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Geotechnical News • September 2017
GEOHAZARDS
Adapting to Climate Change: a Web Based
Intensity-Duration-Frequency (IDF) Tool
Slobodan P. Simonovic
Introduction
Extreme rainfall events affect water
quality, infrastructure management
and public safety. Municipalities
across Canada, including Thunder
Bay, Sault Ste. Marie, Peterborough,
Hamilton, Mississauga, London, Cal-
gary, Edmonton, Moncton, Fredericton
and Winnipeg have recently been
affected by extreme rainfall related
flooding. Together, these events have
caused billions of dollars of damages
and losses for homeowners, insur-
ers and municipalities. The Canadian
insurance industry has experienced a
notable trend in disaster losses over
the past thirty years. Three of the most
expensive insurance industry disaster
loss events from 1983 to 2014 were
associated with flooding, including:
$5.15 billion in southern Alberta
(2013) and $1 billion (2013) and $732
million (2005) in the Greater Toronto
Area.
Rainfall intensity-duration-frequency
(IDF) curves are used for a number
of water management applications
in Canada, including the planning,
design, operation and maintenance
of stormwater management systems,
wastewater systems, stormwater
detention ponds, culverts, bridges,
dams, pumping stations, roads and
master drainage planning.
IDF curves have traditionally been
developed based on the assumption
that analysis of historical rainfall
records can be used to predict future
rainfall conditions. This is commonly
referred to as stationarity; the assump-
tion that the environment will behave
as it always has. According to this
assumption, historical data collected
at rainfall monitoring stations are
analyzed and used to develop statistics
that give an indication of the likeli-
hood of future extreme rainfall events.
For example, municipal stormwater
management systems are typically
designed to accommodate flows asso-
ciated with 2 to 100 year return period
events lasting 10 minutes to 24 hours.
However, it is now widely acknowl-
edged that past climate conditions are
no longer indicative of future climate.
Climate change will result in intensifi-
cation of the global hydrologic cycle,
causing increased intensity of wet
and dry extremes and accompanying
floods and droughts. One of the most
significant expected impacts of climate
change in Canada is an increase in the
intensity and frequency of extreme
weather events. While the impacts
of climate change vary throughout
Canada, an example from southern
Ontario suggests an increase in the fre-
quency of storms of equivalent size. A
1-in-100 year event, for example, may
become a 1-in-30 year event in the
next few decades (Peck et al, 2012).
Consequently infrastructure built to
manage 1-in-100 year rainfall events
based on existing IDF curves will be
grossly under-sized or under-designed
for the job, not perform as intended
and create considerable economic
implications for existing and planned
water management infrastructure
across Canada.
A New IDF Tool
The process of updating and incor-
porating climate change impacts into
local IDF curves is highly technical.
The lack of locally relevant climate
change impact information has been
noted as a challenge that is difficult
to overcome in many municipalities,
including those with very high adap-
tive capacity (Sandink et al, 2016).
The intensity-duration-frequency
under climate change tool (IDF_CC
Tool) was designed to allow water
managers, municipal infrastructure
professionals, provincial and federal
government agencies, researchers,
consultants and non-profit groups to
quickly develop estimates related to
the impact of climate change on IDF
curves for almost any local rain moni-
toring station in Canada.
How does the IDF_CC tool
work?
The IDF_CC Tool was designed as a
simple and generic decision support
system to generate local IDF curve
information that accounts for the
impacts of climate change (Simonovic
et al, 2016). It is publicly accessible
online
), with a
user-friendly Google Maps interface
(Fig. 1). The tool provides precipita-
tion accumulation depths for a variety
of return periods (2, 5, 10, 25, 50 and
100 years) and durations (5, 10, 15
and 30 minutes and 1, 2, 6, 12 and 24
hours), and allows users to generate
IDF curve information based on his-
torical data (Fig.2), as well as future
climate conditions that can inform
infrastructure decisions (Fig. 3).
The IDF_CC Tool allows users to
select multiple future greenhouse
gas concentration scenarios (RCPs)
and apply results from a selection of
9 Global Climate Models (GCMs)
downscaled using two downscaling
methods that simulate various cli-
mate conditions to local rainfall data
(Pacific Climate Impacts Consortium
- PCIC, 2013). The tool also applies
a novel downscaling method with
localized temporal data (Srivastav et
al, 2014).
