During the first phase, researchers confirmed the scope of this research as climate change, adaptation planning, and transport (Note: Researchers recognised the possibility of other transport modes (e.g., oil pipelines are also regarded as a type of transportation), but researchers only focused on the main four modes (i.e., sea, air, road, and rail)). Accordingly, the two groups of 10 keywords, included (1) “climate change”, “impact”, “risk”, “analysis”, and “adaptation” (Group 1); and (2) “transport”, “seaport”, “airport”, “port”, “road” and “rail” (Group 2). Then, those search strings and their substrings (e.g., transport, railway) were entered into the two searching platforms linked by an “AND” function, meaning the combinations of any keyword from each of the two groups. Subsequently, the search results (i.e., all the combination results) were initially analysed through an “OR” function, by which there were 1791 articles elaborated upon.
Afterwards, three filtering and refining stages were set for purifying the most relevant papers, as below. First, only the articles containing more than one keyword (at least one in Group 1 and one in Group 2) were regarded as the targets, assuring that the selected papers were relevant to climate change and transport. Second, only peer-reviewed journal articles were collected, ensuring this research’s authority. Third, the remaining database was further assessed and screened by reviewing each paper’s title, keywords, and abstract to filter out unrelated papers to enhance the review’s reliability. Finally, the three-stage selection procedure helped yield 160 highly relevant representative articles published since 2000.
To interpret different dimensions of transport research on climate adaptation, publication tendencies were first discussed, including publication numbers, citations, dominant journals, and the geographical locations of authorship. Next, a specific assessment was undertaken to reveal each transport mode’s research focus and characteristics.
By counting the publication year of all related publications, the analysis in this part provides readers with an overview of the evolving themes and patterns, particularly the research tendency of each transport mode, with the latest information on this subject.
Through the critical analysis of the selected papers, in general, there were two periods divided by 2013, showing a significant pattern difference. As shown in Figure 1, in the first phase (i.e., from January 2006 to December 2012), the total number of publications was only 11. However, since 2013, there has been a noticeable rise, while the number has started to fluctuate, growing from seven to 29. This was possibly because of the impact of COVID-19, as much transport research efforts (e.g., research grants and special issues leading transport journals) in terms of dealing with the emerging challenges presented by the pandemic over the past 2–3 years. Maintaining a high publication rate of 13.5 per year, the second phase (from January 2013 to April 2023) contributed 93.1% of the total papers, with a peak in 2020 when 29 papers were published. The fast-growing pattern over the recent ten years indicates the strong developing potential of this research area.
Among the papers, sea and road transport were the domain segments, in which 89 studies related to climate risks and adaptation in these two transport segments were found, occupying 56% of the total. However, as elaborated upon in Figure 2, less attention was given to air and rail transport, with only seven and ten papers being presented, respectively. It was worth noting that relatively large proportional studies involved more than one mode. That being said, 28% of the publications stemmed from the multi-modal industry.
The citation trend is another index that allows the measurement of the contribution of climate adaptation research in transport-related fields. Researchers found that the citation number was highly associated with the distribution of the publication of each mode. The top citation was for the multi-modal sector, with 586 citations, beginning from 35 records in 2006, followed by 375 for sea, 250 for road, 108 for rail and 18 for air transport. Thus, it was suggested that multi-modal research attracted attention, but systematic review and analysis were relatively scarce. Meanwhile, there was a relatively mature research pattern in terms of sea and road transport compared with rail and air transport. The latter, especially air transport, had developed slowly and might be overlooked by researchers, industrial professionals, and the government. This is possibly because the current transport adaptation focuses more on infrastructures than operations. Road and railway are associated with many studies, while seaports are often treated as the node and gateway of large door-to-door supply chain services, closely linked with road and railway. Relatively speaking, scholars are more concerned about airport operations than infrastructure, which partially justifies why more attention is given to infrastructure than operations in terms of existing transport adaptation.
To identify the geographical distribution of climate adaptation research in transport, researchers recognised each paper’s first and/or corresponding author as who was usually regarded as the primary author(s). By doing so, researchers could understand the popularity and accessibility of this research topic in different regions. As is demonstrated in Figure 3 and Figure 4, the corresponding researchers primarily came from more than 20 countries. However, researchers from the UK, the US, and Canada were the main forces, with 59 papers published over the past 16 years.
Figure 3. Number of articles by geographic location of the corresponding author (January 2006–April 2023).
Figure 4. Map graph of number of articles by geographic location of the corresponding author (January 2006–April 2023).
Specifically, researchers from the US and Canada formed a pivotal team focusing on the climate adaptation of sea and road transport since 2008. Meanwhile, research on climate adaptation in the rail sector has been predominantly carried out by scholars from Europe, especially the UK, since 2014. The background of the researchers was diversified in geography, including European (e.g., the UK, Germany, the Netherlands), North American (i.e., the US and Canada), and Australian backgrounds. As for multi-modal transport, American and British scholars still played the dominant role, while researchers were less regionalised, scattered from other European countries (e.g., Sweden), and from Asia (e.g., China) to Africa (e.g., South Africa). Thus, it is evident that developed countries (e.g., the US, UK, Canada) have conducted considerable research on the topic in the sea, road, and rail transport sectors. There is enormous potential for climate adaptation research on air transport and shipping to develop research opportunities for international collaboration in multi-modal fields.
3.2. Research Focused on Each Transport Mode
Acknowledging the overall trend in climate adaptation research in transport, one can categorise the selected articles into five groups based on their corresponding transport mode: sea, air, road, rail, and multi-modal. The evolving pattern, current situation, and dilemmas of each transport sector were investigated through context analysis to provide meaningful insights for future research on climate adaptation in transport.
Sea Transport
The first article linking climate change and seaports can be traced back to 2010. Focusing on the impacts of climate change on maritime navigation, Hawkes et al.
[42] discussed how the changes in precipitation, sea level rise, and velocity could influence vessels, accessibility, transport infrastructure, and operation both positively and negatively. Also, they mentioned the utilisation of climate adaptation measures to respond to these impacts, which were clustered into diverse types of adaptation strategies and applied to the seaport sector in northwest Germany by Osthorst and Mänz
[43].
In 2013, Becker et al.
[8] published a paper on the impacts of climate change and adaptation planning in seaports, entitled “
A note on climate change adaptation for seaports: a challenge for global ports, a challenge for global society”. At the time this study took place, it was the highest cited article, stressing for the first time the strategic role of seaports and their vulnerability to climate risks (e.g., sea level rise (SLR) and storms)
[8]. Furthermore, the results from collecting the opinions of worldwide seaport stakeholders concerning climate change impacts and adaptations suggested it was emergent to adapt these impacts through “soft” and “hard” measures with global efforts.
Furthermore, Becker et al.
[4][9] explored how seaport resilience could be strengthened to minimise climate risks by requiring adaptation strategies from associated experts within two US seaports (Port of Providence and Gulfport). They suggested a seaport cluster composed of all of the relevant stakeholders (e.g., seaport authorities, governmental institutions, and insurance companies) to form a long-term master plan with solid leadership from “boundary organisations”
[4][9]. Notwithstanding, until 2019, the stakeholders in the case of Providence still held vague perceptions about who should take a leadership role and offer significant investment for climate adaptation
[6]. More recently, Mclean and Becker
[11] have tended to determine the barriers challenging decision-makers to make resilience investments to climate and extreme weather hazards for seaports. Accordingly, the seven key adaptation barriers were typologies from extensive interviews among 15 seaports in the US (e.g., the absence of understanding of threats, funding, and communication).
Among the reviewed papers, although a considerable number of assessments have been made for measuring climate vulnerabilities to develop adaptation measures, most of these have applied qualitative techniques (e.g., interviews, focus groups, case studies) on small- or medium-sized scales. Some of these studies might be limited by their data representativeness and referential experiences for other regions beyond the investigated scope. In contrast, only a few articles, particularly after 2017, employed quantitative methods to evaluate climate risks and the effectiveness of adaptation measures, while they were coincidently highly cited. For instance, Yang et al.
[38] developed a fuzzy Bayesian model to rank climate risks and the cost-effectiveness of adaptation measures with its applications in 14 container seaports in Greater China (Note: Greater China includes Mainland China, Hong Kong, Macau, and Taiwan). Meanwhile, there have been additional concerns about inter- and intra-port coopetition in terms of seaport adaptation investments, as well as the significance of the market structure of terminal operator companies in determining the size and timing of investment
[44][45][46]. These studies modelled climate disasters under a general form of Knightian uncertainty, establishing a two-period options game model and conducting vulnerability analysis, especially in the condition of asymmetric information about actual climate disasters
[47][48].
Overall, it is widely accepted by both academia and industrial practitioners that SLR, storms, and other climate-related hazards have been threatening diverse aspects of seaports (e.g., Panahi et al.
[49]). Moreover, with growing evidence from scientific reports and research papers, adapting to climate change impacts has been put on the agenda for many seaport administrators worldwide, whilst many are stuck in its implementation
[7]. Thus, the issues on how to stimulate the willingness to conduct adaptation planning and overcome dilemmas during the execution process have triggered considerable discussions in the recent decade. As the latest review paper by Loza and Veloso-Gomes
[50] stated, how to integrate adaptation measures in the initial stage of new port design deserves to be considered as a larger project instead of focusing on narrow aspects or case studies. To tackle this outstanding challenge, topics such as employing quantitative risk assessment methods, building a standardised adaptation framework, and stimulating effective stakeholder collaboration are generating widespread concern associated with urgency.
Air Transport
The aviation sector has been considered to be a key contributor to climate change. The discussion regarding the relationship between climate change and aviation was initially revealed by Bows
[51]. The article highlighted the significant role of the aviation industry in reducing greenhouse gas emissions based on a consensus projection that aviation would contribute up to 5% of global emissions by 2050. However, because airports are primarily situated in or close to urban areas, next to rivers, or alongside coasts, they are vulnerable to the impacts posed by climate change, such as flooding, SLR, increased temperatures, high winds, and extreme weather events
[52][53].
Surprisingly, a few studies, mainly on a regional scale, recently started investigating how to respond to the impacts of climate change in airports with adaptation strategies. For instance, the authors in
[52] illustrated the best practice, namely in Singapore Changi Airport, by implementing climate adaptation planning with solid governmental support. Through collecting data from 13 major Canadian airports, Zhao and Sushama
[53] estimated the changes in temperature and wind influencing aeroplane take-off and landing performance. The study provided practical suggestions for flight operation with growing temperatures by examining three types of flights (long-, medium-, and short-haul) in diverse conditions (i.e., weight restriction days, strong tailwind, and crosswind). Another case study regarding climate risk assessment occurred at Athens International Airport in 2021
[54]. Combining historical climate data with adaptation data from surveys and interviews, they provided a list of risk evaluations with practical recommendations for outdoor workers, drainage systems, and infrastructure design to improve airport climate resilience.
A relatively comprehensive review of the studies regarding climate change impacts and adaption in the aviation sector was undertaken recently
[55]. Analysing more than 40 relevant articles, the authors concluded that the emergent demand for adapting to the impacts posed by climate change had been inadequately researched nor considered by industrial practitioners in the air sector. The literature was considered highly relevant but multi-disciplinal (e.g., tourism is a commonly mixed discipline).
As stated by Tsalis, Botsaropoulou et al.
[55] and Skouloudis, Evangelinos et al.
[56], despite a rising number of sustainability reports being provided by airports, there were neither standard nor mandatory accounting principles for airports in reporting practices, which led to the failure of the assessment of disclosed information regarding climate risks. It partly explained the stagnancy of climate adaptation research in the aviation sector. Also, for an airport that has attempted to adapt to climate change impacts by enhancing the system resilience, measuring the resilience performance of airports in diverse extreme weather events is a challenge. It could be tackled by establishing a resilience metric measured by the speed of recovery, which was applied to a trial of the aviation system in China
[57]. Echoed by Ryley, Baumeister et al.
[58], research on climate adaptation in airports was generally constrained by complicated methods of crossing disciplines and the inaccessibility of researching the climate and airport data involved. Other gaps including the paucity of funding, qualitative investigations, and long-term timespan for adaptation planning were revealed. Therefore, it is suggested to review the literature, better benchmark industrial standards, and offer practical recommendations through best practices for future climate adaptation planning in airports.
Road Transport
Behind sea transport, road transport was the second most investigated sector regarding climate adaptation. Through the analysis of the 44 selected papers, it was found that existing studies have mainly focused on the physical dimensions of transport infrastructure (e.g., road pavements, drainage, tunnels, and bridges) on a national or regional scale (e.g., Tighe et al.
[59], Guest et al.
[60]). Moreover, instead of conducting comprehensive literature reviews or using conceptual frameworks, researchers used quantitative methods, mainly modelling, to deal with specific demands in transport networks due to the impacts posed by climate change.
One of the most popular articles was published in 2014, in which Schweikert et al. developed comprehensive software called the Infrastructure Planning Support System to assist in decision-making for long-term road infrastructure planning
[12]. The system in Schweikert et al.’s work provided an effective tool for cost–benefit analysis by considering technical, economic, and social factors in both quantitative and qualitative ways, given its wide practical applications in more than 50 countries. Another recently published article assessed the impacts of increased groundwater levels on road pavements in coastal areas owing to SLR
[61]. The study found that rising groundwater could flow into the unbound materials. Based on the multilayer elastic theory, a groundwater flow model was designed to assess pavement performance in diverse climate scenarios to determine the magnitude of fatigue and reduction in the rutting life of the pavement.
North America has been the hotspot region for road adaptation to climate change since 2008. The latest research topics have included an assessment of the construction of the Tibbitt to Contwoyto Winter Road in threshold freezing conditions due to permafrost peatlands in Canada
[62], an investigation of a modelling approach for bridge deck design against a corrosion attack in major Canadian cities
[60], as well as an examination of the potential economic effects through a climate adaptation measure (i.e., upgrading the asphalt binder) to improve pavement resilience against growing temperatures in Virginia, USA
[63].
Different from sea and rail transport (to be further discussed in the next sub-section), climate adaptation research on road transportation involved a wider geographical distribution. In addition to central European (e.g., the Netherlands, Germany) regions, a few developing countries (e.g., Malaysia, Saudi Arabia) were included. For instance, Shahid and Minhans
[64] conducted a literature review by connecting climate change with road accidents to examine how climatic factors could influence road safety in Malaysia. Another study related to road safety was undertaken in Saudi Arabia that quantified the costs of road traffic accidents because of increased death and injuries due to changing climate variables, namely, precipitation, temperature, and sandstorms
[65]. The latest survey investigated the mobility impacts on the road posed by flooding and heavy precipitation within urban residences in Ghana, Africa
[66].
Scholars have made some achievements over the past decade. Nevertheless, there are still gaps that are yet to be bridged in terms of climate adaptation in the road industry. Guest et al.
[60] stated that profound discussions regarding road research are significant when transforming revealed technical issues into effective institutional policies and long-term adaptation plans. Meanwhile, with abundant mathematical models being established and applied to regional cases, it has been suggested to re-test the results of climate risk analysis in diverse regions and tailor utilisation in other and multi-modal transport systems
[37].
Rail Transport
Papers concerning rail transport were much fewer than those regarding sea and road transport. This might be because the relevant literature had not been generated until 2014. In the meantime, the research had a significant geographical feature that was narrowed to European countries, while five out of the ten selected papers concerned British railways.
Only two articles in 2016 elaborated on the climate risk analysis procedure for the high-speed rail network in Malaysia and Singapore
[67]. It critically reviewed the climatic variables impacting the Malaysian railway infrastructure. Increased temperatures, heavy rainfall and flooding, lightning, and high winds were considered threats causing the delay of rail services, deterioration in operation, and failures of asset systems.
An assessment regarding existing and future flooding impacts on European railway infrastructure was conducted by Bubeck et al.
[68], who utilised an infrastructure-specific damage model to project annual flooding damage in each climatic scenario. They stated that over US$340 million in annual losses could be avoided by controlling global warming to 1.5 °C, confirming climate adaptation’s significance for European railways. Other European research included the investigation of critical barriers of organisations in transferring scientific climate change information into adaptation planning in the French rail system
[69] and the evaluation of flooding risks on underground transport with an application in terms of the Barcelona metro lines through a hydrodynamic model
[70].
A few studies have been undertaken concerning specific climate risks related to specific dimensions regarding the UK rail system. Jenkins et al.
[71] studied how hotter weather could alter passengers’ demand and service expectations on the London Underground. Their results showed that various adaptation measures of cooling down infrastructure temperatures were expected to reach the satisfied thermal conditions for most lines in the mid-21st century under a high-emission scenario. SLR was a significant climate hazard for the coastal Dawlish railway in the UK. Dawson et al.
[72] investigated the correlations between rail incidents and SLR over the past century through a semi-empirical model, followed by investigation of the relationship between future projections. In southeast England, rail incidents triggered by higher temperatures and heatwaves were discovered, including but not limited to the sagging of overhead lines, the breakdown of electrical assets, and track buckling. By introducing failure harvesting, Ferranti et al.
[73] found the different resilience of rail infrastructure systems to temperature over different seasons. Taking the Minnamurra Railway Bridge in Australia as a case study, Kaewunruen et al.
[74] applied building information modelling to facilitate the resilience of the bridge in terms of climate adaptation regarding asset management, operation, and maintenance.
Meanwhile, bridge scours, as a primary risk threatening the rail network in the southwest of England and Wales. were modelled by simulating the causal chain between scour hazard and climate change
[75]. More recently, Wang et al.
[31] surveyed the critical climate risks in the UK rail network, using fuzzy Bayesian reasoning (FBR) for risk prioritisation. Damage of the bridge foundation and collapse were highlighted as the pivotal risks owing to flooding and landslips.
As the climate adaptation research in the rail system started relatively late, restricted to regional or national cases, its development is less mature, with a few gaps that have yet to be bridged. For instance, during climate risk evaluation in coastal lines, besides fiscal losses, indirect economic and other socio-economic costs that are hard to project precisely need to be factored into consideration
[68]. Adaptation planning, in the meantime, demands cross-departmental involvement with a broad range of stakeholders
[72]. Furthermore, given the deficiency of comprehensive climate adaptation studies on railways, some advanced risk assessment methods, such as the failure-harvesting approach
[25] and FBR model
[37], can be re-designed to fit the requirements of other rail projects and promote adaptation strategies.