Explanation of relationship between California fires and flooding

Before New Yorker discovered a surefire path to profitability in continuously reminding readers how much smarter they are than Republicans, the magazine had space for some interesting articles. Back in 1988, for example, they published a series of long articles by John McPhee titled “The Control of Nature”. Given the latest fires then flooding/mudslides in California, a good place to start is “Los Angeles against the Mountains-I”. Here’s an excerpt explaining how the fire blocks subsequent rain from being absorbed:

In the course of a conflagration, chaparral soil, which is not much for soaking up water in the first place, experiences a chemical change and, a little below its surface, becomes waterproof.

In the slow progression of normal decay, chaparral litter seems to give up to the soil what have been vaguely described as “waxlike complexes of long-chain aliphatic hydrocarbons.” These waxy substances are what make unburned chaparral soil somewhat resistant to water, or “slightly nonwettable,” as Wells and his colleagues are wont to describe it. When the wildfires burn, and temperatures at the surface of the ground are six or seven hundred centigrade degrees, the soil is so effective as an insulator that the temperature one centimetre below the surface may not be hot enough to boil water. The heavy waxlike substances vaporize at the surface and recondense in the cooler temperatures below. Acting like oil, they coat soil particles and establish the hydrophobic layer—one to six centimetres down.

In the first rains after a fire, water quickly saturates the thin permeable layer, and liquefied soil drips downhill like runs of excess paint. These miniature debris flows stripe the mountainsides with miniature streambeds—countless scarlike rills that are soon the predominant characteristic of the burned terrain. As more rain comes, each rill is going to deliver a little more debris to the accumulating load in the canyon below. But, more to the point, each rill—its natural levees framing its impermeable bed—will increase the speed of the surface water. As rain sheds off a mountainside like water off a tin roof, the rill network, as it is called, may actually cube the speed, and therefore the power, of the runoff. The transport capacity of the watershed—how much bulk it can move—may increase a thousandfold. The rill network is prepared to deliver water with enough force and volume to mobilize the deposits lying in the canyons below.

More:

[Let’s compare this 1988 piece, just as interesting 30 years later, to what they’ve  published lately:

Who will want to read the above in 2048?]

 

6 Comments

  1. Russil Wvong

    January 10, 2018 @ 6:08 pm

    1

    Fascinating. I checked Google Scholar and found an article discussing this phenomenon: The role of fire and soil heating on water repellency in wildland environments.

  2. wally

    January 10, 2018 @ 7:07 pm

    2

    John McPhee rocks, and it was through my now-defunct NYer subscription that I discovered him. Alas, through that same subscription I also discovered shrill, school-marmish David Remnick. Hence the defunctness.

  3. Jack

    January 10, 2018 @ 9:26 pm

    3

    I gave up the New Yorker decades ago & my recollection is that this same political point of view and smug tone was there when McPhee was writing for them. The golden age of the New Yorker (like the golden age of New York City) was way before the McPhee era.

  4. Rick

    January 10, 2018 @ 9:27 pm

    4

    The McPee book “Oranges” is a delicious read. Wonderful writer.

  5. philg

    January 10, 2018 @ 9:52 pm

    5

    Rick: I’m hoping that “McPee” is not a new McDonald’s product!

    Jack: https://www.newyorker.com/magazine/1988/09/26 is the issue in which the cited Control of Nature article appears. A Presidential election was just a few weeks away yet I can’t see any political content at all.

    https://www.newyorker.com/magazine/1988/10/17 has an article by the now-blacklisted Garrison Keillor and he alludes to the upcoming election, but doesn’t say whom he supports.

    https://www.newyorker.com/magazine/1988/10/31/letter-from-washington-278 is about a VP debate (the Democrat is better/smarter!)

    https://www.newyorker.com/magazine/1988/11/07 has an election cover (teh election was a day later), but less political content than the average issue today.

    https://www.newyorker.com/magazine/1988/11/14 is after the election, but also light on political stuff.

    https://www.newyorker.com/magazine/1988/11/21 is where the writers, having had some time to reflect on King Bush I’s victory (on 11/8), pour out their thoughts.

    Based on these issues I would say that the focus of the New Yorker has dramatically shifted toward politics and toward competing with daily newspapers with stories that immediately follow events.

  6. the Other Donald

    January 11, 2018 @ 3:17 pm

    6

    It’s looking like Montecito is a mistake.

Log in