Why *did* the hydrants in LA run dry?

[Stranger_On_A_Train]

Water is an incompressible fluid. This means you can only push so much of it through a given diameter pipe at a time, and if you draw more than the system can deliver, the pressure drops precipitously, notwithstanding all of the compromised water lines going into houses that have burned down to the foundation and are leaking any water coming into them. Many of these older developments (which both Pacific Palisades and Altadena are) are already stressing the water systems just because of how built up they have become, and they certainly can’t deliver the vast quantities of water necessary to suppress a massive fire covering thousands of acres of flammable structures and foliage, notwithstanding that there is basically nothing firefighters can do to suppress a firestorm driven by gale-force winds.

From an earlier thread:

@Stranger_On_A_Train

It is also a fact that regardless of how much water is available in reservoirs and fire cisterns, the municipal water supplies (which are not controlled by the state) can only provide so much volume of water at a time before pressure drops cause the hydrants to run dry. Those systems are sized for typical residential and modest commercial use, and in the case of older neighborhoods are often already stressed by the amount of additional housing since they were originally installed. Relying on that system to provide water volume to fight a massive wind-driven firestorm is hopeless, notwithstanding that as houses burn to the ground their own water supply systems fail and release pressure.

The City of San Francisco actually has an entirely separate High Pressure Auxiliary Water Supply System specifically for fire service use because of the history the city has had with massive urban fires (most recently the 1906 earthquake and fire, but also the “Great Conflagration” in 1851 that burned most of the structures in the city to the ground). To install such a system in fire-threatened neighborhoods today would require digging up streets, sidewalks, and lawns at almost incalculable cost, and would still not prevent the kind of gale-force-wind-driven firestorms that consumed Pacific Palisades and Altadena.

As for it somehow being Gavin Newsom’s fault, he doesn’t control municipal water supplies, has limited control over fire abatement measures at the municipal and county level, and CalFire only responds to events when they threaten to cross fire districts.

Stranger