The climate of the UK

Temperature

The Gulf Stream has a warming effect on the UK, especially bringing mild winters for it latitude. The combination of southerly latitude and the urban heat island effect means that London is the warmest place in the UK, with an annual mean temperature of 11°C, ranging from 5°C in January to 18°C in July. In the winter, coastal areas are milder as their temperatures are moderated by the relatively warm sea, so coastal areas of south-west England are the mildest in winter. Further north, Manchester has an annual mean temperature of 9.5°C, Edinburgh 8.5°C, and Stornoway in the far north-west 8°C. Frost can occur anywhere in the UK, but is most common away from the coast (18).

Precipitation

The high ground in the west of the UK leaves the east in a rain shadow from the prevailing westerlies, so that there is a distinct west-east pattern to average rainfall amounts. The orographic enhancement means that the wettest places are in west Scotland, northwest England and north Wales, with annual average rainfall of over 3000 mm in places. More typical of western locations are the annual average amounts, decreasing from north to south, of Stornoway (1170 mm), Glasgow (1050 mm), Manchester (810 mm) and Exeter (760 mm). In the east, annual average rainfall amounts are 670 mm at Edinburgh and 610 mm at London, with parts of East Anglia having totals down to 500 mm. Autumn and winter tend to be the wettest seasons, with the rainfall coming from frontal systems. In the summer there is still a moderate amount of rainfall, much of which comes as heavy showers from convective activity (18).

The highest frequencies and intensities of hourly extreme rainfall occur during summer (37).

Air temperature changes until now

The summer of 2018

The summer of 2018 (June, July, August) in the United Kingdom 
was the joint hottest on record for mean temperature in a national series dating from 1884. The hot summer was largely a consequence of the atmospheric circulation anomalies and elevated sea-surface temperature in the proximity of the United Kingdom, but these alone are insufficient to fully explain the magnitude of the observed temperature anomalies for the season overall. The warming climate was also a significant factor. The present-day likelihood of a summer temperature anomaly at or above that of 2018 is approximately 11–12%, which is a factor of 30 higher than estimated for a world without man-made greenhouse gas emissions. The latest set of UK climate projections (UKCP18) estimate that a 2018-like summer could be more common than not by the mid- twenty-first century (43,45).

The chance of summer 2018 temperatures has risen sharply from 1960 to present day. Warm UK summers that occurred with a 1-in-5 frequency in the 1981 - 2010 period now occur with double that frequency (45). 

UK

UK heat wave activity has increased twofold to threefold from 1878 to the present since the late 1800's: the return period of a 6-day heat wave with a daily maximum temperature of at least 28°C has changed from about 6-8 years to about 2-4 years, about two to three times more frequent on average (42).

Central England Temperature (CET) is the longest instrumental climate series in the world. The monthly record extends back to 1659 and presents a unique opportunity to examine climate variability in the Region over long time scales (7). The average of three observing stations in Hertfordshire, Worcestershire and Lancashire, has been monitored instrumentally since 1772, and long term changes in it are representative of those across most of the UK (1). From 1901 to 1999, annual mean CET temperatures showed a warming of +0.6°C over this period. The warming has been greatest from mid-summer to late autumn: July (+ 0.8°C), August (+ 1.2°C), September (+0.9°C), October (+ 1.2°C) and November (+ 1.3°C) respectively. With the exception of March (+ 1.0°C), the remaining months showed no statistically significant warming over the century (7). After a period of relative stability for most of the 20th century, CET has increased by about a degree Celsius since the 1970s (1). Eight of the ten warmest years recorded have been since 1990 with 2006 being the warmest year on record (3). Studies have shown that this observed rate of warming cannot be explained by natural climate variations, but is consistent with the response to increasing greenhouse gases and aerosols simulated by the Met Office Hadley Centre climate model. It is likely, therefore, that global man-made emissions of greenhouse gases have played a significant role in the recent warming of the UK (1).

Regions

Wales. Temperatures in Wales, Scotland and Northern Ireland have risen by about 0.7–0.8ºC since about 1980. However, because the length of data in each case is relatively short, research to date has not attributed these changes to specific causes (1).

Annual mean temperature in Wales shows a slight warming trend over the period from 1901 to 1998 (0.3⁰C per century), with five of the nine warmest years occurring in the last decade (1989, 1990, 1995, 1997 and 1998: all these years were between 0.9ºC and 1.1ºC warmer than the average for 1961-1990). The warming has been greatest in autumn and winter; summer temperatures have shown little trend over the century. There has been a small decrease in the diurnal temperature range due to night-time minima increasing more rapidly than day-time maxima (2).

England. The 1990s was the warmest decade in central England since records began in the 1660s (5). As a result the growing season for plants in central England has lengthened by about one month since 1900, heat waves have become more frequent in summer, while there are now fewer frosts and winter cold spells, winters over the last 200 years have become much wetter relative to summers throughout the UK, and a larger proportion of winter precipitation (rain and snow) now falls on heavy rainfall days than was the case 50 years ago (4). Besides, the nocturnal urban heat island is intensifying (6)

The largest increase in numbers of hot days is found in the south east of England, where at the 50% probability level (central estimate) an increase from around 20 to more than 50 days per year is expected (1).

Precipitation changes until now

Mean precipitation

Annual mean precipitation over England and Wales has not changed significantly since records began in 1766. Seasonal-mean precipitation is highly variable, but appears to have decreased in summer and increased in winter, although with little change in the latter over the last 50 yr (1). From a country-wide dataset over the period 1931- 2014 no significant trends in annual or seasonal precipitation totals can be distinguished from temporal variability (30). Winter precipitation increased from the 1960s to a maximum in the early 1990s, but has decreased since then, removing the significant upward trend reported previously by others (31). Previous reported negative trends for the summer season (32) have been reversed since 2007, as all summers between 2007 and 2012 were anomalously wet, with 2007 and 2012 being the two wettest summers on record in this dataset (30).

Heavy precipitation events

There have also been changes to the proportion of winter rainfall coming from heavy precipitation events: in winter all regions of the UK have experienced an increase over the past 45 yr; in summer all regions except NE England and N Scotland have experienced decreases (1). No significant trends of changes in rainfall intensity in England and Wales have been found between 1931 and 2014 (30). 

It is estimated, that the magnitude of extreme rainfall has increased two-fold over parts of the UK since the 1960s (8, see als 28). Intensities previously experienced, on average, every 25 years now occur at 6 year intervals; a consequence of both increased event frequency and changes in seasonality (8). These climatic changes may be explained by persistent atmospheric circulation anomalies and have huge economic and social implications in terms of increased flooding (8).

Multi-day rainfall events are an important cause of recent severe flooding in the UK, and any change in the magnitude of such events may have severe impacts upon urban structures such as dams, urban drainage systems and flood defences and cause failures to occur. There has been a two-part change in extreme rainfall event occurrence across the UK from 1961 to 2000. Little change is observed at 1 and 2 days duration, but significant decadal-level changes are seen in 5- and 10-day events in many regions (9).

In the south of the UK, 5- and 10-day annual maxima have decreased during the 1990s. However, in the north, the 10-day growth curve has steepened and annual maxima have risen during the 1990s. This is particularly evident in Scotland. The 50 year event in Scotland during 1961-90 has become an 8-year, 11-year and 25-year event in the East, South and North Scotland pooling regions respectively during the 1990s. In northern England the average recurrence interval has also halved. This may have severe implications for design and planning practices in flood control (9).

Recurrence of the autumn-2000 floods

During October and November 2000 many areas of the United Kingdom experienced a period of persistent heavy rainfall which resulted in widespread flooding (Marsh 2001) and extensive damage. For many catchments, the return periods of the rainfall which produced these floods have been estimated to be in excess of 200 years (15).

It has been studied whether, in general, increases in atmospheric carbon dioxide will result in more frequent extreme rainfall events. The periods are chosen to represent the change from the unperturbed ‘preindustrial’ climate to the observed period (1961–1990), to the present (2000), and to a possible future climate at the end of the century (2080–2100). The analysis focused on three regions near the towns of Lewes, Shrewsbury and York, all of which were very badly affected by the autumn-2000 floods (10).

Of particular interest are rainfall totals over 30 consecutive days, because sustained heavy rainfall was the main cause of the autumn-2000 floods. Model predictions for regions upstream of the towns of Lewes and Shrewsbury and the city of York suggest that it is likely that return periods of extreme 30-day rainfall will have reduced between pre-industrial times and the present. In particular, an event that had a 5% chance of occurring in any year may now have a 12% chance of happening (10.

Under a scenario of increases in greenhouse gases that lies in the mid-range of current IPCC estimates, this modelling system also predicts that these reductions will continue into the future. Statistically significant changes (at the 5% level) are seen in the return periods of the annual maximum 30-day rainfall amount for the climate around 2090. For example, the pre-industrial 20-year return-period event (that with a 5% chance of occurring each year) is predicted to become, for the three locations, around a two- or three-year return-period event (i.e. with a 30–50% chance of happening each year) (10).

Dry spells

Modest increases in the number of dry spells are found across the country and substantial increases in the south and east associated with lower summer rainfall (1).

Regions

England and Wales. In 2007, heavy flooding in England and Wales followed very high daily and 5-day totals of rainfall, resulting in economic losses of approximately £3 billion (29). Are these observed extreme events just bad luck or is heavy rainfall in summer, especially in July, something we have reasons to expect in the future and should begin adapting to in terms of infrastructure planning? This has been studied by modeling the historic situation and a situation of the “world that might have been” without anthropogenic forcing of climate change (28). In this study, initial conditions were varied for large ensembles of regional climate model (RCM) simulations (based on one general circulation models (GCM).

Three time slices were studied: the decades with the historic situation for 1960-1970 and 2000-2010, and the decade 2000-2010 in a representation of a world that might have been without anthropogenic climate change. The study focused on 5-day means of rainfall since 5-day means were considered to be a better proxy for flood risk than daily means (28).

The results show that high precipitation events like that which caused the floods in 2007 have become more likely. The risk of 2007 type July extreme precipitation has more than doubled due to anthropogenic climate change. The same cannot be said for summer precipitation as a whole as results for August and especially June are less clear (28). 

The flooding events over the last years do not seem to be related to changes in the magnitude of the daily rainfall accumulations. It is the frequency of multi-day precipitation accumulations that has changed: four recent years (2000, 2007, 2008 and 2012) have a greater number of extreme events in the 3- and 5-day accumulations than any previous year in the record. It is the duration of precipitation events in these years that is remarkable, rather than the magnitude of the daily accumulations (30). The extreme precipitation periods occurred in different seasons for each of these years (autumn 2000, summer 2007, spring 2008, summer/autumn 2012), suggesting a similar behaviour throughout the year with more extremes on the multi-day accumulation scale in the recent years (30). 

Wales. From 1901 to 1998, annual precipitation in Wales has increased only very slightly (+3%) over this period. Summer precipitation has fallen by up to 15% since the early 1900s, with the summer of 1976 being the driest (about 60% below normal). The summer of 1995 was about 50 per cent below normal. There has been a slight compensating increase (nearly 10%) in winter precipitation over the course of the century, with the two wettest winters on record occurring in 1989/90 and 1994/95 (2).

West Midlands. Summer rainfall has decreased since the 1880s, and winter rainfall has increased over the last 150-200 years. More winter rain days and longer wet-spells have occurred since the 1960s. Heavy storms have contributed more to winter rainfall totals since the 1960s (6).

East Midlands. Relative to the 1930s, annual precipitation increased slightly (+ 3%) over the period 1931 to 1999, even though both winter (–3%) and summer (–2%) showed slight declines. Individual months and years show far larger departures from the long-term average. For example, December rainfall totals have increased by + 38% since the 1930s, and July totals have fallen by -31% over the same period. The summers of 1995 and 1976 were the two driest since 1931, with seasonal totals respectively –68% and –62% below normal. Conversely, the two wettest winters were 1937/38 (+ 56%) and 1977/78 (+ 55%) (7).

Scotland. Scotland is on average 20% wetter then it was in 1961 (3). A trend analysis of Scottish climate between 1961 and 2005 shows a general reduction in the number of days of snow cover in each season, and a shorter snow season (27).

Snow cover changes until now

Data for 1960-2010 show a long-term decline in average yearly snow cover with greatest declines in some mountain areas, notably in northern England (44).

Wind climate changes until now

A study of gale activity over the UK for the period 1881–1997 showed no long–term trend, but the average frequency of severe gales did attain a maximum in the 1990s (corresponding to the pronounced westerly phase of the North Atlantic Oscillation during that decade) (7). The more frequent windstorms in the past few decades, however, did not exceed the frequency in the 1920s (3).

A northward shift in mean storm track position since about 1950 is consistent in studies on wind climate in northwestern Europe over the last decades (35). This northeast shift together with the trend pattern of decreasing cyclone activity for southern mid- latitudes and increasing trends north of 55 - 60°N after around 1950 seems consistent with scenario simulations to 2100 under increasing greenhouse gas concentrations (36).

Sea water temperature changes until now

Sea surface temperatures around the UK coast have risen over the past three decades by about 0.7ºC (1).

Air temperature changes in the 21st century

Average annual temperature UK

By 2040, average annual temperature for the UK is expected to rise by between 0.5 and 1°C, depending on region. By 2100, average annual temperature for the UK could rise by between 1 and 5°C, depending on region and emissions scenario (3,12).

In all seasons, and for all scenarios, there is a northwest to southeast gradient in the magnitude of the warming over the UK, the southeast consistently warming by at least several tenths of a degree Celsius more than the northwest (3,12). This is probably the reason why for parts of the UK higher future temperatures have been reported. For England, for instance, annual warming of between 0.5 and 1.5°C has been reported by the 2020s, and between 0.5 and 3.0°C by the 2050s (4).

Summer temperature in the UK

At present, the highest temperature recorded in the UK is 38.7°C. By the end of the century, according to climate models projections, the unprecedented high temperature of 40°C would be reached somewhere in the UK about once every 15 years to once every 3 to 4 years under a medium and high-end scenario of climate change, respectively (49).

By 2040, average summer temperature for the UK is expected to rise by between 0.5 and 2°C, depending on region. By 2100, average summer temperature for the UK is expected to rise by between 1 and 6°C, depending on region and emissions scenario (3).

According to the UKCP09 scenarios, changes in summer mean temperatures are greatest in parts of southern England (up to 4.2°C (2.2–6.8°C)) in the 2080s compared with 1961–1990. Increases in the summer mean daily maximum temperatures are up to 5.4°C (2.2–9.5°C) in parts of southern England (24).

All areas of the UK warm by the 2080s relative to a 1961–1990 baseline, more so in summer than in winter. These changes have been estimated under the Medium emissions scenario and are shown as the central estimate of change that presents the 50% probability level. Also, in brackets, the limits are shown that very likely will be exceeded, and very likely will not be exceeded (10 and 90% probability levels, respectively) (1):

• Changes in summer mean temperatures are greatest in parts of southern England (up to 4.2ºC (limits: 2.2/6.8ºC)) and least in the Scottish islands (just over 2.5ºC (limits: 1.2/4.1ºC)). Changes in the warmest day of summer range from +2.4ºC (limits: –2.4/+6.8ºC) to +4.8ºC (+0.2/+12.3ºC), depending on location, but with no simple geographical pattern.
• Mean daily maximum temperatures increase everywhere. Increases in the summer average are up to 5.4ºC (limits: 2.2/9.5ºC) in parts of southern England and 2.8ºC (limits: 1/5ºC) in parts of northern Britain. Increases in winter average are 1.5ºC (0.7/2.7ºC) to 2.5ºC (1.3/4.4ºC) across the country.  Mean daily minimum temperatures increase on average in winter by about 2.1ºC (0.6/3.7ºC) to 3.5ºC (1.5/5.9ºC) depending on location. In summer it increases by 2.7ºC (1.3/4.5ºC) to 4.1ºC (2.0/7.1ºC), with the biggest increases in southern Britain and the smallest in northern Scotland.

Heatwaves in the UK

The summer heat wave experienced in 2003 is likely to become a normal event by the 2040s and considered cool by the 2060s (11,46). A summer as hot as that of 2018, which is the joint warmest summer in the UK since 1884, could occur every other year by mid-century (48).

For the UK, the Met Office defines a heatwave over a location as when it records maximum temperatures greater than or equal to a temperature threshold for at least three consecutive days. This threshold varies from 25°C in Scotland, Northern Ireland and most of Wales to 28°C in Greater London (51). Based on this definition, England and Wales are expected to experience at least one heatwave every year by mid-century, under a high-end scenario of climate change (50). In Scotland and Northern Ireland, the chances of a heatwave occurring in a year are expected to increase to over 50% by mid-century (50).  

Winter temperature in the UK

By 2040, average winter temperature for the UK is expected to rise by between 0.5 and 1°C, depending on region. By 2100, average winter temperature for the UK could rise by between 1 and 4°C depending on region and emissions scenario (20). According to the UKCP09 scenarios, increases in winter mean daily maximum temperatures are 1.5°C (0.7–2.7°C) to 2.5°C (1.3–4.4°C) across the UK in the 2080s compared with 1961–1990 (24).

Future cold spells in Western Europe are projected to become about 5°C warmer (and remain above freezing point), thus having a significant climatic impact. This conclusion is based on research in which a cold spell (CS) is defined as a non-interrupted sequence of days in which the 5-day average temperature falls below a threshold value Tcold (20).

Regions

East Midlands. According to the Future Climate Scenarios for the East Midlands from UKCIP98, the climate warming ranges from +1.1°C for the Low scenario (a relatively slow increase in future greenhouse gas concentrations of approximately 0.5% per annum) to +3.2°C for the High scenario by the 2080s (a relatively rapid increase in future concentrations of approximately 1% per annum). Year-to-year variability in seasonal temperatures also changes in the future. Winter variability decreases, indicating that very cold winters become rarer. Conversely, summer variability increases, indicating that very hot summers occur more frequently (7).

Under the Medium-high scenario, individual sites across the East Midlands may show a reduction in frost frequencies of about 50% by the 2050s. Under this scenario, potential evaporation over Eastern England increases in all seasons except winter (which shows no change); by the 2050s summer evaporation increases by 15%, autumn evaporation by 29%, and annual evaporation by + 14% by the 2050s (7).

West Midlands. The average annual mean temperature in Birmingham is expected to increase by between 0.5⁰C and 1.5⁰C by the 2020s and between 1.0⁰C and 2.5⁰C by the 2050s with respect to the 1961–1990. Most of the warming is expected to take place in summer although winters are also expected to be significantly warmer (6).

The potential changes in soil moisture are quite dramatic. Soil moisture is a function of temperature, precipitation, humidity, sunshine and wind speed. Overall in summer the region would be drier and warmer and hence soil moisture could fall by between 5% in the north west of the region and 35% in the south east by the 2050s. In winter however, the increased precipitation could lead to higher soil moisture levels and the increased probability of flooding. Summer soil moisture may be reduced by 40% or more over large parts of England by the 2080s (6).

Daily maximum temperatures of 33ºC, which occur about 1 day per summer in the south-east, could occur 10 days per summer by the 2080s. In central Birmingham the urban heat island effect could add a further 3 to 4ºC to temperatures during summer nights (6).

East Anglia and North West England. Increases in mean annual temperature, relative to 1961-1990, range from 0.3 to 1.1°C by the 2020s and 0.5 to 2.6°C by the 2050s (12).

East of England. For the East of England by the 2080s annual temperature may increase between 2-2.5⁰C (for the low emissions scenario) and 3.5-4.5⁰C (for the high emissions scenario) with respect to 1961-1990. For these scenarios summer temperature may increase between 2-3⁰C and up to 5⁰C. The number of ‘extremely warm days’ (defined as the daily-average temperature for the baseline period 1961-1990 that is exceeded 10% of the days) increases especially in summer and autumn up to 14 (low emissions) or 30 days (high emissions). In addition the number of very cold days in winter decreases.

As a result, the thermal growing season (period with daily-average temperatures > 5.5⁰C) increases by between 45 and 55 days (low emissions) and up to 100 days (high emissions).

Wales. The rate of future climate warming in Wales ranges from 1.0 ºC per century for the low emissionsscenario to 2.9 ºC per century for the high emissionsscenario. A slightly more rapid warming is predicted for autumn and winter than for spring and summer. In winter, minimum temperatures rise more rapidly than maximum temperatures which reduces the diurnal temperature range. In summer the opposite occurs (2).

The year-to-year variability in seasonal temperatures also changes in the future. Winter variability decreases (very cold winters become rare) whereas summer temperature variability increases (very hot summers occur more frequently). For instance, for the UKCIP98 medium-high scenario, ‘hot’ summers that presently occur once-a-decade (e.g. 1975) occur 64 per cent of the time by the 2050s and 80 per cent of the time by the 2080s. The one-in-ten ‘cold’ winter (e.g. 1995/96) virtually disappears, whereas ‘mild’ winters (e.g. 1994/95) occur in 85 per cent of years by the 2080s (2).

By 2050s an extreme summer may be up to 3.7ºC warmer than the average for the baseline 1961-1990 (2). Likewise, by the 2050s, about half of all winters may be as mild as the one of 1988/89, the mildest recorded in Wales this century with mean temperature 2.4ºC above the 1961-1990 average (for the UKCIP98 medium-high emissionsscenario). In fact, an individual winter in the 2050s may be 4.2ºC milder than the 1961-1990 average (2).

Southwest of England. For the Southwest of England higher average seasonal temperatures are predicted by the 2050s of 1-2⁰C in winter and spring, 1.5-3.5⁰C in summer, and 1.5-3⁰C in autumn (UKCIP02 scenarios) (13). By the 2080s the predicted warming is 1.5-3.5⁰C in winter and spring, 2-5.5⁰C in summer, and 2-5⁰C in autumn (13).

Warming in the winter will be greater in the night than during the day; the opposite holds for the summer. Warming will be greater in summer and autumn than in winter and spring (13).

Northern Ireland. Projections of future change (measured relative to the 1960-1991 baseline) for Northern Ireland if high emissions continue are an increase in mean winter temperature very likely to be between 0.3-1.7ºC by 2020s, 1-2.9ºC by 2050s and 1.7-4.4ºC by 2080s, and an increase in mean summer temperature very likely to be between 0.3-2.1ºC by 2020s, 1.1-4ºC by 2050s and 4.2-6.2ºC (16).

Output from three GCMs and two IPCC emissions scenarios (A2 and B2) have been used to downscale daily maximum and minimum temperatures to nine climatological stations across Northern Ireland (21). Results illustrate a progressive warming for both maximum and minimum temperatures. The results, averaged across all GCMs, emissions scenarios, sites, and seasons, are:

Period Maximum temp. Range Minimum temp. Range 2011-2040 0.8 0.0-1.6 0.8 0.0-1.8 2041-2070 1.4 0.5-2.3 1.4 0.5-2.6 2070-2099 2.2 0.9-3.8 2.1 0.8-4.2

These results lie within the temperature range of previous studies (22). Autumn is the season projected to experience the most warming, for both maximum and minimum temperatures, with spring projected to increase the least. The number of frost days is projected to decline considerably for all sites, with an average of 219 less frost days over the 30-year period centred on the 2080s from the modelled baseline period 1961–1990 (21).

London. According projections for London, based on a medium emissions scenario, during summers in London in 2050 the average summer day will be 2.7°C warmer and very hot days 6.5°C warmer than the baseline average (1961-1990). By the end of the century the hottest day of the year could be 10°C hotter than the hottest day today. Winters will be warmer, with the average winter day being 2.2°C warmer and a very warm winter day 3.5°C above the baseline (17).

Precipitation changes in the 21st century

UK

Average annual precipitation probably will not change much (1,24).This is reported for both the UK as a whole (1) and several regions (6,7,12).

A future simulation of summer precipitation for the future period 2031 - 2036 with a detailed weather model and a high-end scenario of climate change (RCP8.5) suggests that, compared with the period 1990 - 1995, the summers will possibly be drier, with longer dry spells, shorter wet spells and heavier precipitation, especially in the southeast of the UK. Overall, the UK will be ∼10% dryer for this period. In general, when it rains, it rains harder (38,39). The maximum peak summer hourly precipitation rate, however, does not noticeably increase (38).

In winter, precipitation increases are in the range +10 to +30% over the majority of the country. Increases are smaller than this in some parts of the country, generally on higher ground (1). Heavier winter precipitation is expected to become more frequent (3). According to the UKCP09 scenarios, the biggest changes in precipitation amounts in winter, with increases up to +33% (+9% to +70%) in the 2080s compared with 1961–1990, are seen along the western side of the UK. Decreases of a few percent (–11% to +7%) are seen over parts of the Scottish highlands (24).

According to the UKCP09 scenarios, the biggest changes in precipitation amounts in summer, down to about –40% (–65% to –6%) in the 2080s compared with 1961–1990, are seen in parts of the far south of England (24). In summer, there is a general south to north gradient, from decreases of almost 40% in Southwest England to almost no change in Shetland. Also in the summer the intensity of extreme events will increase (see also 23). 

The most comprehensive study of UK climate projections has been the UKCP09 Report (19). For the 2080s, in winter, the central estimate is for increases in precipitation on the wettest day of the year of up to 30% in a few areas of southern England, with a reduction to near zero change in northern Scotland. For the 2080s, in summer, the central estimate shows reductions in wettest day precipitation over southern and eastern England, but increases of up to 10% in other areas of the UK (19).

According to regional climate model simulations, extreme hourly precipitation may be up to 112% higher in the UK by the end of the century under a high-end scenario of climate change (RCP 8.5) relative to the reference period 1980-2005 (47).

Hailstorms

Storms producing large damaging hailstones are rare in the UK, and almost always occur during the summer months (26). No trend in storms producing hailstones with diameters of 40mm or greater was identified between 1800 and 1999 over the UK, or in the number of damaging hailstorms (hailstones greater than 15mm diameter) between 1930 and 2000 (26). Due to climate change, a downward trend in the total number of damaging hailstorms during the 21st century was projected, from a single (regional) model simulation of future climate (the A1B medium emissions scenario) (25). This downward trend showed statistically significant trends for hailstones with diameters between 21 and 50 mm. These results are subject to large uncertainties, however.

Regions

Northern versus southern UK domain. For the northern part of the United Kingdom, a precipitation increase in winter and a large decrease in summer (30-50%) are projected for the end of this century under a high-end scenario of climate change (the RCP8.5 scenario). In both seasons, precipitation extremes will intensify (39).

A summer drying is projected for the whole northern UK domain, with many areas seeing a decrease of 25-50% in daily mean precipitation under a high-end scenario of climate change, including the relatively densely populated Scottish Central Lowlands. In contrast, a precipitation increase of 10-35% or more is projected for most regions in winter (39). A similar increase for the winter was projected for the southern UK domain, with the largest increase over Wales (40). Projections show that precipitation extremes still intensify while the future mean precipitation decreases. The most detailed model used in this study shows that a 20% mean increase in summer intensity is outweighed by 50-60% decrease in overall precipitation frequency (39). Again this agrees with previous results for the southern UK domain, although the projected intensification of summer precipitation is larger for the northern than for the southern UK (41). Also in the winter, precipitation intensities are projected to increase.

Southwest of England. For the Southwest of England drier seasons are predicted by the 2050s by 15-30% in summer and 0-10% in autumn (UKCIP02 scenarios), and wetter winters by 5-15%, whereas precipitation totals in spring will stay more or less the same (13). By the 2080s drier seasons are predicted by 25-55% in summer and 5-15% in autumn (UKCIP02 scenarios), and wetter winters by 10-30%, whereas again precipitation totals in spring will stay more or less the same (13). By the 2080s snowfall in winter is predicted to decrease by 70-90% (13).

West Midlands. The mean annual precipitation is expected to change by less than 10% by the 2050s. However, this hides a dramatic change in seasonal precipitation. Winter precipitation might increase by between 0% and 10% by the 2020s and up to 20% by the 2050s. On the other hand, summer precipitation might decrease by between 0% and 20% by the 2020s and up to 30% by the 2050s (6).

East England. In the East of England, by the 2080s, precipitation is projected to increase in the winter by 10-20% (low emissions scenario) or 25-35% (high emissions scenario). In the summer the projected rainfall decrease is 20-30% (low emissions scenario) or 40-60% (high emissions scenario). On an annual basis an overall precipitation reduction of 0-10% is projected (14).

In their 5th Assessment Report the IPCC presented a precipitation decrease at the end of the 21st century for April through September up to 10% for England, Belgium, the Netherlands and northern Germany, under the intermediate RCP4.5 scenario of climate change. These projected changes, however, do not exceed natural climate variability across the region. For October through March a precipitation increase up to 10% was projected for this North Sea region; these projected changes do exceed natural climate variability across the region (33).

Wales. Annual precipitation over Wales increases in all four UKCIP98 scenarios, by between 3 and 5% by the 2050s. Winter precipitation increases over Wales by between 7 and 15% by the 2050s. Summer precipitation decreases by up to about 10% by the same period. Spring precipitation changes little. All of these changes are for 30-year averages calculated with respect to the 1961-1990 average (2).

‘Dry’ summers that presently occur just once-a-decade (e.g. 1996) almost double in frequency by the 2080s, whereas ‘wet’ winters (e.g. 1993/94) become at least three times more frequent than at present (2).

The UKCIP98 scenarios also suggest that daily precipitation intensities will increase in the future, most notably in winter. Thus as well as experiencing wetter winters, Wales may expect to see more of this increased winter precipitation falling in more intense storm events than at present. There is little change in summer precipitation intensities in the UKCIP98 scenarios (2).

Northern Ireland. Projections of future change (measured relative to the 1960-1991 baseline) for Northern Ireland if high emissions continue are a change in winter mean precipitation very likely to be between -3 to +10% by 2020s, 2 to 19% by 2050s and +6 to +34% by 2080s, and a change in summer mean precipitation very likely to be between -15 to +10% by 2020s, -28 to +4% by 2050s and -39 to +4% by 2080s (16).

London. According projections for London, based on a medium emissions scenario, the average summer in London in 2050 will be19% drier and the driest summer 39% drier than the baseline average (1961-1990). Winters will be wetter, with the average winter 14% wetter and the wettest winter 33% wetter than the baseline average (17).

Snow cover changes in the 21st century

Further declines in snow cover are projected in the future: average yearly snow cover will probably predominantly be confined to Great Britain mountain areas by the 2050s (44).

Wind climate changes in the 21st century

UK

Projected changes in storms are very different in different climate models. Future changes in anticyclonic weather are equally unclear. Probabilistic projections of changes in wind speed cannot yet be provided. The Met Office Hadley Centre regional climate model projects decreases in winter mean wind speed of a few percent over the UK (1).

These differences between individual models, and also between different types of model ensemble, indicate that robust projections of changes in storm track are not yet possible. Unfortunately, just as with storm tracks, model projections do not give a clear picture of changes to anticyclones. There is no compelling evidence that the frequency, duration or intensity of those affecting the UK will change markedly either way, although neither can it be ruled out (1).

A review of recent scientific literature shows that the projected changes in wind extremes (speed and direction) for the North Sea region are typically within the range of natural variability and can even have opposite signs for different scenarios either simulated by different climate models or for different future periods (34). 

Uncertainties in climate projections

Factors such as inertia in the climate system mean that climate change over the first two or three decades from now is relatively insensitive to the choice of emissions scenarios. However, after the 2040s, projections based on different emissions scenarios increasingly diverge (1).

Uncertainties in model results

Although it is important that prospective users understand the limitations and caveats, it is also worth emphasising that (a) current models are capable of simulating many aspects of global and regional climate with considerable skill; and (b) they do capture, albeit imperfectly, all the major physical and biogeochemical processes known to be likely to exert a significant influence on global and regional climate over the next 100 year or so (1).

While resolution is progressively increasing as computer power increases, it is not yet possible to use GCMs to resolve the rainmaking processes (storms and fronts, and their interaction with the topography) in sufficient detail to predict extreme rainfall behaviour. Physical consistency can be maintained by predicting rainfall behaviour for different atmospheric greenhouse-gas concentrations using a limited-area (10).

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for the United Kingdom.

1. Jenkins et al. (2009)
2. Farrar and Vaze (2000)
3. Department of Energy and Climate Change of the United Kingdom (2009)
4. West and Gawith (2005)
5. Hulme et al. (2002), in: West and Gawith (2005)
6. Anderson et al. (2003)
7. Kersey et al. (2000)
8. Fowler and Kilsby (2003a)
9. Fowler and Kilsby (2003b)
10. Huntingford et al. (2003)
11. Defra (2008)
12. Holman et al. (2007)
13. C-CLIF and GEMRU (2003)
14. Land Use Consultants, CAG Consultants and SQW Limited (2003b)
15. JCHMR (2001), in: Huntingford et al. (2003)
16. UKCIP09 UL Climate Projections 09, in: Northern Ireland Environment Agency (2009?)
17. Greater London Authority (2010)
18. Met Office (2011)
19. Murphy et al. (2009), in: Met Office (2011)
20. De Vries et al. (2012)
21. Mullan et al. (2012)
22. Arkell et al. (2007); Fealy and Sweeney (2008), both in: Mullan et al. (2012)
23. Kendon et al. (2014)
24. Jenkins et al. (2009), in: Charlton and Arnell (2014)
25. Sanderson et al. (2015)
26. Webb et al. (2009, in: Sanderson et al. (2015)
27. Barnett et al. (2006), in: Kay and Crooks (2014)
28. Otto et al. (2015)
29. Report Environment Agency UK (2010), in: Otto et al. (2015)
30. De Leeuw et al. (2016)
31. Jones and Conway (1997); Osborn et al. (2000), both in: De Leeuw et al. (2016)
32. Osborn and Hulme (2002), in: De Leeuw et al. (2016)
33. IPCC (2013), in: May et al. (2016)
34. May et al. (2016)
35. Feser et al. (2015a), in: Stendel et al. (2016)
36. Ulbrich et al. (2009); Feser et al. (2015a), both in: Stendel et al. (2016) 
37. Blenkinsop et al. (2017)
38. Gadian et al. (2018)
39. Chan et al. (2018)
40. Kendon et al. (2012, 2014), both in: Chan et al. (2018)
41. Chan et al. (2014a, 2016); Kendon et al. (2014), all in: Chan et al. (2018) 
42. Chapman et al. (2019)
43. McCarthy et al. (2019)
44. Brown, I. (2019)
45. Kay et al. (2020)
46. Murphy et al. (2019) in: Brimicombe et al. (2021)
47. Rau et al. (2020)
48. Lowe et al. (2019), in: Lo and Mitchell (2021)
49. Christidis et al. (2020), in: Lo and Mitchell (2021)
50. Arnell et al. (2021), in: Lo and Mitchell (2021)
51. Lo and Mitchell (2021)