Spring, Floods, and Pavement

New England landscapes are being transformed by climate change–but so far, most of that change is due to urbanization, not global temperatures. Over the weekend, I encountered two pieces of evidence that Bostonians need to take to heart; a talk by Richard Primack on the altered ecology of Concord, Massachusetts; and Belmont state representative Will Brownsberger’s web page on the Flood of 2010.

Primack studies spring! Well, really, he studies phenology, the timing of biological events, to answer the question; is New England getting warmer? In spring’s early days, Primack and his students spy red-winged blackbirds as they alight on reeds in the Great Meadows; in May, they search for bluets softly opening their sky-eyes amid venerable cemetery lawns.

Most of the year, though, Primack looks for records other people have made of when flowers, trees, birds and insects emerge from winter’s grasp. His work in Concord is based on notes taken by Henry David Thoreau and a Concord physician named Alfred Hosmer. Thoreau tracked local flora from 1851-1858; Hosmer, from 1888-1902. Primack has also used evidence ranging from Memorial Day photographs of cemeteries to dated herbarium specimens to bird-banding records figure out what was around when.

Primack’s conclusion? Spring is starting earlier, and plants that haven’t adapted to the warming weather are disappearing. Primack estimates that the temperatures around Boston have risen two degrees Fahrenheit since Thoreau started tracking wildflower blooms, but Primack says two-thirds of that rise is due to the “heat island effect.” In short, buildings make places hotter. Pavement, roofs, and walls heat up faster than vegetated ground, and don’t retain water that could evaporate and cool the area on hot days. Although 60% of Concord’s land is still open space and farms, enough of that town and the surrounding Boston suburbs have been developed that 63% of the species Thoreau observed are either extinct or very rare in Concord.

Now, about all that water that isn’t retained by roads and roofs; I’m sure many of you have had intimate contact with storm water over the last week. Conveniently, it may have visited you in your own basement. And you can expect more visits in years to come.

When water falls on soil that’s covered by grass, trees, or crops, it falls on a giant sponge. The water sinks in and gradually seeps down into the ground water. That’s why rivers flow even when it isn’t raining; the water, also called recharge, is gradually traveling through the ground.

Cover the earth with pavement, and instead of pouring water on a sponge, you’re pouring water on a plate. The storm water becomes run-off–carrying whatever motor oil, gas, and tire fragments were sitting on the road with it– and rushes into storm drains. Instead of staying in the local ecosystem, providing moisture to plants and evaporating in the summer to cool the air, the water flushes out to Boston Harbor.

According to Will Brownsberger’s site, the average daily flow of the Aberjona River in Winchester is 10 cubic feet of water per second. On Monday, March 15, it was 1420 cubic feet per second. That number is impressive–140 times the normal flow!–but it’s even more startling to think that fifty years ago, water numbers that high simply didn’t exist.

Hydrologists use the word “100 year storm” to mean storms that have a 1% chance of happening in a year. In the 1950’s, the 100 year storm flow for the Aberjona river was estimated at 500 cubic feet/second. In 2006, that number had increased to 1500 cubic feet/second. And Tufts University hydrologist Richard Vogel estimates that that 100 year flow level may be as high as 2700 cubic feet per second, all due to buildings and pavement. That’s more than five times as much water as came down the river during the worst floods fifty years ago! No wonder all the basements are leaking… yet come summer, we may find that the soil is dry, because our groundwater has swept out to sea.

Development in Concord, Winchester, and other Boston-area towns is making the local climate hotter and promoting floods–before global climate change takes full effect. If you want a dry basement and purple fringed orchids in your parks, think about how keep more water in the ground in your town.

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