The Wildfire-Urban Interface

Most of California has a Mediterranean climate.

  • Mediterranean climates are those found on the west coasts of continents in the subtropical/temperate latitudes (usually between ~30°N or S and ~40°N or S.

    [ global map of Mediterranean climates, UC Master Gardener Program 
of Sonoma County, http://ucanr.edu/sites/scmg/, now WayBack Machine ]

  • They feature what is essentially a two season climate:

    • Cool or mild and rainy (sometimes snowy in the mountains), with storms brought in by the Polar Jet Stream aloft and the Prevailing Westerlies at the surface.

      • The storms are typically triggered in high latitude oceans (such as near the Aleutians), where there's a sharp contrast between the extreme coldness (and dryness and high density) of the high latitude continents (e.g., Siberia, Canada, Greenland, Antarctica) and the much warmer, moister, and less dense air that forms over such warm currents as the North Pacific Drift or the North Atlantic Drift (or, in the Southern Hemisphere, the West-Wind Drift off the coast of Antarctica). Here is a generalized map of the world's ocean currents: http://images.slideplayer.com/16/4898370/slides/slide_1.jpg

      • A sharp contrast in air mass properties, such as cold/dry versus warm/humid, leads to air instability and low pressure centers, and these will move eastward under the influence of the Polar Jet and the Prevailing Westerlies, giving us (sometimes, kind of unreliably) a rainy, mild winter.

    • In summer, the heating of the landmasses means that the continents are now much hotter than the slowly-changing oceans, especially at our latitudes.

      • In fact, the global ocean circulation puts a cold current right offshore on the west coasts of continents (as anyone knows who's swum off the Jersey Shore (Gulf Stream) and then tried swimming off Malibu and met the California Current without a wetsuit!!!).

      • So, there's a really sharp contrast between hot continents and cool or cold ocean water that can't evaporate a lot of water into the atmosphere.

      • This configuration favors sinking air out at sea, which warms and dries, and pushes airflow onto the continents (at first, bringing us "June gloom" in coastal California and, later, sticky monsoonal air). This condition of sinking, warming air expands and eventually moves onshore in the summer, giving us a taste of life in the Sahara Desert (where the air sinks, dries, and warms pretty much all the time).

      • And that gives us our characteristic summer drought, which can go on for six months!

The Mediterranean climate is particularly challenging for plants

  • The optimal time to photosynthesize is the summer, in most climates: High sun angle and plenty of water. Here in California and other Mediterranean climates, plants have to try to do a lot of their photosynthesis in the winter, when water is (or may be) available, and sun angles aren't that low in our subtropical location. It's less efficient but there's not much in the way of choice for them.

  • Summer is really awful for plants in Mediterranean climates. They have to "worry" more about water loss through transpiration (water intake for photosynthesis, water evaporation and loss through respiration) than about making food.

  • So, they give up features that would promote efficiency in photosynthesis in exchange for adaptations that help them reduce water loss (and none of their competitors are in any better shape, so they're not losing a competitive advantage):

    • Some, especially in chaparral, have really deep root systems. You see them in road cuts, some meter high non-descript plant, with roots going down something like 15 meters.

    • Others, especially in California sage scrub (CSS), have dense shallower roots, ready to catch any stray moisture that hits the ground from coastal fog-drip or the occasional summer thundershower inland

    • Both chaparral and CSS have high root to shoot ratios: The vast bulk of their biomass is underground (this becomes important in a bit).

    • Sclerophylly (tough, leathery leaves with fewer stomata for transpiration, more common in chaparral than CSS)

    • Reduced size (think of a California oak with its small leaves versus an oak Down South with its large leaves)

    • Dense, tough bark (think of Spain's and Portugal's cork oaks and our own manzanitas, those weird shrubs that look like their branches were dipped in molten red plastic)

    • Sometimes a greyish color formed by a faint fuzz on the leaf surfaces, which provides micro-shading and reduces wind speed over the leaf surface, as seen here in purple sage (Salvia leucophylla)

    • Sometimes a greyish color formed by a waxy covering (think of eucalyptus), which also retards water loss, as seen here in big-berry manzanita (Arctostaphylos glauca)

    • Many of the plants have oily leaves, sometimes to discourage predation, sometimes to reduce water loss (like slapping lotion on your face and( hands in really dry weather), and sometimes to "snuff" the seedlings of plants trying to establish in their root zone (chemical warfare among plants or allelopathy), which is why these vegetations often smell so great, so spicy, something I really missed when I moved to Massachusetts years ago!. An example of a strong-scented plant in chaparral and CSS is California sagebrush (Artemisia californica), sometimes called "cowboy cologne"!

    • Some CSS plants have "facultative summer deciduousness." They can drop their leaves if the summer is really bad -- or keep them if conditions are tolerable (California encelia does this). This is really unique, as true deciduousness is genetically linked to the onset of winter, but these plants have "figured out" how to game the system and show some degree of control over it.

    • If you would like to learn more about the plants in your area (in California), Calflora has a wonderful resource called What Grows Here?. You can search by area or by plant names or life forms (tree, shrub, herb, etc.). You'll get lists of species that fit your criteria, with basic desciptions, links to more information, and photos.

  • Now, here's the kicker: The Mediterranean scrub vegetations are not only adapted to the summer drought, but they are also well-adapted to the late summer and fall fires that are also a feature of this climate régime. And this makes life in California "interesting."

Chaparral and CSS adaptations to living with fire include:

  • The high root to shoot ratio:

    • Even if every scrap above ground goes up in smoke, the plant itself often can survive because most of it is below ground.

    • Many species, such as toyon, lemonadeberry, sugarbush, and laurel sumac, just resprout from their charred stumps.

    • In a manner of speaking, a fire sort of prunes the plants of deadwood, the way we prune rosebushes, and thereby reinvigorates the plants.

  • Other species, such as those belonging to the Ceanothus genus, produce seeds that cannot germinate unless they've been charred and cracked by the heat of a fire!

    • They generally cannot reproduce without fire.

    • Fire produces a cleared landscape with access to plenty of sunshine, reduced competition, and the conversion of old biomass to ash fertilizer, so these plants' strategies make sense. They place their "babies" in conditions that are optimal for their survival into adulthood.

  • Since fire renews some adult plants through resprouting and allows other species to germinate, it's almost as though the chaparral and CSS depend on fire to one extent or another. Depending on fire, it's in the plants' interest to make sure fire eventually takes place.

    • One mechanism of doing so is the steady accumulation of deadwood above ground and decay-resistant, often somewhat oily or waxy, litter on the ground.

    • Fuel accumulates through time and that can increase both the probability and the magnitude of the next fire.

    • Chaparral, particularly, has been described as a pyrogenic vegetation.

  • Successful firefighting, then, would seem to increase the risk and magnitude of wildfire by allowing fuel to increase.

This is the nub of the "firefight" between Richard Minnich and Jon Keeley, the authors of this week's readings.

  • Minnich's argument:

    • He feels that the epic, landscape-clearing firestorms we've seen the last several decades are actually something new in the California fire ecology.

      • He thought that references to these kinds of fires were sparse in the nineteenth century newspapers, on the one hand.

      • On the other, he analyzed fire scars in the then-new Landsat imagery of Southern California and northern Baja California and reported very different spatial patterning of fire on either side of the border.

        • On the Baja side, he saw small patches of fire

        • On this side, he saw some really huge patches.

      • In trying to explain the differences across the international border, he argued that fire management practices are entirely different

        • The Mexicans pretty much leave most fires to just burn as they will, without intervening, and that creates a fine-grained patchy mosaic.

        • Americans apply heavy-duty fire suppression, which only lets the fuel build up until, one day, one fine Santa Ana sets the whole country ablaze, leading to very large, very hot landscape-clearing conflagrations.

      • He concluded from this that heroic firefighting measures only delay the inevitable and make it much, much worse when it does, finally, hit.

      • In terms of fire hazard management policy, he argues for trying to use controlled burning in the early summer to recreate a fine-grained patchy mosaic that he feels would starve huge wildfires of fuel.

  • Keeley and his colleagues beg to differ, and they differ about everything Minnich has ever said:

    • Policy

    • Claims about fire behavior and cultural fire history

    • Data and methods Minnich used to make his argument about the ecological effects of trying to burn the chaparral and CSS more frequently

    • They claim he cooked the Landsat analysis by including two huge fires that were not part of the years the Landsat images covered -- they even experimented with taking those fires out and said that the resulting maps made the international contrast go away

    • They claim that the nature of the winds and precipitation in Baja are quite different from Southern California due to differences in topography and position with respect to global circulation patterns

    • They claim that old newspapers are so spotty in coverage as to be useless

    • They also point out that a lot of Minnich's analysis about the frequency of fire depend on lightning, but lightning, while common in the desert-facing slopes of the San Bernardinos, is almost unheard of in the Santa Monicas and other coastal locations. Fire ignitions there are almost completely human-related and were even before the Spanish came to California: The Native Californians were active fire users and landscape managers.

    • Some scholars allied with Keeley (e.g., Max Moritz) have taken Minnich to task about the importance of different aged patches of chaparral.

      • They claim that meteorology is far more important than the age of the vegetation and how much deadwood is in it.

      • If you get a bad enough Santa Ana condition and a fire starts somewhere, you'll get a landscape-clearing firestorm no matter how old or young the vegetation is.

      • They very fundamentally question the argument that fire probability and magnitude increase through time. If the right weather comes along, old and young chaparral and CSS go up.

    • Keeley and some other people have argued that too-frequent fire is a very bad thing in chaparral and CSS.

      • If it recurs more than about every 5 years, you get "type-conversion," or wholesale replacement of scrub vegetation with annual grassland.

      • Annual grassland in California is almost exclusively comprised of exotic (non-native) species and it comes with problems of its own.

      • It is really susceptible to invasion by particularly aggressive non-native species.

      • It produces a pattern of light and dry fuels that very fundamentally change the fire régime, making for even more frequent fires, to which they are better adapted than chaparral or CSS. The grasses are overwhelmingly annuals and they go through their whole life cycles, from germination to seed-setting and drying out/dying off in the winter and spring, before the onset of summer and fall fire season. So, a fire is no biggie for them: They're already dead, their seeds waiting in "suspended animation" for the winter rains. The light, fast-moving fires in grass tend not to get hot enough to kill all their seeds. The shrubs of chaparral and CSS are longer-lived and slower-growing, so too-frequent fires eventually just wear down their ability to recuperate and reproduce (and the fires will get really hot once they get into the shrubs), thus shifting the balance of competition to the short-lived annual exotics. This is what produces type-conversion.

      • Annual grassland in California is susceptible to invasion by such pests as yellow-star thistle, assorted other thistles, fennel, black mustard, and all kinds of other critters, and some of these are really impressive at building up huge amounts of bone dry fuel in just one season.

    • Policy-wise, Keeley and his partners feel that money spent in early-season "controlled" burns is money wasted:

      • The right kind of Santa Ana-driven firestorm will burn it all anyhow.

      • They point out that it is very hard to "control" burns in chaparral and even CSS, which makes the practice quite dangerous in the Wildfire-Urban Interface or WUI.

      • And it leads to landscape invasion by even worse exotics.

    • In fact, they endorse heroic firefighting efforts to suppress wildfire, claiming that "human subsidy of fire ignitions" is making fire too frequent.

      • That is, fire ignitions are not the result of lightning in the Coastal, Transverse, and Peninsular ranges of California but the result of human activities, accidental and intentional, that are, statistically, simple functions of human population density.

      • The more people, the more fire.

      • There are now so many people and so many ignitions that heroic and suppressive firefighting is necessary just to keep things kind of "natural" in term of fire régime!

    • Can't get any more different from Minnich than that!

Now, as we discussed earlier, risk assessment science and risk management policy are two distinct functions that have to interact with one another but which are sometimes at cross-purposes in the best of situations.

  • Even when science is clear about the mechanisms behind a given hazard and can clearly quantify risks, getting that message to effective risk management levels is contentious and risk managers, particularly elected ones, can be quick to cherry pick among scientific findings to suit a prior commitment to the precautionary principle or the de minimis principle. We're seeing this sort of thing in the climate change arena, for example.

  • But what is the take-away message when the scientists themselves are at fundamental loggerheads? This is a situation that can encourage mistaken policy, no policy, or that wonderful political tendency to kick a can down the road into the next administration.

Here are my own impressions about the fire biogeography situation.

  • I think there is some merit to the idea that the longer chaparral goes without fire, the greater the fuel load, meaning a hotter fire once it does go up. In this sense, I agree with Minnich.

  • I agree with Keeley and Moritz that meteorology is a far more significant factor in the creation of huge landscape clearing fires, coupled with human ignition sources.

  • I'm not completely convinced about the type-conversion argument. Some fieldwork I've been involved with the last few summers suggests that CSS, at least, is capable of re-invading grassland even with frequent fire: What stops it cold is not fire but mechanical disturbance of the soil. If a plot was plowed even once many decades ago, you can still spot it in the patch of invasive species dominating it (we've seen this in the Palos Verdes Peninsula, the Santa Monica Mountains, and the Sepulveda Dam basin in Southern California). I don't think the type-conversion argument is wrong, but it needs to account for our discordant data.

  • I don't think the magnitude-frequency relationship for chaparral and CSS wildfires can be worked out to everyone's satisfaction, either here or in northern Mexico, because the kind of data used to reconstruct fire histories before record-keeping is not available: You can't do tree-coring, for example, when fire completely destroys all above-ground vegetation. All other proxies are too imprecise in spatial and temporal resolution to give us the information we need to do these magnitude-frequency analyses. So, a lot of the fighting on this particular point is actually kind of like "how many angels can dance on the head of a pin?"

  • I agree with Keeley and his partners that the whole idea of trying to mimic some undiscernible and perhaps romanticized fire history with controlled burns is probably a waste of time and money and an additional hazard, given that "controlled" burns here often aren't.

  • I agree with Keeley and his partners that human ignitions are far, far more important than lightning ignitions anywhere near the coast and they always were, during the Mexican era here and the Spanish era before it -- and during the time of the Native California Indians, too, who were firebugs, too.

What I think is a far more important issue than either Minnich or Keeley has spent much time on is the question of human occupance of the WUI. For a hazard to exist, you have to have an intersection between natural forces and human beings. Dealing with the human side of this equation is THE big issue and, oddly enough, it is the one that Minnich and Keeley can agree on (and I've talked it over with Keeley). From a hazard management point of view, it is completely insane to allow further residential development in the WUI. It only guarantees the intersection of people with unstoppable natural forces and, indeed, contributes a lot of human ignitions to the fire régime. It endangers firefighters' lives and it costs buckets of taxpayer money to subsidize dysfunctional residential choices.

  • What really frosts me is the social geography of the situation. Here, the people most at risk to chaparral and CSS wildfire are not the poorest members of society like you see with so many other hazards, where people who have no choice are relegated to the most dangerous environments. No, these are the wealthiest people in California, choosing to buy homes with spectacular views, which means in the mountains, which means in Mediterranean scrub vegetation, which means in the "fire frontier."

  • Even though the risk falls disproportionately on the well-to-do, they are rarely vulnerable to this hazard (except when they do sometimes suffer death, injury, or bereavement by wildfire, which can move far faster than people can drive, ride, or run). They have means of outsourcing much of their vulnerability or, more precisely, externalizing its costs. The benefits of living in the WUI are privatized, but the costs are socialized:

    • Tax moneys spent on fighting fires and buying equipment to fight fire and leasing Canadian aircraft to fight fire.

    • Firefighters' lives are needlessly endangered, too: the grimmest subsidy of all.

    • And then there's the insurance mechanism. Insurance companies are not stupid: They will do everything they can to avoid issuing a fire policy for a home in the WUI. And even wealthy people need to get a mortgage to buy a home, and mortgage lenders require fire insurance. So, if you try to buy a home up there, you will be denied coverage, and that threatens your ability to get a mortgage.

    • Not to worry, though. Once you collect three fire policy rejections, you trot over to the State of California FAIR Plan (http://www.cfpnet.com/ ). This is an assigned risk pool, kind of like how really bad drivers get insurance. The State requires all insurance companies writing policies in California to participate in the Plan. They must accept homes randomly assigned to them from the Plan to a level proportionate to their market share in California.

    • The real beauty of the Plan, however, is that the insurance premium must be "affordable." This means that the insurers are not allowed to charge the level of premium necessary for them to recoup the exposure they're taking on. So, given that they're not in the insurance biz for charity, where do you suppose the money for that risk exposure comes from? Yes. Everyone else's fire and other policies have to be raised enough to ensure the company has the assets to pay claims from their FAIR Plan policies during a firestorm.

  • So, that's why I wound up having to differentiate risk from vulnerability in an old study I did on chaparral fire hazard (https://home.csulb.edu/~rodrigue/fire.html ). The risk hits the well-to-do, but most of the vulnerability is shifted to other taxpayers and insurance policy holders (not to mention firefighters) in a hidden upward income transfer. Without that veiled upward income transfer, a "home with a view" in the WUI would not be economically feasible even for very wealthy people.

  • It gets even better. There was an old study of flood risk (Sorkin, Alan. 1982. Economic Aspects of Natural Hazards. Lexington, MA, and Toronto: Lexington Books) that talked about how individual households do a kind of calculus on the costs of living on the floodplain and the benefits of living there. If insurance is available and if the premia are not fully recouping the assets at risk, this lowers the household's perceived cost:benefit ratio, making life in the hazardous area that much more desirable. As many households shift their cost:benefit perceptions, the value of that land increases, because so many others are now desiring it. One response to an increase in land value is subdivision into more, smaller lots -- and exclusion of the poorer households no longer able to pay the land costs. This means that population density increases and the number of people at risk increases (and their social status increases)! This is a perverse result of insurance premia that are too low for a company to recoup its losses in flood claims. I suspect a similar, probably stronger calculus occurs in the WUI because of the State FAIR Plan. This might make a rather nifty thesis for somebody one day, tracking down the disparity between insurance premia and home values to test the idea!

  • Anyhow, the situation of population densification in the chaparral/CSS WUI is creating large scale social vulnerability while privatizing the benefits of life in the WUI.

    • The obvious solutions include rezoning these areas to discourage further residential development ... and gradually making the State FAIR Plan, well, fair.

    • As obvious as these solutions are, however, they are politically unrealistic: Real-estate developers and homeowners' associations are quite influential in municipal, county, and State politics, and they really do not want this issue resolved.

    • Why should they, given everyone else is paying for it unawares?

  • Biogeographers and ecologists have been aware of the fire ecology of chaparral and CSS for decades now, and some of the social ironies involved. Mike Davis tried to bring this to public attention in his books about Los Angeles, one with a chapter having the catchy title, "The case for letting Malibu burn"! You would not believe the character assassination campaign directed against him for this, led by none other than a Malibu realtor posing as a historian with a fake name. Mike Davis started getting death threats. Chaparral wildfire hazard is a politically explosive issue in California! Here's a link to an article I did on that http://www.colorado.edu/hazards/publications/wp/wp106/wp106.html

  • Removing the perverse effect of fire insurance might provide enough of a sticker shock to make some people reconsider living up there -- and might make the rest more informed about their risk and willing to do something to mitigate it. And there is a lot that the household and community can do. It is possible to live in the WUI with greater safety and less dependance on social subsidies.

  • Jack Cohen is a fire behavior modeller at the Missoula Fire Research Center in Montana.

    • He has established the distances from a wildfire's flame wall beyond which the heat of the fire cannot ignite the walls of a home.

      • It's a probabilistic concept, depending on such factors as the specific construction materials of which the home is made and the intensity of the fire itself, and it obeys a distance-decay function.

      • That is, the probability of ignition from direct radiation and conduction declines exponentially from the firewall, tapering down to near 0 past about 20 m or 66 feet.

      • To utilize the precautionary principle, that works out to trying to keep flames at least 30 m (100 feet) away from a home.

      • To exploit this idea further, it draws our attention to the materials surrounding a home going out about 60 m. If you want to keep the firewall back a safe distance, you need to look at how well landscaping within the 60 m functions: Does it let the fire establish a small beachhead in the 30 m zone from which temperatures just hot enough to light the home's walls might emanate? Does it provide a ladder letting the cooler flames going across a lawn or other ground-cover find a way to climb shrubbery onto the house? Does the landscaping use plants that might explode like a Roman candle and provide the necessary close-in heat?

    • Besides radiative and conductive heat transfer, the other big source of structure ignitions is the brands of burning material that are carried in the wind and deposited well in front of the firewall itself.

      • These can settle on a home's roof, deck, welcome mat, windowsills, or what have you and quietly transfer their energy to the building, eventually producing the conductive heat transfer that can ignite whatever it's sitting on.

      • Thinking of this, Cohen points out that there are all kinds of things that can be done architecturally and in terms of non-structural mitigations to make sure that embers don't find something easily ignitable to land on.

        • Shake rooves, of course, are the worst offenders. They're illegal in most California communities but not all. Where it's illegal to build new homes with shake rooves, they are usually not mandated to be torn out (though San Bernardino County is requiring them to be taken out and reroofed). Where existing shake rooves have been grandfathered in, it's okay to "repair" them, which means replacing no more than 20% of them each year. Soooo, there are all kinds of idiots out there, reroofing over a 5 year time frame instead of finding similar-looking fake shakes that aren't fire hazards or just going for comp. roofing. The saga of attempts to rein in wood shake rooves against all kinds of political resistance is chronicled in an archive on the topic in the Los Angeles Times: http://articles.latimes.com/keyword/wood-roofs. Why anyone wants shake rooves is beyond me, personally: I think they're ugly and they are always needing little repairs and they seem to be real rat-magnets, but I digress.

        • A surprising finding is that a lot of homes in the WUI go up because of something as inconspicuous as a hemp or sisal "Welcome" mat out on the front porch!

        • Wooden decks cost many homeowners their homes, particularly if there are any light fuels (like mats) on them.

        • Eaves are a surprising offender. In California, it's normal to put fairly extensive eaves on a home to take advantage of shade in the summer and yet let in light and heat in the winter. These wonderful passive solar systems, however, also create vortices under them, between themselves and the walls of the home. These trap embers and sometimes shoot them through soffit vents into the attic, where they might burn a house down long after the wildfire's gone through! If you're going to live in the WUI, Cohen suggests not building homes with eaves and even having them cut off existing homes. At a minimum, he suggests covering all soffit vents with very fine mesh, kind of like mosquito netting or window screens (now there's a home improvement project to ruin more than a single weekend if you've ever futzed around in your attic trying to insulate better....).

    • Homeowners in the WUI can do an awful lot with landscaping to keep the firewall back, and it's more than just creating the "defensible space" that firefighters need tactically in an incident. And they can modify their homes structurally (no eaves, swap out the rat-trap roof) and non-structurally (don't forget to pick up that welcome mat when a fire's bearing down on you)

    • Unfortunately, our insurance and social subsidies discourage homeowners from really looking at their situations and, if they choose to live up there, managing their risks far more effectively.

    • Here is the Missoula Fire Laboratory web site: http://www.firelab.org/ , and you can do an online search on "Jack Cohen fire" to get lots of his stuff.

    • The US Geological Survey's Western Ecological Research Center has a project called the Southern California Wildfire Scenario Project that is working on GIS-based modelling of fire dynamics and providing science-based advice for living with wildfire.

  • Firewise!

    • Another great idea to improve WUI safety for homeowners (and firefighters) and reduce the externalization of costs to taxpayers and ratepayers is community-oriented simultaneous fire-mitigation projects.

    • What good does it do you to fix up your landscaping and redo your home to make it more fire safe, if your neighbors aren't, especially if your lots are smaller than, say, 60 m in all directions from your house? This really is a big disincentive to responsible homeownership in the WUI.

    • So, now there's Project Firewise. This is a community-based project to assess the specific fire hazard in a specific location and engage community leaders, homeowners, planners, firefighting professionals, and even developers to coming up with locally-tailored assessments and mitigation and preparation projects.

    • Communities can try for recognized Firewise Community status and qualify for funding to make the process of community-based fire hazard mitigation easier.

    • Here's their web site: http://www.firewise.org/

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