Tangible Approaches to Quantify Climate Change - APWA Conference

OHM-ADVISORS.COM
Quantifying Climate Change for
Stormwater & Wastewater
Systems
Gregory P. Kacvinsky, P.E.
OHM Advisors
APWA Michigan Annual Conference
May 21, 2015
ARCHITECTS. ENGINEERS. PLANNERS.

Climate is what you expect;
weather is what you get
Edward Lorenz
Mathematician and Meteorologist
OHM-ADVISORS.COM ARCHITECTS. ENGINEERS. PLANNERS.

• Long design life of infrastructure
• Increasing precipitation already
observed across the Midwest
• Climate models predict
continued increases in both
average and extreme rainfall
Why is this important?

• We state that the ‘design life’ is 50
years, BUT:
• Detroit, MI: Average age of Detroit Water
and Sewerage pipes is 80 years
• Minnesota: One third of state’s sewers are
older than 50 years
• Philadelphia, PA: Average age of sewers is
100 years, with some pipes as old as 190
years
• New Jersey: Average age of sewers is 70
years
How Long will it Last?

• Infrastructure built in
the 1950s:
• Simplified methods
• Few (if any) rainfall statistics
to rely on (pre-TP-40)
• Less knowledge of flood
potential (pre-FIRM era)
• We are still living with this
infrastructure

• Rehabilitating sewers increases life
expectancy, BUT:
• Pipe lining typically results in a smaller effective
diameter
• Rehabilitated pipe can have a reduced flow
capacity
• We should assume that the pipe we
design will be in service 80-100 years
from now.

Climate models (forward-looking)
Rainfall statistics (rear-looking)
Modeling – how does all this impact utility sizing?

Predicted Changes in
Annual Average Precipitation
• 1986-2005 data compared to 2081-2100 multi-model mean
• 10-20% increase in Great Lakes Region
• IPCC Summary for Policy Makers

• National Climate
Assessment, US Global
Change Research Program
• 1971-2000 versus 2041-
2070 with continued
emissions scenario
• Michigan existing average
is about 32.2” per year, so
increase in range of 2.4” to
4.0” means 7% to 12%
more rain predicted
Annual Average Precipitation

Assessment, US Global
Change Research Program
• “Heavy” rains defined as top
2% largest rainfall events of
each year
• 1971-2000 vs 2041-2070
with continued emissions
scenario
• Projections indicate heavy
rains will occur more
frequently
Heavy Rain Events

Bottom Line:
In Michigan, we should be prepared for
more rain: heavy rains should become
more frequent and rainfall intensities
should increase by 10-20%.
Precipitation

Observed Changes in Very
Heavy Precipitation
Assessment
• “Very Heavy” rains
defined as top 1% of
all observed daily
events (1958 to
2012)
• Big storms have
gotten more intense
over the past 50
years

Recent Rainfall Statistics
• Technical Paper 40 – Published in 1961
• Length of record: Ranged from 14-48 years
• Most recent data: 1958
• 57 years out of date
• Bulletin 71 – Published in 1992
• Length of record: up to 87 years (60 years in Michigan)
• Most recent data: late 1980s
• 25-30 years out of date
• NOAA Atlas 14 – Published in 2013 (for Michigan)
• Length of record: Ranged from 30 to over 119 years
• Most recent data: 2012

Recent Rainfall Statistics
• NOAA Atlas 14
• Denser grid of
observations than
previous studies
• Significant
differences
compared to
previous studies
(especially for less
frequent storms)
Source: NOAA Atlas 14, Volume 8 (2013)
Percent difference between NOAA Atlas 14 and TP40
for the 100-yr 24-hr rainfall

3.0
3.5
4.0
4.5
5.0
5.5
6.0
100-yr 24-hr
100-yr 3-hr
2.0
2.5
3.0
3.5
4.0
↑ 24%
↑ 38%
3.0
3.5
4.0
4.5
5.0
NOAAAtlas14
TP40
Bulletin71
LEGEND

10-yr 2-hr
100-yr 3-hr
↑ 26%
2.0
2.5
3.0
3.5
4.0
1.6
1.7
1.8
1.9
2.0
2.1 ↑ 14%
3.0
3.5
4.0
4.5
5.0
NOAAAtlas14
TP40
Bulletin71
LEGEND

2.0
2.5
3.0
3.5
4.0
1.6
1.7
1.8
1.9
2.0
10-yr 2-hr
100-yr 3-hr
↑ 40%
↑ 11%
3.0
3.5
4.0
4.5
5.0
NOAAAtlas14
TP40
Bulletin71
LEGEND

2.5
3.0
3.5
4.0
1.7
1.8
1.9
2.0
2.1
10-yr 2-hr
100-yr 3-hr
↑ 22%
↑ 11%
3.0
3.5
4.0
4.5
5.0
NOAAAtlas14
TP40
Bulletin71
LEGEND

Comparing Statistics
• August 11-12, 2014
• Catastrophic rainfall event in
Metro Detroit
• Local press coverage
categorized this as a 500-yr
storm in some locations
• However, using recent
statistics shows us it wasn’t
as rare as we thought

City
Peak 3-hour
rainfall (in.) TP 40 Bulletin 71 NOAA Atlas 14
Garden City 2.89 63 >100 28
Exceedance
Interval
Detroit (west fringe) 3.21 >100 >100 48 25-yr to 50-yr
Romulus 2.84 56 >100 28 50-yr to 75-yr
Westland 2.91 66 >100 29 75-yr to 100-yr
Royal Oak 4.26 >500*
>500*
275 >100 yr
*
Extrapolated
August 11-12, 2014 Rainfall Event
Exceedance Interval (years)
Key

City
Peak 6-hour
Garden City 3.49 79 >100 37
Exceedance
Interval
Detroit (west fringe) 3.59 91 >100 43 25-yr to 50-yr
Romulus 3.65 98 >100 48 50-yr to 75-yr
Westland 3.49 79 >100 36 75-yr to 100-yr
>500*
200 >100 yr
*
Extrapolated
Key

City
Peak 12-hour
Garden City 3.91 68 >100 30
Exceedance
Interval
Detroit (west fringe) 4.24 93 >100 36 25-yr to 50-yr
Romulus 4.03 77 >100 28 50-yr to 75-yr
Westland 3.94 70 >100 23 75-yr to 100-yr
>500*
167 >100 yr
*
Extrapolated
Key

• Flow rates and pipe sizes dependent on selection of climate
data
• Climate data based on past statistics only and are not
forward-looking
• Need new tools to address future climate patterns
Uncertainty in Design
?

• Several Independent Methods:
 Updating Rainfall Statistics (national AND local
data, if available)
 EPA Stormwater Calculator
 Confidence Intervals
Tools for Addressing Climate Trends

• 1949-2012 Detroit City Airport Rainfall Data
• Compared peak annual rainfall totals (1949-2012) against
more recent subset (1990-2012)
• Results showed a recent increase in peak rainfall depths,
which tends to reflect NOAA Atlas 14 findings
• 7.4% increase for 10 year, 24 hour storm
• 10.2% increase for 10 year, 1 hour storm
Updating Rainfall Statistics

7.4% increase
for 10-yr, 24-hr
storm

Using Models to Design for
Climate Change

EPA Stormwater Calculator
http://www2.epa.gov/water-research/national-stormwater-calculator
Estimates annual
amount of
rainwater &
frequency of
runoff from a
specific site based
on local soil
conditions, land
cover, and historic
rainfall records.

EPA Stormwater Calculator:
Climate Change Options
• Scenarios:
 Hot/Dry
 Median Change
 Warm/Wet
• Time Period:
 Near Term
(2020-2049)
 Far Term
(2045-2074)

Ann Arbor Example
Applying
Rainfall
generated
to a
Sanitary
Sewer
Analysis

Ann Arbor Example
• Far Term (2045-2074) was selected because design life is
>50 years
• Warm/Wet scenario was selected to be conservative
• Predicted percent change in monthly rainfall data were
extracted from the tool

Ann Arbor Example

Ann Arbor Example
Perform
frequency
analysis
using
hydrologic
model
output
based on
past rainfall
data to get
existing
design flow

Ann Arbor Example
Rainfall data
adjusted for
climate change
based on
predicted
monthly %
change
Ran adjusted
rain through
model
10% increase in
future design
flow
10%
increase for
25-yr flow

Ann Arbor Example
• Consider 10% increase in peak flow at WWTP to account
for future climate change (2045-2074).
• Technical Oversight and Advisory Group (TOAG) quote:
…TOAG Members indicated that the
recommendation to increase the 25 year Design
Event flow rate by 10% is reasonable since this is
a mid-range value which falls near the center of
the climate change forecast models showing
“best case” and “worst case” future conditions…

Novi Study

Novi Study
10-year flow = 22.5 cfs
based on running all 64
years (1949-2012) of
rainfall through model

Novi Study
22.5 cfs = 10-year flow
based on running 1949-
2012 rain data through
model
model
7% increase based
on recent trends

Novi Study
model
7% increase based
on recent trends
based on adding 10%
for future climate
change predictions
10% increase
based on future
climate change

Novi Study
How does this impact pipe size?
22.5 cfs: 30-inch sewer
26.5 cfs: 36-inch sewer
18% increase in flows, due to
both rear-looking statistics and
forward-looking climate models

Novi Study
30-inch sewer will be ok TODAY,
but will surcharge above surface
elevation (SSO) if statistics and
climate projections hold

Stormwater Footprint
NOAA Atlas 14 rainfall statistics
show a large increase in the
100-yr 24-hr storm. In some
parts of Michigan, it has gone up
20%-25%

• Using confidence intervals (in NOAA Atlas 14 data)
may be a reasonable way to address future climate
variability:
• Example: (NW Oakland County)
• 100-yr 24-hr rainfall = 5.45 inches
• Climate models put the likely range closer to
6.0-6.5 inches (second half of 21st Century)
• How will this impact developability?
Stormwater Footprint

Confidence Intervals
• 90% probability of observing a value within the
range
• Climate models predict an increase in future
precipitation values so use a value towards
the upper bound of the confidence interval

NOAA Atlas 14
Confidence Intervals
http://www.nws.noaa.gov/oh/hdsc/index.html
• Frequency
estimates for
Detroit, MI
• 90% confidence
intervals given
• Lower bounds
are 13.3% lower
than average
• Upper bounds
are 20% higher
than average

• Recent statistics indicate rainfall depths for design
storms have been increasing in Michigan
• Climate models project further increases in rainfall
depth for future storms
• Tools are available to estimate future rainfall increases
and develop future design flows for different parts of
the state
• Using these tools for SE Michigan communities
indicated future design flows should be increased
~10%-20% above existing
Conclusions

• In most cases, this translates to an increase of one pipe
size:
• 12-inch to 15-inch
• 30-inch to 36-inch
• Etc.
• When replacing storm or sanitary sewers, consider this
change
• Also consider that the pipe may be lined in the future
(design for reduced future diameter)
Conclusions

Tangible Approaches to Quantify Climate Change - APWA Conference

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