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1 Introduction

Over the last 30 years, several studies have sought to quantify the potential impacts of climate change in the UK in order to understand how risks might change and to inform adaptation and resilience policy in specific areas. Since 1998, a series of national climate projections have been produced, with the most recent UK Climate Projections published in 2018 (UKCP18) [1]. The UK Climate Resilience Programme (UKCR) funded a series of projects that characterised future climate risks and opportunities across UK sectors under its ‘Climate Risks’ theme. This chapter draws together published results from these projects. It focuses on indicators of change in climate hazard and resource and concentrates on how these indicators change in a world with continued high emissions. The indicators characterise change in vulnerability and risk, and therefore, help inform the development of policy and decision-making on adaptation and resilience.

The paper is organised into three sections, outlining the potential changes in hazard and resource that have been calculated during the UKCR programme, summarising how the results are being used and identifying important remaining gaps.

2 Changes in Hazard and Resource Across the UK

The weather and climate at a place constitute both a hazard (something that has the potential to cause harm, such as drought and flooding) and a resource (something that enables or constrains an activity, such as renewable energy generation). Heatwaves, floods and droughts are the most obvious hazards, while agriculture and building heating requirements are strongly influenced by climate resources. A change in climate alters these hazards and resources and will impact many areas, including health, infrastructure and the natural environment. Future impacts will depend on how the economy and society changes over time—and what measures are put in place to adapt and increase resilience—so are sensitive to assumptions about both trends and decisions. Another way of looking at the effects of climate change is to examine how indicators that relate to decisions and actions might change: how often, for example, would the thresholds that trigger emergency plans, or that are known to cause operational challenges, be crossed? Such information helps inform the development of adaptation and resilience policy.

Several UKCR projects took this approach; the results are summarised here, grouped into three sectors as classified in the Technical Report for the Third Climate Change Risk Assessment (CCRA3) [2]: (1) natural environment and assets; (2) infrastructure; and (3) health, communities and the built environment. Table 1 presents a high-level overview of changes in hazard and resource, together with some example quantifications for the 2050s, while the following sections provide more detail. It is important to emphasise that the indicators presented do not necessarily characterise the full range of climate risks in the UK, and that the summary concentrates on research undertaken by UKCR projects specifically.

Table 1 Changes in indicators of climate hazard and resource by the 2050s, based on the central estimate from the HadGEM UKCP18 strand (global, regional or local), with very high RCP8.5 emissions
Full size table

The indicators referred to in this chapter are listed in Table 1, alongside the corresponding UKCR projects. These studies used the latest UKCP18 climate projections [1], so the following section outlines these projections and details how they have been used.

2.1 Climate Projections and the Construction of Climate Scenarios

The UKCP18 land climate projections consist of four strands [1, 15], three of which (global, regional and local) describe changes in climate with the very high emissions ‘RCP8.5’ scenario, where global average temperature increases well above 4°C by the end of the twenty-first century. The three strands are based on climate models at different spatial resolutions, so provide information at different scales. The finer resolution models typically provide better information on short-duration, localised weather processes. All are based on variants of the Met Office HadGEM3.05 climate model, and therefore represent only a portion of the range of possible modelled future climates. The global strand combines the HadGEM3.05 model with other climate models, so gives a broader range of possible outcomes.

The fourth strand—the probabilistic projections—not only includes many more climate models, but also includes projections for a wider range of assumptions about future emissions. The projections are intended to characterise the most complete range of uncertainty in how climate is likely to change in the UK in future. In practice, most of the studies of the UKCR programme have used the regional and local strand HadGEM RCP8.5 projections because they are spatially and temporally coherent; very few have used the probabilistic projections. Different studies have used slightly different time periods to define the current reference period and have used a variety of approaches (bias-adjustment or delta methods) to create climate scenarios.

2.2 Natural Environment and Assets

While this sector encompasses natural environments, agriculture, forestry and the landscape [16], studies published thus far have concentrated on wildfire (the hazard) and on indicators relevant to agriculture.

Wildfires in the UK are typically a result of human action (usually inadvertent), but the fire danger at a place depends on current and preceding weather. Projected higher temperatures, lower humidity and increased drought conditions result in increased wildfire danger across the UK, particularly in the south and east [5, 6]. Each indicator presents a different degree of change with respect to wildfire danger, but all point to an increase in risk.

Regarding UK agriculture, projected warmer temperatures increase the duration of the growing season, which serves to both increase growing degree days and reduce early season frost frequency—conditions that benefit grass and potentially other crops such as vines [3, 4, 9, 17]. However, summer soil moisture deficits increase across the UK (particularly in the south and east) due to drier summers and greater evaporation. This potentially limits production of crops without supplementary irrigation. Agricultural drought risk increases with increasing temperature across the UK, with a large uncertainty range primarily due to uncertainty in projected changes in rainfall [9, 17]. With very high RCP8.5 emissions, the chance of having two warm and dry summer months in a year—which is challenging to agriculture—would increase from less than 10% now to over 40% by the 2050s, but again with a large uncertainty range [4].

Projected high temperatures, coupled with high humidity, also lead to increased risk of potato blight (particularly in typically cool areas) [4], lower milk yields from dairy cattle owing to increased heat stress (particularly in the south and east) [4, 17] and a substantial increase in the occurrence of debilitating sheep parasites (in the south and west) [17]. The annual number of days with very wet soils, which limits access to land, decreases in future [17]. This reduction occurs mainly during autumn, which would potentially help with the drilling of winter crops and establishment of robust rooting systems.

Taken together, these changes in climate imply some opportunities for UK agriculture (especially at lower emission scenarios), but also mean increasingly challenging conditions associated with extreme events for many types of farming. The precise impacts on yields will vary between crop type and variety, depending on their resilience to changes in temperature, rainfall and associated pests and diseases.

2.3 Infrastructure

This sector covers the UK infrastructure providing services such as heating, lighting, mobility, freshwater and sanitation to society and protecting against extreme events [18].

The number of days with ‘heavy’ rainfall above thresholds used in the Met Office National Severe Weather Warning Service is projected to increase into the future [9], implying more frequent flash flooding. The magnitude of rainfall events with a specific chance of occurring—such as one in 30 years—is projected to increase [8, 19]. The increases are proportionally greater in the north and west.

Changes in hourly and daily extreme rainfall such as these would directly affect flash flood risk (e.g. in urban areas), but not necessarily directly affect river flood risk. Small and impermeable catchments respond rapidly to short-duration rainfall, while flooding in larger catchments or catchments with more storage reflects longer-term accumulations of rainfall over days or weeks. The general picture is for an increase in flood risk (interpreted as change in either magnitude or frequency) across northern and western parts of the UK, resulting from increased rainfall and potentially slower-moving rainstorms [20]. In the south and east, there is more of a mixed picture [10, 21], with considerable uncertainty in the amount of change. The projected increase in flooding increases the erosion risk to bridges and other infrastructure [22].

At the same time, reductions in spring, summer and autumn rainfall across southern and eastern England result in lower summer and autumn river flows [10, 21], increased frequencies of hydrological drought [23] and associated pressure on water resources and the water environment—although the uncertainty range is again large.

High temperature extremes affect the performance and maintenance of road and rail infrastructure (e.g. causing road surfaces to melt and track/signalling equipment to malfunction), while low temperatures increase road accident risk through road icing [23]. High temperature extremes are projected to become much more frequent, reducing the reliability of road and rail infrastructure and increasing the frequency of failure. Low temperature extremes become less frequent but will continue to occur.

Adverse weather conditions can also affect operations on the railways. Characterised as hot, cold, wet and windy extremes, occurrences of ‘adverse weather’ impacts punctuality standards. Across England and Wales, the number of days with adverse weather is projected to increase with warming [23], primarily because hot days increasingly dominate. In contrast, adverse conditions in Scotland are strongly influenced by cold weather, and these decrease over time.

The reliability of renewable energy supplies is potentially affected by changes in climate, but changing demand (see below) will be more important than the projected small variation in the frequency of ‘wind drought’ [24, 25].

2.4 Health, Communities and the Built Environment

This sector concentrates on risks to the UK population, focusing on health and wellbeing, as well as the built environment [26].

Extreme high temperatures in the UK are projected to increase more rapidly than global average temperatures [13, 27]; the number of days above specific temperature thresholds increases substantially, particularly in the south and east [9, 23]. Two definitions of heatwave are currently used operationally, one by the Met Office to declare a heatwave (primarily for communications purposes) and one used in England in the health and social care system. Under both definitions, the number of events is projected to increase significantly. When translated into risk of human mortality [14, 28], risks increase with temperature in a very non-linear way and accelerate as temperature rises. Extreme heat stress arises where high temperatures are associated with high humidity; high heat-stress days are currently very rare in the UK, but the chance of experiencing them in future increases very substantially in the south-east [12, 13]. At the other extreme, cold weather events become less frequent [9, 12], but will still occur with sufficient frequency that they need to be considered for planning purposes.

Extreme windstorms are likely to increase in frequency throughout the twenty-first century, with a large proportion likely to feature very high windspeeds due to ‘sting jets’ [29] leading to an increased risk of property damage.

Heating degree days (a proxy for the demand for residential heating) decrease by about 18% and 35% at 2°C and 4°C warming, respectively [9, 23], with the percentage change relatively consistent across the UK. The uncertainty range is small because there is relatively little uncertainty in how UK average temperature changes with global average temperature. Cooling degree days (a proxy for overheating and therefore cooling requirements) increase from a low baseline, and therefore, percentage changes are potentially misleading. However, there is much more variability across the UK, with the greatest increase experienced in the south and east.

3 How Have the Results Been Used so Far?

A wide range of indicators of current and future climate hazard and resource across the UK are available from the Climate Risk Indicators website, an interactive tool enabling users to map indicators and plot time series at scales ranging from local authority area to the four nations of the UK. This resource has been used by several organisations to understand local and regional climate risks, and some (e.g. The Wildlife Trusts) [30] have combined the indicators with their own data to create customised risk maps. Results and figures also figure prominently in the CCRA3 Technical and Synthesis Reports. The UK Heat Stress Vulnerability website allows users to produce maps of current and future heat stress, combining metrics of heat hazard with metrics of vulnerability, which has been used by the Welsh Government [31]. The projected changes in short-duration rainfall produced in the UKCR project ‘FUTURE-DRAINAGE’ [18] have been used to define new peak rainfall climate change allowances for both England [32] and Scotland [33]. The UK Government’s CCRA3 [34] refers to both the climate risk indicators website and ‘FUTURE-DRAINAGE’. The results from several projects have also been used as the basis for more specific investigations for individual public and private sector organisations.

4 Gaps and Challenges

Taken together, the UKCR-funded studies of changing climate risk in the UK have demonstrated the potential for large, adverse impacts and increases in risk. Also highlighted, however, are the large uncertainty ranges, primarily due to uncertainty in how mean and extreme rainfall across the UK will change over time. The studies have used slightly different approaches in detail, but all produce comparable results. There are, however, three main gaps.

First, the studies summarised here have typically focused on specific sectors or physical hazards on the land. While these were all assumed to be important, they were not selected on the basis of their relative contributions to climate change risk in the UK and do not provide a comprehensive coverage. For example, no studies have yet published indicators relating to potential risks to the natural environment (except due to wildfire hazard).

Second, most of the assessments so far have focused on the regional and local strands of the UKCP18 projections, which assume a very high rate of increase in future emissions [35, 36]. It is difficult to link these directly to potential changes under lower emissions, following the Climate change Committee’s guidance [37] to adapt to a two degree world but prepare for four degrees—although some analysis has been undertaken using subsets of the probabilistic strand [7] or presented impacts by level of warming [9, 13, 23]. In practice, there is little difference between emissions scenarios to the 2040s, compared with the uncertainty range, so the gap is more relevant over the longer term. Also, the regional and local strands used in most studies are based on a climate model with a relatively high climate sensitivity. The use of just a subset of the full suite of UKCP18 projections means that uncertainty ranges are probably underestimated.

Third, with the exception of the agriculturally focused 2021 study by Garry and others [4], there have been few assessments of how compound events and extremes might change in future (e.g. the cumulative impact of wind, rain and storm surges, or hot, dry and high fire danger conditions).

5 Conclusions

The studies summarised here together enable a consistent assessment of potential changes in climate hazards and resources across the UK using the same underlying climate scenarios, in terms directly relevant to the management of climate risks. Future risk and future impacts depend on how these changes in hazard and resource interact with changes in exposure and vulnerability.