RISK THRESHOLDS RELATED TO CLIMATE CHANGE IN ROADINFRASTRUCTURE IN SPAIN
F. JIMÉNEZ, L. CRESPO, A. GIL & L. PARRAThe Centre for Applied Technical Studies (CETA) & the Centre for Transport Studies(CET)
The Centre for Public Works Studies and Experimentation (CEDEX) at the Ministry ofTransport, Mobility and Urban Agenda, Spain
fernando.jimenez@cedex.eslaura.crespo@cedex.es
alberto.gil@cedex.eslaura.parra@cedex.es
M.L. ALONSO
Planning and Projects Service, Infrastructure Area, Provincial Council of Valencia, Spain
monicalaura.alonso@dival.es
F. COLLAZOS-ARIAS
Ministry of Transport, Mobility and Urban Agenda - Directorate-General of Highways,
Spainfcollazos@mitma.es
SUMMARY
The potential risks to road infrastructure posed by climate change need to be studied ingreater detail. The methodology utilised for this purpose by the World Road Association(PIARC) addresses, among other issues, the exposure of the assets and services provided
by the infrastructure and the probability of the threat or impact occurring. Vulnerability andrisk will therefore vary in the future, depending on the different scenarios that are taken into
consideration as a result of the pathways that may be taken if one type of mitigation policy
is promoted over another. In turn, this is conditioned by the efforts that are made to move
forward with the decarbonisation of the energy system.
These threats depend on the variability of the climate. It is likely that the main impacts will
come from the increase in precipitation over short periods of time. To assess these impacts,
we need to understand the characteristics of the territory where the phenomenon takes
place. These characteristics are defined by its drainage capacity, which depends – among
other factors – on its orography, geology and vegetation. Thus, for each territory we need to
set thresholds, which should be considered as values that trigger action protocols to ensurethat the effects of climate events have as little impact as possible.
Identifying these thresholds is not a simple task, and to this end the data from previous
events are being analysed. For this article we have worked with infrastructure managers ona specific pilot study to analyse the risk arising from the impact of maximum precipitation
within 24 hours on two assets that form part of the road network in the region of Cantabria
in northern Spain.
1. INTRODUCTION AND PURPOSE
Climate change is one of the main environmental issues we are facing us today. It obliges
us to develop a new approach to land management, in order to get ahead of the adverse
phenomena that are forecast, and which will cause significant losses with regard to theprovision of road services.
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27th World Road CongressOf all the climate variables analysed, those that are of the greatest relevance for transport
infrastructure are precipitation, in all its forms, and to a lesser extent extreme temperatures
and thermal oscillations throughout the day.
These climate variables trigger direct impacts on road infrastructure assets, such as
overflows on cross-drainage works or bridges, which in the most extreme cases can bring
down decks and piers or undermine abutments, piers and slopes. On occasion, they caninterrupt the provision of the service by preventing access to certain parts of the road
network and can even cut off population centres.
To address these impacts, we propose a methodology involving a vulnerability and risk
analysis for services and assets in relation to climate change, with the aim of prioritising anintervention programme that lends greater resilience to transport infrastructure. To this end,
it is necessary to focus on different behaviours in the territories in question, in order toanalyse the programme’s operation. To achieve this, and for each territory, we need tocharacterise the thresholds or tipping points of the climate indices that provide warning signs
in the locations where there is a high probability of occurrence. In these locations,inspections must be more thorough and corrective measures must be anticipated in orderto prevent collapses in mobility, chiefly as a result of damage to drainage works orearthworks.
It is necessary to detail the methodological development that will allow us to characterise
the different management thresholds that trigger impacts on the various infrastructures. The
aim is for this methodology to be implemented in the different administrations withresponsibility for road management, in order to identify, with a certain degree of accuracy
and foresight, the appearance of failures in the system. This will make managers aware of
the need to systematically document the events affecting the infrastructure, which in turn will
help to identify the risks and impact levels and therefore determine the necessary speed ofintervention.
This methodology has been designed by the Working Group on Climate Change and Road
Resilience, which reports to the Technical Committee for the Environment (part of theTechnical Association for Spanish Roads, ATC-PIARC). The Technical Committee
comprises professionals from public administrations with responsibility for roads, researchorganisations focusing on the transport system, academia, consultancy firms, andcompanies dedicated to the construction and preservation of transport infrastructure.
Some of the earliest and most notable references in the study of potential impacts on roads
can be found in the European RIMAROCC1, ROADAPT2 and INFRARISK3 projects. These
projects provide guidelines for identifying the main elements that form part of an analysis of
the potential impacts of climate change on roads. Subsequently, a number of other
European projects (among which CLARITY 4 and FORESEE 5 stand out for their recent
completion) have moved forward with the georeferencing of assets while taking into
consideration the effects of climate change, in accordance with the AdapteCCa6 platform
developed by the Spanish Meteorological Agency (AEMET).
1 Risk Management for Roads in a Changing Climate | TRIMIS (europa.eu)
2 ROADAPT_integrating_main_guidelines.pdf (cedr.eu)

3 Drupal | Novel Indicators for identifying critical INFRAstructure at RISK from natural hazards (infrarisk-fp7.eu)
4 Home | Clarity (clarity-h2020.eu)

5 https://cordis.europa.eu/project/id/769373

6 Platform for consulting and exchanging information on the subject of impacts, vulnerability and adaptation to climatechange. Spanish Ministry for Ecological Transition and the Demographic Challenge (MITERD).

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27th World Road CongressAt the international level, there are also many projects that serve as benchmarks for studying
the impact of climate change on roads. However, within the scope of this study we will chiefly
focus on the work carried out by PIARC. In 2016 PIARC published its first study on thissubject [1], where it was proposed an initial version of a methodological framework to help
conduct these analyses. In 2019 it published two new documents, [2] and [3]. The firstprovides an update to the methodological framework, while the second presents acompilation of the main case studies that were collated. The case studies analysed by
PIARC include contributions from the Mexican Institute of Transportation (IMT) ([4] and [5]).
Lastly, we should also mention three other benchmarks for the study of adaptation to climatechange.
The first consists of the reports drafted by the Intergovernmental Panel on Climate Change(IPCC). The IPCC’s sixth assessment report places particular emphasis on the protection ofcritical infrastructure, including energy and transport systems. This infrastructure isincreasingly affected by hazards such as heat waves, storms, wildfires, droughts and floods,
as well as changes that occur more slowly, such as rising sea levels [6].
Figure 1 outlines the approach proposed by the IPCC for the study of risks. It shows that the“ingredients” of risk analysis in relation to climate change-related impacts are hazards,
vulnerability and exposure.

Figure 1 - From climate risk to climate resilient development: climate, ecosystems (including
biodiversity) and human society as coupled systems [6]The second is the European Commission notice [7] providing technical guidance on the
climate proofing of infrastructure in the period 2021-2027.

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The diagram presented in Figure 2 summarises the methodology followed with regard toadaptation to climate change.
Climate resilience
Adaptation to climate change
Phase 1. Screening
Phase 2. Detailed Analysis
 Sensitivity Analysis
 Likelihood Analysis
 Exposure Analysis
 Impact Analysis7
 Vulnerability Analysis
 Risk Assessment
 Identify adaptation options
 Appraise adaptation options
 Plan the adaptation
Figure 2 - Diagram of the European Commission methodology.
Own creation, based on [7]As a third and final reference, from a normative point of view, it is the ISO 14090:2019
standard [8]. The application of this standard may help to show interested parties that anorganisation’s approach to climate change adaptation is credible. This ISO standard isdesigned to help organisations develop measures and report on adaptation activity in averifiable way. Its structure covers pre-planning, the assessment of impacts (including
opportunities), adaptation planning, implementation, monitoring and evaluation, andreporting and communication.
2. GENERAL FEATURES OF THE METHODOLOGY: PHASESThe terms used in a risk analysis refer to its constituent components, which are useddifferently depending on the methodology or guide that is employed. This hinders thedissemination of the results of studies that help decision-makers and the stakeholders or
affected parties [9].
Consequently, as a first step to help understand the terminology used, and in order to gaina better understanding of the scope of the study of the risks associated with climate change
proposed in this methodology, we have drawn a parallel between the different stages ofanalysis that comprise the methodology and the different parts of a climate event,transformed into a descriptive story. The story acts as a “mini-narrative” that brings together
the factors that need to be studied in order to understand and quantify the potential impact
on a road asset or service caused by a current or future climate threat, which could be
modified by the effects of climate change. This “story” is the common thread of themethodology proposed within the framework of the ATC-PIARC.
Through the following simple example, which has been transformed into a “story”, we
present “a possible analysis of the effects of a climate event on a road”. It is an exercise inapproximation designed to facilitate an understanding of the methodology [10].

7This part of the methodology of [7] is equivalent to the severity analysis in the majority of the methodologies
analysed, including the one proposed in this report.

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27th World Road CongressExample “story”:
Intense rain (threat) causes a landslide (impact) on a road embankment(asset) located in the area of study (exposure), due to its geologicalcharacteristics, gradient and height (sensitivity). This happens every two
years (probability) and results in moderate social, environmental andeconomic losses (severity), and also has an effect on traffic and nearby urban
areas (criticality).
Figure 3 below describes the steps that comprise the proposed methodology. The workflow
is consistent with the specifications of [1], [2] and [7], and is structured in accordance withthe following phases:
Impactassessment

Vulnerability
assessment

Risk
assessment

Resilienceassessment

Figure 3 - Diagram of the ATC-PIARC Methodology for the Adaptation of Road
Infrastructure to Climate Change
Table 1 - Summary of definitions of concepts used in the ATC-PIARC methodology
Asset orService
Element(road
Asset ortraffic
Service)that
receives
the action(Impact)

ThreatImpactExposure

Sensitivity

Element
thattriggers theaction(Impact)

Action that happens
to the road Asset orService as a result of
the Threat

Defined by theplace where
the Impact
occursCharacteristicsof the Asset orService thatcondition theeffect or
degree of the
Impact (anddetermine
how theImpact occurs)

Adaptive
Capacity
Refers to thefactors that
increase the
Resilience of
the Asset orService,therebyimproving the
response of
the elementsthat create
Vulnerability

Risk

Criticality

Resilience

Combinationof Probability
and Severity.
Depends onthecharacteristicsof the Threat.
Not directly
associatedwith anyelement in thestory

Characteristics
that make an
Asset orService
indispensable
and whichsuffer the
ImpactAnalysis of allof theprevious
elements inorder tooptimise theresponse of
the Service orAsset inrelation toclimatechangeProbability
When andhow many
Impacts
occur withina period oftime

Severity(Seriousness,
Magnitude,
Consequences)
The extent andconsequences of
the Impact that
occurs[5]

Vulnerability
Combination of
Exposure andSensitivity.
Depends onthecharacteristicsof the Asset orService andthe type of
Impact. Not
directlyassociated withany element in
the story

27th World Road CongressTo provide more detail, Table 1 defines the working concepts that support themethodological framework presented in the ATC-PIARC.
2.1. IMPACT ASSESSMENT (PHASE 1)
In this initial phase it is necessary to establish the scope of the study. A particular roadadministration may be interested in identifying only its most vulnerable assets, in order todevelop and implement a general improvement plan (e.g. plans to clean up cross-drainage
works) for all of them. In other cases, the administration may wish to go a step further andidentify the assets that present a genuine risk to management of the network, in order topropose additional specific adaptation measures. It is also necessary to resolve otherquestions, such as whether the study includes all of the roads in the country, those in aparticular territory, a specific corridor or section, etc.
It will then be necessary to describe the characteristics of the territory where the road
network in question is located, as well as the characteristics of the road network itself(infrastructure criticality) and identify the available information sources. Lastly, it isnecessary to assemble a group of experts to provide support throughout the assessment
process and compare the assessment results against the historical evidence.
Once the scope of the study has been defined, it is necessary to categorise the assets orservices as either “priority” or “secondary”, and then break them down by type. This is dueto the fact that, initially, it will not be possible to analyse all of the assets in the network; thestudy requires a certain level of detail which, in turn, means that we have to optimise ourefforts with regard to resources. Therefore, we propose first tackling the assets that (on ana priori basis) present the greatest potential risk, in view of the previous studies and projects
analysed and taking into account the experience of the group of experts.
The main aim of this first phase is to identify the potential impacts on the assets or servicesof the section of road that is the focus of the study. We will begin with a list of pre-defined
impacts and identify which of them are relevant with regard to the section of road being
studied. In order to draw up this list we must identify the main impacts that habitually affectroad networks and may be associated with climate conditions (both current and future). To
do this, we will start by studying the types of failure that could be suffered by the different
assets or services.
For the purposes of this methodology, the climate conditions or set of climate conditions thattrigger or have a decisive impact on the type of failure will be known as “threats”.
Consequently, a threat is directly related to one or more climate variables, which are studied
directly in the process.
2.1.1 Map of threats
In order to study the threats, we need to identify any reference materials for climate variables
and climate change projections that can be used to create a map of threats. From the list of
potential impacts we can also generate a list of the main threats that are to be studied on ana priori basis. Maps will be drawn up, containing information on the threat in both its current
state and for different time frames and scenarios in the future. In turn, the projection of theclimate variables implies the selection of a particular RCP8.
We recommend using the climate indices and variable projections corresponding to RCPs
4.5 and 8.5. RCP 4.5 represents the emissions mitigation pathway that is most likely to apply
8 The IPCC’s Representative Concentration Pathways.

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27th World Road Congressbased on the current implementation of emissions reduction policies. RCP 8.5 is a more
pessimistic scenario in which the emissions reduction policies have not achieved the desired
effect. These are the pathways for which information on potentially threatening climate
variables is available from a variety of sources, studies and projections. We also recommend
using the RCP projections for different periods (Historical, 1971-2000; Near Future, 20112040; Mid-Future, 2041-2070; and Far Future, 2071-2100). The main reference for carryingout these foresight studies is AdapteCCa, although there are other sources of information –such as [11], Copernicus9 and the National Flood Zone Mapping System (SNCZI)10 – thatenable the characterisation of impacts and threats.
2.2. VULNERABILITY ASSESSMENT (PHASE 2)
The vulnerability assessment is based on the exposure, sensitivity and adaptive capacity of
the assets or services. In the documentary references of [7] the concept of sensitivity refers
to the intrinsic characteristics of the asset or service, including its adaptive capacity.
Vulnerability = Exposure x Sensitivity
Assessing exposure consists of determining the extent to which an asset or service, by virtue
of its geographical location, may be affected by the different potential threats that are being
assessed. Expressed in more casual terms, it consists of determining “whether our asset orservice is in harm’s way”.
For its part, the sensitivity of an asset or service is related to the specific characteristics that
determine the extent to which it is affected by a particular impact. In order to assess
sensitivity, we have created a sensitivity matrix for each asset or service. Each sensitivity
matrix will have different sensitivity factors, which refer to the features that may influence
the extent to which an asset or service is affected by a particular impact. For thismethodology, adaptive capacity is included in the sensitivity analysis.
The outcome of this phase is a list of the assets or services, categorised according to theirlevel of vulnerability, which must be analysed in order to determine the associated risk.
2.3. RISK ASSESSMENT (PHASE 3)
The risk assessment is based on the probability and severity of the impact on the assets orservices.
Risk = Probability x Severity (Seriousness, Magnitude or Consequences)
The quantification of both probability and severity presents a number of difficulties. It should
be noted that the main problem we are facing is the lack of available information for thesetypes of study.
The probability or likelihood of a climatic phenomenon occurring is uncertain, and so it isdifficult to estimate a specific time frame within which a particular event will take place. Within
the framework of this methodology, to determine the probability of an asset or service being
impacted we suggest using the calculation of return periods based on the meteorological
data for a climate variable, or collating information on previous experiences. In this latter
case, the aim is to estimate, in a qualitative manner, the probability of the event or impact
9 The European Union’s Earth observation programme.

10 A tool designed to support the management of river areas, help prevent risk, aid territorial planning and promote
administrative transparency on the part of MITERD.

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27th World Road Congressoccurring. A suitable approach would be to identify the maximum number of events thathave occurred on the stretch of road in question over as long a time frame as possible. This
would make it possible to compare thresholds for risk management.
Severity can be related to the magnitude or intensity of the event, the size of the impact
caused by the event, or the consequences should the event occur. This concept is assessedusing a scale to categorise the severity of the consequences, and different factors can betaken into account for the purposes of the assessment.
The outcome of this phase is the identification and prioritisation of the assets or services
that are at risk. These assets or services will need to be subjected to a resilience assessment
and an adaptation plan drawn up accordingly.
2.4. RESILIENCE ASSESSMENT (PHASE 4)
The purpose of this phase is to provide road managers (administrations and companies)
with analytical tools to help increase the network’s resilience, in order to prevent accidents
or reduce the impact that meteorological conditions (both normal and extreme, and both
now and for the time frames assessed) are having on the road infrastructure. During thisphase we aim to identify and select a number of adaptation measures for particular casestudies, while remaining aware of the fact that for each risk there are adaptation measuresthat may be specific or, in some cases, complementary.
Owing to the lack of resources, it is necessary to select and prioritise the adaptation
strategies and responses, adopting a rationalised approach and giving priority to the mosteffective measures for each case. The methods proposed for this type of approach consistof a multi-criteria analysis (MCA) and cost-benefit analysis (CBA), which are described
below. These workflows are those that are most frequently followed in the reference
documents ([1], [5] and [7]).
When conducting the MCA we can define certain criteria related to the cost of implementing
the measure, the feasibility of implementing it, the potential environment impacts it may
cause and its capacity to adapt to new circumstances, among others ([5]).
The CBA utilises a logical and structured process in which all of the different factors (costs
and benefits) are quantified. The total quantifiable and non-quantifiable value of the benefits
must compensate for the costs in order for a project to be considered worthwhile. There aredifferent types of CBA, although the most complete is the Triple Bottom Line (TBL) model.
A TBL analysis assesses a measure or strategy on the basis of its economic, environmental
and social impacts, all of which are duly combined [12].
The final step of this phase, and of the methodology, is the implementation and monitoringof the Adaptation Plan. This consists of incorporating the chosen climate change resiliencemeasures into the project’s technical design or into the maintenance and operation plans forthe assets. To this end, it is necessary to draw up an action plan (implementation andfunding) and a monitoring and response plan, which should include a plan for carrying out
periodic reviews of the vulnerability assessment and climate risk hypotheses (among
others). The aim is to collate a series of indicators that make it possible to assess the
progress of the plan and can also be used to review and improve the operation of themethodology. It is also necessary to draw up a communication plan in order to coordinate
all of the stakeholders involved.

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The outcome of this implementation and monitoring phase will be a complete and organised
plan, with structured time frames, to enhance the resilience of the network by improving theassets or services that are at risk.
2.5. PRELIMINARY REFLECTIONS ON THE APPLICATION OF THE METHODOLOGYAs stated above, one of the main difficulties that have been identified with regard to theapplication of this methodology is the availability of reliable data and information with which
to carry out the constituent phases. The biggest challenges are the climate variables orthreats that are to be studied (particularly with regard to future projections that include theeffects of climate change); identifying the characteristics of the assets or services affectedby the events caused by these threats; and the lack of detailed records on impacts to the
network caused by the climate. This makes it difficult to set thresholds for establishingcategories of exposure and probability, as well as to determine indicators, which are key
parts of a climate change adaptation plan. The following sections discuss, in greater detail,how to tackle these challenges using the example of a pilot study set in the region ofCantabria (Spain).
3. THE MOST RELEVANTTEMPERATURE

CLIMATE

VARIABLES:PRECIPITATIONAND

Climate change gives rise to other changes that are going to affect the provision of services
across all areas of society. As stated above, the climate variables with the potential to havethe greatest impact on the operation of road infrastructure, at both the structural andoperational level, are precipitation and temperature. These variables are also the moststudied, and the ones for which there is the most amount of information available in termsof future projections that take climate change into account.
3.1. PRECIPITATIONThe AdapteCCa platform can be used to find details on the variable of precipitation, for bothSpain as a whole and for each Autonomous Community and province, and broken down by
maximum precipitation within 24 hours (Pmax24h) and maximum precipitation accumulated
over five days. It provides information on the impacts that may be suffered by the assets on
both an occasional and cumulative basis, which in turn enables us to assess the potential
threats of landslide to which cuttings are exposed across different time frames.
However, there is hardly any information on the concept of “torrentiality”, which refers tointense periods of precipitation over short spaces of time. The only study of this climate
variable in Spain can be found in [11], where the number of variables analysed from previous
works has been expanded to include maximum precipitation in intervals of less than one day(3, 6 and 12 hours). The study took into account a control period (1971-2000), three impact
periods (2011-2040, 2041-2070 and 2071-2100) and two scenarios (RCP 4.5 and RCP 8.5),
with the aim of assessing impact over the course of the 21st century and with reference tothree return periods (10, 100 and 500 years).
3.2. TEMPERATURE
The temperature variable has a number of parameters that can determine its effect on roadassets. These include minimum temperature, maximum temperature, temperature range,
extreme maximum temperature and extreme minimum temperature. In the Cantabria pilot
study the implications of this variable were not analysed in relation to the impact on assets.
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27th World Road CongressIn any case, it should be noted that it is difficult to work with the data associated with climate
variables. In this respect, it is worth mentioning various initiatives promoted by the European
Commission to develop climate services, such as the one promoted via the CLARITY
project, which aims to simplify access to climate-related information. Ultimately, however,problems related to the maintenance of the applications mean that the data have to beprocessed on a case-by-case basis, which makes it difficult to access the information.
4. CASE STUDIES OF THE MAIN ASSETS AFFECTED BY THE PRECIPITATIONVARIABLE: PILOT STUDY
Around the world, numerous road assets are becoming more vulnerable to climate change[13], much to the concern of the scientific community and governments. In Spain, 45% of
the main road network and 4% of the total road network have suffered some form of climaterelated impact [14]. The region of Cantabria is no exception: various studies havedocumented the increasing number of climate-related impacts (in terms of both extreme
events and processes that occur more slowly) on infrastructure.
In order to demonstrate a practical application of the methodology described above, we
carried out a pilot study in which we analysed two assets located in the Autonomous
Community of Cantabria (see Figure 4), specifically on the A67 (Cutting_A67_km175) andN623 (Cutting_N623_km117) roads. In this pilot study the climate variable analysed isprecipitation, specifically PMax24h.

Figure 4 - Location of the two assets studied within the region of Cantabria

The region of Cantabria is located in northern Spain and has a population of 585,222 (2022census). It is a coastal region that also has a mountainous topography owing to the presenceof the Cantabrian Mountains. Consequently, it has a high level of climate variability, whichranges from the temperate oceanic climate on the coast to the warm, summery
Mediterranean climate that can be found inland.
The Government of Spain has 600 km of strategic roads in this region, which provide accessto the main healthcare, tourist and commercial services. The network is managed by the
Directorate-General of Highways, which forms part of the Ministry of Transport, Mobility and
Urban Agenda (MITMA).

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Historically, Cantabria was connected to the Meseta region and central and southern Spainby two roads: the N-611 from Palencia to Santander and the N-623 from Burgos toSantander. Due to the large volumes of traffic (more than 60,000 vehicles/day) on the final
section of the N-611 between Torrelavega and Santander, Cantabria’s two largest
population centres, in the 1980s work began on a new, more advanced road: the A-67
highway from Santander to Torrelavega. Construction was completed in 1990. The road was
subsequently extended out to Palencia and became the A-67 motorway upon theextension’s completion in 2008.
Today, the A-67 is the main artery connecting Cantabria to the Meseta region and on into
central and southern Spain, and also performs the vital function of providing accessibility
throughout the region it serves.
One of the two assets studied, Cutting_A67_km175, is located on the section of road linking
Torrelavega to Los Corrales de Buelna Norte, which was opened in 2000. This section ofroad acts as a duplicate of the Torrelavega bypass and – importantly – is located between
the tunnel of Las Caldas de Besaya and the viaduct above the road linking Cartes toVillanueva de la Peña. The terrain is rugged, with gradients of 8%.
The other asset studied, Cutting_N623_km117, is located on the N-623 in the municipalityof Entrambasmestas. Although the terrain is also rugged, this particular section of the roadruns parallel to the River Pas, with the river on one side and slopes with steep transverse
gradients on the other. The road’s longitudinal gradient is low, and it is used by traffic of amore local nature.
In a number of places on these two roads, intense storm precipitation can saturate the soil
and cause the embankments or slopes to become unstable, giving rise to landslides. Rockfall can also occur in fractured zones, potentially resulting in full or partial closure of the roadto traffic.
After analysing the potential impacts of precipitation, the following are of particular note: Service affected by intense precipitation, potentially resulting in interruptions to traffic.
 Detachment of rocks and/or earth from the slope. This could be particularly significant
in areas of karst terrain.
 Translational or rotational (deep) slides.
 Surface sliding of the slope.
 Settlement and overturning of retaining walls.
 Settlement of embankments due to submersion as a result of the foundations failingor collapse of the embankment body. This may also result in deformation and/or fullor partial breakage of the road surface.
 Decreased road safety caused by water build-up on the pavement due to intense
precipitation.
 Increased number of problems related to scouring, affecting the piers and abutmentsof crossings.
5. PRECIPITATION THRESHOLDS: PILOT STUDY
To assess exposure (vulnerability phase) and probability (risk phase) for the pilot study
proposed it is necessary to set thresholds, which depend on each variable, climate index or
threat and are specific to each territory. These thresholds will be set in accordance with duly
recorded and documented experience, and must be consistent with the study area.
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One of the factors that may mark a difference between the various territories, with regard to
establishing thresholds that define where and when an impact caused by a climate event
will happen, is the existence of man-made terrain. The same amount of precipitation in twoareas with different capacities for retaining or absorbing a given amount of rain, owing to thesponge effect of soil that is well-protected by vegetation, could cause the thresholds
established for an impact to vary greatly. It may be the case that areas with lower
precipitation suffer greater impacts than areas with higher precipitation, due to the fact that
their territorial characteristics are determined by the land planning regulations or because
they have lost part of their functionality with regard to the provision of ecosystem services.
Depending on the resources available, thresholds can be established at different levels,
whether national, regional or local. Logically, setting thresholds with a higher spatial
resolution (i.e. within a smaller territory) will make it possible to identify the risks associatedwith climate events more precisely, while also requiring more time for analysis.
In order to increase the level of knowledge, and thereby establish a more suitable
categorisation of exposure and probability levels, it is necessary to have a department thatsystematically inventories climate events and the effects that have occurred in the past, as
well as those that will occur in the future.
The records made must specify, at a minimum, the location and date of the occurrence; theclimate data for the “triggering” threat; details of the element affected; a description of thedamage suffered; and details of the costs of repair or replacement. As stated above, thisinformation will make it possible to establish thresholds, which will aid the task of preparing
to mitigate the potential effects of climate change, enable analysis of the causes of the
impacts and make it possible to anticipate future impacts.
Some countries have made a great deal of progress in the characterisation of these events,
mostly with regard to hydro-meteorological phenomena (which are the ones that have thelargest socio-economic impact; some 98% of the total, according to [5]). Mexico counts withdepartments that monitor climate variables and work with future projections that take into
account the variability imposed by climate change. They predict that not all of the futureclimate changes will be of significance to the local or regional transport network, although
the rate at which these impacts occur will increase.
5.1. EXPOSURE THRESHOLDS IN THE PILOT STUDY
To assess the exposure of the assets studied we must begin by selecting the threat that is
posed to them and the impact that will occur. In this case we used PMax24h, as the threatthat can cause rock fall in the two cuttings studied. To this end we generated a map of
threats, in which we established categories of exposure based on specific thresholds thatwere set in accordance with duly recorded and documented experience and are consistent
with the study area.
In order to carry out this pilot study, the State Roads Department in Cantabria provided dataof events previously recorded in the area. This information was then linked to PMax24 andmade it possible to establish the reference thresholds. Using these thresholds weestablished five threat categories: Very Low (1), Low (2), Medium (3), High (4) and VeryHigh (5). By cross-referencing these with the location of the assets, we were able todetermine their exposure within the context of our study (see Table 2).

[12]27th World Road CongressTable 2 - Matrix of exposure to PMax24h (mm/day), Cantabria pilot study
Exposure

Very Low

PMax24h(mm/day)< 25

Low Medium High Very High25-30 30-40 40-60> 60

Based on these thresholds, the asset’s exposure will be determined by its location and by
the threat for each of the periods and scenarios established in the methodology. The asset’svulnerability to climate change can then be calculated based on this exposure and its
sensitivity.
5.2. PROBABILITY THRESHOLDS IN THE PILOT STUDYWith regard to determining probability, there is potential for conflict in relation to the scopeof the assessment. In some cases, it is the probability of the threat occurring (e.g. PMax24h
above a particular threshold) that is analysed, while in other cases the analysis focuses on
the probability of the impact, damage or effect occurring. In general, and owing to thedifficulty of obtaining data to support the assessments, the information that is available ineach case should be used.
This pilot study aims to investigate the level of occurrence for the impacts in relation to theassets; consequently, for the probability assessment, in addition to studying the events(which was already done in order to establish the exposure thresholds) we also calculated
the return periods in order to identify when the impacts will take place. Return periods arecommonly used to represent an estimate of the probability of a given event occurring withina given time frame.
We took the PMax24h for the following stations as a reference, as they are the ones thatare closest to the assets studied11 for the current period:
1. Cutting_A67_km175. Station 1124A, Villacarriedo (data from 1990 to 2021)
2. Cutting_N623_km117. Station 1154H, Torrelavega-Sierrapando (data from 1994 to
2021; missing 1999 and 2000)
The data were subjected to a statistical analysis (Gumbel distribution) for each of the stations
in order to obtain the PMax24h for seven return periods, which were thus defined so thatthey could be linked to a risk classification scale. With these data, and using the inverse
distance weighting (IDW) interpolation method provided by the QGIS Geographic
Information System, we obtained a single PMax24h value per return period for the area ofstudy in which the two assets analysed in the pilot study are located (see Table 3).

11This selection was made using the Thiessen polygon method, taking into account weather stations with datasetsthat were large enough to be representative.
[13]

27th World Road CongressTable 3 - Identification of the return periods for PMax24h by station using the Gumbel distribution.
Reference value interpolated at the level of the territory in which the assets are locatedReference
ReturnStationStationPMax24h
Period (T)
1154H
1124A
(mm)
2
63.4147
78.3875
76.04975
77.3032
100.4764
96.857910
86.4987
115.1012
110.6351
25
98.1172133.5796
128.043050
106.7364 147.2879
140.9564100
115.2920 160.8950
153.7747500
135.0627 192.3390
183.3961

Based on these data, we propose the following categories for the probability of the impact
occurring (Table 4). The impact is defined as detachment of rocks and/or earth from theslope caused by the threat of PMax24h. For this exercise, we took into account the
precipitation thresholds (as per the exposure matrix) above which the event occurs, and thereturn period of precipitation in the area of study (probability of the threat).
Table 4 - Probability matrix of the impact occurring due to PMax24h (mm/day).
Current period, Cantabria pilot study
Probability

Very Low

Low

Medium High Very High

PMax24h (mm/day)

< 25

25-30

30-40 40-60> 60

In this case, as the PMax24 value for the return period of two years is higher than the levelof precipitation at which the impact analysed usually occurs, it was established that theprobability of the impact occurring is very high (see Table 4).
The return periods serve to establish the thresholds, while the PMax24h values for thecorresponding period and scenario, obtained from AdapteCCa, are used to ascertain
whether these thresholds are exceeded in the specific area of study where the impact may
occur.
For the future periods included in the climate change scenarios it is necessary to calculate
the corresponding probability of the threat occurring, although this presents difficulties dueto the uncertainty associated with the climate models. To determine the impacts for the
future periods and scenarios, the same thresholds as for the current period will be used.
The risks posed to each asset by the effects of climate change will be determined based on
the probability of the impact occurring (taking the thresholds established as a reference) andthe severity of said impact.

[14]

27th World Road Congress6. CONCLUSIONS
Spain’s geography is the product of a mosaic of microclimates and geomorphological andphysiographic units. Consequently, depending on the specific details and needs regarding
resolution capacity when calculating the risks posed to assets by climate change, we could
propose many different scales for assessing the thresholds that determine the assets’exposure and the probability of the impact occurring.
Additionally, in urban and peri-urban areas, one of the factors that conditions territorial
resilience is the extent to which the terrain is man-made. Land in urban areas has lost all of
its capacity to provide ecosystem services to the surrounding environment and to theterritory as a whole; instead, its characteristics are determined by the urban planning
process and the detailed studies carried out in relation. The characteristics of the city’s
drainage systems, sanitation system, sewer system and green spaces condition thedrainage capacity of its streets, squares and urban spaces. Road transport infrastructures
require a detailed analysis in order to determine the thresholds that need to be defined foreach type of asset and climate variable.
In the specific case of road assets affected by hydro-meteorological phenomena, more
precise tools are needed to calculate the probability of the phenomena occurring and thelevel of impact. We are still some distance from knowing with a certain degree of accuracy
the extent to which torrentiality occurs, including maximum precipitation in intervals of lessthan one day (duration of 1, 3, 6 and 12 hours), for Spain as a whole.
The information that is obtained from roads with regard to events and impacts associatedwith climate change must be organised at a nationwide level. This entails:‐ Facilitating access to climate-related information.
‐ Compiling asset inventories containing information that is relevant in terms ofassessing their sensitivity.
‐ Establishing a historical record of events that have taken place and their impacts, forthe various modes of transport and for different assets.
Setting up this historical record is key, as with this information the competent territorial
authorities would be able to establish specific management thresholds tailored to each typeof asset, climate variable and territory.
For the specific case discussed in this article, in order to determine the thresholds we only
took two assets into account, along with the corresponding data from the two nearest
weather stations. Using a greater number of stations and assets would help to obtain more
precise results, and provide a more accurate view of the current situation with regard to therisks to road infrastructure posed by climate change and the measures that could potentiallybe carried out in order to address its impacts.
Exploring and implementing this set of methodologies suppose large economic, social andenvironmental benefits for road agencies measurable by various methods such as CBA.
This allows them to characterize road assets and services at high risk against current andfuture climate change effects. These benefits are observed when adaptation measures are
implemented, among which early warning systems and emergency transportation
operations response can be highlighted. To improve these systems and services, advanced
methods for infrastructure monitoring should be implemented, such as remote sensing,drone surveillance, big data and data analytics.

[15]

27th World Road CongressACKNOWLEDGEMENTSDavid López Oliver, Marta Pertierra Rodríguez, David Carracedo Esteban and Adriana Mata
Calvo from the Spanish company INES Ingenieros Consultores, which also forms part of the
ATC-PIARC Working Group, have provided invaluable assistance in the drafting of thisarticle, particularly with regard to determining the most suitable weather stations in the areaof study and calculating the return period in order to establish the probability categories.
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27th World Road Congress