From a letter to the editor of the Valley News in Lebanon, NH
Published October 14, 1997
SEVERE POWER OUTAGES COMING
To the Editor:
With the health of trees rapidly worsening, the probability of serious winter power outages caused by falling limbs and trees has increased significantly.
Last winter, New England experienced some of its most costly and prolonged power outages on record, following storms that were not unusually severe, although many people associated the storms' severity with the duration and scope of the power outages. In one storm in mid-December, Public Service Co. of New Hampshire lost power to 94,000 customers for up to several days and suffered more than $4 million worth of damage to its transmission lines.
I wrote and called PSNH to gather more details and was told that the status of its tree-trimming program was the best it had been in years, despite critics' claims to the contrary. The most severe damage was caused by trees outside the legal rights-of-way breaking off or uprooting and falling with sufficient force to snap power poles as well as lines. Many limbs snapped instead of just bending under the weight of snow. Previously I had noticed that trees were becoming more prone to breakage and uprooting.
Other storms last winter caused additional prolonged and widespread power outages throughout New England.
From what I have been observing, the trees are now in a much more weakened condition than they were at the beginning of last winter, and we can expect much more severe and widespread power outages unless the winter is exceptionally mild and storm free.
If it has not already been done, I think a quick assessment should be made of how extensive and costly the power outages in New England were last winter and what the causes of the outages were, tabulated by approximate percentages. A rough correlation should then be made between the meteorological severity of the weather and the severity of the outages to see if historical ratios of damage to storm intensity were exceeded. simultaneously a program should be instituted to train both power company and environmental assessment teams to more accurately evaluate the health of trees bordering power-line rights-of-way. The tree health assessments should be made available as quickly as possible to the general public and government officials as well as to power company officials.
Gerry
Hawkes
Woodstock
*************
From the FOREST e-mail list:
Gerry Hawkes (ghawkes@sover.net)
Fri, 10 Oct 1997 07:02:00 -0500
The following information posted by Brian Potter, while not
from the
official weather record, is a very useful start for general
discussion of
the relative severity of the storms that hit New England last
winter and
the amount of tree damage they might be expected to cause to
healthy trees.
Because deciduous trees lose their foliage during the winter
months and the
bare limbs and branches present little surface for snow
accumulation, heavy
wet snows tend to have minimal loading effect on the trees.
Couple this
with winds strong enough to move the limbs and tops of trees, and
little
snow will accumulate. Healthy conifers cope with heavy snows by
shedding
it off as their limbs bend down.
Ice storms, not snow storms cause the most severe damage to
healthy trees.
Ice can freeze in thick layers on both hardwoods and conifers,
often more
on one side of the tree than the other until the point is reached
where
limbs and trees snap. Wind aggravates this stress and does little
to
dislodge the ice until it begins to melt.
To the best of my knowledge there was little if any icing
associated with
these storms and winds were not exceptionally strong for trees
without
their foliage. Also it is my impression that rights-of-way tree
trimming
practices have generally become more aggressive over the years
and many
power companies have been moving their distribution lines, where
possible,
from straight line runs through the woods to roadside where they
can
maintain and repair them much more easily.
Given the circumstances I outline above, it seems unlikely
that some of the
most prolonged and widespread power outages on record would occur
last
winter unless the trees were unusually weak and prone to damage.
- Gerry Hawkes
Forest Management & Utilization Consultant
Woodstock, Vermont
At 04:13 PM 10/9/97 -0400, Brian Potter wrote:
>Hi,
>I thought I would do a quick check on the weather of the
Northeast this last
>winter after Gerry Hawkes post about power outages in the
area. I didn't go
>to the trouble to call up the NOAA/NWS records of snowfall
or any such, but
>instead went to the magazine Weatherwise. It's a bimonthly
that summarizes
>previous months' weather in every issue, and while it's
not anything
>official, they do a very good job of summarizing the NCDC
(National Climatic
>Data Center) data.
>
>The April/May 1997 issue summarizes Dec. 1996 and Jan.
1997 weather. The
>discussion mentions "back-to-back" heavy snows
in the first week of December
>in "an otherwise winter-free month." These snows
knocked out power for
>600,000 people and were accompanied by 25-30"
snowfalls and strong winds. I
>presume these are the storms Mr. Hawkes referred to. For
January, the
>Northeast "was one of the few areas that escaped
heavy snowfall."
>The summary for February (in the June/July issue) mentions
no storms
>specifically damaging or intense in the Northeast. It does
note, however,
>that monthly snowfalls were somewhat high in the
"interior Northeast." For
>March, there is reference to an explosive cyclone that
dumped heavy snow
>under heavy winds from New York to Caribou, ME. There is
no mention of
>power outages here.
>(A quick perusal of the summaries for Dec 1995-March 1996
shows heavier
>snows in several instances, but there is a notable lack of
mention of the
>strong winds mentioned above.)
>
>My assessment is that the weather included strong winds
and some heavy, wet
>snows that are prone to break trees. But the Northeast is
prone to that
>sort of snow, simply because of its maritime nature. That
said, I don't
>think I agree with Mr. Hawkes that the storms were
"not unusually severe
>meteorologically." There were 3 events with 15+
inches of (wet) snow in 24
>hours, all accompanied by 60+ mph winds.
>
>Trying to correlate storm intensity to damage would be
exceptionally
>difficult, if not impossible. The spatial sampling of the
meteorlogical
>data is quite sparse for this purpose, and storms of this
sort can show
>strong spatial and temporal variability. Not only would
the raw wind speed
>and snowfall matter, but the snow density, the air temp,
and the timing of
>the snow relative to the winds. Wind then snow would not
be as destructive
>as snow then wind.
>
>Brian Potter
>Research Meteorologist
>USDA Forest Service
>
>
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