What if floods are part of the new normal in San Francisco?

We have all been conditioned over the past few years to think about the future of California as dry. Drought looms over every major development policy decision: The Central Valley and the South need more water, the governor wants more dams, the Colorado River is drying up, large parts of the Southland can’t survive as they are today without more water that doesn’t exist.

That’s very real. Climate models suggest that water is going to be a serious problem in the Western United States, maybe enough a problem to jeopardize not just growth but the massive existing agricultural system that provides food, particularly produce, for the entire nation.

Ah, but the Climate is tricky—we know humans are heating up the planet, and that our global ecology will change, but on the local and regional level particularly, we don’t know exactly how.

It’s entirely possible, for example, that both drought and floods could be part of the future of California. It’s possible that what we have seen in the past several days, and what we will see more in the next few days, is not going to be an anomaly, but a new normal.

That is: Short-term winter flash floods, perhaps devastating, combined with long-term water shortages:

The short answer for why these seemingly opposite things are happening at once is that climate change is making our atmosphere thirstier. Or, in more scientific terms, as the Earth warms, its atmosphere can hold more water vapor. This happens at an exponential rate: The back-of-the-napkin math is that the atmosphere can store about 7 percent more water per degree Celsius of warming, and we’re currently at about 1.2°C above pre-industrial temperatures. The result is an atmosphere that takes longer to get saturated with water, which means fewer rainstorms, but when they do occur, those storms dump more water at once, resulting in floods.

As I noted yesterday, San Francisco was unprepared for the New Year’s Eve flooding. The city may be slightly better prepared for the mid-week repeat, just because we now know what to expect—but if this is going to be part of the city’s future, and not just a rare event, it could impact a whole lot of decision, including city planning.

Just one example: On Thursday/5, the Planning Commission will consider a proposal for a six-story building with 64 housing units at 98 Pennsylvania Street. Right now that’s a parking lot on the edge of Mission Bay.

That site was pretty wet this weekend, and just a few yards away, an I-280 Freeway ramp totally flooded, stranding motorists and leading to a shutdown of the freeway. I saw it; the water rose really fast and nobody was ready.

Is it safe to build according the current plans, with an underground garage, in what could soon be a major flood zone?

That was never discussed when the project was first approved in 2016, but never built. The current Planning Department approval memo mentions the word “flooding” only three times, in passing, and in every case dismisses any concerns.

The SFPUC and Planning Department’s 100-year flood map, which is supposed to show the areas vulnerable to a flood that would happen once a century, misses areas that flooded this weekend:

San Francisco has paid out substantial sums of money to businesses and landlords in the past because the city’s sewage and drainage systems couldn’t handle (rare) flooding, particularly around the 15^th and Folsom area.

In fact, the city’s sewage system is still a hybrid, which uses some of the same culverts and pipes for storm water and wastewater, which means during the most serious floods raw sewage can get discharged into the Bay.

The SF Public Utilities Commission has been making big strides over the years to reduce that problem—but the existing infrastructure isn’t set up to handle the kind of flooding we saw in the past few days, not on a regular basis.

Maybe this is just a freaky wet winter; we’ve had them before. Maybe we should be a lot more worried about drought than flooding, and just deal with the odd downpour now and then.

But what if this isn’t an isolated event? Add in king tides and sea-level rise. What if the city needs to be ready for severe flooding every winter?

That’s a big deal. Because we are not.