River floods United Kingdom
UK: Different types of flood
The most common types of floods are (21,50):
- River (fluvial) flooding that occurs when a watercourse cannot cope with the water draining into it from the surrounding land. This can happen, for example, when heavy rain falls on an already waterlogged catchment.
- Coastal flooding that results from a combination of high tides and stormy conditions. If low atmospheric pressure coincides with a high tide, a tidal surge may happen which can cause serious flooding.
- Surface water (pluvial) flooding which occurs when heavy rainfall overwhelms the drainage capacity of the local area. It is difficult to predict and pinpoint, much more so than river or coastal flooding.
- Sewer flooding that occurs when sewers are overwhelmed by heavy rainfall or when they become blocked. The likelihood of flooding depends on the capacity of the local sewerage system. Land and property can be flooded with water contaminated with raw sewage as a result. Rivers can also become polluted by sewer overflows.
- Groundwater flooding that occurs when water levels in the ground rise above surface levels. It is most likely to occur in areas underlain by permeable rocks, called aquifers. These can be extensive, regional aquifers, such as chalk or sandstone, or may be more local sand or river gravels in valley bottoms underlain by less permeable rocks.
UK: History UK flood risk management policy
Tunstall et al. (22) describe the history of flood risk management policy in the UK.
In the decades following the second world war, through to the late 1970s, the focus of river and coastal management was on rural land drainage and flood defence. The aim of which was to increase agricultural productivity and self-sufficiency in food production and to protect farm profitability, as much as it was on flood defence to protect urban assets.
In keeping with the societal values and engineering orthodoxy of the time, structural solutions and ‘hard engineering’ schemes dominated with little regard for the environmental impact. Rivers were dredged, straightened and channelised, and coastal and riverine wetlands were drained in land drainage and ‘river improvement’ schemes designed to take water away as fast as possible. Much development has taken place in riverine and coastal flood plains even in areas where flooding has occurred since 1945, building up the damage potential and threat to life posed by floods.
The 1980s into the 1990s was a period of transition in which there was a gradual shift away from agricultural land drainage towards urban flood defence. Throughout the period, structural flood defences continued to be the main focus of activity and expenditure and little attention was paid to the development of flood warning systems and to land use planning and development control issues.
From the mid-1990s onwards, there has been a gradual transition towards a more strategic, multi-method, and integrated approach to land and water management: a flood risk management approach. This moves away from the traditional focus on defending against floods to a focus on managing the flood risks in terms of both probabilities and consequences. The integrated approach combinedflood abatement (the prevention of flood waves, e.g. through reforestation), flood control (the prevention of floods, e.g. through embankments), and flood alleviation (the reduction of flood impacts, e.g. through land use regulation). Changes in knowledge and understanding, for example, of climate change, and the development of ‘soft’ and bio-engineering techniques encouraged approaches to flood defence that sought to work ‘with’ nature rather than ‘against’ it, including beach nourishment, river and flood plain restoration and managed realignment on rivers and coasts. This shift towards a strategic and holistic approach to catchment management based on an ecosystems perspective is now central to policy.
According to Tunstall et al. (22) the flood events of 1947, 1953, 1998 and 2000 acted as catalysts for policy change.
- The 1998 Easter flood had a specific policy outcome in terms of the flood warning system and public awareness raising through the Bye Report, its acceptance by central government and the Environment Agency and its implementation by the Agency through its Action Plan.
- The autumn 2000 floods, which affected over 700 locations in all regions in England and Wales and a total of 10,000 properties, was the cumulative result of rainfall unprecedented during the previous 270 years. It served to reinforce the view that it was essential to plan for extreme events which might occur as a result of climate change.
Local flood management strategy for the future is presented in so-called Catchment Flood Management Plans (CFMPs). According to the Environment Agency (21) they will produce CFMPs for 68 main catchments in England during 2009. They are high-level planning tools and set out objectives for flood risk management across each river catchment and estuary. They also identify flood risk management policies that are economically practical, have a potential life of 50 to 100 years, and will help us work with others to put them in place.
The CFMPs consider inland flood risk from rivers, surface water, groundwater and tidal flooding but do not cover sewer flooding. However, at present our understanding of river and tidal flooding is stronger than that from other sources. Shoreline Management Plans (SMP) are mainly produced by coastal groups/local authorities and perform a similar role to CFMPs but examine coastal flooding and erosion risks. SMPs cover the entire coastline. These are under review, with second generation SMPs due for completion by 2010.
UK: 2007 floods
The rainfall during June and July 2007 was unprecedented. The severe flooding which followed came after the wettest ever May to July period since national records began in 1766. Met Office records show that the total cumulative rainfall in May, June and July 2007 averaged 395.1mm across England and Wales – well over double usual levels. The exceptionally heavy rain resulted in two severe and disruptive flooding events; the first during the week of 20 June and the second during the week of 18 July.
It has been stated that the level of flooding that occurred during the summer 2007 had a probability of 1/150 per year, but it is in fact virtually impossible to assign a meaningful probability on the whole sequence of events (23).
The events of the summer were characterised by fluvial and pluvial flooding. Rivers flooded surrounding areas and, following the exceptionally high rainfall, there was direct flooding of areas with insufficient drainage capacity:natural and man-made drainage systems have insufficient capacity to deal with the volume of rainfall (23). These types of storms, which triggered the extreme convective rainfall in 2007, are expected to form part of climate change in the future.
55,000 properties were flooded. Around 7,000 people were rescued from the flood waters by the emergency services and 13 people died (23). We also saw the largest loss of essential services since World War II, with almost half a million people without mains water or electricity. Transport networks failed, a dam breach was narrowly averted and emergency facilities were put out of action. The insurance industry expects to pay out over £3 billion – other substantial costs will be met by central government, local public bodies, businesses and private individuals.
Perhaps the most significant feature of last summer’s events was the high proportion of surface water flooding compared with flooding from rivers. Currently, no organisation is responsible for overseeing and planning for surface water flooding, creating problems which were particularly evident in places like Hull and parts of Sheffield. There are no warnings for this type of flooding, which can occur very rapidly, and people, including the response organisations, were not well prepared (23).
UK: 2013/2014 floods
The winter of 2013/2014, and January in particular, saw above-average precipitation over England and Wales. A near-continuous succession of low-pressure systems moved in from the Atlantic and across southern England. This persistent atmospheric circulation pattern resulted in extreme precipitation, flooding and storm surges in large parts of southern England and Wales. Daily total precipitation, recorded since 1767 in Oxford, shows January 2014, as well as winter 2013/2014, precipitation set a record. Sustained high precipitation amounts during the whole winter led to this record, rather than a few very wet days (60) Total winter rainfall in the Thames catchment in this winter was the highest on record. Similarly, sustained high flows were observed across other major rivers in southeast England and parts of Scotland, reflecting high rainfall amounts (50).
The event was not unprecedented, but damage was significant. The flooding led to £451 million insured losses in southern England. Whether anthropogenic climate change contributed to this event was much discussed at the time: British Prime Minister David Cameron told Parliament ‘I very much suspect that it is’ (60).
Cameron’s suspicion has been assessed: a range of model simulations has been conducted and observations have been analyzed to estimate anthropogenic influence on the risk of experiencing such atmospheric flow and precipitation. Both thermodynamic and dynamic effects are important. Thermodynamic effects refer to the fact that a warmer atmosphere holds more water vapour, causing an increase in risk of heavy winter rainfall. The dynamic effects refer to anthropogenic forcings altering the probability of occurrence of the atmospheric circulation that favoured the winter 2013/2014 conditions (60).
The assessment showed that human influence indeed increased the risk of low-pressure northwest of Britain and the number of days with low-pressure systems moving in from the Atlantic. Human influence increased the risk of heavy precipitation in southern England. This increased the chance of extreme flows for the River Thames over several weeks. The assessment further indicated that although thermodynamic effects cause most of the increase in precipitation, around one-third is caused by changes in circulation. The results are highly uncertain, however. David Cameron was right to ‘suspect’ a human influence on the 2013/2014 winter flooding. The uncertainties do not allow for firmer statements than ‘a suspicion’, however (60).
In another study, potential climate change influences on these floods have also been assessed (50). Although there is some observational evidence of intensification of UK rainfall, there is little suggestion of emerging trends in precipitation-driven (that is, non-tidal) high-magnitude UK floods; less UK ice and snowmelt in a warming world may suppress flood risk. A lack of trends cannot, however, be taken to mean there is no underlying emerging climate change signal, given the low signal-to-noise ratio in flood records (50).
UK: 2019/2020 floods
Exceptional flooding occurred during the summer in parts of north Wales and central and northern England, and this created conditions for flooding in the winter of 2019/2020. The late winter saw a series of intense storms that triggered a remarkably widespread and protracted flood episode across many major river systems of central Britain, causing severe impacts across southern Scotland, northern England and Wales (61).
The flood events that occurred between June 2019 and February 2020 started when some parts of England recorded more than 250% of their average June rainfall, which led to daily flow records for June on some rivers. In the remainder of the summer and autumn, many parts of central and northern England received more than twice the average rainfall for this period. The wet conditions in early autumn saturated the soils and increased the susceptibility to flooding at the start of November. There was extensive fluvial flooding in central and northern England with 1100 properties inundated. The severe wet weather returned with renewed intensity and three storms during February (61).
The – predominantly fluvial – flooding of November 2019 and February 2020 was not uncommon during the winter half-year (October–March) in the UK. Northern and central England were impacted on both occasions. In terms of flow magnitude, the events of 2019/2020 were amongst the top 10 highest peak flows ever recorded across a broad swathe of Wales and northern and central England. In some catchments, peak river flows in November 2019 and February 2020 comprised two of the five highest flows on record. To have two such flows from independent events within a few months of one another is remarkable. The duration of the flooding in February 2020 was perhaps its most remarkable characteristic of all. High flows triggered by three storm events were maintained by further rainfall in between (61).
The total number of properties flooded during the June 2019 to February 2020 period was around 6000. This number is comparable with some of the other major flood events of the last decade, including 7000 in winter 2013/2014 (62) and 8000 in 2012 (63), although falling short of the more than 16,000 in winter 2015/2016 (64). Besides, between 1 February and 1 March, 38 landslides were reported in Great Britain, triggered by rainfall (65).
Major flood events in 2007, 2009, 2012, 2013/2014, 2015/2016 and 2019/2020 have led to the suggestion that flooding is becoming worse. The recurrence of long duration and/or large spatial footprint flood events in recent times (often impacting the same locations) is perhaps an early indication of the influence of climate change on flooding in the UK. However, with a few exceptions, present and future changes in frequency, duration and spatial extent have not been thoroughly assessed (61).
UK: River flood probability
Scenarios produced by the Met Office Hadley Centre, Tyndall Centre and UK Climate Impacts Programme in 2002 (UKCIP02) suggest that for the UK climate change means, on average, hotter drier summers and milder, wetter winters combined with more extreme weather events such as heat waves and periods of heavy rainfall. These changing climatic conditions mean that we can expect to experience more frequent periods of heavy rainfall, especially in winter, leading to increased flooding (24). For the Severn catchment, for instance, initial research has suggested that increases in peak flow of around 20% for a given return period could be experienced within 50 years (25). An increase of flood risk has also been projected by more recent studies (43).
Anthropogenic greenhouse-gas emissions are thought to have substantially increased the risk of autumn floods in England and Wales, such as those observed in 2000, by >20% (with 90% confidence) and possibly by as much as 90% (with 66% confidence) (47).
UK: Potential damage in river floodplains
A national-scale flood risk assessment has been carried out for England and Wales, for both coastal and river flood risk (26). The expected annual damage from flooding for the year 2002 was estimated to be approximately £1 billion. This figure is comparable with records of recent flood damage. The methodology has subsequently been applied to examine the effects of climate and socio-economic change 50 and 80 years in the future.
The analysis predicts increasing flood risk unless current flood management policies, practices and investment levels are changed – up to 20-fold increase in real terms economic risk by the 2080s in the scenario with highest economic growth. The increase is attributable primarily to a combination of climate change (in particular sea level rise and increasing precipitation in parts of the UK) and increasing economic vulnerability (26).
Land use change is a significant contributory factor in exacerbating flood events. Arable crops such as maize or oil seed rape planted on soils liable to erosion (such as silty soils) leave the soils exposed as they provide minimal cover during their early stages of growth. Soil erosion and floods could be an increasing problem with the increasing amount of maize cultivated under a warmer regime together with a change in rainfall patterns (27).
UK: Vulnerabilities - Present river flood risk UK
The National Flood Risk Assessment uses three flood risk categories (21):
- Low risk: flood probability is less than 0.5% per year (1/200 per year)
- Moderate risk: flood probability is 0.5% - 1.3% per year (1/200 – 1/75 per year)
- Significant risk: flood probability is more than 1.3% per year (1/75 per year)
Flood risk category varies with the economic value of the flood-prone area. Indicative standards of protection for fluvial flood defences are (28):
- High density urban area: flood probability = 1/100 per year
- Low density urban or rural communities with high productivity agricultural land: flood probability = 1/25 per year
- Arable farming with isolated properties and medium productivity agricultural land: flood probability = 1/10 per year
- Extensive pasture with few properties at risk and low productivity agricultural land: flood probability = once a year
Flood risk is dependent on a number of factors e.g. land use (transport, housing, agriculture etc.), soil type, availability of drainage and level of flood protection. Urban areas may experience flooding from drainage systems that are inundated during extreme events (30).
For the UK as a whole, nearly 2 million properties in floodplains along rivers estuaries and coasts are presently estimated to be at risk of flooding. In England and Wales alone, over 4 million people and over £200 billion worth of properties are currently at risk of riverine and coastal flooding (29).
Vulnerabilities - Regional differences
West and Gawith (31) present an overview of expected climate change impacts on several activities for different regions of the United Kingdom, based on several regional scoping studies. The impacts on river flood risk are mainly negative and are listed below.
A blank cell indicates that no specific issues were identified for the region besidesthose noted in the first row.Each region identified and discussed issues differently, so this table might not provide comprehensive coverage of all issues.
|Region||Expected negative impact on river flood risk|
|Majority of regions||Increased of riverine flooding. Increased erosion risk|
|South West||Increased sediment yield and mobilisation and land slipping|
|London||Vulnerable to inundation of floodplains by river water. Local flooding from tidal surges in the Thames|
|East of England|
|East Midlands||Increased pumping costs for land drainage|
|West Midlands||Increased flood risk on major rivers such as River Severn. Increased winter recharge to reservoirs and groundwater could raise groundwater under Birmingham during winter|
|North West||Risks from contaminated land and toxic wastes might increase as old mine workings and industrial areas flood|
|Yorkshire & Humber||Flooding problems in Bradford and other cities to increase. More land on 'high' flood risk planning areas|
|North East||Flood prevention measures could prevent development of wet woodland|
|Scotland||Flooding and storms disrupt services|
UK: Vulnerabilities - Future river flood risk UK
Changes in snowmelt affect the size and timing of flood peaks in Britain. Most of Britain does not experience sustained periods of lying snow, and flow regimes in Britain are generally dominated by rainfall rather than snowmelt (58). However, snow is a major component of flow for some catchments, particularly in Scotland (59), and individual snow events can affect flows anywhere in the country.
The possible impacts of climate change on snow and peak river flows across Britain have been assessed for the period 2069 - 2099 compared with 1960 - 1990 (57). This was done for a scenario of moderate climate change (the so-called A1B scenario). The results confirm that under a warmer climate there would be a reduction in the number of days of lying snow across the country. For the more northerly regions this leads to a tendency for peak river flows to occur earlier in the water year, either because of less snow or earlier snowmelt, but for more southerly regions the changes are less straightforward and likely to be driven by changes in rainfall rather than snow. Overall, the results highlight considerable spatial variability in fluvial response to projected climate change (57).
The Foresight Future Flooding Study (9) provided visions of flood risk in the UK over a 30 to 100 year timescale to help inform long-term policy. The update by the Pitt Review Team considered evidence and research that had become available since 2004, including evidence gathered in relation to the summer 2007 floods (23).
There are two main changes to the risks faced from climate change since the Foresight assessment in 2004, which are: (21) the potential increases in rainfall volume and intensity, and temperature, are greater than previously assumed. For instance, under the worst case scenario, total winter precipitation increases by 40% as compared with the 25% estimated in 2004. This means we may have to cater for bigger increases in river flows than previously envisaged; and (22) there is a greater risk of extreme sea level rise (23).
UK: Vulnerabilities - Present river flood risk England and Wales
River-flow records show relatively little evidence for long-term increase in UK flood severity (51), although identification of trends can be confounded by dam construction, river engineering, major land-use change and abstractions. To minimize these confounding effects, networks of relatively undisturbed UK catchments with good-quality hydrometric records have been identified. These show some trends (52,55), notably increases in high-flow frequency and magnitude, particularly in the winter half-year, and for upland areas of the north and west. This is consistent with other studies finding increases in heavy rainfall for those seasons and regions (53). A general upward trend in flood magnitude was detected in Wales (56).
Currently about 1.85 million homes, 185,000 commercial properties and approximately 5 million people are estimated to be at risk from flooding in England and Wales (32). 5% of England’s population lives in the 2,200 km² of land most at risk from flooding by the sea, while 10,000 km² is threatened by flooding from rivers. In all, about 10 to 15% of urban areas and about half the best agricultural land is at risk.
With the exception of flooding in Lynmouth, Devon, in 1952 and the east coasts floods of 1953, floods have directly claimed few lives in the UK since the turn of the century. There is, however, growing evidence that UK floods have long-term effects on the psychological health of their victims and, as elsewhere, cause much distress and disruption to lives and livelihoods (32).
Floods can cause serious indirect impacts, including damage to important energy, water, communication and transport infrastructure (21). They can also interfere with basic public services such as schools and hospitals. For example, the 2007 floods disabled major infrastructure in Gloucestershire. Flooding at Tewkesbury’s Mythe water treatment works left 140,000 homes without clean water for up to 17 days. It was also necessary to shut down Castle Meads electricity sub-station, leaving 42,000 people without power in Gloucester for 24 hours. Flooding on the M5 motorway trapped 10,000 people, with many others stranded on the rail network.
Water-related infrastructure like treatment works need to be close to rivers as their running depends on them. As a result, a high percentage of water company plant is in flood risk areas. For example, more than 900 pumping stations and treatment works, over half of those in England, are in flood risk areas. Other types of important national infrastructure are also at risk. About 7,000 electricity infrastructure sites, some 14% of all in England, are at flood risk. In addition, about 10% of main roads and 21% of railways are at risk (21).
Flood management studies suggest a greater risk of flooding in the Lancashire Humber corridor and particularly on the coasts in South East England and on major estuaries. However, the projected cost of such impacts varies widely (from £1 billion to £27 billion) depending on the socio-economic scenarios considered (31).
UK: Vulnerabilities - Future river flood risk England and Wales
Hall et al. (33) report the results of a flood risk assessment for England and Wales over the period 2030–2100. The assessment involved the use of socio-economic and climate change scenarios. The analysis predicts increasing flood risk up to 20-fold increase in economic risk by the 2080s in the scenario with highest economic growth, unless current flood management policies, practices and investment levels are changed. The increase is attributable to a combination of climate change (in particular increasing precipitation and relative sea level rise in parts of the UK) and increasing socio-economic vulnerability, particularly in terms of household/industrial contents and infrastructure vulnerability.
Hall et al. (33) used the UKCIP02 climate scenarios for the UK (34) and the Foresight Futures socio-economic scenarios for possible long-term futures, exploring alternative directions in which social, economic, and technological changes may evolve over coming decades. There is no direct correspondence between the UKCIP02 scenarios and the Foresight Futures, not least because the Foresight Futures are specifically aimed at the UK whereas the emissions scenarios used in UKCIP02 are global emissions scenarios (taken from the IPCC).
Greater climate change by the 2080s, together with the increased floodplain occupancy means that two of the Foresight scenarios (World Markets and National Enterprise) will see more than twice the number of people at risk from flooding more frequently than 1:75 years. In the other two Foresight scenarios (Local Stewardship and Global Sustainability), flooding is predicted to remove a lesser proportion of national wealth since these scenarios tend to be less vulnerable to flood damage and are expected to be subject to somewhat less climate change. The results of the flood risk assessment for England and Wales (excluding sewer flooding) are shown in the table below:
|2002||World markets 2080s||National enterprise 2080s||Global sustainability 2080s||Local stewardship 2080s|
|Number of people within the indicative floodplain (millions)||4.5||6.9||6.3||4.6||4.5|
|Number of people exposed to flooding (depth >0) with a frequency >1:75 years (millions)||1.6||3.5||3.6||2.4||2.3|
|Expected annual economic damage (residential and commercial properties) (£ billions)||1.0||20.5||15.0||4.9||1.5|
|Annual economic damage relative to GDP (%)||0.10||0.14||0.31||0.06||0.05|
|Expected annual economic damage (agricultural production) (£ millions)||5.9||34.4||41.3||43.9||63.5|
The effect of increasing urbanisation on flood risk will be relatively low, since even in the 2080s, the majority of flood risk will be located in urban areas that exist now. However, in those rural areas that are urbanised the increase in risk is dramatic and practically irreversible (33).
Flood impacts on infrastructure are recognised as an important driver in societies that will be increasingly dependent on these infrastructures, which, due to increasing use of technology, may become increasingly vulnerable to flood damage. Infrastructure failure during major floods may have considerable knock-on effects, disrupting warning, evacuation, and recovery (33).
The agricultural impacts of flooding are very small in economic terms and are projected to decrease under scenarios where support for agricultural production is expected to decrease. Measures to protect agricultural land from flooding will be a reducing economic priority. However, some farming communities will be very vulnerable (33).
High risk areas
London and the Thames Estuary (due to rapid urbanisation), the South East coast (due to rising relative sea levels), and urban areas of Northern England (due to high predicted increases in intense rainfall) stand out as areas where the growth in economic risk will be greatest (33).
UK: Vulnerabilities - Present river flood risk in London
The last major inundation of central London took place in 1928 (50). For the Thames, there is no compelling statistical evidence of an increase in flood magnitude for the period 1883 to 2010. In relation to flood risk generally, sustained river management, for example increasing channel capacities and constructing more hydraulically efficient weirs, has certainly been beneficial; there has been a significant decline in annual maximum levels in the Thames since the 1880s (54).
Regionally, London has the highest number of people at risk from flooding. In the Greater London area there are 542,000 properties – around one million people – located in the floodplain. However, although London does have the largest number of people at risk, 458,000 of those properties at risk in London – 84% – are in areas with a low chance of flooding. This is mainly due to the major flood defences and flood defence structures in the Thames Estuary, including the Thames Barrier, reducing the risk of tidal flooding (21).
The 84,000 properties – 16% - in London where the risks are significant or moderate are located on the tributaries of the River Thames in north and south London. On these rivers, such as the Lee, Brent and Ravensbourne, the risk is from fluvial, or river flooding, after heavy rainfall. The number of properties in areas with a significant chance of flooding are highest in the south east, which has 25,000 more properties – around 64,000 people – in this highest risk category compared with the south west. The south east also has the largest number of properties in areas with a moderate or significant chance of flooding, with 259,000 properties, or around 460,000 people (21).
Vulnerability of the London population is high as there are a large number of flood-vulnerable communities and assets at risk (15% of London lies on the floodplains of London’s rivers). Warning times for fluvial and surface water flooding are short and public awareness and capacity to act are low (42).
UK: Vulnerabilities - Future river flood risk in London
Simulated flood frequency at the downstream end of the fluvial Thames (near Kingston in the vicinity of Teddington Weir) for 1960–1990 and 2069–2099 (UKCP09 Climate Projections, A1B emissions scenario) has shown a 36% increase of flood peaks for a 20-year return period (with a range of -11% to +68%) (49). Across the Thames Basin, the simulations upstream show few changes outside the range of current natural variability for some rivers (or parts of rivers), and more changes outside of this range for other rivers (49).
UK: Vulnerabilities - Present river flood risk in East Anglia
Holman et al. (28) reported about river flood risk in East Anglia and North West England. For these areas they showed thatclimate change could have profound implications for coastal areas and river valleys. While the Low climate change scenario causes relatively minor impacts to the 2050s, the High climate change scenario raises the risk of flooding significantly. Without any adaptation, increased flooding would have important implications for land use and the magnitude of flood damage.
In the Fens, as in many other coastal lowlands, the interaction of sea-level rise, increased river floods and subsidence could lead to severe flood impacts and in the worst-case, the large-scale abandonment of this prime agricultural area. In this area there will probably be severe and routine flooding over a wide area, sometimes including urban areas and infrastructure such as roads, without further adaptation through investments in flood defences (28).
However, as the models do not include snow melt, the future flood risk in catchments that currently experience flooding primarily due to snow melt in the spring may be less in 2050s, due to the raised winter temperatures and consequently lower snow amounts (28).
It is estimated that there are around 283,000 residential properties and 14,000 commercial properties at risk from fluvial or coastal flooding in the Anglian region. Besides, there are 305,000 hectares of Grade 1 and 2 agricultural land at risk from fluvial flooding, and 54,000 ha at risk from coastal flooding (35).
UK: Vulnerabilities - Present and future river flood risk in Scotland
Some 77,000 homes in Scotland are currently at risk from inland flooding. 80,000 properties in towns and cities in Scotland are presently at risk from flooding from overwhelmed urban drains during heavy downpours. By the 2020speak river flows may increase by 10-20% in Scotland (under the low and high scenarios respectively) (36).
Without consideration of existing or future flood defences, damage to properties by coastal and river floods in Scotland may rise by 86%by the 2050s, and by 115% by the 2080s.The frequency of current 1 in 50 year floods may double (36).
UK: Responsibilities flood risk management England and Wales
The summary below of who is responsible for flood risk management in England and Wales is based on (21) and (37).
Flood risk management is the preferred term used by the Environment Agency for inland fluvial flood risk management, whilst flood and coastal defence refers to both defence from flooding from the sea and measures to protect the land against erosion and encroachment by the sea (‘coast protection’).
Defra has overall policy responsibility for flood risk management and flood and coastal defence in England and provides grant aid to the flood and coastal defence operating authorities (Environment Agency, local authorities and internal drainage boards) to support their investment in capital works. Defra does not build defences, nor direct the authorities on what specific projects to do. The works programme to manage risk is driven by the operating authorities.
The Environment Agency
The Environment Agency is the principal flood defence operating authority in England and Wales. Generally speaking, the EA is responsible under the Water Resources Act 1991 for managing flood risk arising from designated "main" rivers and the sea. It is responsible for forecasting and mapping flood risk, providing warnings, advising on development in the floodplain, building and keeping defences in good order and taking part in emergency planning and response.
The Environment Agency manages central government grants for capital projects carried out by local authorities and internal drainage boards. The Environment Agency is responsible for some 25,400 miles of flood defences and about 36,000 sluices, outfalls, floodgates and barriers in England. Using the average cost of building each of the different defences, and applying these to our database of flood defence structures, we estimate replacing all defences that we maintain would cost over £20 billion.
Local authorities have powers to undertake flood defence works under the Land Drainage Act 1991, on watercourses which have not been designated as main and which are not within internal drainage board areas; maritime district councils have powers to protect the land against coastal erosion under the Coast Protection Act 1949. Defra provides grant aid to local authorities for flood defence works and coast protection works.
Internal drainage boards
Internal drainage boards (IDB’s) are statutory bodies, empowered under the Land Drainage Act 1991, to undertake flood defence works for watercourses which have not been designated as "main", in specified districts with special drainage needs. The IDB’s in the East of England have a key role in managing the extensive low-lying areas of farmland in the area.
Defra grant aids IDB capital flood defence works. Special rates are available for works to implement water level management plans (WLMPs) in internationally important conservation areas and in areas of national importance. This is in recognition of the fact that IDBs are partly funded by private landowners while the works in question provide benefits nationally. The balance of IDBs' costs of work after grant has to be met by local agricultural drainage ratepayers whereas the capital expenditure of the Environment Agency and local authorities is largely met from the public purse.
Regional flood defence committees
Regional flood defence committees (RFDCs) have a duty to take an interest in all flood matters in their area. They are responsible for decisions about the annual programmes of improvement and maintenance work carried out by the Environment Agency.
Local resilience forums
Local resilience forums (LRFs) are the local planning forums for all emergencies, including flooding. They bring together the emergency services, Environment Agency, NHS and other bodies like water and energy companies. Together they plan for prevention, control and reducing the impact of floods on the public.
The Association of British Insurers (ABI) and its members is vital in providing cover and handling claims for damages caused by a flood. Under an agreement with the Government, they have committed to continue insurance coverage for most properties, even some at significant risk, in return for action by government to identify and manage risks.
National Flood Forum
National Flood Forum is a registered charity providing advice to those at risk and campaigning for better protection from flooding.
Europe: casualties in the past
The annual number of reported flood disasters in Europe increased considerably in 1973-2002 (1). A disaster was defined here as causing the death of at least ten people, or affecting seriously at least 100 people, or requiring immediate emergency assistance. The total number of reported victims was 2626 during the whole period, the most deadly floods occurred in Spain in 1973 (272 victims), in Italy in 1998 (147 victims) and in Russia in 1993 (125 victims) (2).
Throughout the 20th century as a whole flood-related deaths have been either stable or decreasing while economic burdens of flooding and related societal disruptions have become decidedly worse. 20th century flood disaster death tolls have been typically averaging fewer than 250 per year (3).
Europe: flood losses in the past
The reported damages also increased. Three countries had damages in excess of €10 billion (Italy, Spain, Germany), three in excess of 5 billion (United Kingdom, Poland, France) (2).
Expressed in 2006 US$ normalised values, total flood losses over the 1970–2006 period amounted to 140 billion, with an average annual flood loss of 3.8 billion (4). Results show no detectable sign of human-induced climate change in normalised flood losses in Europe. There is evidence that societal change and economic development are the principal factors responsible for the increasing losses from natural disasters to date (5).
Policy makers should not expect an unequivocal answer to questions concerning the linkage between flood-disaster losses and anthropogenic climate change, as this field will very likely remain an important area of research for years to come. Longer time-series of losses are necessary for more conclusive results (6).
Europe: flood frequency trends in the past
In 2012 the IPCC concluded that there is limited to medium evidence available to assess climate-driven observed changes in the magnitude and frequency of floods at a regional scale because the available instrumental records of floods at gauge stations are limited in space and time, and because of confounding effects of changes in land use and engineering. Furthermore, there is low agreement in this evidence, and thus overall low confidence at the global scale regarding even the sign of these changes. There is low confidence (due to limited evidence) that anthropogenic climate change has affected the magnitude or frequency of floods, though it has detectably influenced several components of the hydrological cycle such as precipitation and snowmelt (medium confidence to high confidence), which may impact flood trends (45).
Despite the considerable rise in the number of reported major flood events and economic losses caused by floods in Europe over recent decades, no significant general climate‑related trend in extreme high river flows that induce floods has yet been detected (7).
Hydrological data series do not indicate clear upward trends in the frequency and magnitude of floods in Europe. The direct anthropogenic causes include land use change, river channel modifications and increased activities in areas vulnerable to floods. Thousands of square kilometres of impermeable surfaces have been created, coastal urbanization has been extensive. The overall impact of these changes probably exceeds the impact of trends in meteorological variables in today's Europe (8).
In western and central Europe, annual and monthly mean river flow series appear to have been stationary over the 20th century (9). In mountainous regions of central Europe, however, the main identified trends are an increase in annual river flow due to increases in winter, spring and autumn river flow. In southern parts of Europe, a slightly decreasing trend in annual river flow has been observed (10).
In the Nordic countries, snowmelt floods have occurred earlier because of warmer winters (11). In Portugal, changed precipitation patterns have resulted in larger and more frequent floods during autumn but a decline in the number of floods in winter and spring (12). Comparisons of historic climate variability with flood records suggest, however, that many of the changes observed in recent decades could have resulted from natural climatic variation. Changes in the terrestrial system, such as urbanisation, deforestation, loss of natural floodplain storage, as well as river and flood management have also strongly affected flood occurrence (13).
Europe: projections for the future
In 2012 the IPCC concluded that considerable uncertainty remains in the projections of flood changes, especially regarding their magnitude and frequency. They concluded, therefore, that there is low confidence (due to limited evidence) in future changes in flood magnitude and frequency derived from river discharge simulations. Projected precipitation and temperature changes imply possible changes in floods, although overall there is low confidence in projections of changes in fluvial floods. Confidence is low due to limited evidence and because the causes of regional changes are complex, although there are exceptions to this statement. There is medium confidence (based on physical reasoning) that projected increases in heavy rainfall would contribute to increases in rain-generated local flooding, in some catchments or regions. Earlier spring peak flows in snowmelt- and glacier-fed rivers are very likely, but there is low confidence in their projected magnitude (45).
More frequent flash floods
Although there is as yet no proof that the extreme flood events of recent years are a direct consequence of climate change, they may give an indication of what can be expected: the frequency and intensity of floods in large parts of Europe is projected to increase (14). In particular, flash and urban floods, triggered by local intense precipitation events, are likely to be more frequent throughout Europe (15).
More frequent floods in the winter
Flood hazard will also probably increase during wetter and warmer winters, with more frequent rain and less frequent snow (16). Even in regions where mean river flows will drop significantly, as in the Iberian Peninsula, the projected increase in precipitation intensity and variability may cause more floods.
Reduction spring snowmelt floods
In snow‑dominated regions such as the Alps, the Carpathian Mountains and northern parts of Europe, spring snowmelt floods are projected to decrease due to a shorter snow season and less snow accumulation in warmer winters (17). Earlier snowmelt and reduced summer precipitation will reduce river flows in summer (18), when demand is typically highest.
For the period 2071-2100 the general feature is a decrease of extreme flows in areas where snowmelt floods are dominating in the present climate. The hundred year floods will attenuate by 10-50% in northern Russia, Finland and most mountainous catchments throughout Europe. An increase by similar amount is projected in large areas elsewhere, whereas a mixed pattern is likely in Sweden, Germany and the Iberian Peninsula (2).
Increase flood losses
Losses from river flood disasters in Europe have worsened in recent years and climate change is expected to exacerbate this trend. The PESETA study, for example, estimates that by the 2080s, some 250-400 million Europeans could be affected each year (compared with 200 million in the period between 1961 and 1990). At the same time, annual losses due to river flooding in Europe could rise to €8-15 billion by the end of the century compared with an average of €6 billion today (40).
From an assessment of the implications of climate change for future flood damage and people exposed by floods in Europe it was concluded that the expected annual damages (EAD) and expected annual population exposed (EAP) will see an increase in several countries in Europe in the coming century (46). Most notable increases in flood losses across the different climate futures are projected for countries in Western Europe (Belgium, Denmark, France, Germany, Ireland, Luxembourg, the Netherlands and the United Kingdom), as well as for Hungary and Slovakia. A consistent decrease across the scenarios is projected for northern countries (Estonia, Finland, Latvia, Lithuania and Sweden). For EU27 as a whole, current EAD of approximately €6.4 billion is projected to at least double or triple by the end of this century (in today’s prices), depending on the scenario. Changes in EAP reflect well the changes in EAD, and for EU27 an additional 250,000 to nearly 400,000 people are expected to be affected by flooding yearly, depending on the scenario. The authors stress that the monetary estimates of flood damage are uncertain because of several assumptions underlying the calculations (only two emission scenarios, only two regional climate models driven by two general circulation models, no discounting of inflation to future damages, no growth in exposed values and population or adjustments, estimates of flood protection standards); the results are indicative of changes in flood damage due to climate change, however, rather than estimates of absolute values of flood damage (46).
Large differences across Europe
Annual river flow is projected to decrease in southern and south-eastern Europe and increase in northern and north-eastern Europe (19).
Strong changes are also projected in the seasonality of river flows, with large differences across Europe. Winter and spring river flows are projected to increase in most parts of Europe, except for the most southern and south-eastern regions. In summer and autumn, river flows are projected to decrease in most of Europe, except for northern and north-eastern regions where autumn flows are projected to increase (20). Predicted reductions in summer flow are greatest for southern and south-eastern Europe, in line with the predicted increase in the frequency and severity of drought in this region.
Climate-related changes in flood frequency are complex and dependent on the flood generating mechanism (e.g. heavy rainfall vs spring snowmelt), affected in different ways by climate change. Hence, in the regions where floods can be caused by several possible mechanisms, the net effect of climate change on flood risk is not trivial and a general and ubiquitously valid, flat-rate statement on change in flood risk cannot be made (41).
Flood risk tends to increase over many areas owing to a range of climatic and non-climatic impacts, whose relative importance is site-specific. Flood risk is controlled by a number of non-climatic factors, such as changes in economic and social systems, and in terrestrial systems (hydrological systems and ecosystems). Land-use changes, which induce land-cover changes, control the rainfall-runoff relations in the drainage basin. Deforestation, urbanization and reduction of wetlands diminish the available water-storage capacity and increase the runoff coefficient, leading to growth in the flow amplitude and reduction of the time-to-peak. Furthermore, in many regions, people have been encroaching into, and developing, flood-prone areas, thereby increasing the damage potential. Important factors of relevance to flood risk are population and economy growth, flood protection strategy, flood risk awareness (or flood risk ignorance) behaviour and a compensation culture (41).
Adaptation strategy - Spatial planning
Land use planning decisions (increase development in areas of flood risk and eroding coastlines, increase area of hard surfacing) potentially increase the vulnerability of some areas to climate impacts. Equally, adaptation measures such as investment in flood defences and use of property-level measures can at least in part offset this vulnerability. However, development decisions may be locking in a legacy of future costs from the maintenance of infrastructure (such as flood defences) and impacts from residual climate damages. Questions remain as to how these costs will be met in the future (44).
In order to manage vulnerability more effectively, local authorities should explicitly weigh up the potential long-term costs of climate impacts against social and economic benefits from development that are more immediately realised (44).
One flood defence measure which has proved to be increasingly successful is use of green/open spaces for temporary water storage to alleviate flooding (39). Keeping water away from urban areas and slowing its progress to minimise runoff proved successful in the summer (23).
According to the Pitt Review Team,the Government should commit to a strategic long-term approach to its investment in flood risk management, planning up to 25 years ahead (23).
Around 10% of properties in England are located on the floodplain. In addition, 11% of new homes in England have been built in flood hazard areas since 2000 (23). The Pitt Review Team (23) is of the opinion that, wherever possible, new development should not take place in flood risk areas and that there should be a strong resumption against building on the floodplain.The Government’s Planning Policy Statement 25 (PPS 25) requires that flood risk be a consideration at all stages of a planning application. This will help avoid development in areas at risk of flooding, and discourage building in areas of highest risk (21).
A number of spatial guiding principles for living with climate change in the East of England are (25,37):
- Protect existing land uses from the impacts of sea level rise and fluvial flooding only where the benefits of doing so in environmental, economic and social terms clearly outweigh the capital and revenue costs.
- Avoid allowing development in locations that could constrain or reduce effectiveness of future options for adaptation (e.g. allowing development in areas that might prevent effective coastal and fluvial flood management in the future).
- Minimise the requirement for ‘technical fixes’ to solve flooding and water supply issues.
- Encourage local access to goods, services and facilities in order to reduce the need for movement and reliance on transport infrastructure that could be vulnerable to climate change impacts.
- Guide new development to areas not at risk from fluvial flooding. Unsustainable floodplain development needs to be prevented in areas of increased flood risk. The planning system must be reviewed and adjusted to ensure this control.
UK Government’s policy
When considering whether investments in flood-prone areas should be allowed or not, UK Government’s policy discriminates between three zones based on their inundation probability (Table below: ‘exception’ refers to investments that should be subjected to an exception test to find out whether they should be allowed or not) (48):
Annual fluvial or coastal flood probability < 0.1%
Annual fluvial flood probability 0.1-1%
Annual coastal flood probability 0.1-0.5%
Annual fluvial flood probability >1%
Annual coastal flood probability >0.5%
Functional floodplain: land where water has to flow or be stored in times of flood
(e.g. evacuation routes and strategic utility infrastructure)
(e.g. docks, flood control, and water transmission)
(e.g. emergency services, caravans, and hazardous materials)
|Appropriate||Exception||Should not be permitted||Should not be permitted|
(e.g. hospitals, care homes, and hotels)
|Appropriate||Appropriate||Exception||Should not be permitted|
(e.g. shops, offices, and water treatment)
|Appropriate||Appropriate||Appropriate||Should not be permitted|
Adaptation strategy - Infrastructure
Possible solutions to flooding include: providing more flood storage (e.g. reservoirs), flood relief channels to bypass vulnerable stretches of the river, channel maintenance (vegetation control, deepening and widening); confinement of high water levels with flood embankments or walls.On the north and south banks of the Thames and London’s other rivers green corridors can function as a flooding buffer zone and creation of areas for habitats and species (38).
A precautionary approach should be adoptedin case the implications of climate change appear more radical than is currently perceived. This would imply reinforcing existing defences to a higher standard of protection than is currently considered necessary based on analysis of historic data and hydrological modelling. There would clearly be a significant price tag attached to such reinforcements. Note, however, that where replacement of the defences is already happening, a change in the standard of protection from a 1:100 to a 1:200 year return frequency is relatively inexpensive. Hence at a minimum a precautionary approach might imply reinforcing new defences to a higher level than suggested by analysis of historical data (27).
A methodology is required for the evaluation and implementation of floodplain areas with the potential for managed retreat (within the options of hold, retreat or advance defences). Shoreline Management Plans provide a vehicle for this type of assessment in estuarine environments (25).
A study into potential UK adaptation strategies for climate change estimates the cost of strengthening and adapting current fluvial defences in England over the next 50 years to be approximately £390 million (39).
Flood proofing on buildings at increased risk from flooding should be promoted. Guidance on building design and developments that will be able to adapt to climate change should be included in the GLA’s planned supplementary planning guidance on sustainable buildings (38).
Adaptation strategy - Contingency planning
The opportunity exists to shift in particular circumstances from structural engineering measures to more sustainable measures including behavioural approaches such as effective flood warning systems (25). Adequate resources and systems need to be available for responses to climate related emergency events e.g. flooding (38).
The role of local authorities should be enhanced so that they take on responsibility for leading the coordination of flood risk management in their areas (23). Local authorities already have a substantial role because of their responsibilities for ordinary watercourses, drainage, highways and planning. Their place-shaping role and local democratic accountability will help to ensure that the right local action is taken.
However, the last twenty or thirty years have seen the technical departments of local authorities significantly diminished and in some places closed or merged. local government and society must begin to value more highly the importance of technical and engineering skills.
Central government crisis machinery should always be activated if significant wide-area and high-impact flooding is expected or occurs (23).
During the 2007 floods many people were frustrated at having to access a number of websites to find information on flood-related issues such as the disconnection or restoration of electricity and water supplies, health notices and flood warnings. Many websites were poorly constructed or crashed under the volume of information requests. Some people could not find the information they needed as they did not know where to start looking.
It would be of great value if a single website provided links to all other websites needed for a comprehensive set of advice on flood-related matters, including where to go for more specific information and what to do during the emergency. This could be the area’s LRF website, with all Category 1 responders linking back to this ‘hub’ (23).
The public needs to be aware of a flooding risk before they can take action to minimise it. There is, however, a widespread apathy and tendency for people to deny the risk and assume it will never happen to them. Of respondents living in flood risk areas, only half (52%) were aware that their property was at risk of flooding and of those, only 57% had taken any measures to prepare in advance, for flooding (3).
With climate change likely to lead to more varied weather patterns and a greater risk of flooding, householders and businesses need to take greater ownership of the risks and take precautionary action in the same way as they do against other hazards, for example fire (23).
Citizens can improve their resilience to flood risk by taking measures themselves. Floodresistance measures, such as door guards, help prevent floodwater getting into a property. Resilience measures are those that minimise the damage when floodwater is in a property. A typical example is water resistant wall plaster (21).
Adaptation strategies - EU Directive on flood risk management
The new EU Directive on flood risk management, which entered into force in November 2006, introduces new instruments to manage risks from flooding, and is thus highly relevant in the context of adaptation to climate change impacts. The Directive introduces a three-step approach (2):
- Member States have to undertake a preliminary assessment of flood risk in river basins and coastal zones.
- Where significant risk is identified, flood hazard maps and flood risk maps have to be developed.
- Flood risk management plans must be developed for these zones. These plans have to include measures that will reduce the potential adverse consequences of flooding for human health, the environment cultural heritage and economic activity, and they should focus on prevention, protection and preparedness.
Adaptation strategies - London
Increases in rainfall due to climate change are projected to increase peak river flows in the Thames by up to 40% by the end of the century. It is not possible to store this increase in flow in the upper catchment of the Thames to significantly reduce the flood risk to riverside development in west London. Existing development adjacent to the flood defences will limit opportunities to set back flood defences, making improved flood prevention measures difficult to implement. For the non-tidal Thames, more emphasis needs to be given to development control and land-use planning, as well as emergency planning and flood warning to help reduce the consequences of flooding. In the tributaries also little can de done in terms of flood risk management other than flood warnings, local flood resilience measures and ultimately evacuation of the areas at risk (42).
The London Flood Response Strategic Plan aims to ensure a co-ordinated response to a flood to protect life and wellbeing, but also to reduce damage to the environment and property. The plan covers tidal and fluvial flooding, but the procedures apply also to surface water flooding resulting from excessive rainfall (42).
To reduce and manage current and future flood risk in London, focus will be on (42):
- improve the understanding of flood risk in London and how climate change will alter the risks, to improve the ability to manage flood risk;
- reduce flood risk to the most critical assets and vulnerable communities, to target the greatest effort on London’s most vulnerable assets;
- raise public awareness of flooding and individual and community capacity to cope and recover from a flood, to improve London’s resilience to flood events.
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.
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