January 24, 2011

What does climate change mean for Lexington? - More floods

It is becoming clear that one of the primary effects of global warming is to increase the frequency of extreme flooding events around the world. As we warm the climate, the warmer air 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%.  

Here's one way to think about how much extra water that is. 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. 

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 this week has resulted in over 665 dead in Brazil and over 300,000 homeless in Sri Lanka. 

So what does this mean for Lexington, Massachusetts? 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 in one day (that was in 1962). 

Since 1990 we've had 7 days when we've had 4 inches or more of rain. That means Lexington was 12 times as likely to have an extreme precipitation event or a superstorm during the last 20 years, compared to the previous 33 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. 

The consequences of these intense storms directly affect our lives, causing flooding in our basements, inundating our stormwater system and even disrupting our water supply. 

The intense flooding from those two superstorms in March was one of the primary causes of the water main break that disrupted most of Metro Boston's water supply. 

The weather patterns in Lexington have changed dramatically in the last 20 years and we will need to implement plans to ensure that we have the proper infrastructure and systems in place to deal with this new reality.

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