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 ConferenceMay 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



• 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






• 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






• “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

Predicted Changes in Heavy Rain Events





• “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

Predicted Changes in 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%.

Predicted Changes in 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



• 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



• 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

NO

AA

Atl

as

14

TP

40

Bu

lleti

n 7

1

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

NO

AA

Atl

as

14

TP

40

Bu

lleti

n 7

1

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

NO

AA

Atl

as

14

TP

40

Bu

lleti

n 7

1

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

NO

AA

Atl

as

14

TP

40

Bu

lleti

n 7

1

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



CityPeak 3-hour rainfall (in.) TP 40 Bulletin 71 NOAA Atlas 14

Garden City 2.89 63 >100 28Exceedance 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





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



Key






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




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)


EPA Stormwater Calculator: Ann Arbor Example


Applying

Rainfall

generated

to a

Sanitary

Sewer

Analysis



• 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





Perform frequency analysis

using hydrologic

model output

based on past rainfall data to get

existing design flow



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



• 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


Novi Study

10-year flow = 22.5 cfs based on

running all 64 years (1949-2012) of rainfall through

model


Novi Study


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

26.5 cfs = 10-year flow 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 FootprintNOAA 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


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


Engineering

Tangible Approaches to Quantify Climate Change - APWA Conference