Ellicott City Double Flood Nightmare: Perhaps Climate Change, But Lots Of Other Factors

Aftermath of Sunday's Ellicott City, Maryland on Sunday.

As I noted yesterday, Ellicott City, Maryland, a charming, historic community not far from Baltimore, on Sunday suffered its second devastating, extreme flood in less than two years.

Raging water tore through the city's downtown, gutting buildings, sending cars careering down through the torrents. One person is missing, and once again, Ellicott City is a terrible disaster zone.

If anything, Sunday's flood was worse than the one in July, 2016. Water reported rose somewhat higher than it did in 2016, nearly reaching the second floor of some buildings. Adjacent Cantonsville reported 9.71 inches of rain Sunday, nearly twice the amount that should have fallen in the entire month of May, says Accuweather. 

Accuweather also reports that the Patapsco River near Catonsville rose above 17.8 feet in less than two hours, setting an all-time record at that spot.

CLIMATE CHANGE?

Floodwaters crash through Ellicott City, Maryland on Sunday

We're often told that climate change is bringing about more, and more frequent weather extremes. Is climate change to blame for Ellicott City's double nightmare in 2016 an 2018?

It might be one factor, but there are surely other things going on as well. And most of those other things have nothing to do with global warming.

But I will start with the climate change question. It's impossible, or at least nearly so, to blame one isolated weather event, like Sunday's Ellicott City disaster, on climate change. The only thing we can say is the extreme flood is consistent with climate change.

Here's why we can say that: A warmer atmosphere can hold more water vapor than a cooler one. For every degree of warming, the amount of water vapor the air can hold goes up by roughly 7 percent, says the Center for Climate and Energy Solutions.

That extra water vapor makes the potential for downpours greater, and can make those downpours more intense than they otherwise would be.

Extreme downpours are already becoming more common because of this added atmospheric moisture. The 2014 National Climate Assessment says that between 1958 and 2012, the number of extreme rainfall events increased by 71 percent in the Northeast, 37 percent in the Midwest and 27 percent in the Southeast.

Devastation from Sunday's flood in Ellicott City, Maryland 

Ellicott City on Sunday was certainly an extreme rainfall event. Which means it's possible that the downpour there was worse than it otherwise would have been without climate change.

Both the rainfall rates in 2016 and 2018 are considered once in 1,000 year events, so that's something to note.

A note on that: There's some dispute as to whether either flood was a 1,000 - year event. Slight changes mean big differences in the ratings. According to the Baltimore Sun, some meteorologists consider the 2016 flood a one in 75 year event in terms of rainfall, and Sunday's storm a one in 200 year event.  

That said, there have always been extreme rainfalls, with or without climate change, so the Ellicott city downpour was at least partly dumb bad luck.

OTHER FACTORS

As I noted, there are other very big factors that contributed to Ellicott City's flood, both on Sunday and going back through history. These factors have nothing to do with climate change.

Downtown Ellicott City is in a lousy place. It's along a river, and if flanked by steep hillsides. During heavy downpours, water sweeps down these hills, and has nowhere to go but into the river that goes through downtown Ellicott City. If the river goes over its banks, the city floods. Part of the Main Street in Ellicott City is a fairly steep hill, so the water rushes through.

Ellicott City has been through devastating floods frequently - in 1768, 1817, 1847, 1868, 1901, 1917, 1923, 1952, 1952, 1972, 1975, 1989, 2011, 2016 and now 2018. They shouldn't have built Ellicott City where it is. (However, the 2016 and 2018 floods were the worst, or nearly the worst of the bunch.)

The population in and around Ellicott City has gone up tremendously in recent decades. Undeveloped land consists of fields and forests,  and heavy rains can partly soak into those areas, minimizing the amount of runoff headed toward Ellicott City.

Now, there are so many more parking lots, streets, roofs and other impermeable surfaces than there once was. Which means every time it rains, there's more runoff than there used to be. Which means nine inches of rain in one afternoon would create a worse flood in 2018 than the same storm would have caused 100 years ago.

Ellicott City had barely recovered from the 2016 flood. FEMA had just announced earlier this month that the community had gotten a $1 million flood mitigation grant, which we now learned came too late.

Everybody in Ellicott City must be terribly demoralized today. I do hope the city can recover, and I also encourage local, state and federal governments to find ways to minimize the inevitable future floods there.