Floods in your future?

Governor Patrick told us back in March that the flooding we experienced in the greater Boston area was the result of “two 50-year storms in the course of two or three weeks.” Standard probability analysis would suggest that the likelihood of experiencing two 50-year storms a couple weeks apart would be a once in 2,500 year event.  Does that mean we can relax and go back to business as usual? 

Perhaps the local weather records can shed some light on that question. The weather records from Hanscom Air Force Base since 1957 show that during the period from 1957 to 1990, we had only one day with more than 4 inches of rain (that was in 1962). 

Since 1990 we've had 7 days with 4 inches or more of rain. That means that over the last 20 years Lexington has been 12 times as likely to experience an extreme precipitation event or a superstorm, compared to the previous 30 years of data. 

The two storms we had in March of 2010 dumped 25% of our total annual rainfall on us in just 7 days, including one day when we had 4.3 inches of rain. That works out to 13 times more rain than the 7 day average. 

As we learned in March, our storm water drainage systems haven’t been designed to accommodate these increasingly frequent storms that can dump over 10% of our annual precipitation on us in one day. The consequences of intense storms directly affect our lives, causing flooding in our basements, inundating our storm water system, incurring emergency response costs and even disrupting our water supply. 

You may be surprised to learn that the increased frequency of intense storms is the direct result of a warmer climate. As the climate warms, the warmer air in our atmosphere holds more moisture. Scientists calculate that the 1 degree of warming that has already occurred causes an increase in the amount of water vapor in the air of 4%.  

A 4% increase in atmospheric water vapor over the US is the equivalent to adding all the water from Lake Superior to the air over the US. And what goes up must come down. And when it does come down, that precipitation is coming down in increasingly intense superstorms - which can cause devastating floods. 

Extreme flooding events aren’t only confined to the area surrounding Lexington. One of the primary effects of global warming has been to increase the frequency of intense storms and extreme flooding events around the world.

In the last twelve months we've seen the worst flooding on record for Pakistan, Tennessee, Brazil, Columbia, Australia, and now Sri Lanka. Pakistan still has millions who are homeless. Australia has an area the size of Texas under water. Flooding two weeks ago has resulted in over 665 dead in Brazil and over 300,000 homeless in Sri Lanka. 

So what does this mean for Lexington, Massachusetts? Unfortunately the answer is more flooding. 

The weather patterns in Lexington have changed dramatically in the last 20 years. It is time to begin planning to address these changes if we are to ensure that we have the proper infrastructure and systems in place to deal with this new reality.