BYU professor: people need to understand water system limitations
BYU professor Rob Sowby teaches and studies environmental engineering, urban water infrastructure and sustainability. He has particular expertise in the planning, design, construction and operation of public water systems. That expertise has been increasingly important (and regularly sought out) in the wake of apocalyptic wildfires that have taxed those public water systems. In this Q&A he explains how the water systems people assume can save us from disaster were never meant for such a task.
Q: The Maui and Los Angeles wildfires were catastrophic. What caused those two fires to be so devastating?
A: Both fires started in the mountains and spread downhill to populated areas near coasts. The main drivers were major winds and dry vegetation. Water was a limitation in both: In Maui, power outages prevented more water from being pumped; in Los Angeles, the fires were so extensive that water couldn't suppress them. Exceptional rain in Los Angeles last year was followed by nine months of drought leading up to the fire. California fire season peaks in July; a January fire seemed to catch everyone off guard.
Q: What are other factors in the challenge to contain wildfires? Does urban expansion play a role? What about climate change?
A: Urban areas continue to encroach on wildlands. These interfaces often have dense vegetation, wind exposure, tight structure spacing, small water tanks, and steep, narrow roads, all of which increase fire risks or limit response. In a changing climate, conditions may be hotter and drier than in the past, drying out vegetation that is ready to ignite.
Q: In the wake of the LA fires in particular, people pointed to supposed weaknesses in the water infrastructure. What were the criticisms?
A: Critics questioned why fire hydrants were going dry in an emergency. The criticism reflects poor understanding of how public water systems work. A fire hydrant is not an unlimited supply of water; it's just the most visible endpoint of a largely hidden system whose main purpose is to provide reliable drinking water every day, not extinguish a wildfire.
Q: U.S. water systems are typically engineered to support brief, localized fires. How much water can they provide for how long?
A: Water systems serving residential areas are designed to supply fire flows of about 1,500 gallons per minute. That might be one or two open fire hydrants. Larger buildings like offices and warehouses require more, perhaps 4,000 gallons per minute. But any fire flow is an extreme case that can be sustained only for a few hours. In the Palisades fire, where 11 million gallons of stored water drained in half a day, the flow was about 15,000 gallons per minute— 10 times the typical residential fire flow.
Q: Why not increase fire flow standards?
A: Fortifying water systems this way would require 10 times larger water sources, 10 times larger tanks and 10 times larger pipes. It's prohibitively expensive and intrusive to satisfy a demand that happens very rarely in any given area. U.S. fire flow standards are already higher than many other countries', but we're not necessarily any better at putting out fires. Water is not always the limiting factor in firefighting.
Q: It seems like a big part of this is managing expectations of the public when it comes to water systems. To be clear, tell me what water systems can and cannot do when it comes to firefighting.
A: Public water systems are meant to reliably supply clean drinking water round the clock. They can also help fight brief, isolated fires. But once more than a few hydrants are opened in the same area or when a fire lasts longer than a couple hours, the water simply runs out. They can't operate in that extreme range for long.
Q: What can we learn from these incidents to help us prepare for future fires?
A: Land use planners ought to limit development at wildland-urban interfaces and help potential residents understand the risks of building there. Further, fire protection guidelines caution against depending on a single safeguard like a public water system. Structures may also need to have fire sprinklers, fire-resistant building materials, and clear space around them.
Sowby recently presented on his research at The National Academies of Sciences, Engineering and Medicine spring meetings. To read more about his research on water systems and wildfires click here.
