- I'd like to welcome Jason Schafer,
who's with the Northern Vermont University.
This talk is on extreme weather changes
and implications for forest health.
- Thanks everyone, it's great to be here today.
And I just want to say happy 30 year anniversary
to the FEMC, so it's a pleasure to be here.
And I'm here today to talk about
some of our work that we've done with electric utilities.
I want to thank my co-authors,
Kevin Cronin and Connor Pasquale.
Connor is a student at Northern Vermont University,
Kevin's a Research Associate at Northview Weather.
And we're approaching this from
both the research perspective,
but also very applied concept here,
looking at extreme weather and resilience on the power grid.
So our perspective really is the electric grid ecosystem.
And a few things just to get us oriented here
for our frame on this is
most of power outages are caused by weather.
And then a lot of those power outages
are caused by trees,
and trees conflicting with power lines and poles.
And power companies, of course, they're very interested
in being prepared for storms.
But the question that we're trying to answer
is climate change and how extreme weather
is gonna impact power outages,
but also how the vegetation itself may change
under climate change.
And that really is where we're trying to get
out of our silo and learn a little bit more
and share some of our work with your community.
And we are really interested in this
because the costs to maintain vegetation along power lines
are one of the top three cost drivers for electricity.
So when you're paying your bill in the Northeast,
a lot of that is actually for the power companies
to manage vegetation along those right of ways.
A very quick 101 of the electric grid system.
And we have a generation,
somewhere where the energy is being generated
on the left-hand side here.
And then it's stepped down to transmission lines
that take that energy.
And then the, the voltages gets stepped down
in substations and transformers
and then that gets to the distribution system.
So I want you to think about
the distribution and transmission system
as being two different systems that work together
to deliver power to people.
And then the Vermont transmission system,
this work was funded by VELCO, the transmission company.
They own and operate all the transmission lines.
The green lines on this map show
all of the transmission lines.
We've got about 750 miles of lines,
55 substations,
and they own and manage 13,000 acres of right of ways.
And because the transmission infrastructure
is much more important to the backbone of grid,
the right of ways are very large
and rarely do you have problems with trees
conflicting with power lines here.
So, the transmission system is pretty resilient
to extreme weather.
Now, if you have snow loading or really strong winds,
you can take down those wooden structures.
But that is at a much more extreme level.
The distribution grid really
is where our vulnerabilities are.
So the left-hand side shows a color-coded map
just of all the overhead power lines,
which we have about 14,000 miles of distribution lines
in the State of Vermont.
And following like land use percentages,
we also have about 75% of forested along those lines.
And the tree trimming cycles can take five to 10 years.
And I love this picture here in the top right
that shows how we've got power lines
really running through this tree here.
And that's just a recipe for trouble,
some point down the line.
But it takes some utilities almost 10 years
to go through and fully trim
and manage all the vegetation along their lines.
And a 10 year period, you can get a lot of new growth.
So, and you're gonna be doing it all over again.
And then some of the more progressive utilities
that might have more funding or be more on top of it,
and smaller, more urbanized areas
might be able to do this every three years.
But in Vermont, a more rural nature,
we're still on a longer trim cycle
around eight years for the best, the best utility right now.
So if you look at power outages,
and these are from severe storms over a nine year period,
we looked at all power outage data
from Green Mountain Power and Vermont Electric Cooperative.
You see a bi-modal seasonal signal
where there's a peak in the winter, winter time,
or sorry, summertime, from thunderstorms.
And then we have a fall peak with wind and wet snow.
Wet snow storms are predominantly the signal here.
Ice is only 20% of this, of course ice storms,
when they do happen can be very severe,
but their frequency is just much less, right?
Now if you look at this from a duration standpoint
of an impact, this is just the number of events,
and when they occur.
If you look at this from a duration and impact standpoint,
it turns out we have the highest number
of power outage risks to the grid
in October, November, and December.
So over half of all of our customer impacts
from power outages, in terms of the duration of them,
the severity of the storms, happen in those three months.
Which is very interesting because,
you go to January actually has the least number.
So this is where some of those seasonal risk factors
in intersecting vegetation health and tree health
are really important to predict,
and also just to understand
from a climate change perspective.
So some of those risk factors are,
as you could imagine, the tree canopy itself.
If you have leaf on or leaf out periods
in the month of October, you could still have leaves on.
And then also there's another factor
where you just have a whole year of putting on new growth,
and the trees just haven't been hardened by mother nature.
So there's a certain natural hardening
that happens into the season,
and it takes a little bit of time.
And then soil conditions are really important to this too.
Turns out wetter soils are much more vulnerable
because you could have a uprooting of trees that are easier.
And then once you hit January,
our climate's still cold enough for the most part
that the trees just get naturally
a little more resilient to weather.
It's not that we don't have weather in the middle of winter,
it's just that the impacts are, are much more muted.
So another way of looking at this here,
a plot looking at peak wind gusts on the y-axis,
and this is just Julian day of the calendar year.
And these color of these dots is showing
basically the severity of the storms.
So all I want to point out here
is that the magical week of the year
seems to be late October, early November
is where we have these dots that are larger in size
going into the fall.
And we've had a number of large storms then
that tend to produce a lot more outages
during that timeframe,
and you see a much more resilient grid
during the middle of winter.
And even the summertime, a lot of the summertime outages
you can get from thunderstorms,
but they tend to be much more localized and short-lived.
So go looking at some catastrophic ice storms.
This is where we're trying to intersect
looking at some of the forestry research
and understanding catastrophic
and predicting the most catastrophic storms
is probably the most important thing to get right.
So in January of 1998,
we had the most catastrophic ice storm in recent history,
which is around a one in 100 year event.
And then the red areas show heavy damage to the crowns
in the canopy of the forest over Northern New York,
where the cold air was able to work in
across the St. Lawrence Valley.
And then in Maine, we also have this
in southern and central areas.
Not, coastal areas were too warm
to keep this as freezing rain.
And then in Vermont and New Hampshire,
anyone who may remember this storm,
or read some literature on it,
the cold air was actually confined to middle elevations.
The valleys, we didn't have quite enough cold air,
so we had extreme damage
from about 1500 to 3000 feet elevation.
And it ended up being that heavier severe damage
was approximately, you know, 20% of forests here.
And looking into literature ahead of this talk,
we see that in parts of Quebec and in other areas,
that even after 20 years after the storm,
that tree mortality rates remaining pretty high.
So the recovery of this is taking,
taking a fair amount of time.
Another, on the other end of the spectrum
in the warm season,
hurricanes are probably our other most impactful event.
The hurricane of 1938, at least for Vermont,
is where we had the most catastrophic wind storm.
Now, the other thing about meteorology is
that the right hand side of hurricanes
is where we tend to have the most damaging storm
impacts from wind.
If you look at the left-hand side,
you can see this storm survey that looked at
where there was extreme and moderate timber damage.
And you could see that that was over a pretty large area.
This was a category three hurricane
when it made landfall in Long Island.
And it maintain hurricane strength
all the way through parts of Vermont.
This storm also produced over 500 people lost their life,
and storm surges that were close to 20 feet
all the way up to Providence, Rhode Island.
So, storms like this can happen,
they're just not as frequent for them to happen.
It's just a matter of time until
something like this happens again.
So we've summarized quite a bit of work here
over the last 40 years.
Looking at power outages,
we reconstructed this looking backwards,
and here's our main conclusions.
Before I get to the climate aspect of this work,
here's our summary for the power outage work that we found.
At the 20 year trends are showing that
risks have increased by a few percent,
most of that's being driven by wet snow,
a little bit less by wind storms.
And high-impact storms are not necessarily
increasing on their frequency,
but if we sample out and subset
the really high impact storms,
so like the top 1% of storms,
it turns out that they're increasing in intensity
by about 15% riskier, or more risks.
So the most intense storms are becoming more intense,
it would appear with climate change.
We'll talk about why that isn't just a minute.
All right. Catastrophic large-scale storms,
again, the frequency on those
is just a little too low to say a whole lot about.
But I think the big takeaway here,
especially for the warm season, as climate warms,
you add a little bit more fuel.
Your speed limit to how strong storms can get
just to get a little bit higher.
So there could be a potential for those storms
to keep their intensity or maintain stronger.
All right.
So a little bit about climate change signals.
We use the ERA5 reanalysis data
and a variety of methods to come up with this.
I don't want to go into too much detail here.
I'd rather focus on the results.
What we see in Vermont is consistent with the region.
We've got a large warming signal
with temperatures in the last 40 years.
The month of September has actually warmed the fastest.
And the month of fall has actually warmed,
the season of fall is warmed greater
than any of the years.
So what's happening here is that summertime and fall
is just becoming,
warm seasons becoming more prolonged, right?
And then what we see that's showing up
in a variety of areas,
this is also a regional
and large-scale continental signal too.
So falls are getting warmer across most of the country,
and one of the faster warming seasons
of all the seasons that we see.
From a growing season perspective,
what we see is this is growing degree days,
over a 50 degree base, we've got about almost a 10% increase
in net growing degree days
in this last 40 year period in Vermont.
And 60% of those increases are due to August
and September being warmer.
So, we're trying to answer this question of
does this, the growing season getting longer
mean you're gonna put on more growth for your trees
and maybe increase your vegetation management programs.
It would appear that perhaps that a later season increase
in the growing season for most species
is not gonna allow for that.
So that's something that we're,
we're still trying to sort out.
But most of it's, the growing season is
the duration of the season getting longer on the other end,
not the beginning or the end of it.
And then precipitation trends.
It's no big surprise,
as the climate gets warmer in our neck of the woods,
it gets wetter.
We still have enough storm activity
to extract that moisture out of this.
And we know the availability of water
and the evapotranspiration rates are really important
for how much growth you can have.
Just because you have warmer growing seasons
doesn't mean you're necessarily gonna have more growth,
you still need the water capacity to be able to grow.
So let's look at precipitation annually,
it is increasing.
There is a strong seasonality signal to this.
In Vermont, winters are getting warmer.
Our wettest, fastest 11% increase
in annual winter precipitation in the last 40 years.
Otherwise, there was a 2% increase
across the rest of the seasons.
And then on a month to month basis,
it's a little more lopsided,
just given that variability we have in the signals.
But you see what that warming we have
in August and September,
we also tend to have a little bit of drying.
And I mean that was a pretty strong signal with drought
this year that we had.
Just because we're getting more precipitation
doesn't mean we're not more prone to drought signals too.
So speaking of, let me skip ahead here.
We'll talk about drought in a second.
I just want to talk about extreme precipitation events,
right?
What we see is that extreme precipitation events
are more likely in the fall and late summer,
and that's mostly due to tropical systems
interacting with mid-latitude storm systems,
of the peak, again, in that magical month of October.
In a lot of ways, October kind of stood out for us
as the most interesting month in this research.
And then if you look at this spatially across Vermont,
you see is that there's been an increase
in heavy precipitation days as well.
It's not uniformly distributed,
but generally we've got about a 10% increase
in these really heavy precipitation days,
which is defined here as a 24 hour storm
over at least a one inch over the county level basis.
So we're getting, and this increase is actually much faster
than the annual rate increase.
Speaking of drought, looking at long-term drought signals,
red areas, and this, this research shows where
it's been getting a little bit drier tendency for drought
and blue areas maybe not so much.
Putting my meteorologist's hat suit on,
what you'll see is that the reason this happens
is probably because westerly flow,
storms coming from the west tend to break apart,
and they don't tend to bring as much precipitation
to coastal areas before they do that.
Whereas southerly storms tend to bring more precipitation
perhaps up the coast.
So the meteorology is really important for that as well.
And other research has shown,
from your community is that,
of course drought occurring early in the season
when we're putting on more growth
has more negative impacts on growth as well.
So the timing of drought is pretty important
for the overall growth.
So we had done quite a bit of literature review
and trying to figure out one area,
or a few areas where we could dial in on this.
And what really happened was,
quite honestly a lot of themes that came out of this,
and things that were beyond our expertise
or our capabilities,
looking at windthrow biomass,
which is just debris that comes through after wind storms,
and how it affects carbon cycling, and nitrogen cycling,
and nutrients uptake and things like that.
Species dependency on climate change.
That's a really big question
that we're still trying to get at, too.
Age of the forest influencing the resiliency,
old versus newer growth forests.
All of the right of ways are also on the edges of trees,
edges of forests, that's a factor to this.
And then seasonality of this,
trying to sugar out that whole seasonality signal
of what we're getting at here.
Just to wrap up here, I'm kind of curious,
this is just, if anyone wants to reach out with me
maybe outside of this talk,
or if there were any other known major losses in trees
or damage to trees in Vermont for these three storms.
All right.
And here we have power outage profiles for the storm.
In the last decade,
especially that October windstorm of 2017
was the largest power outage storm,
which you could see
on the time series graph shows
that there was over 30% of electric customers
that were without power.
And it took almost a week to restore the power
from that storm.
So December, 2013 ice, and then
December, 2014, wet snow.
So those are the other two big storms
that in the last decade, that kind of intersect our world.
And just to wrap this up here,
what we see is that wind storms appear to be the top causes,
they definitely are for power outages,
and also for the forest damage.
All right, even though you can get
a one-off major ice storm.
Catastrophic wind storms,
they don't appear to be getting more frequent,
but their intensity does appear to be increasing slightly.
And then for ice storms,
what we think is that there's no detectable frequency
or intensity changes to them.
And the climate could still support
major ice storm like '98.
But the other thing we're seeing
is that there's more mixed phase storms,
even though winter's getting warmer, we're still having
low and moderate-end icing in that setting.
That's going up.
The severe icing events,
it's a little harder to get all those ingredients
to come together just right.
Overall, power outage severity has increased
from warmer and wetter storms.
As the widening of that warm season increases,
that fall power outage season
I think that that the vulnerability to vegetation
in major storms is probably gonna increase
in that signal as climate continues to warm.
And then, this was mentioned earlier,
but storms like Superstorm Sandy
is a good ghost of Christmas future in a lot of ways,
is that I think more of the risk lies
probably in the warm season
looking at things like hurricanes
interacting with midlatitude storms,
such as a Superstorm Sandy.
Okay, that's all I have here.
I appreciate being here today,
and being able to share our work with you.
- Jerry Carlson, what's the relationship
between vegetation piece size and power outage?
And how, would, or could you,
could cable installation offset the power outage problems?
- Yeah, so there's a lot of asset hardening
that's happening.
The utilities put up tree wire,
which is basically insulated lines.
And that's constantly being done.
It's just a matter of cost to do that.
And that actually helps quite a bit.
When you've got relatively small branches,
just maybe touching a line and then blowing a fuse,
you avoid a lot of those outages.
The basically the larger, the more dangerous the tree,
the larger the tree, the more mass
that basically you've got to clean up falls in the line,
the more damage you're gonna get.
But Green Mountain Power is,
they actively are investing in a lot of tree wire.
They identified their risk areas,
and the utilities are aware of this.
It's just a matter of their capital expenses,
being able to keep up with this.
There's a pretty big need here.
There's still some old copper wire out there,
even our old systems.
So the grid is, is a power grid,
definitely needs a lot of modernization,
and a little bit more hardening, I think.
If I was to put dollars into the grid,
I would definitely be more aggressive
with the vegetation management, just generally.
- Okay, next one from Joanne Garten.
Do you have any data on what tree species in size diameter
of trees are falling on power lines
perhaps broken up regionally, if not a specific point data?
- Yeah, that's a really good question.
And the answer is, no.
Because the power companies aren't required to report that,
nor are they sophisticated enough to know that.
There's constantly a rush
if there's something broken to fix it.
And what we've found is that, their not their due diligence
with keeping their data is not as good as we'd like it,
because we struggle with the quality
of some of their power outage data.
We've had to make a lot of assumptions with this.
They do map.
They have LIDAR that maps the species types pretty well.
So there's some knowledge of that.
But we don't have good data on exactly the age of the tree,
that the species of the tree, the size of the tree
that may have failed or caused a problem.
Most of the trees are actually danger trees.
So they're actually outside the right of way,
and they fall in.
And they're trees that the power companies
can't do anything about
without permission to the landowners
to take down or do something about.
And no one wants to cut those down
unless they absolutely have to either,
because oftentimes those trees
are prized by landowners as well,
or the towns that they're in.
- Okay.
We don't have any more questions at the moment.
But we have a bit of time to wait a minute, if you'd like.
Again, if you have any questions in the chat.
Okay.
- Oh, it looks like there's another one here.
Yep. (woman laughing)
- Okay. Nancy Harris,
given that you aren't necessarily seeing an increase
in frequency of extreme events,
do you think it is important to be monitoring the frequency
of moderate events as well?
- Yeah, absolutely.
The moderate events,
so the top end events we talked about,
maybe only account for 15% of all the power outages.
So those moderate and events
probably are somewhere around that 50th percentile.
And oftentimes that's where we're on the fence
as meteorologists,
try to utility companies to plan resources or not.
So we keep our eyes on that pretty closely.
And that's part of our research too.
Absolutely.
But they're probably not causing problems
to the forest at all,
forests are pretty resilient in the way that
that everyone here might be thinking,
or people who do research on this might be thinking about.
It's really the catastrophic storms
that I think from the forestry management side is where
you might be thinking about it.