Changes in climate will threaten the infrastructure – the water, transport, energy, communication and other systems – that sustains society. Rising sea levels, higher temperatures and changing frequency of droughts and floods will all pose challenges. Lord Krebs and Professor Jim Hall, of the statutory Climate Change Committee, explain how decisions are being made to adapt infrastructure systems to a changing climate.
Flooding on a road in England
Recent natural disasters, such as the widespread flooding across the UK in the summer of 2007 and again in Cumbria in November 2009, illustrated the vulnerability of infrastructure systems in the UK to climatic extremes. Electricity, transport and water supplies experienced disruptions. Other services, such as telecommunications and water treatment, also came under pressure.
Engineers can design complex infrastructure systems to be very reliable, even when those systems come under extreme environmental loads – witness the safety record in the civil aerospace industry. However, achieving that reliability requires careful analysis of the resistance of the system to extreme loading; its robustness to potential unforeseen loads; and the system’s resilience – its capacity to recover from disruption. The concept of resilience is rapidly gaining currency in the design and management of critical infrastructure. The threat of climate change means that infrastructure systems have to be designed so they are not only resilient to today’s extremes but also adaptable to the climatic conditions we will experience in future.
Climate threats to infrastructure
Some industries are in a good position to adapt relatively easily to changing climatic conditions, year on year: insurers can adjust their premiums and farmers can modify when and what they plant. However, other sectors require long-term climate-sensitive decisions that are hard to reverse. Typical examples of systems that need to be considered include major investment projects, such as water supply reservoirs, highways and power stations. We also need to consider land-use planning decisions that affect where people live and the building regulations that determine how houses and other buildings will cope with future climates.
In the UK, the most serious weather related hazards that need to be considered in the adaptation of infrastructure are:
Flooding: The frequency of river flooding, along with surface water flooding from heavy rainfall, is likely to increase in future.
Sea level rise: Mean sea levels around the UK are unlikely to rise by more than a metre before the end of the 21st century, but even this rise brings long term implications for coastal infrastructure.
Water scarcity: Water resources in many of the UK’s river basins are already over-exploited. Climate change will exacerbate this problem, especially
in the south of England, by changing patterns of precipitation and potentially increasing demand.
Extreme heat: Excessive heat in buildings and transport systems that are not designed for very hot weather will cause equipment failures, discomfort and a consequent reduction in productivity.
Beyond these headline impacts, increasing frequency or severity of wind storms could also have a disruptive impact, though the scientific evidence on the likelihood of changing storminess is inconclusive. Changing temperatures and precipitation will influence the stability of railway and highway embankments and cuttings and may also exacerbate ground subsidence, damaging foundations and buried infrastructure.
Figure 1. UKCP09 projections of change in summer mean precipitation (%) for 2050s (high carbon emissions) © UK Climate Projections 2009, http://ukclimateprojections.defra.gov.uk
Recent climate projections
The latest climate scenarios for the UK, known as the UK Climate Projections (UKCP09), were released in June 2009. The projections are based on over 300 runs of the Met Office Hadley Centre’s global climate model, combined with more detailed modelling to provide results for the UK on a 25 km grid. The results were validated by comparison with observed climate changes and presented as probabilities that show the uncertainty surrounding future climate changes. This new information on uncertainties means that engineers are now better equipped to make decisions on adaptation strategies, based on the balance of probabilities and consequences.
Climate change risk assessment
Adapting to climate change involves taking proportionate action to manage the level of risk, within acceptable limits. Quantifying the probabilities and consequences of climate impacts is therefore fundamental to any decisions made regarding adaptation. For many weather or climate-related risks, there are well established metrics. Flood risk, for example, is most commonly measured in terms of the direct economic damage that occurs during a flood. None of these metrics is immune from criticism – for example the victims of flooding tend to be as concerned about the distress and disruption of flooding as with the direct economic loss – so instead it is possible to use a diverse package of metrics (see opposite The principles of climate change risk assessment).
Adaptation decision making
Risk assessment provides a rational basis for making adaptation decisions. Making a decision requires one or more adaptation options, alongside the default option of taking no adaptation action (see Benefit-cost analysis). Given the uncertainties surrounding future climate, it is wise to identify flexible solutions that can be modified in future, and to avoid designs that exclude possible adaptation options in the future. As an example of how an adaptive approach works in practice, consider the problem of water resource management when rainfall and river flows are uncertain.
One of the great contributions of engineering to society has been the provision of a safe and reliable water supply. Many of the reservoirs, pumping stations and treatment plants that we rely on were designed using historic climate records. Do these designs need adaptation for a future changing climate and if so, what would be the most effective strategy?
Responding to water scarcity will require a strategic approach that combines water conservation and demand management with new resources and more efficient sharing of resources among water companies. The average water use in England is about 150 litres per person per day, equivalent to approximately one tonne of water per week. Current best practice in water efficiency could reduce use to 105 litres per day. Water reuse and rainwater harvesting could achieve further substantial savings. Currently, only 30% of households in England have a water meter, which means the majority of domestic water users do not have the information they need to efficiently minimise their water use. On average, households reduce their water consumption by around 10% after a meter is fitted. The introduction of variable tariffs to encourage efficient water use – such as seasonal tariffs linking price to seasonal availability – could provide an incentive to reduce water consumption further still in metered households. Reducing leakage rates from the water supply system, currently 23% on average, would be another adaptive solution.
We will also have to explore new water resources. The UK can learn from countries around the world that have to cope with water scarcity. For example, Singapore uses two-thirds of the rainfall that falls on the island, which is a remarkable proportion given that Singapore Island is mostly urbanised. Waste water is directly reused by treating discharges from sewage treatment works and returning it to provide one-third of the water supply. Singapore also uses desalination but, despite technological improvements in reverse osmosis, this approach is still energy intensive. Future developments include desalination by freezing, using liquefied natural gas regasification as a heat sink.
It is in the national interest to prepare for a changing climate. Doing so will yield immediate benefit in terms of reduced risk from weather-related hazards, as well as preparing for longer-term changes. However, in many respects the UK is still at the beginning of a process that will see climate change adaptation becoming embedded in all aspects of decision making.
The Climate Change Act (2008) provides an important stimulus. Under the Act, the Government is committed to a long-term framework for adaptation, including national Climate Change Risk Assessment, a national adaptation programme, and measures to encourage infrastructure owners to assess their own risk and to develop adaptation plans. Using adaptive management for critical infrastructure systems could be the key for engineers to optimise the future performance of infrastructure, old and new.