14  Example of an adaptation process for pluvial floods

This fact sheet describes an example of a municipality’s adaptation process for the risk of pluvial (stormwater) flooding. The steps described in fact sheets 10 to 12 are repeated in the following paragraphs. For further details and other application examples, readers can consult Ouranos and MELCCFP (2024), as well as the accompanying workbooks¹. The following example is purely fictitious. Implementing an adaptation process requires human and financial resources that can be significant. That means it will have to be adjusted in accordance with the resources available. It is not necessarily possible to transpose the following example to all municipalities. The procedure used to estimate future rainfall intensities that is presented in Table 14.2 is described in Chapter 7 of Mailhot, Alain and Bolduc, Samual and Talbot, Guillaume (2024).

Objectives, scope and context of the adaptation process

The objective is to determine whether the intensification of extreme rainfall in a future climate will lead to an increase in the risks of pluvial flooding in certain areas of the municipality under study and, if necessary, to identify adaptation measures and develop a plan for implementing them in order to keep the long-term risks steady or bring them down to levels that are deemed acceptable.

Portrait of the organization and the territory under its jurisdiction

The municipality is located in the Québec City region. It offers the normal services and has the usual powers of a Quebec municipality. In particular, it is responsible for managing the stormwater collection system and the collection and treatment of wastewater. Part of its territory has separate systems for stormwater and sewage, and another part has a combined system. There are several overflow structures, some of which handle overflows at a high frequency. The receiving environment is considered vulnerable. An inventory of the systems and infrastructure, along with their characteristics (technical, maintenance, etc.), as well as a review of the budgets, responsibilities, regulations and jurisdictions in terms of stormwater management must be carried out.

Identification of hazards, systems and impacts

The hazard considered, pluvial flooding, is itself linked to the hazard of extreme rainfall. However, according to the available climate projections, this type of rainfall event is expected to increase in frequency and intensity in the future. The systems involved are stormwater management infrastructure and land use and development (permeable and impermeable surfaces, water storage infrastructure, pondage areas, basins, etc.), which determine the volumes of water stored on the surface, infiltrated and running off into the system, as well as the areas that are likely to be flooded.

A brainstorming session was organized to identify the systems and components likely to be affected by this hazard. Four sectors of the municipality, A, B, C and D, were identified as being at risk further to this exercise. This evaluation was based on past experiences and on a risk assessment by water management system managers. These sectors are shown in Table 14.1. Note that sector D was included even though it has not been flooded in the past, since the consequences of flooding in this sector would be dramatic. Other sectors may also be included for similar reasons. Risk evaluation in these cases involves ensuring that future patterns of extreme rainfall will not lead to an undue increase in flood risk for these areas.

The hourly rainfall with a 25-year return period was chosen as the index and climate threshold for sectors A, B and C. The corresponding value for the reference period was 40.2 mm in one hour. That value, which was proposed by the system managers based on their past experience, defines the threshold beyond which rain is likely to cause sewer backups and significant disruptions in these sectors². The hourly rainfall with a 100-year return period was considered for sector D, since the managers believed that pluvial flooding is possible beyond that threshold and that it would have significant consequences for this sector. The corresponding value for the reference period was 49.7 mm in one hour.

Table 14.2 shows the values of these indices for the reference period and for the medium-term (2041–2070) and long-term (2071–2100) future horizons based on SSP2-4.5, SSP3-7.0 and SSP5-8.5³. The annual probabilities of occurrence of 40.2 mm rainfall or more in one hour for sectors A, B and C and of 49.7 mm in one hour for sector D for the different future horizons are also indicated. For example, the annual probability of having rainfall of 40.2 mm or more in one hour is 0.14 for the period 2071–2100 under SSP3-7.0, which means that during this period, such an event will be recorded on average every 7 years, while it occurred on average every 25 years during the reference period. The increases in the intensities and probabilities of occurrence of the extreme rainfall reported in Table 14.2 are major. These probabilities will be used to establish the likelihood scales (Table 14.7). The impacts of possible pluvial flooding for the different sectors are listed in Table 14.3.

Assessing climate risks

This step (Fact Sheet 11) begins with the identification of the risks associated with each hazard-system-impact combination based on climate information, vulnerabilities, and potential consequences in the current and future climates.

An exposure analysis is carried out first, using the climate thresholds in Table 14.2. Preliminary evaluations have established that exceeding these thresholds would result in several elements of these four sectors being exposed. The list of the exposed elements, as well as their level of exposure, will depend on the climate threshold set; a higher threshold results in a greater number of exposed elements and a higher level of exposure. The climate threshold must be set so that breaching it will have significant consequences. Some sectors could be subdivided and different climate thresholds considered for these subsectors. Several climate thresholds could also be considered in the event that exceeding these thresholds would mark a significant increase in the levels of consequences and risks. The risk assessment consists of determining how much more often the threshold(s) will be exceeded in a future climate.

In this case, with the reference of a 1-hour rainfall of 40.2 mm or more, or 49.7 mm or more, depending on the sector, the exposed elements and the vulnerability levels of each of the exposed elements are evaluated. A list of the exposed elements is then drawn up and a vulnerability rating assigned to each sector.

The vulnerability is estimated by combining and . The most vulnerable elements are those with high sensitivity and low adaptive capacity. The allocation of ratings to each sector is based on a series of criteria to be defined by the committee responsible for the adaptation process. Table B.6d provides a possible list of these criteria. Many are based on a review of past floods or on the expertise and experience of either the personnel in charge of these systems or people who intervene in the event of emergencies (engineers, managers, blue-collar workers, emergency services, public health professionals, etc.).

The sensitivity and adaptive capacity ratings are then assigned by the members of the committee responsible for the adaptation process. External experts may be consulted if necessary. These scores are then used to establish the vulnerability score (VU), which is obtained by taking the product of the sensitivity (S) and adaptive capacity scores (VU = S x AC). Vulnerability scores can be assigned directly without breaking them down into sensitivity and adaptive capacity scores, using the criteria in Table 14.4.

Table 14.5 shows the vulnerability assessment grid for the example considered. It should be noted that previous preliminary analyses had already identified these sectors as being exposed and vulnerable. Note that the highest vulnerability rating was assigned to sector B, followed by sector C. A “moderate” vulnerability rating was assigned to sector A, while sector D has a “low” vulnerability rating. These ratings are explained as follows:

• Sector A had already been exposed to flooding and had certain characteristics that made it vulnerable to this hazard (e.g. negative-slope driveways, finished basements); however, the residents of this sector are socio-economically better equipped to deal with disasters and the adaptive capacity is considered high (moderate vulnerability rating).

• Sector B had already been heavily exposed in the past and has a very vulnerable community that is socio-economically poorly equipped for adaptation (high vulnerability rating).

• Sector C is critical for mobility (e.g. emergency services) and was already problematic; improvement work was already planned for this sector, so the adaptive capacity is considered high (moderate vulnerability rating).

• Sector D had not experienced flooding in the past; however, the consequences of a flood could be catastrophic in the event of an increase in extreme rainfall, hence its “high” sensitivity rating. For this sector, it was important to assess the risk in a future climate following an increase in the probability of flooding occurring in this sector (high vulnerability rating).

The risk analysis is then carried out. It consists of estimating the level of risk of each exposed system and component, for all of the climate hazards, time horizons and radiative forcing scenarios selected. First, it involves estimating the likelihood of the flood hazard and the consequences of this hazard for each of the sectors identified as vulnerable or potentially vulnerable. A risk matrix similar to the one in Fact Sheet B.5 is used, where likelihood and consequences are divided into five levels.

The likelihood ratings are set based on the values of the climate index “maximum annual rainfall in 1 hour”, shown in Table 14.2. It can be seen that the projected increases are greater for more distant future horizons and for more significant radiative forcing scenarios. The likelihood scale was established on the basis of the annual occurrence probabilities for 1 hour of rainfall with a 25-year and 100-year return period in the reference period (Table 14.7).

The consequence ratings are established by the committee members on the basis of the vulnerability analyses shown in Table 14.5. They represent the severity of the damage, disruption and other consequences if the threshold is exceeded. As they are largely subjective, they must be discussed and adopted by consensus among the committee members.

An important point to remember is that if the probability of crossing the threshold is greater in a future climate, the average intensity of the hazard crossing this threshold will be greater. In this case, it may be useful to consider several thresholds in order to better calibrate the progressive evolution of the consequences. Thus, if the magnitude of the sewer backups and the area exposed to flooding increases significantly when a second threshold is crossed, then it might be wise to add this new threshold into the analysis in order to better understand how the consequences and risks change for more extreme hazards. For example, previous analyses indicated that the maximum 1-hour rainfall with a 100-year return period in the reference period would occur every 12-13 years by 2071–2100, under SSP5-8.5. The corollary of this assertion is that rainfalls of an intensity well above the historical threshold will be possible in the future, with even more devastating consequences. An analysis of the risks associated with these more extreme events could be beneficial.

The sectors’ risk matrices are then constructed (Fact Sheet 11). Table 14.8 and 14.9 present these risk matrices for the periods 2041–2070 and 2071–2100 respectively, based on the three SSPs considered. An examination of these matrices shows that sectors B and D will be at major risk by 2041–2070 (risk scores of 12 and 10 respectively) under SSP3-7.0. Sector A is added when the 2071–2100 horizon is considered. The situation becomes much more critical under SSP5-8.5, since sectors A, C and D are at major risk and sector B is at extreme risk by 2041–2070. Sector D goes from major risk by 2041–2070 to extreme risk by 2071–2100, under the same SSP.

The consequence scores in the risk matrix are intentionally unchanged between the baseline period and the future horizons. In this way, the impact of the hazards’ change in frequency on the risk is analyzed. Considering the projected intensification of extreme rainfall, unprecedented rainfall events that will far exceed historical values are likely to occur. Thus, not only will the climate threshold be exceeded more often, but it will be exceeded by a greater amount and the consequences will be even more significant than in previous events. In order to take this aspect into account, several climate thresholds associated with higher consequence ratings can be defined. Different scenarios looking at the consequences of lack of maintenance or underinvestment in infrastructure, or an increase in the vulnerability of certain populations, can be explored.

A broader review of the other sectors of this municipality should probably be undertaken in light of these results, since even areas that were historically protected from flooding could very well become exposed to this hazard and suffer its repercussions.

Based on the results of the risk analysis, sectors B and D should be prioritized, since they are most at risk in the 2041–2070 and 2171–2100 time horizons under both SSP3-7.0 and SSP5-8.5.

Risk management

The main goal of climate risk management is to define specific adaptation objectives, identify and select adaptation measures, plan their implementation, and develop monitoring indicators.

To identify the appropriate adaptation measures for each sector, a broad-based list is made of the possible types of measures along with the suitability and feasibility criteria to be considered for their implementation. Table 14.10 shows an example of such a list and the criteria. Table 14.10 also highlights some important factors to consider. This analysis requires the municipality to collect a significant amount of information on the infrastructure in place, the known failures, the planning of future work and the projected development of the sectors. The best possible diagnosis of the state of the system and of critical structures and sites is key. This information is essential to get an overview of the adaptation options that are possible for each of the sectors, even if it is a broad one. Lastly, based on these criteria, the sectors where these measures could be implemented are identified (Table 14.11).

Table 14.1: Problematic or potentially problematic sectors.

Sector	Features	Flood history
A	Separated system, medium density residential, several negative-slope driveways, moderate to high level of impermeable surfaces, some green spaces	Several basements flooded during heavy rain
B	Combined system, apartments, heavily urbanized and impermeable, flat with several low points, several apartments in basements, heat island problems	Heavy accumulation of surface water in some places during medium-intensity rainfall events, flooding of basement apartments due to sewer backups following heavy rainfall
C	Low points located in underpasses or on major traffic routes	Several episodes with significant water accumulation at certain low points
D	Sector with several critical buildings and key infrastructure (e.g. hospitals, long-term care facilities) and several vulnerable populations	Although there have been no flood episodes in the past, the consequences of flooding would be dramatic for this sector.

Table 14.2: 1-hour rainfall intensity (mm) with a 25-year return period (sectors A, B and C) and 100-year return period (sector D) for the reference period (1961–2021)⁴ and the medium-term (2041–2070) and long-term (2071–2100) future horizons under the SSP2-4.5, SSP3-7.0 and SSP5-8.5 scenarios⁵.

Radiative forcing	Period	Sectors A, B, C		Sector D
		Intensity (mm/h)	Annual probability of occurrence of 40.2 mm of rain in one hour	Intensity (mm/h)	Annual probability of occurrence of 49.7 mm of rain in one hour
Historical	1961-2021 (reference)	40.2	0.04	49.7	0.01
SSP2-4.5	2041-2070	46.1	0.09	57.0	0.03
	2071-2100	48.3	0.11	59.7	0.04
SSP3-7.0	2041-2070	46.5	0.09	57.5	0.03
	2071-2100	51.0	0.14	62.9	0.05
SSP5-8.5	2041-2070	48.3	0.11	59.7	0.04
	2071-2100	54.8	0.18	67.7	0.08

Table 14.3: List of the main impacts of a pluvial flood for each sector.

Sector	Impacts
A, B	Flooded basements and streets, damage to property (furniture, appliances, etc.) and buildings, disruption of socio-economic activities, cleanup work for the affected residents and for the city, unsanitary conditions, economic inequity between insured and uninsured people, stress and psychological distress, loss of property values
C	Road traffic disruption, broken down vehicles, reduced accessibility for certain areas and for emergency services
D	Accessibility issues, critical services interrupted or severely disrupted, areas cut off

Table 14.4: Non-exhaustive list of elements/criteria to be considered in order to establish the sensitivity and adaptive capacity⁶ ratings used to estimate the vulnerability rating for the pluvial flood hazard.

Variable	List of elements/criteria to consider
Sensitivity	How have the elements/infrastructure in different sectors behaved in the past when faced with extreme rainfall? Has the area experienced several floods in the past and, if so, how extreme was the associated rainfall? Are there any known or suspected structural issues for this sector, like undersized elements or low points? Is the existing infrastructure (e.g. the stormwater management system) often at full capacity? How old is the sector and how outdated are the buildings and infrastructure there? Are there many basins, basement apartments, negative-slope layouts or areas that encourage water to accumulate in certain places? Are there strategic systems (e.g. infrastructure, municipal buildings, hospitals, public services) or communities (e.g. vulnerable, economically disadvantaged populations) that would make a flood, even if very unlikely, have catastrophic consequences?
Adaptive capacity	What are the socio-economic and demographic profiles of the exposed sectors? What is the fraction of tenants vs. owners? To what extent do residents in the exposed sectors have the financial means to prepare (e.g. setting up temporary protective structures around houses), recover in the event of a disaster (e.g. insurance coverage) and implement certain adaptation measures (e.g. waterproofing buildings)? Is rehabilitation work on certain infrastructure (e.g. sewers, streets, parks) planned in the short or medium term? To what extent do the sector’s configuration and types of occupancy offer adaptation options? Which ones?

Table 14.5: Vulnerability analysis detailing the exposed elements in each of the sectors (see Table 14.1) and the sensitivity, adaptive capacity and vulnerability ratings assigned to them. The vulnerability values and scales⁷ are shown in Table 14.6.

Sector	Exposed elements	Sensitivity	Adaptive capacity	Vulnerability
A	Houses on AA Street between numbers A.1 and A.2; buildings A.1, small shopping centre to the south of the sector; row houses with negative-slope driveways on X Street	Moderate (2)	Moderate (2)	Moderate (4)
B	Basement apartments between numbers B.1 and B.7 on BB streets; medical clinic and fire station on Laflamme Street	High (3)	Low (3)	High (9)
C	Intersection of CC and DD boulevards and EE street	High (3)	High (1)	Moderate (3)
D	Several critical buildings and key infrastructure (e.g. hospitals, long-term care facilities) and several vulnerable populations	High (3)	Moderate (2)	High (6)

Table 14.6: Vulnerability matrix⁸, combining sensitivity and adaptive capacity⁹.

			Sensitivity
			1	2	3
			Low	Moderate	High
Adaptive capacity	1	High	1	2	3
	2	Moderate	2	4	6
	3	Low	3	6	9

Table 14.7: Likelihood scale¹⁰ based on the probabilities of occurrence of the annual maximum 1-hour rainfall and the average number of years when these events have occurred in a 30-year period.

Likelihood rating	Frequency	Annual probability of occurrence	Average number of years of occurrence over a 30-year period
1	Very rare	0.0 ≤ p ≤ 0.03	0 ≤ N < 1
2	Infrequent	0.03 < p ≤ 0.07	1 ≤ N < 2
3	Moderately frequent	0.07 < p ≤ 0.15	2 ≤ N < 5
4	Frequent	0.15 < p ≤ 0.3	5 ≤ N ≤ 10
5	Very frequent	0.3 < p ≤ 1	15 < N ≤ 30

Table 14.8: Risk analysis for the four sectors selected for the 2041–2170 horizon (L: Likelihood; C: Consequence; R: Risk). The risk classification and the corresponding colour code are described in Fact Sheet 11 (TODO: je pense que c’est Table 13.1).

Sector	Reference period			SSP2-4.5			SSP3-7.0			SSP5-8.5
	L	C	R	L	C	R	L	C	R	L	C	R
A	1	3	3	2	3	6	3	3	9	5	3	15
B	1	4	4	2	4	8	3	4	12	5	4	20
C	1	2	2	2	2	4	3	2	6	5	2	10
D	1	5	5	1	5	5	2	5	10	3	5	15

Table 14.9: Risk analysis for the four sectors selected for the 2071–2100 horizon (L: Likelihood; C: Consequence; R: Risk). The risk classification and the corresponding colour code are described in Fact Sheet 11 (TODO: je pense que c’est Table 13.1).

Sector	Reference period			SSP2-4.5			SSP3-7.0			SSP5-8.5
	L	C	R	L	C	R	L	C	R	L	C	R
A	1	3	3	3	3	9	4	3	12	5	3	15
B	1	4	4	3	4	12	4	4	16	5	4	20
C	1	2	2	3	2	6	4	2	8	5	2	10
D	1	5	5	1	5	5	3	5	15	5	5	25

Table 14.10: Types of possible measures, their suitability and feasibility criteria, and the possible sectors for their implementation¹¹.

Type of measure	Suitability and feasibility criteria	Comments
Improvement, reconfiguration, rehabilitation of streets and system12	Parts of systems that are obsolete or deemed problematic Planned street redevelopment and system improvement Addition of retention capacity (basin, conduits, etc.) Potential for the development of temporary retention areas (e.g. parks, sports grounds, “water squares”)	Effective measures for medium and heavy rainfall Detailed characterization and diagnosis of existing essential systems Make the most of planned work to maximize adaptation Ensure water retention structures and temporary retention zones are designed to manage more extreme rainfall events Must be included in the asset management plan
Source inspection and green infrastructure	Significant input of runoff and potential to reduce or redirect runoff to infiltration or storage areas (e.g. disconnecting eavestroughs or redirecting runoff to infiltration areas) Detailed review of sectors to identify possible sites for implementing a significant number of these measures	Measures to reduce water inputs into the system Includes measures such as disconnecting eavestroughs, green (or planted) infrastructure Effective for low- and medium-intensity rainfall Some of these measures have social acceptability issues Commitment and cost assessment are important to ensure adequate long-term maintenance of these structures
Land use planning	Presence of numerous basins and low points13 and potential to reduce or redirect water from upstream areas Possibility of reducing impermeable surfaces (e.g. reduction of street width, replacing impermeable surfaces with permeable ones)	Land use planning measures to reduce water inputs into the system (e.g. replacing impermeable surfaces with permeable ones, maintenance of wetlands, parks and green spaces in urban settings) Measures included in the sectors’ urban planning and redevelopment plans
Regulation, taxation, governance and financing	Stricter by-laws (e.g. restrictions on basement apartments or on construction and rebuilding in certain areas) Circumscribe water inputs from new developments and those undergoing rehabilitation Encourage (or force) commercial, institutional and industrial organizations to reduce their “stormwater footprint” Strengthening and enforcing by-laws on the control of runoff from construction sites Financial incentives to promote adaptation (e.g. rain garden development, tree planting)	Identify regulatory and fiscal methods to encourage residents and institutions to adopt behaviours or implement certain measures (reduction of impermeable surfaces, implementation of green infrastructure, waterproofing, etc.) Major social acceptability issues Assessment of the socio-economic impacts of any new regulation or by-law Consider new ways to share stormwater management responsibilities and governance
Prevention and emergency measures	Identify failures in past prevention and emergency responses and possible ways to improve (e.g. improving communications between municipal services or with the public) Raising public awareness in certain sectors so that residents consider certain options (e.g. waterproofing buildings, disconnecting eavestroughs, inspecting backflow preventers, improving drainage)	Major communications and public consultation issues Ask other municipalities about their approach to emergency situations Organize mechanisms for mutual assistance between neighbouring municipalities Maximize coordination with various government bodies and public services (e.g. Ministère de la Sécurité Publique, Hydro-Québec)
Catastrophic events14	Measures to limit the impacts if the capacities of the existing structures are significantly exceeded (where will the water go and how can it be redirected to lower-risk areas?) Planning for emergency measures in the event of a catastrophic situation (e.g. access to the most impacted areas by emergency services) Plan for evacuations in the event of an emergency Identify sites where evacuees can take refuge or be relocated in the short and medium term Review and simplify post-event financial aid and assistance processes	Consider a very high climate threshold associated with a rare flood whose consequences would be catastrophic For analysis purposes, look at the impacts of a major rain event that has struck another municipality Analyze the flooding following such an event List of impacts (affected neighbourhoods and streets, displaced population) List of essential services disrupted (e.g. power outage, inability of emergency services to respond) List possible impact chains, also called “domino effects” (e.g. torrential rain → system overload → discharge of wastewater into receiving environment → contamination of drinking water sources)15

Table 14.11: Table B.6k. List of measures chosen at the municipal level and for each sectors with the deliverables to be produced and the performance indicators selected¹⁶.

Area	Measures	Deliverables and performance indicators
Municipality	Improve coordination between different municipal departments by setting up a climate change adaptation coordination office17 Define the roles, powers and responsibilities of the climate change adaptation coordination office Review municipal governance to grant the climate change adaptation coordination office the powers it needs Define the office’s mandates (coordination of CC adaptation activities, development and implementation of an adaptation plan, coordination between departments in implementing measures, etc.) Produce an adaptation plan Consider regulatory measures or financial incentives (e.g. incentives for the inspection of backflow preventers, restriction on basement apartments or on construction and rebuilding in certain areas) Develop a consultation strategy and a communication plan for the public and for institutions	Conduct a detailed analysis of past floods and a diagnosis of the causes of the failures observed and possible solutions Climate change adaptation plan Relevant information and resources for implementing the adaptation plan (e.g. historical weather data, basin map, infrastructure data, land use maps) Indicators: compliance with deadlines in the climate change adaptation coordination office’s work, commitment level of the various departments to CC adaptation
Sector A	Several problematic negative slopes and sections of streets in basins: local solutions to redirect runoff water and temporarily store surface water Development of green infrastructure Implementation of a backflow prevention valve inspection program and awareness-raising on stormwater issues (e.g. the vulnerabilities of basements)	List of measures selected and detailed plan for their implementation Indicators for monitoring the implementation of the measures (e.g. number of houses visited) Document the impacts of all rainfall events, even minor ones
Sector B	In certain areas of the sector, integrate improvements to increase capacity and reconfigure surface runoff into the rehabilitation work to separate the combined system Take advantage of all rehabilitation or development work to include measures to reduce impermeable surfaces (e.g. reduction in street width, addition of permeable surfaces) or to reduce water contributions to the system (e.g. surface or underground storage) Develop a disaster response plan adapted to the realities of this sector (e.g. working in collaboration with community organizations to identify the most vulnerable individuals or families)	List of measures selected and detailed plan for their implementation Indicators for monitoring the implementation of the measures (e.g. number of houses visited) Document the impacts of all rainfall events, even minor ones
Sector C	Addition of a retention structure and increase in collector capacity Addition of a signalling system to notify motorists that a section of a road is flooded Adapt emergency response plans to redirect emergency vehicles in the event of flooding in these sections	List of measures selected and detailed plan for their implementation Indicators for monitoring the implementation of the measures (e.g. number of houses visited) Document the impacts of all rainfall events, even minor ones
Sector D	Determine the extent of the areas exposed to flooding Develop an emergency response and evacuation plan for this sector in the event of flooding Consider whether certain adjustments could reduce the impacts	Determine the extent of the areas exposed to flooding Establish a list of inaccessible services Document the possible impact chains in the event of flooding in this sector

Mailhot, Alain and Bolduc, Samual and Talbot, Guillaume. 2024. “Outils d’analyse Des Risques Aux Infrastructures Posés Par Les Changements Climatiques – Contribution INRS.” Institut national de la recherche scientifique, Centre Eau, Terre et Environnement.

Ministère du Développement durable, de l’Environnement et de la Lutte contre les changements climatiques. 2017. “Manuel de Calcul Et de Conception Des Ouvrages Municipaux de Gestion Des Eaux Pluviales.” Gouvernment du Québec. http://www.mddelcc.gouv.qc.ca/eau/pluviales/manuel-calcul-conception/index.htm.

Ouranos and MELCCFP. 2024. “Élaborer Un Plan d’adaptation Aux Changements Climatiques – Guide Pour Les Organismes Municipaux.” https://cdn-contenu.quebec.ca/cdn-contenu/adm/min/environnement/publications-adm/plan-economie-verte/outils/guide-elaborer-plan-adaptation-organismes-municipaux.pdf.

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1. Workbook 1 – Method for carrying out a climate risk assessment; Workbook 2 – Method for carrying out a climate risk assessment (fictitious example); Workbook 3 – Planning the implementation of measures; Workbook 4 – Planning the monitoring of measures. Please note that the example in the fact sheet is different from the one in Workbook 2.

2. Other indices of the same type are also possible. The choice of index depends on local configurations and must be determined after discussion with stakeholders in the field. It is approximate, but is still useful in the adaptation process. The effective duration of this 40.2 mm rainfall will have major impacts; the shorter the duration, the greater the impacts. Hydrological/hydraulic modelling of the sector (surface and sewer systems) could also be used to establish a link between future changes in extreme rainfall and flood risks. However, implementing such a model requires significant resources that are not available to all municipalities.

3. SSP5-8.5 may be considered for certain critical infrastructure located in very vulnerable sectors with a useful life extending until 2100. The corresponding increases will be very high, however.

4. The reference climate values come from the Intensity-Duration-Frequency (IDF) curves from the Jean-Lesage Airport station in Québec City, produced by Environment and Climate Change Canada (ECCC). These values are based on the series for the period 1961–2021.

5. These values were estimated for the grid point covering Québec City. The procedure used to estimate these values is described in Chapter 7 of Mailhot, Alain and Bolduc, Samual and Talbot, Guillaume (2024)

6. Adaptive capacity also includes considerations on the municipality’s technical and financial capacity to adapt. These factors apply uniformly to the four sectors considered, but may vary significantly between municipalities, particularly between small and large municipalities.

7. Vulnerability scale: low (1 to 2), moderate (3 to 5), high (6 to 9).

8. Vulnerability scale: low (1-2 in green), moderate (3-4 in yellow), high (6-9 in red).

9. Note that the sensitivity and adaptive capacity scales are inverted; a low sensitivity value corresponds to a value of 1 while low adaptive capacity is associated with a value of 3.

10. The likelihood score of 1 is defined based on the annual maximum 1-hour rainfall with a return period of 25 (p = 0.04) or 100 years (p = 0.01). Thus, the 4% annual probabilities of occurrence for sectors A, B and C, and 1% for sector D, are qualified as “very rare.” Ratings of 2 to 5 correspond to a progressive increase in the probability of occurrence of this rainfall.

11. This list is not exhaustive. Several documents can be consulted on this subject. For more details, readers can consult Ministère du Développement durable, de l’Environnement et de la Lutte contre les changements climatiques. (2017).

12. The capacities of the structures will have to be adapted in keeping with the increases in rainfall shown in Table B.6b. A map of the basins and low points could prove very useful. The upstream areas and the directions of surface flows towards these points would also be indicated.

13. A map of the basins and low points could prove very useful. The upstream areas and the directions of surface flows towards these points would also be indicated.

14. The aim here is to examine what would happen if an exceptional catastrophic event were to strike the municipality and what measures should be put in place to improve risk management in a situation where the capacities of the infrastructure in place or its tolerance thresholds are exceeded. This “theoretical” exercise is essential because unprecedented events are likely to occur in the context of climate change.

15. Appendix G of Ouranos and MELCCFP (2024) discusses this issue and gives various examples of possible impact chains for different hazards.

16. This list is hypothetical.

17. In the case of a small municipality, this role could be assumed by an individual. In the case of very small municipalities, this type of resource could be allocated by higher levels of government.