Impact of climate change on railway operation and maintenance in Sweden: A State-of-the-art review

2.1. Canada

Due to the geographical location of Canada, it has been subjected to various extreme weather events. These events have had significant impacts on the operation and maintenance of railway infrastructure in terms of traffic disruption, accidents, and an increase in maintenance costs. Temperature increase in summer and further recurrent freeze-thaw cycle during winter would rise destruction to ground results in a surge in maintenance intervention costs [21]. Mills [22] assessed that there is higher confidence in the increased effect of permafrost, sea-level rise, storm surge, and lower confidence in landslide/avalanche impacts on mobility and maintenance of railway infrastructure. Nevertheless, sea-level rise can also have a compounding effect on bridges and drainage systems surrounding railway infrastructure. Canada may have some optimistic impacts due to decreased amount of snow and ice due to climate change though, design and construction adaption procedures may be expensive [23].

2.2. United Kingdom

Diaz-Neto [24] has analyzed three different climate change scenarios at 2020, 2050, and 2080 and identified that there would be an increase in flooding risk from rivers and sea-level led to inadequate drainage conditions that could lead to an increase in the deterioration of railway infrastructure. The study further concluded that there is a need to consider the climate change impacts during the planning of maintenance and renewal actions, especially at vulnerable geographical locations. In addition, it was emphasized that there is a need to improve the knowledge and awareness of climate change impacts on railway systems within infrastructure managers, experts, related stakeholders, etc. It was recommended to revise the technical standards and policies to adapt the infrastructure to climate change by modifying design guidelines during construction and appropriately conduct research studies to solve problems for future needs. Necessitate emergency and contingency plans will also be needed to be adopted to handle extreme weather events and their impacts.

The United Kingdom has commenced creating a transport roadmap for climate change adaptation. They emphasized that the transport infrastructure needs to be resilient until 2050 and allocate necessary resources to operate and maintain appropriately without additional unexpected and unwarranted costs. Furthermore, they emphasize that the level of awareness of society about climatic change impacts on railway infrastructure was not high. Hence, it was highlighted that there is a need to devise an efficient way of communication and knowledge awareness against climate change among railway stakeholders. They also recommended incorporating a risk management approach during design, operation, and maintenance considering climate change impacts and further encourage cross-modal knowledge-sharing networks [10], [13], [25], [26].

2.3. United States

Humphrey [6] has systematically analyzed the possible impacts of climate change on US railway infrastructure. This research realizes that the impact will be differed by modes of transport and will be prevalent and expensive in both social and economic provisions that will necessitate major changes in life cycle phases of the railway system. The research recommended actions, for example, integrating climate change variations into investment assessments, assimilate contingency planning and emergency response systems into transport operations, revise design standards, incorporate climate change variabilities during the planning phase and develop the new organizational framework. The research further highlighted those future costly investments and disruptions in the operations that can be reduced if the infrastructure owners would focus more on the climate change impacts on infrastructure during planning.

Another US study [27] evaluates the impact of sea-level rise globally on railway infrastructure. The estimated global sea-level rise beneath different situations ranges from 18-59 cm. Their analysis stated that the rising sea levels in combination with the hurricanes and additional weather correlated events might cause enduring floods. This could lead to further recurrent short-term flooding of railway infrastructure and could lead to major consequences to transportation of goods and people in the US.

2.4. Asia

The IPCC Fourth Assessment Report foresees that global warming is well above the global mean in ranges from 2.5 °C to 4.3 °C in Asia [18]. However, these values are updated to (2 °C) rise in the fifth assessment report [28]. Rainfall in boreal winter is expected to rise in most parts of Asia and precipitation in summer is extremely likely to rise in most parts of Asia, however, it is expected to decline in the central part of Asia. It is expected that the heat waves in summer be lengthier interval, and more severe and regular in Asia. Less too chilly days are expected as well. There is very probable to increase in the occurrence of severe rainfall events. Extreme precipitation and winds related to tropical cyclones are expected to increase in most parts of Asia. Sea levels are expected to increase from 18 cm to 59 cm from different scenarios.

Several extreme weather events in the past in Asia consist of severe floods, cyclones, and tsunamis that was a devastating impact on not only transport infrastructure but other infrastructures as well. These extreme events had harshly disrupted their operations with already existing degrading infrastructure and a further burden on them due to an increase in population and higher temperature ranges. The damage prone to transport infrastructure in Bangladesh by 2007 floods was approximately 34 % (the US $ 363 million). The Aceh Flood 2007 in Indonesia impacted substantial destruction to the transportation system lead to the US $ 35 million that is approximately 25 % of infrastructure costs [7].

3.1. Temperature

According to Klimatanpassning [31], the average global temperature is expected to increase between 0.5 °C to 5 °C by the year 2100. Marginally higher warming up than the global average and it is likened through a similar period.

The regional climate scenarios customized for Sweden, centered on global climate scenarios RCP4.5 and RCP8.5, showed that the annual mean temperature of Sweden will increase by 2 °C to 7 °C in the time 2071-2100 when contrasted to the mention time 1961-1990. The highest temperature rise is highly likely to be through the winter, amid 2 °C and 9 °C by the ending of the period. In summer, changes are projected to be a smaller amount than compared to winter, amid 1 °C and 6 °C hotter. These variations are affected by substantial regional disparities with the highest effect in the northern part of Sweden.

The overall duration of the growing season (number of days once the average daily temperature is over 5 °C for a specific period) is likely to increase by 1-2 months all over Sweden, apart from the south where there will be an increase that is projected to be up to 3 months. A greater mean temperature of 5 °C implies that Sundsvall (north of Sweden) in the future will have a similar average temperature as of today in Stockholm.

Average temperature, the occurrence of several days with temperatures in particular periods, and the duration of the extremes are the major important factors for natural systems and society. A soaring mean temperature affects steady changes, much for temperature extremes in means of both their range and frequency.

In addition to the temperature variation, uncertainties from internal variability must be also considered for climate adaptation activities by railway stakeholders and decision-makers from the government [32].

3.2. Zero crossings

If the temperature frequently changes around 0 °C, it influences areas such as transport and farming. The word ‘zero crossings’ defines the number of days with the change of temperature. A day with zero crossing is identified “as a day with temperature both below 0 °C and above 0 °C calculated from two meters above the ground” [31].

Zero crossings are extremely frequent in the central part of Sweden with a mean of 100-120 days per year. The minimum number of zero crossings arises in the southern part of Sweden. Usually, the number of zero crossings is larger throughout spring, although they are as common as throughout equally winter and autumn. During the summer, the trend happens rarely in all areas of the country.

According to SMHI’s latest estimated climate scenarios, where zero crossings have exclusively been analyzed, the findings showed a reduction in amount all over the country throughout spring and autumn. In the winter, the total amount of days with zero crossings will reduce in the southern part of Sweden however there will be a rise in northern and central parts of Sweden [31].

3.3. Windstorm

Due to the complexity of the windstorm occurrence, climate scenarios analyst was not able to provide proper estimates on how wind climate might change in the future. Some many intricate factors and conditions affect the course of event, intensity, and occurrence of these storms. For example, a warmer ocean surface and consist of above water vapor present in the environment could impact the origination of storms.

At a similar moment, ocean warming could lead to decreased variations involving both cold and warm air masses, which might perform an essential role in the origination of severe storms. This might in sequence neutralize by the increasing influence that warming up has on the development of the storm. The low-pressure systems that can grow into these storms are usually projected to turn into less frequent in the northern hemisphere during warmer climate. It is hard to derive suppositions from the various scenarios about regional changes that surpass irregularity naturally happening in the system.

Weaker winters with higher rainfall are projected to grow to be more frequent in future, and steadily the circumstances for soil frost will alter. Consequently, the possible risk of damage due to storm might rise irrespective of variations in the wind climate. The magnitude of the destruction also differs on other aspects that are usually associated with behavior of human and susceptibility to traffic disruptions in the infrastructure, further dependency on electricity [31].

3.4. Snow

Sweden is a sizable country with huge discrepancies in temperature and rainfall. This is particularly evident by studying the extent of snow cover. Due to climate change, the duration of snow cover is likely to decline. Huge volumes of snow can affect key disruptions in traffic, destruction to buildings, trees, and overhead power lines. The difficulties tend to get harsher in combination with fierce winds or if the snow is further damp and heavy.

The quantity of water that is required in the snow cover throughout the winter and by that melt in the spring, disturbs the overflow of our watercourses in various seasons. When a heavy snow cover melts quickly, triggering a bigger flood in spring. Snow cover can also facilitate chances for leisure for, example skiing sports after the snow cover is dense and long-lasting.

In the mountain valleys situated in the northern part of Sweden, the first snow cover usually develops at the beginning of October. In mountains, this occurs mostly in September. There is an explanation of why coastal areas typically consist of tiny amounts of snow in early winter is because the temperature is comparatively extreme throughout autumn and near the beginning of winter across coastal areas and lakes.

It may take a long time before a further enduring snow cover is created, particularly in the southern part of Sweden. The snow cover could not persist during the winter from the central part of Sweden, Värmland, via the south of Dalarna and to central Gästrikland. Due to climate change, the snow cover period is likely to reduce, and in southern Sweden where there is expected to be no way of enduring snow cover in any way [31].

3.5. Floods

In the future, floods will grow to be more frequent all along the southern coast of Sweden, due to increasing sea levels. For lakes and streams, the risks differ throughout the country, where several parts are likely to have a higher risk of flooding and others are lesser at risk. The fundamental causes will vary depending on where the flooding happens near the coasts, rivers, and lakes or mostly in cities.

The risk of flooding in lakes and waterways might change over in the future but fluctuates among various parts of the country. The risk of flooding is also relying on additional aspects such as how watercourses are controlled, what preventive methods are implemented, and how infrastructure will vary over time because of replacements and renewals.

Severe precipitation through a brief period can create flooding in cities and transport infrastructure. In urban areas, overflow frequently happens from small areas with excessive amounts of impermeable surfaces, that cannot absorb any water. Stormwater systems hence must manage a larger part of the rainfall which it fails could affect the beneath the surface of infrastructure. Research into severe precipitation in a future climate indicates that this type of event is projected to develop more commonly in the future due to bad planning, congestion, and over usage of stormwater. Climate change adaptation attempts need to be prepared to build up resilience to severe precipitation in urban areas [31]. In addition, it is reported that in several areas' railway embankments can act as a dam in the occurrence of extreme precipitation due to capacity and /or poor maintenance of drainage system [33].

4.1. Impact of extreme weather events on vulnerable railway assets

Fig. 1 [36] provides an interrelation between failure causes of extreme weather events on railway infrastructure failure modes, consequences, and failure effects. It was observed that these extreme weather events could disrupt and affect essential functions of the railway transport infrastructure.

Fig. 1Failure causes, failure modes, asset failures, and failure effects on rail infrastructure

All railway infrastructure components such as tracks, catenary, bridges, embankments, tracks, etc., are impacted by extreme weather events. In some cases, such as track, the higher temperatures/lower temperatures, precipitation, and snowstorm could lead to traffic disruptions and in the worst cases lead to damage to the track. However, in some of the cases such as permafrost and zero-crossing, it is hard to measure the impact of these events on railway infrastructure. Hence, a suitable understanding of weather events during the plan, design, operation, and maintenance of railway infrastructure is to be assessed to increase the serviceability and life of the assets. Provided that the railway transportation infrastructure is the backbone drive of the economy of the country, it is necessary to assess these impacts for further organizing of standards and policies and allocate sufficient funding to improve the resilience of the transportation sector [7]. Table 1 reported the impact matrix among the various vulnerable components in infrastructure and its impact on climate events.

The potential impacts on the infrastructure and railway operation and maintenance depending upon the severity and occurrence of an event. It also needed to consider several other recommended actions such as increase in inspection, reduction in operating speeds, risk assessment of effects of climate change can be adopted to mitigate the risk and its failures. These failures can lead to having a compounding effect socially such as inconvenience, economic losses due to disruptions, and an increase in carbon emissions due to additional transportation effects to reach the destination. In some cases, it might lead to serious consequences such as train derailments, damage to the railway infrastructure, and danger to human life. The various possible effects and their gaps in practice, knowledge, and information are tabulated in Table 2.

In a study using fuzzy Bayesian approach [1], the climate results of every climate parameter of environmental factors related to UK rails were computed and ranked in Table 3.

There exist several weather-associated effects on infrastructure functioning that vary across geographical areas. Table 4 provides an outline of the possible impacts of climate change on railway assets and their performance [36].

In addition to the above effects, several research studies were conducted on the effect of several extreme weather events on vulnerable railway assets in different countries are tabulated in Table 5. This research provides possible vulnerable assets that are relevant for the Swedish climate.

The railway needs to have safe and reliable transport and necessary to be more resilient towards effects of weather for the future. To understand these risk sites, there is a need to focus particularly on various assets of railway infrastructure which are prone to extreme weather events. Initially, to estimate the climate impacts, it is imperative to draw trends of extreme weather events in the future by considering both spatial and temporal resolution by evaluating various forecasting models. Geographic Information Systems (GIS) can also be used to assist the detection, identification, and further mapping of vulnerable areas of infrastructure [37].

To implement the climate adaptation of railway infrastructure, it is necessary to conduct a risk assessment for expected occurrences, severity, and associated consequences for the potential vulnerable assets [38]. Based on the questionnaire, interviews, and discussions from various stakeholders, they calculated risk by anticipating severity, occurrence, and consequence of each of the extreme weather events on each of the vulnerable assets.

By conducting this vulnerability analysis, the most vulnerable areas were identified as signaling, track, heating, traction systems, telecommunication systems, embankments, culverts, and bridges. This vulnerability analysis could highlight the necessity of considering both quantity and duration of effect of extreme weather events on infrastructure by understanding failures and consequences to railways to specific locations [39]. Floods have possible lesser effects compared to other extreme weather events due to exposure to only a few areas of spatial nature and specific regions of railway assets.

For climate adaptation of the railway infrastructure, it is important to consider the isolated events on the infrastructure so that necessary measures can be taken in the future to reduce its impact. Those events such as floods, landslides, and harsh winters can accommodate prolonged nature because of awareness [71], [72]. To implement these recommendary actions, revision of policies, standards and sufficient funding needs to be in place to accommodate these additional costs of implementation during design, operation, and maintenance. Several countries compiled reports on climate adaption for railway infrastructure such as France [73], Germany [74], United Kingdom [10], [13], [14], [42], [75], India [76], South Africa [77], Canada [23], [78], Russia [79] and Sweden [34], [80].

Furthermore, a suitable early warning system and emergency response system needs to be adapted to monitor trends in climate, detect and predict the effect of extreme weather events, and developing of necessary firefighting guidelines to reduce its impact and rapid recovery from adverse weather events [81]. Swedish Civil Contingencies Agency (MSB) plays this role to prepare for the emergency response and contingency planning to reduce the climatic impacts on railway infrastructure. One such policy development was carried out in Västra Götland [82]. In addition, there is also needed to combine climate models with infrastructure degradation models for quantification of impacts of climate change on railway infrastructure.