Introduction

Scientific knowledge of anthropogenic climate change and its effects on ecosystems, society, and various sectors of human life is now more extensive than ever before. For example, in its fifth assessment report, the Intergovernmental Panel on Climate Change (IPCC) stated with 90% probability that anthropogenic greenhouse gas (GHG) emissions have caused most global warming since the mid-20th century (IPCC, 2014).

Over the last century, anthropogenic activity has caused significant climate change across the globe (Fischer & Knutti, 2015). Patterns of change are statistically most robust when they refer to temperature-related variables like warming trends over land masses and within oceans, to sea-ice reductions, or to sea-level rises. Observed changes are attributable to the growing amount of GHGs in the atmosphere resulting from continued combustion of fossil fuels and land-use changes (Dale, 1997; Delucchi, 2010; Plevin et al., 2010), which alters the balance between incoming solar and outgoing infrared radiation. Future consequences of potential human behavioral pathways (e.g., RCP2.6, COP21, RCP8.5, or business as usual; van Vuuren et al., 2011) can be depicted through ensembles of climate change projections produced by global climate models (GCMs; IPCC, 2014). Taking into account globally averaged temperatures, projected increases range from about 1.4°C (COP21) to 5.8°C (business as usual; IPCC, 2014). When climate change information is required on regional or local scales, a further modeling step required, and the corresponding methodologies are generally referred to as “downscaling,” which allows GCM output (which is to be interpreted on continental scales) to be scaled down to the desired spatial resolution (Benestad et al., 2008; Maraun & Widmann, 2018; Maraun et al., 2010; Matulla et al., 2008; von Storch et al., 1993).

However, scientific studies suggest that the impacts (e.g., more extreme weather events, more very hot days and heavy precipitation events, rising sea levels, retreating glaciers) accompanying increases in global temperatures above 2°C by 2100 will be both uncontrollable and catastrophic (King & Karoly, 2017; Kjellström et al., 2018; New et al., 2011). It is therefore essential to keep global warming below this level.

A growing problem for the transport sector is the impact that climate change can have on land transport (road, rail, inland navigation). In the early decades of the 21st century, approximately 30% of all GHGs emitted in the European Union could be attributed to transportation (European Environment Agency [EEA], 2020). So, transportation is on the one hand driving climate change through emissions, and, on the other hand, it is threatened by climate change impacts. So far, however, discussions and endeavors related to transport and climate change have focused almost entirely on mitigation (Chapman, 2007). While mitigation is essential, the design of accompanying and supporting adaptation strategies has only recently become the focus of scientists and practitioners (Moretti & Loprencipe, 2018; Oswald, 2009; Stamos et al., 2015).

If adaptation is not assessed at the same level as mitigation, there is a danger that poor economic investments will lead to infrastructure and traffic failure. This is because the need to adapt transportation to the climate change impacts that will occur during the decades ahead has not yet been fully recognized. Planning of adaptive measures is thus required to set up sustainable development strategies. Adaptation to climate change can be integrated into the transportation planning process by employing risk assessments, by incorporating the results of decision-supporting instruments, and by the prioritization of sustainable and effective strategies (Ford et al., 2018; Matulla et al., 2020; Oswald, 2009). The reason why transportation agencies have so far barely addressed this issue is partly the uncertainties inherent in climate projections.

However, climate proofing of transport infrastructure is increasingly becoming the focus of attention because extreme weather events have caused considerable damage in recent years (Chinowsky et al., 2014; Grams et al., 2014; Meyer et al., 2016; Mirza, 2011; Nissen & Ulbrich, 2017; Robertson et al., 2007) and ensembles of future climate projections driven by different human behavioral pathways (Forzieri et al., 2018; van Vuuren et al., 2011) indicate no relief (Koetse & Rietveld, 2009).

The physical impacts of climate variability and climate change are visible across different transport modes (Michaelides, 2013), affecting transport infrastructure (Baker et al., 2009; Schlögl & Matulla, 2018; Yang & Ge, 2020) as well as traffic and travelers (Jenkins et al., 2014; Postance et al., 2017; Schlögl et al., 2019).

Large intergovernmental organizations and agencies, including World Meteorological Organization (2020), the Organisation for Economic Co-operation and Development (2018), the United Nations Development Programme (2011), and EEA (2014), as well as international and national associations, such as the Conference of European Directors of Roads (2016), the Transportation Research Board (2016), and the European Freight Leaders Forum (F&L), have recognized the need for action, too. Consequently, ongoing efforts across all modes of transport focus on the improvement of their resilience and the reduction of their vulnerability to climate change impacts.

Thus, there is a robust linkage between effective mitigation and supporting adaptation programs. In order to reduce the vulnerability of different modes of transport to climate change impacts, it is mandatory to adapt each mode (for example, in the case of roads, by mounting safety nets for protection against falling rocks) to the extent required in order to support mitigation efforts focusing on the reduction of anthropogenic GHG emissions (Oswald, 2011). In addition to an overview of climate change impacts, this article presents a survey showing how climate change and its effects are currently perceived by transport agencies and a discussion of how adaptation measures—drawing on decision-theoretical methods—may be integrated into transport planning. Transport planning is illustrated by an example related to inland navigation in the European Alps.

Stakeholder’s Perception of Climate Change Impacts on Transportation and the Need for Adaptation

With the increasing availability of regional to local ensembles of climate projections driven by different pathways of human development, and due to the fact that GHG emissions from transportation are—in contrast to other sectors—still on the rise, the topic of transportation and climate change has become a focus of scientific research since the mid-2000s. The research acknowledges that transportation plays a dual role: on the one hand, it is a significant driver of climate change, and, on the other hand, it is vulnerable to climate change’s impacts (especially altered precipitation patterns, the increased frequency and intensity of extreme weather events, and sea-level rise). Therefore, much attention has been paid to mitigation strategies (i.e., minimizing GHG emissions caused by transport; Alic, 2016; Banister et al., 2012; McKinnon, 2018).

Because of carbon dioxide’s long residence time in the atmosphere and the fact that, due to anthropogenic influence, the atmospheric CO₂ content now exceeds 400 ppm (which is far beyond the range experienced over the last million years: 190–290 ppm), climate change will continue to unfold. Therefore, mitigation alone is not sufficient to grant protection over the decades to come, and it will be vital to safeguard transportation with adaptation measures, too, which increase its resilience to the impacts of climate change (EEA, 2014; Eisenack et al., 2011; Koetse & Rietveld, 2009; Rattanachot et al., 2015). Initially, most of the attention the scientific community paid to the topic of climate change and its impacts on the transport sector since the mid-2000s was in research done in North America and Europe. However, since the early 2010s, increasing numbers of papers from researchers in Asia, South America, Africa, and Australia have enriched the body of knowledge on this issue substantially (Wang et al., 2020). Of all the contributions, though, only a small fraction reflect the perceptions of the stakeholders actually involved with the issue (Wang et al., 2020). This may be one of the reasons that, until recently, most providers and operators in transportation have not implemented adaptation concepts in their business-development strategies (Oswald, 2011; Stern, 2006).

Nevertheless, a user-needs survey has been conducted among stakeholders in the realm of transportation (infrastructure providers, logistics companies, and rescue organizations) as part of an international cooperative effort.¹ On the basis of the insights gained from the survey, a new practice-oriented World Meteorological Organization (WMO) Service Delivery Guide to Land Transportation has been established to ensure that developed services are actually tailored to stakeholder needs.

Moreover, the survey results also indicate how much the topic of climate change and related hazards for the transport sector has gained in importance over recent years, or whether the issue still has barely entered the conscience of the stakeholders.

The survey results include: (a) an assessment of climate-change-induced extreme events in terms of their damaging effects on transportation (Figure 1), (b) stakeholders’ expectations regarding future developments of climate-change-related impacts (Figure 2, top), and (c) an evaluation of time horizons (short, medium, and long-term) for which stakeholders demand support (Figure 2, bottom).

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Figure 1. Assessment of extreme events and associated hazards in terms of their damaging impacts on transportation according to the opinion of about 110 stakeholders.

Source: Authors

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Figure 2. Stakeholders’ expectations concerning future impacts under accelerating climate change (top) as well as time horizons for which stakeholders demand suitable services (bottom).

Source: Authors

Figure 1 ranks extreme weather events and associated hazards (e.g., landslides) threatening the transportation sector according to their descending significance in causing damage, fatalities, losses, and delays. This assessment was carried out by the stakeholders, who assigned integer values (1 to 5) to each category, with 1 corresponding to “lowest damage potential” and 5 to “highest damage potential.” This procedure yielded for each event a distribution across the five categories (normalized to the total number of ratings n—see the second column from right) and an average value μ‎ in the rightmost column. The former is displayed as a horizontal bar (scale on bottom), while the average is indicated by a black dot (scale on top).

Figure 1 shows only the parts of the assessment that share approximately the same number of ratings (Matulla et al., 2020). Floods (first line), for instance, were rated 106 times in total and were assigned to category 5 53 times, which is why category 5 extends over 50% of the bar for floods. Freezing (bottom line), on the other hand, was rated 93 times and almost 50% of the ratings were category 1 or 2, so the corresponding averages for floods and freezing are 3.8 and 2.9, respectively.

Figure 1 shows how stakeholders’ perception of climate change impacts has changed and how the problem of climate change is now addressed much more consciously and precisely than earlier, because the figure indicates that stakeholders are well aware of climate-change-driven threats to transportation. Furthermore, stakeholders’ awareness of the need to enhance their sector’s resilience under accelerating climate change can be seen in Figure 2 (top panel), which illustrates stakeholders’ expectations about the development of damage processes in the coming decades.

While only 6.7% of stakeholders anticipated benefits, the vast majority (74.2%) assumed negative impacts of future climate change on the transport sector, and 19.1% expected advantages and disadvantages to balance out one another. Therefore, 93% of stakeholders surveyed did not foresee that the situation would ease.

Figure 2 (lower half) also depicts the demand for services and products supporting the successful execution of tasks on different planning horizons (short-term, medium-term, long-term). As in Figure 1, the demand was evaluated by respondents’ assigning numbers from 1 (“no demand”) to 5 (“highest importance”) to the three time scales. Since—in contrast to Figure 1 and the top of Figure 2, which concern the transport sector as a whole—different results were anticipated among infrastructure managers and stakeholders in freight, logistics, and transport concerning the long-term time scale, a distinction among the groups was made possible in this case.

Short-term scales provide information on present conditions in services up to estimates 2 weeks in advance. Therefore, they provide support for the completion of current and forthcoming orders in freight and logistics.

Products associated with medium-term time horizons offer support to projects whose completion takes from one season to several years. These projects include activities like operational decision-making, staff and maintenance planning, resource allocation, preparation for major events (e.g., low water levels in rivers), or planning phases of infrastructure programs. Adaptation measures offered in this context help to increase economic efficiency, to prevent bottlenecks in the supply of goods, and to avoid malinvestments.

The third time horizon stretches decades to a century. Corresponding service products help to facilitate forward-looking decision-making, business-development planning, and protection of large infrastructure investments. This is attained by setting up strategies that ensure, for example, sustainable acquisition of mobile assets as well as designing, constructing, operating, and maintaining infrastructure assets so that they sustain their capacities (despite future shifts in risk landscapes) until they complete their life cycle. Such services will rapidly gain importance with accelerating climate change. Risk assessments that take into account future climate threats are needed to manage risks via anticipatory designed adaptation strategies in coordination with mitigation measures.

The bold red bar in Figure 2 (lower half) illustrates the assessment made by stakeholders associated with supply-chain business. Because responsibilities among this group and infrastructure providers mainly differ on the long-term time scale, the assessment carried out by infrastructure providers focused on that time scale only. Therefore, a second, hatched bar is laid over the solid one to represent the result achieved by the joint examination of both groups.

One notable aspect of the ratings displayed as bold bars in Figure 2 is their low dispersion among the time scales. This is surprising because a large fraction of supply-chain operations are short term (de Bruin et al., 2020; Task Force on Climate-related Financial Disclosures, 2017), and therefore one might have anticipated a significantly higher demand for service products on this time scale. The high demand for medium-term services may be due to the droughts experienced in recent years. During droughts, low water levels restricted inland navigation and thus posed considerable challenges for transport by rail and road, which had to take on additional deliveries. This may be one reason why nowadays more weight is placed on scheduling of tasks related to resource allocation, staff, and maintenance planning, etc., than a decade ago. Considering the limited resources available for transport infrastructure planning as well as the uncertainty inherent in future climate change projections, the need to prioritize investments in high-risk assets seems obvious (Mouratidis, 2020).

The demand for long-term support refers to mastering challenges involved in designing strategic business-development programs. Climate change and its effects, which have become increasingly apparent in recent decades, have made clear that it is no longer sufficient to rely solely on past experience as a basis for corporate decision-making regarding long-term business-development strategies and the design of appropriate governance concepts. The slightly lower rating of the importance of having measures available to assist in the implementation of programs on long-term scales indicates not only that the issue of climate change has arrived in the transport sector, but also that its significance is now perceived rather differently than it was a decade earlier.

The survey findings demonstrate that stakeholders in transportation: (a) are very aware of the dangers posed by extreme weather events and the resulting hazards for transport, freight, and logistics; (b) show a high degree of differentiation in the assessment of extreme events and the damage triggered by them with regard to potential impacts on transport and supply-chain operations; (c) show a sophisticated evaluation of different transport assets with respect to their vulnerability to extreme events and hazards; (d) are aware of the fact that severity and frequency of damaging extreme events depend on prevailing climate conditions; (e) have experienced such changes themselves over the last decades; (f) expect—under accelerating climate change—further deleterious developments in risk landscapes for transport; (g) have a clear understanding about which services of the WMO and national meteorological and hydrological services (NMHSs) are required on different time horizons; (h) need services associated with short timescales (up to 2 weeks), medium timescales (seasons to year), and long timescales (years to decades).

Results demonstrate a clear commitment of transportation, freight, and logistics to cooperate and a distinct mandate for WMO and NMHSs to develop and provide suitable services. There is an urgent need for weather/climate services on timescales from days to decades ahead, and it is very important to meet this need, because society, the economy, and industry depend decisively on trouble-free, functioning supply-chain operations in all land transportation modes (road, rail, and inland navigation).

Transportation—Driving Climate Change and Being Exposed to Its Impacts

After providing some facts about European transport, this discussion splits into two parts, reflecting the dual role of transportation as a contributor to climate change and as a sector exposed to the consequences of climate change.

In 2017, inland transportation was contributing about 87% of the emissions released by all modes of transportation, which in turn were accountable for 27% of Europe’s total emissions. While railway transport was associated with 0.5%, the rest was attributable to road transportation and inland navigation. Cars accounted for approximately 44% of the emissions, heavy-duty trucks and buses for 19%, light-duty trucks for 9%, and motorcycles for 1%, based on national emissions reported to the EU Greenhouse Gas Monitoring Mechanism provided by the EEA (see Figure 3). Instead of emissions being reduced, which is urgently needed to achieve the target of emitting 60% less GHG than in 1990 (European Commission, 2011), emissions from road transport increased by 23% from 1990 to 2017 (EEA, 2020).

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Figure 3. Share of transport greenhouse gas emissions in the EU-28 (graphical visualization of numerical values published in EEA, 2017).

Source: Authors

In order to attain the 60% emission reduction target set out in the 2001 Transport White Paper (TWP; European Commission, 2011) as well as to reduce Europe’s oil dependency and oil import bills (210 billion euros in 2010, according to the TWP), because Europe’s transport sector is about 96% dependent on oil still (Chapman, 2007), mitigation strategies have been developed. The strategies generally focus on four areas: improving the energy efficiency of vehicles, developing and deploying sustainable fuels and propulsion systems, optimizing the performance of multimodal logistic chains, and using transport and infrastructure more efficiently through improved traffic management and information systems (European Commission, 2011). The implementation of corresponding measures (e.g., improvement and expansion of public transit, restructuring transport infrastructure to promote nonmotorized mobility, such aswalking and biking) is to be financed through regulations and incentive-based policies. These may include surcharges on the purchase of fuel-inefficient vehicles, parking charges, congestion pricing, fuel taxes, or replacing fixed vehicle charges with fees that are based on traveled kilometers (European Commission, 2011; Oswald, 2009).

Since climate change will continue to further unfold over the decades to come—even if drastic mitigation efforts succeed in eliminating GHG emissions—transportation practitioners must assess potential impacts on infrastructure and mobile assets. Identified vulnerabilities permit the development and implementation of adaptation measures that enhance system resilience and protect transportation against threats induced by climate change.

For the purposes of this discussion, potential climate-change-related risks to the transport sector in the European Alps are a good example. The Alpine region of Central Europe has a complex landscape covering large differences in elevation, ranging from low-altitude basins only a little more than 100 meters above mean sea level (MSL), to deep valleys, to high mountains of over 4,800 m above MSL. Roughly, the region’s weather is dominated by three main airflows, originating in the Atlantic, the Mediterranean, and Eastern Europe. The former two are influenced by the oceans, so they are relatively moist and show moderate seasonal temperature variations. Warm and moist Mediterranean air masses can cause severe floods in Central Europe. In contrast, continental air masses are rather dry and are connected to pronounced seasonal temperature variations. The Alpine crest acts as a meteorological divide. The Northern and Central Alps form a barrier for the northwestern airflow. From Vorarlberg across the Bavarian Alps to the Salzburger Alps, mean annual precipitation totals reach values of more than 3,000 mm (Hiebl et al., 2011), with the maximum, as in almost all parts across the European Alps, during summer. Precipitation amounts decrease toward the east. Inner Alpine valleys, such as, for instance, the Inntal, Ötztal, and the Mölltal, are shielded by their surroundings and therefore are particularly dry.

In Austria, in particular, the combination of terrain-specific characteristics and meteorological features suggests a rough subdivision of the territory into three provinces (see Figure 4). The northern parts extending from the foothills of the Alpine ridge across the River Danube northward (henceforth abbreviated as NL = northern lowlands) are geomorphologically characterized by lowlands interspersed with flat hills. Climatologically, the NL is generally influenced by northern and northwestern airflows. The southern basin is defined by flat topography and low-altitude mountains. Weather conditions are largely controlled by air masses advected from the south and southeast, as well as occasionally by a Vb pattern induced through Genoa cyclogenesis. The remaining area, the Alpine territory, is characterized by substantial differences in elevation. Aside from its geomorphological appearance, it is marked by a great diversity in terms of geology as well.

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Figure 4. Climatological and geomorphological distinct regions in the Austrian part of the European Alps.

Source: Authors

According to forecasts by Chimani et al. (2016, 2020) and Gobiet and Kotlarski (2020), the number of very hot days will increase across the Alpine region and the number of cold nights will decrease. Heat waves are expected to appear more frequently and to extend over longer periods of time than experienced until now. In its fifth assessment report (IPCC, 2014), the Intergovernmental Panel on Climate Change pointed out that along with rising global mean temperatures, the occurrence of more hot temperature extremes is virtually certain (> 99% probability) in most regions worldwide. Assuming high GHG emission scenarios, it is likely that, in most land regions, 20-year high temperature events will at least double in frequency, to become annual or 2-year events toward the end of the 21st century.

The implications for transport infrastructure include the thermal expansion of bridge joints, the rutting of asphalt roads, blow-ups of concrete roads, rail deformation, and the relocation of freeze–thaw events (causing frost heaves and falling rocks) toward higher altitudes, all of which therefore will affect other parts of the transportation system more than they have so far (Baker et al., 2009; Nemry & Demirel, 2012; Underwood et al., 2017). This necessitates reinforcement work for safety reasons and for the avoidance of road restrictions or road closures.

Future changes in annual precipitation totals in the Alpine region are anticipated to be much smaller than those for temperature (Chimani et al., 2016, 2020; CH2018, 2018; Lémond et al., 2011). However, expected—and already observable—changes in the nature of precipitation events contributing to annual totals (which will not alter much) are quite significant. Climate change projections show a decline in the number of days with precipitation, leading to more extreme events with increased totals (Blöschl et al., 2018; Frei et al., 2006; Westra et al., 2014). This is in line with results for dry periods, which are characterized by increased persistence and therefore make up a larger fraction of the seasonal cycle than in the past.

Impacts on transport linked to these changes are, for example: increased floods, causing delays, clogged drainage systems, flooded retention basins, failure of water cleaning, and road washout; and landslides, which threaten road users, cause congestion and down-time, and increase the risk of damage to both roads and railway infrastructure (Matulla et al., 2016; Nissen & Ulbrich, 2017; Schlögl & Laaha, 2017; Schlögl & Matulla, 2018; Schlögl et al., 2019).

Weather-triggered damage processes (e.g., falling rocks, dry periods that induce down-times and road closures for repair work, or disturbances and delays in inland navigation that impair bridges and prevent the passage of vessels) are expected to alter in frequency and magnitude along with climate change.

Integration of Appropriate Adaptation Strategies into Transport Planning

Because stakeholders’ perception and awareness of transport’s contributions to climate change as well as its vulnerability to climate change impacts has increased significantly in recent years, stakeholders are no longer skeptical about the integration of adaptation measures into transport planning. If, in addition to this trend, the length of time GHGs remain in the atmosphere is taken into account, it is obvious that mitigation measures alone will not be sufficient for protection. Therefore, mitigation measures (focusing on the elimination of GHG emissions) need to be complemented by adaptation efforts (to reduce the vulnerability of the system and to increase its resilience to the impacts). Therefore, from both an ecological and an economical point of view, it is essential to ensure that the adaptation strategies selected do not contradict mitigation measures already in place, but support them (Ford et al., 2018).

The formulation of appropriate adaptation strategies should be based on the following, very general steps:

The more specific the design of a strategy becomes, the more specifically these steps should provide guidance about how the required information is to be acquired and about which analyses are to be carried out.

The practical implementation of the program will be heavily influenced by the information and data available. Most important in this context is the second step, blending climate-change-induced impacts with the vulnerabilities of the transport assets concerned.

Whenever the interrelationships between damage and associated hazardous processes and their triggering atmospheric phenomena are not known or cannot be deduced from existing data, abstract approaches are applied.

Therefore, in the first step, researchers should investigate climate states that are associated with different impact types (e.g., increases in heavy rainfall events, longer and more intensive heatwaves and droughts, sea-level rise, etc.) and assess their future evolution on different time-horizons (e.g., medium-term, long-term) through the level of significance projected changes are assigned to. Depending on the significance level, the impact types are distributed into categories like “severe,” “moderate,” and “low.” Similarly, the options for action to protect the assets under consideration are initially kept very general—such as, “do nothing,” “mitigate,” “adapt,” or “mitigate and adapt.” These measures might be developed later by means of stakeholder surveys, for example.

There are several procedures available for setting up sustainable adaptation practices that combine potential impacts with possible protective measures. Among them are (see Oswald, 2011): (a) the info-gap method of analysis (Ben-Haim, 2006), (b) the convex analysis theory (Ben-Haim, 1994), (c) the maximum entropy technique (Phillips et al., 2006), (d) the expected value approach (Lempert et al., 2004), and (e) prediction-based analysis (Lempert & Schlesinger, 2000).

If spatially highly resolved daily data on meteorological parameters reaching back several decades, as well as maps of spatiotemporally located damage events, are available, relationships between the events and the regional-scale weather evolution preceding them can be established. For example, floods in the stretch of the Danube that runs through Austria cause damage events that represent a challenge to inland navigation and associated transport infrastructure like bridges.

The relevant data consist of three sets: First, regional-scale weather data are taken from SPARTACUS, the Spatiotemporal Reanalysis Dataset for Climate in Austria (Hiebl & Frei, 2016, 2018). SPARTACUS provides high-quality, daily temperature values and precipitation totals from 1961 onward for a 1-km grid covering the entire territory of Austria. The methodological framework of SPARTACUS was established in an international collaboration. Proceeding from irregularly distributed observations at weather stations operated by ZAMG, it generates regularly distributed data sets for the grid. SPARTACUS is kept operationally up to date and has already been employed in several studies (Duethmann & Blöschl, 2018; Schroeer & Kirchengast, 2018).

Second, the event space (Enigl et al., 2019) contains weather-driven hazard processes (assembled in compliance with internationally used categories; see Hungr et al., 2001, 2013, and Varnes, 1978) from 1951 onward. It aggregates events stored in the three most extensive national damage-process cadastres, Wildbach- und Lawinenverbauung (2017), GBA (Tilch et al., 2011), and VIOLA (Reisenhofer et al., 2017). The event space provides an unprecedented scope of hazard processes (over 20,000 occurrences) in terms of floods, flash floods, slides, flows, and falls and covers a significant part of the European Alps. The scope of events allows for the examination of weather sequences (given by SPARTACUS) driving, for example, floods and landslides within the three climatological regions (see Figure 4).

Third, the so-called ÖKS15 data set (Chimani et al., 2016, 2020) provides ensembles of regional-scale climate change projections (daily temperature values and precipitation totals) on the SPARTACUS grid until 2100 that are driven by the three potential human-behavior pathways (business as usual, COP21, and one in between called RCP4.5; van Vuuren et al., 2011).

The approach is straightforward. Whenever and wherever hazard processes have been observed (as given by the event space; e.g., floods in the NL—Figure 4), the evolution of regional-scale weather (as given by SPARTACUS) over the preceding week, including the day of hazard occurrence, is taken into account. This step results in a fairly large number of hazard occurrences (about 700 in the case of floods) together with associated weather developments over 8 days. In order to identify typical weather pattern sequences for the considered hazard within the region under investigation, assembled data are entered into an empirical orthogonal function analysis (EOF; see von Storch & Navarra, 1999). This multivariate statistical technique diagonalizes the covariance matrix pertaining to the problem under investigation (here, anomalies of daily precipitation totals during the week before and on the day floods occur). The outcome consists of eigenvectors (i.e., EOFs) and so-called time coefficients assigned to each EOF, given by the inner product of the EOF with the observed anomaly sequence. EOFs are widely used in climate research because usually most information on the problem is captured by a small fraction of all EOFs. Therefore, EOFs can be used to greatly reduce the dimensionality of the problem and to help filter out unwanted effects, such as, for instance, random errors in measurements.

After typical sequences of weather (called CIs—climate indices) have been derived for each hazard process and region and a validation procedure has been used to assess their performances, the CIs are searched for in the ÖKS15 ensembles. Changes in their occurrence relative to the past indicate increases or decreases of pertaining hazard occurrences in the future. The resulting evolutions are called hazard development corridors (HDCs; see Figure 5).

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Figure 5. Hazard development corridors driven by RCP2.6 (green, COP21), RCP4.5 (blue), and RCP8.5 (red, business as usual) representing changes in the risk of flooding events relative to current levels along the Danube in Austria.

Source: Authors

In the example presented here, the leading three out of eight EOFs have been retained. They are capable of simulating 77% of the variability observed throughout the considered 8-day periods pertaining to hazard occurrences. Consequently, the space within which weather sequences potentially triggering damages (here, sequences initiating floods) are encased is three-dimensional. Weather sequences are represented by points within this space whose coordinates are given by the time coefficients pertaining to the three leading EOFs. The question of when a particular weather sequence will be rated as triggering a damage process is still pending. One plausible approach, adapted to the problem at hand, is to set the threshold value for the proportion (percentage) of any 8-day precipitation anomaly that is to be captured within the three-dimensional subspace so as to detect as many observed damage events as possible while at the same time minimizing the number of false alarms (i.e., values exceeding the threshold but not accompanied by damage events). This setup needs validation, which requires splitting the observation period into two parts, to calibrate EOFs and the optimized threshold value in one part and to assess the performance of the setup in the part that has not been used for calibration.

The validation experiments carried out showed satisfactory performance levels of selected setups (CIs and chosen thresholds). Moreover, the CIs were assessed by officials of the ministry of sustainability and tourism responsible for civil protection, and, thus, experts on floods judged them to be in accordance with their expertise.

Therefore, the next step was the identification of 8-day sequences in the ensembles of climate change projections until 2100.

The example used here (comprising floods within the stretch of the Danube running through Austria and CIs for the three leading EOFs depicting the evolution of precipitation totals—over 7 days before the onset of the event as well as on the day of hazard occurrence—across representative regional-scale areas) is discussed in much greater detail in Enigl et al. (2019) and Matulla et al. (2020).

The presented results reveal a substantial difference between future threat levels corresponding to the climate-friendly pathway (COP21) and those associated with the business-as-usual scenario. While in the prior case implemented adaptation measures can be expected to complete their service life, threat potentials corresponding to the latter indicate that their replacement becomes necessary toward the final decades of this century.

Given HDCs, the probability of their occurrence as well as the availability of concrete options for action suggest the application of techniques summarized under “decision-making under risk” (Bernoulli, 1954). The procedures detailed here draw on the expected utility hypothesis (Bernoulli, 1954; von Neumann & Morgenstern, 2007).

The application of decision-theory selection rules in anticipatory decision-making arises from the need to compare and rank given options for actions (such as damming to regulate water levels, creation of retention basins, dredging to deepen shipping channels, or altering riverbed dimensions to enhance discharge rates) under different environmental conditions (HDCs) in order to identify forward-looking and sustainable adaptation strategies (and thereby avoid bad investments).

In general, environmental conditions and their probabilities of occurrence are assembled together with available options for action as columns and rows within a decision matrix (Malczewski & Rinner, 2015). In this example, the goal is to sustain current levels of system resistance until the end of this century, which matches the expected lifetime of implemented adaptation measures.

For the identification of best choices, several decision rules are available. Among them are: Maximax and Minimax (Wald, 1947), von Neumann-Morgenstern (von Neumann & Morgenstern, 2007), Hurwicz (Hurwicz, 1951), and Savage-Niehans (Savage, 1951). All these rules are applied for the evaluation of the decision matrix, whereby two time horizons (medium-term and long-term future) are considered. The obtained results do not appear to depend on which decision rule was employed.

While adaptation via dredging and retention measures is marked by equal sustainability on medium-term horizons, sustainability changes when the focus turns to the long-term future. In addition, findings reveal that the relapse in sustainability of investments in damming measures observed in the near future is not attributable to short-term volatility, but instead is attributable to progressively increasing threat levels requiring continuous reinforcement. This is evidenced by the fact that, in the medium term, damming measures only lag a little, while analyses referring to long-term time horizons show a much more pronounced decline toward 2100.

In the present application, analyses for more distant time horizons are crucial, because infrastructure investments in transportation are undertaken on the condition that trouble-free supply-chain operations can apply for many decades. The results have been extensively discussed with stakeholders in transportation and have been assessed as traceable and consistent. Both aspects—methodological robustness and the evaluation of attained findings by stakeholders—indicate their suitability for the development of effective and sustainable adaptation strategies by supporting decision-making processes.

These capabilities are crucial both for the development of adaptation strategies by enhancing sustainability in decision-making and for the design of policy instruments aimed at improving the efficiency of civil protection project implementation.

Conclusions

This article addresses three central aspects of transport and climate change. Both the role of transportation as a driver of climate change and the sector’s vulnerability to climate change impacts are presented. Furthermore, climate-change-induced hazard processes causing damage to the transport system are discussed, with a special focus on the European Alps, for which affected infrastructure and assets as well as potential adaptation measures are briefly outlined.

In order to effectively counter the effects of climate change, stakeholders need to integrate the design of appropriate adaptation strategies into transport planning on different time scales. Until a few years ago, achievement of this goal was limited by barriers to its acceptance. However, current levels of commitment, which are crucial for the implementation of sustainable measures, have been demonstrated by the results of a recent stakeholder survey (which served as a basis for World Meteorological Organization’s new Service Delivery Target). The survey findings demonstrate that the skepticism of recent years has given way to widespread acceptance.

Finally, decision-theoretical procedures allow the integration of adaptation strategies into transport planning, as is shown by the example for inland navigation on the stretch of the Danube running through the Alpine foreland in Austria.