It rained a lot today. According to Environment Canada, Toronto's Pearson Airport saw 97.8 mm of rain fall before 2 PM. This is the fifth rainiest day on record; the record being July 8, 2013, which saw 126 mm fall. But today feels a lot like it did in July 2013. The same rivers, streets, and underpasses flooded. People needed rescuing. Cars got marooned. And more than 167,000 customers were left without power. I lost power in the Junction around lunchtime and it didn't come back on until just before 7 PM. That really hurt productivity, although I did manage to get in a workout during the outage.

Sadly, all of this is expected. The thing about air is that its ability to hold water depends on its temperature. For example, according to Nasa, a given volume of air at 20°C can hold 2x the amount of water vapor compared to air at 10°C. So as the earth's atmosphere warms, it is automatically going to hold more water vapor, and that means the potential for bigger and more severe storms. Some scientists predict that for every 1°C increase in atmospheric temperature, we should expect precipitation intensity during extreme storms to increase by about 7%.

This means that flood and water management are only going to become increasingly more important to all cities -- not just the most vulnerable cities like Miami. And it's going to require constant adaption as we figure out how to best manage the climate damage we've done. Of course, it's easy to want to do something about this on days like today when everyone is sharing videos of flooded streets and floating cars. But the trick is continuing to do something about it once most people have forgotten what July 16 was like.

This is a fascinating little experiment:

From Oct. 12, 2020 to Jan. 3, 2021, Redfin ran an experiment on 17.5 million of its users across the US. As prospective homebuyers entered the site, Redfin assigned them randomly to either a group that was shown flood-risk information on each property or a group that was not.

The flood-risk scores came from First Street Foundation, a climate and technology nonprofit that works to make climate hazards more transparent to the public. In June 2020, First Street published the first public maps that revealed flood risk for every home and property in the contiguous US. 

First Street scores properties on a scale of 1 to 10 based on the likelihood that they will flood in the next 30 years (which is assumed to be a typical mortgage term). A score of 1 means the property has "minimal" risk and a score between 9-10 is considered "extreme" risk.

So what happens once you start showing people flood-risk information? They, not surprisingly, start systematically looking for safer properties. After one week of users being exposed to this new information, prospective buyers who were previously looking at "extreme" homes started looking at homes that were about 7% safer.

After 9 weeks, these same "extreme" home buyers were looking at properties that were about 25% less risky. And for some buyers, in particular those working with a Redfin agent or partner, their flood-risk tolerance dropped by over 50%. (Embedded in this data might be a sales pitch for working with a knowledgeable Redfin agent or partner).

Also interesting is the fact that below "severe" flood risk (a score between 7-8), there was very little change in behavior. "Major" flood risk, it would seem, isn't all that concerning to most buyers. It needs to be "severe". Nevertheless, it is noteworthy that people will in fact make behavioral changes when presented with clear climate-risk data.

I spent a good chunk of this morning talking and thinking about underground building details that most people (unless you're in the industry) would never think to consider. This is not a criticism on most people. I mean, I don't know how iPhones are made. I just use and enjoy them. But when it comes to buildings, I'm paid to ask questions and understand how things work.

There's a lot of risk in the ground.

You have to think about things like bearing capacity, environmental contamination (usually), hydrostatic pressure and, generally, how you're going to manage water, particularly if you have a high groundwater table. Usually this last one is about making sure you're keeping the water out. A pretty important detail both below and above grade.

So when I came home tonight and saw the below tweet, I felt obligated to write about it.

If you read the reply from NYC's Metropolitan Transportation Authority, you'll see that this is them testing something they call a "flex gate." It is a flood barrier that allows them to seal off subway entrances in the case of a storm surge and they run these tests (shown above) for 4 hours at a time to make sure they're installed property. This one was.

Managing water is a big part of city building. New York City, Miami, Venice, and countless others know this all too well right now.