Tuesday, December 18, 2012

Climate Data from Blue Hill Observatory

I love the freedom and creativity involved in designing gardens, trying not to get bogged down in 'rules' and 'guidelines' but looking at each project as a fresh opportunity.  However, I am a bit of a geek at heart and love the science and detective work required to garden.  'Data' is not a topic often covered in gardening and horticultural discussions, but my 'left-brain' wants to come out and stretch its legs.  So, for those who also like to look at graphs, numbers and trends, here is some compelling information from the Blue Hill Observatory at the Blue Hills Reservation in Milton, MA.

The Blue Hill Observatory is home of the "oldest continuous weather record in the United States."  They keep track of lots of meteorological data and some other cool information like local pond freeze/thaw dates and fruit ripening dates.

Before I go any further, I want to be clear that I am not making any political statements for those who may want to infer them from my summaries.  That said, there are some potentially compelling conclusions to be made from trends in the data.  Most of the data collected goes back to 1885, and the temperature data goes back to 1831.

Keeping a good track of rainfall is critical for anyone who cares about plants big and small.  Letting nature water your plants is always better, time-saving, and cheaper than doing it yourself.  While many people these days seem to have some form of automated irrigation for lawns and smaller plants, tracking rainfall over a season is critical for ensuring the health and vigor of your larger plants.  Large shrubs, ornamental trees and larger trees need long deep waterings that an irrigation system or short hand watering just can't provide.

An interesting fact is that the 30-year mean for rainfall has been on a steady rise since 1885, and the last 30+ years have shown an even steeper rise in the 10-year mean.  However, that does not mean that we don't have shorter periods of drought or mini-droughts.  This past July, in a post, Water those ornamentals and trees, they are thirsty, I reminded people that we were in a mini-drought with minimal rainfall and a very low previous winter snowfall.  When this happens we need to get out the hoses and provide a deep, regenerative soaking for our big plants to keep them healthy and happy.  One good deep soaking, keeps moisture in the root zone and helps them through a short stressful period.

If we don't get good snowfall this winter to provide valuable melt in the Spring, we will enter next spring again at a deficit.  As the 2012 graph shows we are 9.36" shy of our 110 year mean for precipitation, that's about a 20% shortfall.  But... in 2011 we were over 20% above the mean.

With the precipitation trends on the rise, it is interesting to note that these increases are coming from rain during the warmer months and not from snowfall.  The long-term snowfall graph reveals that the 30-year mean has deviated slightly above and below, but remains almost exactly at the same level from over 100 years ago.  Any budding meteorologists want to explain this divergence?

Temperature and USDA Zones

Measured temperatures over the past 180 years are rising in our area.  There is no ambiguity with regard to the Blue Hill data, and the USDA this year released a new Plant Hardiness Zone Map and most every zone shifted up a half to a full number. These are the numbers you see on plant tags that say whether the plant is expected to survive in the ground in your area.  Inside 495 but outside of the city is generally zone 6b now.  The semi-tropicals you may buy as annuals for your pots often are often hardy in zones 8, 9 and 10.  You can use plants that have your zone number or lower, however, know that these zones are based upon long term averages and a relatively young plant(without protection) that matches your zone may suffer or die if there are abnormally low temperatures during the winter.  The USDA zones are guidelines for what typically will survive in your area.

The Blue Hill map above is intriguing, if it represented a stock I would buy it on the promise it will be higher over the next ten years.  The next two graphs show that November 2012 was the first time in 21 months that the mean monthly temperature was below its 110 year monthly mean, and that 2012 and 2011 are 3.9 and 3.0 degrees above the 110 year average mean.

One last bit of interesting temperature data from Blue Hill is their tracking of Houghton Pond freeze and thaw dates.  Houghton Pond is a medium-sized kettle pond(like our Winter Ponds here in Winchester) in the Blue Hills Reservation.  It's pretty cool to track this over time, and as you might expect from the temperature data, the pond is freezing later and thawing earlier over time.  For those of us who have skaters and hockey players in our families, we remember last year when we only had one good day of skating on Winter Pond because of the late freeze and terrible slush and freezing rain that ultimately ruined the surface.

I would be interested to know the criteria for determining when a pond is considered frozen or thawed.  The day we skated last year happened only because I was driving by the ponds and saw an unidentified man out in the middle of the pond jumping up and down.  He did not fall in and within an hour we were on the pond with 50 other people.  While this technique may be effective, it could lead to some longevity issues. 
Alex(in black) and a friend skating before the big pick-up game happened
during the only skating day on Little Winter Pond last season.

Other Interesting Information

A previous post covered a critical horticultural measure called Growing Degree Days.  All plants and insects live their lives not on a chronological calendar like humans, but a temperature-based calendar.  When average daily temperatures creep above 50 degrees, the world comes to life in the spring, flowers and fruits appear based upon the accumulation of the degree days.  Blue Hill tracks when the first Blueberries ripen in the area.  Again, as you might expect with the warming temperatures and an understanding of Growing Degree Days, since 1885 the trend is that Blueberries continue to ripen earlier in the year.  Of course, this is far less scientific than tracking temperature since there may be other factors involved in the process, but fun to look at nonetheless.

Now, for total data overload you can go to NOAA (National Oceanic and Atmospheric Administration) and look into just about any bit of weather information you could imagine.


  1. That is all very interesting! I would like to see data from my own area. However, I'm not sure about that method of determining if the pond is frozen!

  2. my geeky heart loves all these data! Thanks for pulling it all together. -Jean