what is normal for the snowpack.

IRA FLATOW: Wow.

CRAIG CLEMENTS: Yeah. And so obviously, areas that don’t receive snow aren’t affected by the snowpack. So that would be like coastal California. But when we look at large timber fires, you know, big forest fires in the Sierra Nevada, the snowpack does play a role, because that snowpack should melt slowly throughout the summer. That means that there’s a lot of water, a lot of soil moisture, for those mid-elevation forests. And this year, we don’t have that. So I would think that we’re going to see, if we do get ignitions in the Sierra Nevada, those fires could be more intense because there’s no moisture there.

IRA FLATOW: Are you able to, with all these factors, to create fire prediction systems, you know, that you put this factor, this factor, and we have a prediction?

CRAIG CLEMENTS: Yeah, so actually that comes out of an agency called Predictive Services. And what they’re stating for this year is that June should be slightly normal for most of California, except for Northern California. July, all the mountainous regions are going to be above normal in terms of large fire potential. So that’s kind of what the agencies are predicting, which corresponds with what we’re seeing and what we’re thinking about.

But there’s also other prediction systems that are really related to how we can use high-resolution weather forecasting to model fire behavior if an ignition were to occur. And we interact with other agencies, so it’s not just us that does this. This is a statewide program.

All the utilities have a fuel-sampling program. For example, PG&E, they have, like, 26 sites that they sample twice a month. And so looking at some of their data, and looking at some of our data, it’s all about the same across the state. Northern California and Southern California, our fuel moistures are lower. So if there’s an ignition, if there’s a fire, it could be severe.

But again, we have to have– generally, our most severe fires are associated with large wind events. And so without the wind, you can still get a big fire, because there’s a lot of heat release– and this is something that fire behavior researchers look at, whether it’s a wind-driven fire or what we call a plume-dominated fire. And so there’s a lot of differences. And I think no matter what, if there’s ignitions, we will have some pretty big fires this year.

IRA FLATOW: Do you have any interaction with the power company? Because aren’t they the source, some of those power lines, of the wildfires?

CRAIG CLEMENTS: We do. We actually have a lot of interaction with them. We work with them in a lot of ways. So we actually have contracts for research.

We’re actually working on a new fuel moisture model for the utilities and using satellite data. We sample the fuels, but there’s also new technologies coming online where we can actually look at them using satellite data. That gives us a better view versus our point measurements. So that’s something that is kind of on the forefront of the research. And hopefully, that’s going to be implemented more widely across the state.

But that is used by the utilities. They have a big reason to have the top science, because they have to either shut off their power through public safety power shutoffs, and they have to be aware of what’s called situational awareness, like what’s going on around their transmission lines? What are the fuels like? Is it going to be windy? They have a lot of sophisticated models and a large team of scientists that are looking at this problem daily.

IRA FLATOW: Wow. Well, we’ll have to just come back and check in on you later and see how that’s all going.

CRAIG CLEMENTS: Yeah, let’s see how it happens. I mean, again, things could turn. We could have a slightly cooler summer, and that could really have a positive impact on our fuels and fire behavior. So you know, we have to hope for the best and see how things pan out. But yeah, I think Californians need to be cautious this year.

IRA FLATOW: Good words to end on, Craig. Thank you very much for taking time to be with us today.

CRAIG CLEMENTS: Well, thanks for having me.

IRA FLATOW: Craig Clements, professor and director at the Wildfire Interdisciplinary Research Center. That’s at the San Jose State University in San Jose, California.

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