Sunday, August 14, 2016

Concord Temperatures, from Thoreau to now

Posted by Richard B. Primack

"The phenomena of the year take place every day in a pond on a small scale... The night is the winter, the morning and evening are the spring and fall, and the noon is the summer."
-Thoreau in Walden

For a week in 1860—June 30 to July 7—Henry David Thoreau used a thermometer, presumably a mercury thermometer, to record the temperature of Concord’s springs, brooks, rivers, ponds, and a swamp. He found that springs have Concord’s coldest water; brooks emerging from shady swamps are colder than brooks from dry, open uplands; and temperatures of rivers and ponds are affected by day-to-day air temperature.

Recently, over the course of 7 years, I repeated many of Thoreau’ observations of water temperatures using a digital thermometer. Springs are still Concord’s coldest waters. For example, Thoreau measured Brister’s Spring at 49 degrees, and it varied from 48 to 52 degrees during my years of measurements.

Brister's Spring in Concord, MA

Many of Concord’s brooks have distinctly warmed since Thoreau’s measurements. This is because a dam pond or beaver pond has slowed the water, giving it more time to be heated by the sun than in the past. The temperatures of the brooks are also affected by yearly variations; they are warmer in warm summers and colder in cool summers. 

The sand pit on Brister's Hill in Concord, MA 

On the afternoon of July 12, 2016 (just about one month ago), with an air temperature of 88 degrees, Concord showed that it still has hot and cold places on land as well. The treeless sand pit near Route 2 on Brister’s Hill is like a solar oven, and that afternoon it had a ground temperature, measured with an infrared thermometer, in the range of 130 to 148 degrees. Inside the nearby wildlife tunnel that passes under Route 2, the temperature was a cool 57 degrees, 31 degrees cooler than the outside air temperature. On a summer’s day, Concord residents can walk through three seasons from the cold waters of Brister’s Spring, to the glaring desert-like conditions of the sand pits, and finally the cool autumn climate of the wildlife tunnel, all without even having to cross a road.

The wildlife tunnel under Route 2 in Concord, MA

A longer version of this article was published in the Concord Journal.

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