Storm intensity not increasing - factual review of engineering data - Canada and Ontario

Review of Weather Event
Statement in
Insurance Bureau of Canada’s
Telling the Weather Story
prepared by
Institute for Catastrophic
Loss Reduction
Robert J. Muir, M.A.Sc., P.Eng.

Content
• Overview
• Telling the Weather Story Statement on Increased Frequency of
Storms and Weather Events
• Contrary Analysis and Data
– Environment Canada Reports
– Environment Canada Data (now Environment and Climate Change)
– Local and National Rain Intensity Trends
• Telling the Weather Story Data Review
– Frequency Shift Theory and Error
– Frequency Shift Data and Source Review
– Comparison to Actual Data
• Telling the Weather Story Theory as Fact
– Economic Reports / Strategies
– Policy (Chamber of Commerce, Energy Policy, Local Civic Policy)
– Insurance (Premium Costs/ Endorsement Advertising)
• Summary
Feb.5, 2016 Telling the Weather Story Review 2

Overview
• Telling the Weather Story makes a statement on the increased frequency
of storms and weather events, indicating that in parts of Canada, events
that occurred every 40 years are occurring every 6 years, due to climate
change – Environment Canada IDF data is cited as the source but not
provided / not available through the authors.
• The statement on increased frequency is unfounded as it is based on a
theoretical shift in temperature frequency from a global climate change
report, and is contrary to Environment and Climate Change Canada’s
actual reports, analysis and data on local rainfall intensity trends.
• The Telling the Weather Story statement, based on temperature theory
has been i) embraced as rainfall facts and research by many
organizations, ii) embellished to apply to extreme rainfall, and iii)
considered in policy and economic reports.
• The unfounded association of increased flood damages to increased
rainfall frequency can misdirect mitigation policies and efforts from the
root causes of increased flood damages and toward low ROI efforts (e.g.,
away from infrastructure rehabilitation and comprehensive risk
management policies and pricing, and instead toward other actions to
address erroneous storm frequency shifts).

Weather Story Statement
• Institute of Catastrophic Loss Reduction (ICLR) report for Insurance Bureau of
Canada (IBC) states there is an increasing frequency of weather events, including
storms, due to climate change (page 15).
• A shift in event “return period” from 40 years to 6 years is noted (a rare storm event
with a previous 2.5% chance per year (1/40), now has a 17% chance per year (1/6))
• The general type of data used by Environment Canada to characterize storm
severity is noted in the reference (page 64), but no actual analysis is provided.

Contrary Analysis & Data - Environment Canada Report 2011
• Environment Canada’s Adaptation and Impacts Research Climate Research Division
reviewed Canadian and Ontario rainfall analysis and found only non-significant
trends in intensity, and reported both increases and decreases in storm severity,
contrary to the Telling the Weather Story statement.
• The Environment Canada report Methodologies to Improve Rainfall, Intensity-
Duration-Frequency (IDF) Estimates, A Southern Ontario Pilot Study (December
2011) describes Canadian and Southern Ontario data in Chapter 6 -IDF Information
in a Changing Climate :
– Canada (page 75): “The majority of trends in daily, multi-day (i.e. 3-, 5-, 10-
day) and sub-daily rainfall have been determined to be non-significant,
varying with duration of precipitation and regional location, and including
decreases as well as increases.”
– Ontario (page 78) “… within Ontario, a number of studies have conducted a
trend analysis of Environment Canada’s short-duration rainfall intensity data
(Adamowski and Bougadis, 2003; Adamowski et al., 2010; Bruce et al., 2007;
Klaassen and Seifert, 2006; Zhang and Burn, 2009; Hogg and Hogg, 2010). The
majority of the trends were determined to be non-significant with no simple
patterns or uniform rates of change evident in the short duration rainfall.”

Contrary Analysis & Data - Environment Canada Report 2014
• Environment Canada staff have published a paper in Atmosphere-Ocean entitled
Trends in Canadian Short‐Duration Extreme Rainfall: Including an Intensity–
Duration–Frequency Perspective, by Mark W. Shephard, Eva Mekis, Robert J.
Morris, Yang Feng, Xuebin Zhang, Karen Kilcup & Rick Fleetwood (November
2014).
• The report indicates no 40-year to 6-year frequency shift (i.e., Weather Story 1
standard deviations shift in the mean of rainfall probability density function),
shows both increases and decreases in extreme rainfall frequency across Canada,
and only a few percentage of statistically significant increases or decreases, e.g. :
– (Abstract): “The single station analysis shows a general lack of a detectable trend
signal, at the 5% significance level … 30-minute to 24-hour durations show that, on
average, 4% of the total number of stations have statistically significant increasing
amounts of rainfall, whereas 1.6% of the cases have significantly decreasing amounts.
– “For the shortest durations of 5–15 minutes, the general overall regional trends in the
extreme amounts are more variable, with increasing and decreasing trends occurring
with similar frequency…”
– “This indicates that at most locations across Canada the traditional single station IDF
assumption that historical extreme rainfall observations are stationary (in terms of the
mean) over the period of record for an individual station is not violated.”

Contrary Analysis & Data - Environment Canada Data
• Environment Canada’s publishes rainfall intensity and frequency data and analysis
for weather stations across Canada through its “Engineering Climate Datasets”
• Data including trends are readily available for 563 locations across Canada from
this site: http://climate.weather.gc.ca/prods_servs/engineering_e.html
• Example rainfall data and statistics for the Toronto Bloor Street weather station are
shown below.

Contrary Analysis & Data - Local Rainfall Intensity Trends
• Environment Canada’s Toronto Bloor Street rainfall data show decreasing trends in
intensity for all storm durations 5 minutes to 24 hours, some statistically significant
decreasing rainfall maxima (file: idf_v2-3_2014_12_21_615_ON_6158355_TORONTO_CITY_t.png)

• Environment Canada’s Toronto Bloor Street rainfall decreasing trends in intensity
result in lower extreme value statistics for drainage design (files: idf_v2-
3_2014_12_21_615_ON_6158355_TORONTO_CITY.txt for version dataset 2.3 to 2007, version 1 to 2003 and
hardcopy records to 1990)

• Environment Canada’s Pearson Airport decreasing and increasing trends in extreme
value statistics for drainage design even after record 2013 event (files: idf_v2-
3_2014_12_21_615_ON_6158731_TORONTO_INTL_A.txt for version dataset 2.3 to 2013, to 2007 per v2.2,
to 2003 per v1, to 1990 per hardcopy records)

• Environment Canada’s data shows decreasing and increasing short duration
intensities in Ontario and notes trends are not significant (Heather Auld, Principal Climate
Scientist Risk Sciences International, “Climate Adaptation Tools: Extreme Rainfall Intensity-Duration-
Frequency (IDF) Curves” , slide 39 shown below).

intensities at Ontario long term stations (R. Muir summary of Engineering Climate Datasets,
version 2.3, per Environment Canada’s most trend file idf_v_2-3_2014_12_24_trends.txt Ontario stations
with 45+ years of record and last year of data within last 10 years).

intensities at Ontario long term stations (R. Muir summary of Engineering Climate Datasets,
with 45+ years of record and last year of data within last 10 years , showing correlation to EC trend plots).

• Environment Canada’s data shows more statistically significant decreasing
intensities at Southern Ontario stations (R. Muir summary of Engineering Climate Datasets,
with latitude below 44 degrees).

Contrary Analysis & Data - National Rainfall Intensity Trends
(minutes) and long duration (hours) intensities, and few statistically significant
trends across Canada as shown in the table summary below for long term stations (R.
Muir summary of Engineering Climate Datasets, version 2.3, per Environment Canada’s most recent trend file
idf_v_2-3_2014_12_24_trends.txt stations with 45+ years of record and last year of data within last 10 years).
No statistically significant upward
or downward trends (West)
More statistically significant downward
than upward trends (Ontario)
More statistically significant upward than
downward trends (East)

(minutes) and long duration (hours) intensities across Canada, few significant trends
as shown in the graphical summary below (R. Muir summary of Engineering Climate Datasets,
version 2.3, per Environment Canada’s most recent trend file idf_v_2-3_2014_12_24_trends.txt).
• Few weather stations show statistically significant increasing trends (only 3% of short
duration data including 5, 10 and 15 minute durations).

(minutes) and long duration (hours) intensities across Canada, few significant trends
as shown in the tabular summaries below grouped by province or territory for each
rainfall duration (R. Muir summary of Engineering Climate Datasets, version 2.3, per Environment
Canada’s most recent trend file idf_v_2-3_2014_12_24_trends.txt).
• Trend counts are predominantly not statistically significant for all storm durations.

• Environment Canada’s data show showing decreasing and increasing short duration
(minutes) and long duration (hours) intensities across Canada have been mapped
across Canada (R. Muir summary of Engineering Climate Datasets, version 2.3, per Environment Canada’s
most recent trend file idf_v_2-3_2014_12_24_trends.txt linked to station coordinates in online mapping,
per http://www.cityfloodmap.com/2015/12/canadian-extreme-rainfall-map-climate.html).

• Environment Canada’s data shows some increasing short duration intensities due to the
increasing sample size for a skewed rain distributions (known skew in Toronto IDF data and
annual maxima per Environment Canada, observed sample mean is underestimated for small samples and only
approaches true population mean per Kirk G. Fleming's article "Yep, We’re Skewed", VOLUME 2/ISSUE 2
CASUALTY ACTUARIAL SOCIETY – greater coefficient of variation requires larger samples to reach true mean)
• Increases over time is statistically expected and does not reflect an underlying change in
the fundamental rainfall ‘population’ characteristics over time (e.g., climate change).

Weather Story Review – Frequency Shift Theory
• The Telling the Weather Story presentation describes shifts in average and extreme
climate data using a theoretical “bell curve” with no actual climate data.
• A whole standard deviation shift in the average is shown to make extremes more
frequent (40 year event becomes a 6 year event in a standardized bell curve).

Weather Story Review – Frequency Shift Error
• After presenting data on observed temperature shifts of many degrees, an error
appears to be made associating “rainfall rate of so many millimetres per hour” with
a 40 year to 6 year frequency shift if “you just shift the mean by one degree’.
• The association of rainfall event frequency is inconsistent with IPCC discussion on
temperature frequency, and the stated shift of ‘one degree’ is inconsistent with a
one standard deviation shift in bell curve average required for a 40 to 6 year shift.

Weather Story Review – Frequency Shift Data
• A 40 year to 6 year return period shift is based on a one standard deviation shift in
the mean of a standard normal distribution, or bell curve. Cumulative probability
tables show this theoretical shift from z = 1.96 to z = 0.96 (i.e., mean shift of 1.0).
Exceedance probability of
P = 17 % with
z= 1.96 - 1.00 = 0.96
Return period of
1/P = 6 years
Exceedance probability of
P = 2.5 % with
z= 1.96
Return period of
1/P = 40 years

Weather Story Review – IPCC Source Review
• The Telling the Weather Story release presentation references an Intergovernmental
Panel on Climate Change (IPCC) report that discusses general aspects of climate data
variations (shifts in statistical average, variability and skew), but does not analyze
actual data and references only temperature, and not rainfall.

Weather Story Review – Comparison to Actual Data
• The Telling the Weather Story’s one standard deviation, bell curve shift in climate
data average contradicts Environment Canada data trends for rain intensity.
“Weather Story” increase
from 16.5 mm to 23.1 mm
over 15 minute duration
(one standard deviation
increase of 6.6 mm)
Actual decreasing trend
over 2 hour duration (one
standard deviation
increase of 10.7 mm)
over 24 hour duration
(one standard deviation
increase of 14.8 mm)

Weather Story Theory as Fact - Economics
• The Telling the Weather Story’s statement “weather events that used to happen
every 40 years are now happening once every 6 years in some regions of the
country” appears to be based on theoretical bell curve shift in weather that is
contrary to Environment Canada data and analysis.
• However economists repeat the theoretical statement as fact in their analysis.
• “severe weather” has been substituted for
Weather Story’s theoretical statement on
“weather events”.

• Media reports substitute ‘storms’ for ‘weather events’ and associates storm
frequency to ‘damaging events’.

• Media reports substitute ‘storms’ for ‘weather events’, although the IPCC reference
on frequency changes relates to temperature, and the IBC presentation did not
reference actual data and suggested
shifts of ‘one degree’.

Weather Story Theory as Fact - Policy
• A Climate Change Adaptation Strategy for Canada by the Canadian Chamber of
Commerce indicates “rising frequency and severity of extreme weather events in
Canada, such as floods, storms and droughts” and references the Weather Story
statement, substituting ‘storms’ for the Weather Story’s ‘weather events’.

Weather Story Theory as Fact – Policy
• Economists have have repeated the theory of frequency shifts as fact, e.g., “The
reality is that the frequency of weather events has increased.” in the context of
disaster mitigation policy.

• Policy organizations repeat the statement from economic analysis, substituting
‘storms’ for the Weather Story’s ‘weather events’ and citing ‘research’ on storms.

• More policy organizations repeat the statement cited from the Toronto Star,
substituting ‘storms’ for the Weather Story’s ‘weather events’ , adding the
statement relates to ‘extreme’ weather events, and that “Ontario is experiencing
significant changes”, contrary to Environment Canada’s Ontario analysis.

Weather Story Theory as Fact (Cont’d)
• Media have related the Weather Story statement on ‘weather events’ to ‘heavy
rainfall’ events, and have stated “severe weather is on the rise” :

• The media reports that “the weather has changed” including “more torrential rain”

• IBC substitutes ‘extreme weather events’ for ‘weather events’, describes trends in
storm regularity, and links this to insurance premium increases.

• Insurance industry credits Weather Story statement to Environment Canada
although statement contradicts Environment Canada data and analysis, and
insurance industry substitutes ‘severe weather events’ for ‘weather events’.

• Insurance industry again credits Environment Canada to promote Aviva Water
Protection, as “As an endorsement to existing Aviva personal property policies that
qualify where sewer back-up protection is in place.”

• Insurance industry repeats Weather Story statement and substitutes ‘extreme
weather events’ for ‘weather events’ and adds and ‘hail’, ‘wind’, and ‘precipitation’
have also had the bell-curve shift in 40 year to 6 year frequency:

• Insurance industry indicates ‘greater instances of extreme weather’ and ‘storms
happening more often and lasting longer’ :

• Insurance industry cites “days of rain” instead of data related to extreme storms ,
and does not consider changing criteria for days with rain:

Progression of “Weather Story”
• Started with a theoretical
discussion from IPCC on the
changes in the distribution of
temperature
• Presented a theoretical shift
in climate data using a bell
curve and a one standard
deviation shift in averages
• Associated theoretical shift in
event frequency to weather
events, implying storms,
happening in parts of Canada
• Referenced Environment
Canada data but did not use
Environment Canada rain
data or analysis that does not
support such intensity trends
• Organizations promoted
theory as fact, associate
weather with severe rain
events, explaining increasing
insurance premiums & tie to
risk mitigation policy.

Summary
• A theoretical discussion from the IPCC on the changes in the distribution of temperature has
been convoluted into:
1) A statement on theoretical probability shifts for a standard normal bell curve
(Telling the Weather Story presentation transcript)
2) A statement on the frequency of actual weather events (once every 40 year events occurring now
every 6 years) caused by climate change
(Telling the Weather Story publication)
• The Telling the Weather Story statement is contrary to Environment Canada rain reports, data
and analysis that does not show an overall increasing rain intensity trend in Canada or
Ontario. In fact, in southern Ontario, there are more statistically significant decreasing rain
intensity trends than increasing ones.
• Observed rainfall intensity averages (sample means) increase over time with larger samples
sizes (years of record) because the underlying rain distribution is skewed (sample mean bias).
• The Telling the Weather Story statement on weather events, originating from average
temperature changes discussions, has been misinterpreted by many to apply to:
1) Severe Weather Events,
2) Extreme Weather Events,
3) Storms,
4) Torrential Rain,
• Many organizations promote the Weather Story statement as fact, describe a this statement
based on theory as ‘reality’ based on ‘research’, credit the statement to Environment Canada
as the source, and use it support economic and other policies.
• Due to the Weather Story statement, policies and efforts toward mitigating increasing urban
flood damages may be misdirected to climate change mitigation, as opposed to more
effective risk identification/management efforts, urban planning/stormwater management
policies and infrastructure remediation/capital investment efforts that address the root
causes of increased damages, not related to theoretical storm frequency shifts.
5) Precipitation,
6) Wind,
7) Hail.

Storm intensity not increasing - factual review of engineering data - Canada and Ontario

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