- Welcome everyone to Wednesday
Nite @ the Lab.
I'm Tom Zinnen.
I work here at the UW-Madison Bi
otechnology Center.
I also work for the Division of
Extension here.
And on behalf of those folks and
our other co-organizers,
Wisconsin Public Television,
the Wisconsin Alumni Association
,
and the UW-Madison Science Alli
ance,
thanks again for coming to Wedn
esday Nite @ the Lab.
We do this every Wednesday night,
50 times a year.
Tonight, it's my pleasure to wel
come Daniel Wright
of the Department of Civil
and Environmental Engineering he
re.
This is a night of perfect weathe
r.
And the irony is we have perfe
ct weather
to talk about what's up with all
these storms and floods.
[audience chuckling]
Daniel was born in Ann Arbor, Mic
higan,
and went to high school in C
helsea, Michigan.
Then he went to the Universi
ty of Michigan
and studied civil and environmen
tal engineering.
Then he went to the Peace Corps
for, two years?
- Two years. - In Bolivia.
And then he came back to the U.S.
and went to Princeton University
and got his PhD in civil and envi
ronmental engineering.
Then he did a postdoc at the Go
ddard Space Flight Center
near Washington, D.C.
In January 2016, he came here to
UW-Madison.
I want to point out that in 2018
,
he won a National Science Founda
tion CAREER grant.
I think they give away maybe 30 o
f those a year
across the country.
That was one of the events
that I got to write the speeches
for
for the director of the National
Science Foundation,
so anytime I introduce somebody
that got a CAREER grant,
it's like, whoa.
[audience laughing]
That's pretty impressive.
So, please join me in welcom
ing Daniel Wright
to talk about What's Up With Al
l These Storms and Floods
here at Wednesday Nite @ the Lab
.
[audience applauding]
- Okay, I'm also very appreciativ
e
of everybody coming out tonight.
It's great to see an almost-full
room.
And yes, indeed, we are goin
g to talk about
what's up with all these storms a
nd floods.
I was asked to try to throw a lit
tle bit
of my own journey as a scientist
into this talk,
so I'll try to do that a li
ttle bit up front
just by sharing one little piece
.
You heard that I was a postdoctor
al research fellow
at Goddard Space Flight Center.
That's one of NASA's research an
d development campuses.
It's just on the road towards Ba
ltimore,
just north of Washington, D.C.
And so, I was living in Wash
ington, D.C., at the time.
And have any of you spent any si
gnificant time
in Washington, D.C., in the past?
Yeah, so a fair number of you.
So, you know the thing that h
appens in D.C.
when you meet somebody for th
e first time,
they immediately ask you what you
do,
I think probably 'cause they wan
t something from you
or they're trying to figure out
if they can get something from y
ou.
So anyways, I would tell them tha
t I work at NASA
and I work on floods.
And then they get a real confused
look on their face
[audience laughing]
and they come back with, "So, flo
ods on Mars?"
[audience laughing]
Which is not such a crazy qu
estion, really,
when you look at an image like th
is.
So, that's an artist's rendition
of the surface of Mars.
And it does actually look from th
at image
that floods did happen there at s
ome point in time.
We're going to keep things
squarely on planet Earth this eve
ning,
and so, just, I'll tell you why
I was spending time at NASA.
So, this video here is showin
g what we call
the constellation of satellites t
hat are part of
the Global Precipitation Measurem
ent mission,
and so some of these are from NAS
A,
some of them are from NOAA,
and some are from other space ag
encies around the world.
And together, over the course
of a day or so,
they can end up filling in a
nice picture
of what precipitation over the
entire globe might look like.
And so, after taking the satellit
e images
from all of these different sate
llites
and stitching them together,
you can get some nice images lik
e this,
which is one day's worth of p
recipitation
over the entire globe.
And this has a ton of useful purp
oses,
both in climate science, weather
science,
and with what I do, which is tr
ying to understand floods
and other hydrologic extremes.
So, I'm not going to say much mo
re
about the satellite side of thin
gs,
but it is a big part of what we
do.
And so, this is the Hydroclimate
Extremes Research Group
at UW-Madison.
And actually, most of them ar
e sitting there in the back.
Why don't you guys raise your h
ands?
[audience applauding]
They're the ones that end up doi
ng most of the work
and I get most of the glory.
[audience laughing]
What is it that we do?
So, I alluded to this on the
previous slide,
but we look a lot at rainfall an
d flood measurements
and try to understand how ac
curate they are.
And if that doesn't sound very i
nteresting to you,
that's perfectly reasonable
and we're not going to talk about
that tonight.
What we're going to focus on inst
ead
is using statistics and comp
uter simulations
to study the role of rainfall and
other factors,
mainly in floods, but we also ha
ve a big project with NASA
on landslides as well.
And then, as engineers, we also w
ork on this last part,
which is developing software, bo
th for our own research
but also to help other people
answer their own sorts of questio
ns.
And so, I'm an engineer by traini
ng
or, I guess, also a hydrologist
by training,
but we end up doing a little bit
of all of these different things
and interacting with people
from all of those different fiel
ds.
And so, that's really one of
the nice things
about this line of work
is that it does bring us into co
ntact
with a lot of different folks an
d a lot of different ideas.
Okay, so let's start talking abou
t floods.
And so, this is a picture
from August of last year in East
Madison.
And just to remind us,
I suppose that most of you were a
round for this,
but we had really, really hea
vy rainfall,
upwards of 15 inches in some
isolated pockets,
falling over the course of about
six hours, and that caused,
particularly in West Madison and
farther west,
localized flash flooding.
And then, as that water made i
ts way
into the chain of lakes,
we had some issues with back
ing up storm sewers
and things of that nature.
So, that's one sort of flavor of
flooding
that you could imagine.
This is another one.
So, this is a picture that I too
k
at the end of May of this year
as we were about to land in Omah
a, Nebraska.
So, if I'm not mistaken, this,
where's my cursor, here, there it
is,
so this is the Missouri River ba
ck here, I think.
Hopefully no one from Omaha can
prove me wrong.
I should've looked at a map ahea
d of time,
but I think that's right.
And so, you see the interstate
is fortunately not under water,
but some of these other arte
rial roads are.
And sort of the scale of this pi
cture
is much bigger than the one on t
he previous slide, right?
And so, what happened here,
and probably many of you are fa
miliar with this,
but basically we had a cold winte
r,
we had a lot of snow, we had a c
old spring,
that snow stuck around for a
long time,
and then the rains started.
And so you had that combination
of maybe not quite as intense rai
nfall
but lasting over long time peri
ods, falling on snow,
melting it, and this whole mess
of things going downstream.
And so, the big difference here i
s not only the scale,
so this was all over the Midwest
,
but also the, I guess, the t
ime scale.
So, taking instead of hours to s
et up, like in Madison,
taking weeks or even months to se
t up.
So, this just gets to the point
that there are some very differen
t sorts of combinations
of processes that can happen to
create floods.
So, this is earlier this week in
Washington, D.C.
Again, another example of one
of these very brief rainstorms
that just dumps a lot of rain
and creates all sorts of problem
s.
I'll come back to that photo
in a second.
And then this is from this mornin
g in New Orleans.
My understanding is that this si
tuation
that was bad in the morning
is getting worse by the minute
and is not likely to let up
any time in the next couple of d
ays,
so that's going to be an interest
ing one
to keep an eye out for.
And in this case, a totally sepa
rate set of circumstances
where you have a developing tropi
cal cyclone
that wasn't present in any of
those other previous examples.
Okay, so what's up with all thes
e storms and floods?
Well, this is the outline
of what we're going to visit ton
ight.
We'll start with talking a li
ttle bit about what we know,
particularly about flood impacts,
and I'll say what I mean by
that later on,
and then also about increases in
temperature and rainfall.
From there, talk a bit about
how floods occur
and why, well, and really, are th
ey changing
in a warming climate?
The answer's a little bit compli
cated.
And then look at two examples
of the link between climate chan
ge and floods
that in particular use comput
er simulations for them,
which is a big part of what w
e end up doing.
Then we'll wrap up with a quick s
ummary
and have plenty of time for
the Q&A session,
which I think is probably the mo
st important part here,
so please be thinking of things
that you would like to talk about
when we reach the end of my pres
entation.
Okay, so floods, as the slide say
s,
they're the most common natural
disaster worldwide.
They're amongst the most impactf
ul.
So, here we can see the total nu
mber
of federal flood declarations sin
ce 1963.
If you do the math on this,
that works out to about one
per day over that time period.
And so, from some perspective th
en,
these are sort of an everyday occ
urrence,
even if we might not think of
them that way
in our own lives.
And then, the other thing that y
ou'll notice
is that the Midwest is at least
as badly affected
by these things as anywhere else
in the country.
One thing that I forgot to m
ention in my bio
is that I did a short stint
at the World Bank
before going to NASA.
And so, we were working on disast
er risk management issues
in Latin America and the Caribbea
n,
and as part of that I put to
gether this map.
And so, each of those dots is a
reported flood.
The dot size is in accordance wi
th the number of people
who were displaced from their h
omes.
And then we highlight
a couple of particular flood
events there.
So, you see some pretty shocki
ng numbers, right?
So, Hurricane Mitch, for example,
killing 15,000 people,
the Tragedia de Vargas in Venezu
ela killing 20,000 people,
and then floods displacing
upwards of a million people or mo
re.
So, really dramatic impacts,
and the same is true in other pa
rts of the world as well.
Okay, so what do I mean when
I say impacts?
What I want to do is draw the dis
tinction here
between impacts and floods thems
elves.
So, I am a flood researcher,
but what I do is really focused o
n
the physical phenomena of floods
: how they happen,
how often they happen, how they m
ight be changing.
But there are other types of flo
od researchers
that focus on different things.
So, for example, the economic imp
acts,
the public health impacts, fatal
ities,
mental health impacts, et cetera
.
And so, I'm going to just revie
w briefly
kind of what we know about the
impact side of things
and then we'll get into more of t
he physical phenomena,
which is my specialty.
So, when it comes to flood fatal
ities,
there's a lot of good news here,
both in the U.S. and elsewhere.
So, we see basically no increase
in flood fatalities
since 1940, despite our popu
lation going up
by roughly two-and-a-half times.
And that's largely due to bett
er weather forecasting
and better flash flood communicat
ion,
and that holds up in other parts
of the world as well.
On the other hand, if you look a
t economic impacts,
so here you can just pay attentio
n to the blue line,
and this is global impacts, but t
his is true
perhaps even more so in the
U.S. specifically,
but these economic impacts are go
ing up and up and up.
And climate change could have so
mething to do with this,
but really the main driver by far
is just the fact that our economi
es
have grown substantially over tha
t time period
and a lot of that growth has
occurred in flood-prone areas.
Another interesting point here,
when you look at flood fatalities
,
basically getting killed in flood
is a guy thing.
[audience laughing]
So, it's not coincidence here
[audience laughing]
that this is the kind of,
that these two gentlemen are in
the situation they're in
and you don't see any women
standing on top of their cars.
The basic story is if there's go
ing to be a flood,
just stay home.
And then, when it comes to managi
ng the impacts of floods,
there is also good, potentia
lly good news,
if decision-makers are willing to
act on it anyway.
So, this is a figure that I took
from a World Bank report
where they basically were looki
ng at the benefit-cost ratios
of different types of investments
or at different types of project
s
that the World Bank likes to get
involved with.
And what you see is that both ear
ly-warning systems
and these measures to reduce dam
age from,
long-term measures to reduce d
amage from floods
are among the most cost-effective
types of projects
that they deal in.
And so, there can be a lot of ban
g for your buck
when it comes to dealing with the
se sorts of problems.
Okay, so now I'm going to shift g
ears
into talking about floods as more
of a physical phenomena,
but I'm going to start talking ab
out temperature.
And the reason for that is really
shown in this graph.
So, this is what we call the Cl
ausius-Clapeyron Equation
in graphical form, I suppose.
And so, we have a number of diff
erent substances here
that are liquids at room temp
eratures, including water.
And the basic story is as the te
mperature goes up,
the vapor pressure of these
liquids goes up,
specifically the saturation vapo
r pressure goes up,
which, in layman's terms, just m
eans that these liquids
will more readily evaporate
into the air.
And so, as long as that liqui
d is present,
you're going to have more of tha
t vapor in the air.
And so, that's of course importa
nt then
when we're talking about heavy ra
infall
because temperatures both regiona
lly
and beyond are going up,
and so we see certainly increase
s in recent decades
in temperatures in the Upper Midw
est.
But it's a little bit more compli
cated story than this,
and this is really where the rese
arch is heading these days.
And we need to look beyond just t
he regional map
to bigger maps of the country
and even beyond the country itse
lf,
because if you think about
the heavy rainfall that falls
here in Wisconsin,
most of that is actually coming f
rom the Gulf of Mexico,
and so you might need to worry pe
rhaps even more so
about the kinds of temperature ch
anges
that are taking place there than
what's happening here.
Okay, so we have regional and na
tional perspectives
that are important,
but we also have local perspectiv
es that are important,
and I'm going to give what I thin
k
is an interesting example of this
much later on in the talk,
but I think we can all relate
to the fact
that urban areas can get quite ho
t.
Basically, your pavement, your
buildings, et cetera,
can absorb and hold heat muc
h more readily
than natural surfaces,
and this we call the urban heat i
sland effect.
And so, the result is just highe
r temperatures
in urban areas compared to t
heir surroundings.
Okay.
So, that's the sort of temperatur
e side of things.
And as I said,
that's going to feed into increa
sing precipitation.
This is annual precipitation in W
isconsin.
So, here, we're not necessarily
talking about
those extreme rainstorms,
but rather on a yearly basis
what's happening,
and that annual rainfall is goin
g up.
And it's likely to continue going
up.
And in fact, here you see an a
rticle
from Weather Underground where
they said the last 12 months
have been the wettest 12 consecu
tive months in U.S. history.
Okay, so that's the sort of annua
l perspective.
This is more on the perspective
of extremes.
So, this is a paper that actually
was accepted
toGeophysical Research Le
tterstwo days ago.
And I just got contacted this
morning
saying they want to do a press r
elease,
so this might actually be co
ming out
to a newspaper near you; we'll se
e how it goes.
But here we're looking at storms
that are larger than the 10-year
storm
or larger than the 100-year storm
.
And so, we don't need to worry ab
out this too much,
but basically 10-year storm
has got a 1 in 10 chance of ha
ppening
in a given year at a given loca
tion.
100-year storm, 1 in 100 chance.
The important thing to just keep
in mind for our purposes
is that 100-year storms are wors
e than 10-year storms,
but they don't happen as often.
Okay.
And here we're looking at the
number of these storms
that are taking place or that ha
ve taken place
over the eastern United States,
both 10-year storms or storms
that exceed the 10-year level,
and then storms that exceed the 1
00-year level,
and they're both going up.
They're going up statistically si
gnificantly.
And if you look, you'll see thes
e percentage increases
that actually the 100-year storms
seem to be happening
or the rate of increase is faster
than for the 10-year storms.
So, that again is a regionable--
Regionable.
Regional to national perspective,
but there are also local factors
that are important as well.
So, this is a paper from my PhD
work.
There in the middle,
that gray blob is Charlotte, Nor
th Carolina.
You can find similar results for
other cities,
but basically this is looking at
summertime rainfall,
both the total summertime rai
nfall and in the number of days
with greater than an inch of rai
nfall.
And you see a local peak
in rainfall activity around the c
ity.
I'm going to come back to that
with a more Wisconsin sort of ex
ample later on in the talk.
Now I'm going to shift gears thou
gh
to another Wisconsin example, ac
tually, the Madison example
of what happened on August 20th.
And so, this picture here,
first of all, actually, I'm su
pposed to do it on the screen.
So, there we go.
So, we have the outline of t
he Yahara Watershed
upstream of Lake Monona,
so any rain that falls within thi
s black boundary
is going to make its way into t
he lakes.
And then we have, let's see, al
l these dots around here.
And what these are, these are
citizen-operated rain gauges.
And so, these are basically weat
her enthusiasts,
they have these sitting in t
heir backyards
and every morning they take a lo
ok
and see how much rain is in there
and then there's a web interface
to report that.
If any of you in the audience do
this, thank you.
It's incredibly helpful.
What we're able to use that i
nformation for
is to basically validate
and correct weather radar observ
ations.
So, the same sort of stuff
that you see on The Weather Chan
nel,
that's shown in blue there.
But weather radar on its own is n
ot very accurate,
and so what we can do is we can
compare the weather radar
against those observations from t
he rain gauges
and we can adjust it up or down.
And so, then at the end of the d
ay,
we have a really nice picture,
spatially complete picture of
a large area of what happened.
And when you do that,
you pick up some really isolated
intense pockets,
like right there and right there,
of rainfall that was upwards of a
bout 15 inches.
Okay, so that's interesting.
One thing that's worth noting her
e
is that if you actually look
at the rain
that fell within the watershed th
ough,
it's not a huge amount in the se
nse that the storm
was actually more to the west
and southwest.
And so, one question that we had
was,
"Well, what could've happened her
e?"
And this shows if that storm
had occurred 10 or 15 miles north
east,
instead of getting about four and
a half inches of rainfall
over the watershed, we would've
been more like eight inches.
And so, those of you who were aro
und at that time
can start to imagine what that w
ould've been like.
Not real great, I don't think.
And so, I mentioned that we do
this work
developing software.
I'm not going to go into the det
ails at all,
but the main piece of software i
s this Rainy Day.
I've been really working on it si
nce my PhD work.
And what it allows us to do, am
ong other things,
is put together figures like thi
s,
and I'm going to just walk you
through what's going on here.
Basically, this is the probabilit
y of different amounts
of rainfall affecting the Yahara
Watershed.
And so, four and a half inches,
what we actually got, is here,
and that works out to about
a 20-year storm.
So, that's, you know, rare, bu
t certainly not unheard of
and definitely within the real
m of the sorts of things
that engineers and city planners
would be worried about happening.
And then, on the other hand,
if this more worst-case scenario
where the storm had been a direc
t hit,
that would've been more like
a 200-year storm or even more.
And so, if any of you are inte
rested
in more information about this,
I do have an article in WisContex
t,
I think there's a link to it
on the Wednesday Nite @ the Lab
webpage,
and I talk about some of these is
sues
in a little more detail.
I'm not going to really say a lot
more
about what to do about this [lau
ghing] issue going forward.
We can talk about that in the
Q&A if you like.
But I will say a little bit a
bout why--
So, some people were calling the
flooding
like a 100-year flood.
I just told you it was a 20-year
storm.
Where's the disconnect there?
And generally speaking, those so
rts of disconnects
can happen for the following reas
ons.
Really, the floods are recipes
with multiple ingredients.
Extreme rainfall's probably the
most important one,
but there's also things like
land cover.
So, in urban areas, for example,
if you pave over everything, wher
e's that water going to go?
And then, other factors like
soil moisture.
So, by that, what we're saying i
s,
I guess the easiest way to t
hink about this
is if you have a storm that hits
and it's been raining for th
e past two weeks,
it's going to be a lot worse
than if it had been dry for
the past two weeks
because the soil is not going to
be able to soak up
very much of that rainfall
because the soil moisture is alr
eady very high.
And then, like any recipe, we ha
ve some additional spices.
So, depending on when and where
you're looking,
you might have snow involved, ag
ricultural practices,
high water levels of various kin
ds,
and the complicated role of infra
structure as well.
And so, if you were trying to
figure out
what the recipe was on August 20
th,
I would say it's probably more o
r less this.
But if you wanted to pick some ot
her flood
in some other place or some othe
r time,
the recipe would be different.
Okay.
All right, so,
we're now shifting gears
from talking mainly about precip
itation
to talking about floods themselve
s.
And so, a lot of people,
including climate scientists th
at I respect very highly,
assume that floods are unequivoca
lly getting worse
because of the increases in heav
y rainfall that we've seen.
This paper that came out last yea
r, it's a review
of our sort of state of the un
derstanding of this issue.
You can see from the title there,
"If Precipitation Extremes are
Increasing, Why Aren't Floods?"
So, that seems to suggest that a
ctually
what we think must be happening
maybe isn't happening.
I'm going to argue a little b
it against this
over the course of a couple diff
erent of examples here,
but I want to just highlight
one key thing
because as scientists,
we're not allowed to just say wh
atever we think,
or we shouldn't do that anyways.
We're allowed to say whatever we
want, I suppose.
We have to have evidence for it.
And so, I think that the authors
of this paper
would also say that things might
be happening,
but we just don't have very good
evidence for it.
And I'll say a little bit about
why that might be the case.
So, I'm going to show you a seri
es of plots here
that are showing typical datasets
that flood researchers would
be looking at
to try to understand this problem
of linkages
between climate change and flood
ing.
And so, what we're looking at her
e,
it says Annual Peak Streamflow.
And so, what this really is is in
each year,
what's the highest flow rate that
that river achieved?
And so, then there are,
I don't know how many years
there are there,
but there's one data point per
year since about 1940
for this particular watershed,
which is the Pecatonica River
in the southwestern part of the
state in the Driftless.
And so, what you see here
are some pretty significant decr
eases
in flood activity up to about 19
80
and then things are pretty stabl
e afterwards.
And so, what is going on there?
It's basically improved farm man
agement practices
that have substantially decr
eased the amount of runoff
that you get in response to heavy
rainfall events.
Okay?
So, there's that.
This is another watershed.
This is in Milwaukee.
There might be, as I'll show you
a bit later on in the talk,
there might be a climate change c
omponent
to what's going on here.
But as I said before, land use
is really, really important.
This place has urbanized over tha
t time period
and so, really, that urbanizatio
n
is what's driving this sort of i
ncrease in flooding,
and similar things can be found
in other watersheds in Milwaukee
as well.
Okay, this is the Iowa River
at Iowa City,
and it might not be quite as obv
ious to you.
What I see when I look at this
is sort of one thing going on
and then a drop, and then maybe
something starting to happen
there towards the end.
And that's exactly what happened
here.
So, upstream of Iowa City in ab
out 1950,
they started building the Coralv
ille Dam
specifically to control floo
ding in Iowa City,
and it seems to have done that,
although people living in Iowa C
ity
would say something seems to be
changing there,
and I think it's an open question
,
and climate is definitely one of
the possibilities.
Okay, and then the last one here
is Turkey River,
northeastern Iowa, actually,
not very far from the Pecatonica
River.
This is sort of a pet watershed
where we do a lot of our work.
It'll show up in some of the anal
yses later on as well.
And here, what I see when I loo
k at this
is something that's more or less
stable over time,
and then towards recent, since ma
ybe 1990,
maybe the smaller floods are ge
tting a bit smaller
and the bigger floods are gettin
g quite a bit bigger.
And so, that might be, and I'
m going to show you later on
that we actually do think indeed
this is an example of climate cha
nge.
But taken together then,
you can start to maybe appreciate
the difficulty of parsing out th
at connection
between climate change and flood
s
because you have to end up contr
olling
for all of those other factors.
And if you look at watersheds acr
oss the country
and around the world, essentiall
y, let me back up here,
essentially all of them are go
ing to be affected
by some of these other factors.
And so, how do you know what is w
hat?
Well, I'm going to show you two e
xamples
where we actually try to step aw
ay, at least to a degree,
not completely but to a degree,
from using observations
and instead try to get at this pr
oblem
using computer simulations.
And one of those examples is inde
ed for this Turkey River,
and then the other is for Milwa
ukee.
Okay, so this is Turkey River.
You can see it there in the nort
heastern part of the state.
This is very much an agricult
ural watershed.
There's really no urban land use
to speak of here
other than a few small towns
here and there.
And again, this is another view o
f that same time series
of annual maximum flood observ
ations
that we saw a few slides back.
So, you see, as we said before,
there seems to be this kind of
stable behavior over time
until about 1990, and then thing
s seem to change
with some low floods and some r
eally big floods.
And so, this gray line though
is the result,
it's what we call a trendline,
it's the result of a statistical
analysis.
And if you look at that line, it
's just about flat.
And so, what you would conclu
de from that is,
well, floods aren't even changing
in Turkey River,
let alone changing due to someth
ing like climate impacts.
Okay, so that's sort of typical p
rocedure.
You could do this, you could get
a lot of these sites,
you could look at them and ru
n this analysis
and see what you find.
We did something a little bit dif
ferent
where one of my PhD students, Gu
o,
who's in the back of the room sa
id,
"Well, let's actually take these
data and classify them
"just by when during the year t
hey occurred."
And so we've got in blue those
floods in March and April
and in red those floods in May t
hrough September.
And what happens when you do that
is that idea of there not being
any change taking place
completely disappears
and you have two statistically
significant results
that, to some degree, may be, at
the annual scale,
sort of canceling each other out
.
But this is an example of how
our typical ways
of thinking about running thes
e statistical analyses
can lead us to very incorrect co
nclusions
about what's happening.
Okay, so what is happening?
So, as these trendlines say,
springtime floods in Turkey Rive
r,
they're decreasing in magnitude,
while the summertime floods a
re increasing.
And that's really important
because in Iowa and other places
, the summertime floods
are the ones that typically are
very, very large,
although I suppose the spring
in western Iowa
is a bit of a counterexample
to that.
Okay, so that is some interestin
g results
based just on observations, bu
t we wanted to attack this
from a bit different standpoint h
ere.
And I'm not going to go throu
gh the details
of how this all works, but I'll
say what we're trying to do
is basically instead of just bein
g stuck with 70-odd years
of flood observations that we hav
e in Turkey River,
wouldn't it be nice if we cou
ld have 10,000
or 100,000 years?
I think that would be great,
so let's see if we can figure out
how to do it.
The way that we do it
is we start with this Rainy Day
software
that I mentioned earlier.
And what that can do for us,
we saw one example of what it
can do earlier on in the talk,
but another thing is that it ca
n be used
to generate really large numbers
of hypothetical rainstorms.
And then, what we can do
is we can put those hypothetical
rainstorms in together
with combinations of these ot
her ingredients
that you need to produce floods
and then run a really large
number of computer simulations
and then analyze what comes out
the other side.
Don't try this at home.
[audience laughing]
We don't try this at home.
We try this on very powerful com
puters.
So, originally doing this
on NASA's Center for Climate Simu
lation system.
Now we use this Center for High
Throughput Computing
at UW-Madison, which is a pr
etty unique system;
well, was unique.
Developed here at UW-Madison,
now it's used across the entire w
orld.
Basically, what it allows us to
do
is things like, if a computer lab
in this building
or other buildings across campus,
if those computers are not in use
,
if it's in the middle of the ni
ght, for example,
we can actually push our analyses
to those computers
and then wake up in the morning
and get our results.
So, it's really nice to have a f
ull night's sleep
and feel like you're getting some
thing done as well.
[audience laughing]
And then we have a number of oth
er of our own servers
mainly for data storage
and some computer processing as
well.
So, that's a big part of what we
do is worry about
how to deal with these complicate
d computer systems.
I'm going to show you what one
of these simulations,
what one of these flood simu
lations looks like.
So, what you're going to see--
So, this is the watershed here.
You can see the river network.
It doesn't turn out so well,
but this sort of dendritic ne
twork here.
And then we have, this is th
e rainstorm,
and you're going to see it move
and you're going to see the floo
d that results from it
moving its way down that river s
ystem.
So, there, the storm has passed,
but the flood is making its way d
own.
And so, that's basically just a
graphical representation
of what our computer models are d
oing.
And so, you don't have to wo
rry too much
about the details here.
I'm going to just give you th
e key points.
But this is showing the results
of,
how many simulations is this?
- Man: 10,000.
- Daniel: 10,000, okay.
And each of these 10,000 hypothet
ical events,
we have the amount of rainfall t
hat fell,
we have the flood magnitude that
resulted.
It's a little hard to tell, but
the dot sizes here
correspond to how much soil moist
ure is present.
Blue dots have snow involved in s
ome way or another.
So, we can look at all sorts of d
ifferent things
and we can look at that for
past conditions,
we can look at it for present co
nditions.
And what we end up finding is th
at fewer floods these days
are being caused by this combinat
ion of moderate rainfall
on top of snow, so fewer of these
springtime floods.
More are being caused by high so
il moisture
plus extreme rainfall in the sum
mertime.
And then, I think what the most i
mportant point is,
at least for engineers and pl
anners,
is that what used to be the
100-year flood in Turkey River
is now about a 20-year flood,
meaning it's happening about five
times as often
as we expected it to and five
times as often
as all the infrastructure that's
in place
is supposed to be able to with
stand.
Okay, so that's Turkey River.
Let's go to a bit more urban exa
mple.
So, this is another paper fr
om my PhD work.
This gray blob here is Milwaukee,
and we're going to focus just ve
ry briefly on Cedar Creek,
which is north of Milwaukee, rela
tively unurbanized,
and then Menomonee River,
which is much more heavily urbani
zed.
And if you take those annual flo
od records
like we've shown for other sites,
here we've broken them apart by t
wo time periods,
an early period and a late perio
d.
And the basic story is that in th
e early period,
these two watersheds were be
having not exactly the same,
but roughly similarly
in terms of when in the year the
floods were happening.
But now, there's been a complete
turnaround
in the Menomonee River
and you see almost all of the
flood events
are taking place in the summertim
e.
And so, my colleague, Long Yang,
when he saw this,
he really wanted to understand
what the explanation was.
And so--
Oh, here's another point that's
an important piece of this.
So, this is again sticking in the
realm of observations.
So, on this side, we've got ra
dar rainfall measurements,
and here we have cloud-to-ground
lightning observations.
And so, in both of those,
you see just a bullseye of heavy
thunderstorm activity
right over Milwaukee as compared
to the surrounding areas.
And so, Long was like,
"Well, that cannot be purely coi
ncidence.
"It doesn't make any sense that i
t would be."
And so, he did a really inte
resting set of simulations
only for the July 2010 storm,
which some of you may remember.
That was a pretty bad one in Mil
waukee.
And what he did was,
the two simulations that we're
going to focus on anyways
are what we call the control si
mulation,
which is the real world,
and then what we're calling the
no urban simulation,
where basically he's taken the ur
ban land cover here,
this red and pink, and replaced i
t just by cropland.
And in this case,
we're not using one of these floo
d simulation models
like I showed you for Turkey Riv
er.
What we're using instead is this
thing
that's called the Weather Resear
ch and Forecasting model,
so this is actually simulating
how the atmosphere is working.
And so, instead of rainfall be
ing an input to the model,
it's actually simulating rainfall
within the model.
And so, when he ran those simula
tions,
he got the following results.
So, if you pull the city out of t
he simulation
so you have that no urban simula
tion,
the peak rainfall for that 2010
storm
goes down by more than 50%.
Okay, so that's interesting.
Certainly, the urban area seems t
o be playing
some important role here.
And so, urban heat island is part
of it,
but it's not the full story.
So, I'm going to explain to you
what's going on here,
at least for 2010,
and we suspect this is going on m
ore generally as well.
So, this is, again, an overhead v
iew of the region,
but what we're going to do
is we're going to sort of turn t
his
into a side view in a second
and look along this A to B trans
ect.
And that's the transect.
So there, we have the city.
Then, to the east, we have the la
ke
or in the no urban simulation
we have farmland and then the lak
e.
Okay, so I'm going to walk yo
u through what happens here.
The July 2010 storm, like other
storms in this region,
most other storms, moved from the
west to the east.
Okay, so it's moving across Wisco
nsin.
It reaches Milwaukee.
Milwaukee's warm because of
this urban heat island effect.
What does warm air do?
It rises.
Okay, when warm air rises, the
water that's held in that air
is going to condense and fall out
as rain
because as the air cools as it ri
ses,
it can't hold as much water vapor
.
That's how most heavy rainfall o
ccurs.
Okay, so that's something that
we've understood pretty well
in different cities around the
country and around the world.
But what happens in Milwaukee is
a little more complicated.
So, what happens when that air,
that storm reaches the city,
the air rises, you have rain fall
ing,
well, as that air rises,
some air has to come and fill in
that void
down near the ground surface,
and the only air that's there is
air that's over the lake
and it's holding a lot of water v
apor
because it's right over that lake
and it's the middle of July.
And so, what ends up happening
is you have the storm coming in,
warm air rising,
moisture rushing in, it's rising
, producing more rainfall,
also pulling more air in.
And so, there's this feedback lo
op
that ends up making this rainfal
l
much worse than it is in the no u
rban simulation.
And so, what this figure is show
ing
is actually the wind patterns alo
ng that transect.
And you see, this is what we call
the lake breeze intrusion,
where the air off the lake i
s making its way
all the way into the city,
whereas here, that moist air
from the lake
isn't intruding at all.
And so, that's just a single sto
rm.
A colleague and I have a pro
posal that's in review right now
to hopefully have the chance
to understand this a little bit b
etter
and in particular to try to und
erstand--
So, the Milwaukee Metropolitan
Sewage District, for example,
has a very ambitious plan,
actually the most ambitious plan
in the entire country
for increasing urban green spaces
.
And so, can that greenification,
I'm not sure that's a word,
but can it help combat this sort
of issue in Milwaukee
in addition to creating some
nice spaces
and having those trees
to soak up some of that runoff as
well.
So, fingers crossed on that p
articular thing.
Okay, so that's basically the en
d of the talk.
[audience laughing]
Just to summarize then,
on the impact side, floods are be
coming less deadly
but becoming much more damaging.
I think this impact side needs a
lot more attention
than it has gotten historically.
It's a really difficult thin
g to look at,
and the paper that we just had ac
cepted this week
does start to look at this sort
of issue,
essentially, at a regional or nat
ional scale,
how adequate is the infrastructu
re that we have in place
compared to what we're facing
these days.
Recent increases in extreme rain
fall,
it's really a combination of
factors
stemming all the way from global
to local features,
with the Milwaukee example being
a clear case
of that local effect.
And then, despite what our ob
servations say--
I showed you that paper that sai
d,
"Well, floods don't seem to
be increasing."
I would say that despite what our
observations say,
that's actually not the case,
because I, in fact, showed y
ou two examples
of how climate is impacting floo
ds.
But in order to really unders
tand these sorts of problems,
it requires really knowing the
place where you're looking.
So, downloading all of the fl
ood measurements
from the whole country and just r
unning some analysis
is not going to work.
You have to understand the specif
ics of what's going on.
But what you do when you start lo
oking at
the specific circumstances in dif
ferent places
and you really understand what's
going on,
you see that, yes, the floods ar
e changing due to climate.
And so, I'm going to stop there
and hopefully we've got some t
ime for questions.
[audience applauding]