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:

• the complete Control of Nature series
• book version of the same material

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

• an article on Oprah Winfrey maybe running for President
• “What the Salvadorans Being Kicked Out by Trump Face Back Home”: “Trump’s revocation of temporary protected status threatens to send two hundred thousand people back to one of the most dangerous countries in the world.” (statistically safer than New Orleans and roughly 2X the murder rate of Washington, D.C. according to citylab.com)
• “Under Trump, a Hard Test for Howard University”: “Trump’s nomination of DeVos, a billionaire businesswoman whom Chuck Schumer, the Senate Minority Leader, called the “least qualified nominee in a historically unqualified Cabinet,” was seen as another affront.”
• “The Increasing Unfitness of Donald Trump”: “Chaotic, corrupt, incurious, infantile, grandiose, and obsessed with gaudy real estate, Donald Trump is of a Neronic temperament. … there is little doubt about who Donald Trump is, the harm he has done already, and the greater harm he threatens. He is unfit to hold any public office, much less the highest in the land.” (maybe the smarter choice for American voters was Hillary Clinton?)

Who will want to read the above in 2048?]