28 May 2018
Just last summer the Baltimore Sun had this story about the historic clock on Main Street in Ellicott City, Maryland. It was rededicated after the devastating “1000-year” flood of July 30,2016 that made national news. That clock was swept away this evening during the second 1000-year flood in two years in the city. Maryland Governor Larry Hogan has declared a state of emergency and rescues are still underway as I write this.
The new GOES-16 weather satellite had an excellent view of the storms before sunset as well:
The damage will be in the millions and there is little doubt about the causes of this flood. If you are thinking an act of Mother Nature, you are wrong. Humans shoulder a great deal of the blame for this disaster.
Look at how devastating this flood was:
Let me start with a paper just published in the AGU Journal Geophysical Research Letters that finds atmospheric rivers of moisture are getting wetter, stronger and longer. I saw some of this research presented at the AMS Annual Meeting last January and it was a powerful talk. These atmospheric rivers show up as gray in the GOES-16 mid-level water vapor image below. Note the connection from the deep tropical Atlantic into the SE U.S. around Sub-tropical storm Alberto.
I wrote a few days ago here about new research showing the connection between Hurricane Harvey’s record rains and our warmer climate. The paper details how the extra 6-7% of water vapor in the atmosphere can make storms larger and more intense, leading to a 30% increase in rainfall.
The location is to blame as well as my friend Matthew Cappucci (who is about to become Harvard Universities first atmospheric science graduate) posted about another major factor in this flood on Twitter:
Ellicott City has had a history of floods going back to the days when Maryland was an English colony but we humans have made this far, far worse:
1. We warmed the climate and that 7 % extra moisture (Clausius-Clapeyron relationship see here) in the air leads to stronger storms with a 25% or higher increase in rainfall.
2. We also greatly over-developed land in a tiny floodplain and channeled the runoff from that development into the rivers, pushing them to go far higher than in the past.
3. We’ve also have made these extreme rainfall events worse because of the greenhouse warming. See below from the National Climate Assessment.
A Hard Truth:
We live in a different climate now. The climate of the 20th century is gone and this new climate will be gone in 30 years replaced by an even more volatile one. What the climate at the end of this century looks like will be the legacy we leave our descendants. Some of whom are alive right now.