Little Irma comes to visit Houston

That tiny swirl in the middle of the Atlantic is Irma, coming straight for Houston.  The big swirls set the stage for hurricanes and they are slow to change.  So lots of hurricanes follow the previous.  Whether they get big depends on how much heat energy the previous one sucked out of the ocean.  Harvey only became a 4 just before landing, so Irma may make it all the way to Houston.

Cold air feeds hurricanes

The English major warmies (emw) can't get the idea that cold air is important.  The big thing now is 'warm air holds more water, therefore we get more rain'.  Pooey.  That moisture would stay in the warm air forever if they're weren't any cold air to wring it out.  When I point out that temperatures are falling like a rock, they come back with a 30 year moving average, which no emw uses for their headlines.  It's all 'Harvey is a made-made disaster' due to warmishing.  Okay, let's put 'paving the entire watershed' up against gorming.  Who wins?

Anyway, the hurricane has moved on, but this shows the tremendous storm activity caused by our cold zooming down from Siberia.  This is a neat picture.

The mythical 100 year flood, 100 year wind, 100 year earthquake, whatever

Everybody who designs things, has to think about extreme events.  My main experience is earthquakes, but the same physics applies to flood, wind, fire, etc.

So, in the 30's when most cities were designed, it was a big thing to go with the 100 year event.  That's what you designed for.  Skyscrapers, drainage channels, etc.  In 1954 Toronto was hit with a 12 inch slug of rain and subsequent drainage was designed for that.  However, Toronto has been been hit by several slugs of about 4 to 6 inches, and the sewer system has been unable to take it.  But these were not major flooding events.

The problem with an initial design is that events overtake it.  Houston was theoretically designed for a 12 inch slug, but then they paved the entire watershed.  They get their 100 year flood almost every year now.  Hurricane Harvey with a 50 inch slug of rain was way over the top.

Because of rampant development, nearly all North American cities are getting frequent flooding.  The initial design is irrelevant because they did not stick to a plan.

ps.  I believe that a city should be able shrug off the 100 year event, and recover quickly from a one in 500 year event.  That goes for all causes, including earthquakes.  Yet, time and time again cities are destroyed by the 500 year event.