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The latest scenarios from the Met Office and other climate change scientists show that the risks and impacts of climate change are an urgent issue for Britain’s population, both today and in the future.

The risks and impacts of a changing climate in the UK mainly relate to rising temperatures and changing rainfall patterns, which are exacerbated by extreme weather events that are hard to predict. 

The impact of drier, warmer summers and milder, wetter winters, together with an increase in the number of extreme weather events, present a number of risks to Hertfordshire’s buildings and their surrounding environments. These can be grouped into a set of four key risk areas.


What is the impact?

Overheating occurs when temperatures increase up to a point when it causes discomfort. The effect can be particularly noticeable at night as a building or built environment soaks up heat from the day, trapping it only to be released overnight as the air temperature cools. In particular, as summer temperatures increase and we experience more frequent extreme hot weather events, overheating is expected to affect buildings such as homes, hospitals and schools which traditionally do not include air conditioning equipment.

The issue of night-time cooling (or lack of it) is often the key factor in determining how vulnerability and susceptible occupants will be to overheating. The use of mechanical cooling and ventilation is expected to rise in offices since these tend to be located in built-up areas that suffer from the ‘urban heat island effect’. Increased use of mechanical cooling, such as air conditioning units, emits heat energy to the external environment therefore increasing air temperatures in the surrounding area. Mechanical cooling may also increase carbon dioxide emissions from the built environment.

The ‘urban heat island effect’ is a phenomenon whereby urban temperatures are higher than the surrounding rural areas due to heat being stored and ‘trapped’ within building structures. The result is urban centres that can be a lot warmer than the surrounding countryside, especially at night. According to the South East Climate Change Partnership the urban heat island currently adds up to a further 5-6°C to summer night temperatures and will intensify in the future. Consequently, overheating of the external environment needs also to be addressed and developers must have regard to the heat island effect on any urban development. 

What are some of the possible consequences for not adapting the built environment to climate change?

  • Increased demand for artificial cooling to help reduce excessive indoor heat. If provided mechanically (such as by air conditioning) this will increase the demand for electricity, further contributing to emissions of CO2 and adding further heat energy to the external urban environment. This is known as a ‘maladaptation’: a short term solution, which in reality, exacerbates the issue as the hot air rejected from the buildings will contribute to increasing the air temperature in the surrounding area.
  • The elderly, young children and the sick are particularly vulnerable to high temperatures. Overheating, of both internal and external environments, will lead to an increase in the number of summer deaths and heat related illness.
  • Our outdoor environments, for example playgrounds, car parks, streets and pavements will become unpleasant places to work, play, relax and move around in within during summer months. This may be exacerbated if existing green and blue spaces are replaced by development that is not designed for climate change adaptation.
  • As our external environment becomes hotter, there will be an increased demand for green and naturally shaded spaces in order to counterbalance areas of hard landscaping and provide refuge from the sun and heat. If green spaces are not designed with climate change impacts in mind, then they will require irrigation, putting additional pressure on water resources.
  • Demand for water to irrigate private gardens will also increase as the amount of summer rainfall decreases, periods of drought increase, and temperatures increase. This will put significant pressure on existing groundwater sources in Hertfordshire and on the need for more energy-intensive water treatment and transportation. Many areas within Hertfordshire will experience acute water stress and could see restrictions placed on water usage, as a worst case scenario.
  • Many of our traditional building materials are not made to cope with hot weather conditions. We will experience increased damage to buildings and other structures from cracking caused by extreme heat. This will lead to a higher number of insurance claims being made, driving up premiums and overall costs to property owners.
  • Similar to traditional building materials, Hertfordshire’s transport network is not designed to withstand long periods of exposure to heat. If the frequency of extreme weather events increases as anticipated the risk of damage to road and rail networks from buckling rails and cracking or melting roads could potentially become a significant issue for Hertfordshire. Such disruption to the transport network occurred during the recent heatwave of 2003 and hot summer of 2006.
  • Even a slight increase in average annual temperatures could alter Hertfordshire’s ecosystems, resulting in a potential reduction of local biodiversity. Habitats characteristic of our current weather patterns could change to adapt to a warmer, drier climate (similar to that of the Mediterranean) meaning a loss of Hertfordshire’s native fauna and flora, and altering the county’s landscape. This will affect landscape design for new development in terms of the species selection (such as trees, shrubs, etc), and the level of water required to irrigate them.
  • As soil moisture is lost from natural environments and new development encroaches on green space, the likelihood of field fires that endanger nearby communities and businesses will increase.

Precipitation and flooding

To identify whether your building or development is situated on land at risk of river (fluvial) flooding, visit the Environment Agency’s Flood Map webpages.   

What is the impact?

Increases in average winter rainfall and the frequency of severe weather events will lead to a greater risk of flooding in Hertfordshire, further exacerbated by increased surface water run-off as areas become more urbanised. Along with ground water flooding, which is difficult to mitigate or manage, surface water flooding (‘pluvial’ flooding) is the greatest source of flood risk for Hertfordshire, more so than river flooding ( ‘fluvial’ flooding).

Rainfall is still expected during the summer months, albeit less than what we experience now. However, when a short but heavy rainfall event does occur following a prolonged period of dry, hot weather the ground will be extremely dry and therefore unable to allow water to infiltrate quickly enough. The resulting excess water will be forced elsewhere creating the risk of flash flooding, particularly where there are impermeable surfaces making it impossible for the water to soak into the ground below. 

What are some of the possible consequences for not adapting the built environment to climate change?

  • Flood damage to non-domestic properties will cause disruption to the day-to-day running of businesses, resulting in financial losses. Where properties are severely damaged and businesses are permanently displaced, this could lead to an increase in the number of vacant buildings and the loss of employment land.
  • Flood damage to public sector buildings and facilities will cause disruption to the services they provide, such as hospitals, schools, and waste collection and sorting.
  • Flood damage to domestic buildings could cause the temporary or permanent displacement of people, affecting people’s quality of life. Where homes are severely damaged and occupants are permanently displaced, this could lead to an increase in the number of vacant, decaying houses and the disintegration of communities.
  • Where flood damage to buildings is repairable, this could incur financial cost for the property owner and cause inconvenience whilst renovating the building.
  • As more properties become damaged due to floodwater, claims for insurance payout will increase. This will drive up premiums and overall costs to the customer. Some homeowners in flood risk areas may find their properties become uninsurable.
  • Surges in runoff, either from surface water or rivers, will put pressure on existing drainage and sewerage infrastructure and could lead to overflowing drains. If floodwater enters the watercourse, such as rivers, streams or lakes, this may have implications for water quality, particularly if the runoff is from a source of potential contamination, such as car parks or industrial areas. Overflowing drains could also impact upon public health, particularly in residential areas or other urban environments.
  • Following the heavy, prolonged snow fall in Hertfordshire in 2009, many people experienced severe disruption to road and rail networks. This impacted upon businesses, public services and personal circumstances, and contributed to a large number of travel-related incidents. It is predicted that Hertfordshire will experience an increase in the frequency of severe winter weather events, and could therefore experience more regular transport disruption. However, it is anticipated that these severe weather events are more likely to be storms and rainfall rather than snow.
  • A prolonged period of snow and ice, and exposure to salt and grit, also causes significant damage to infrastructure, such as roads, rail tracks and exposed pipes. The following clear-up operation could incur significant cost, and the repairs required to the road network will require substantial investment.
  • Prolonged periods of heavy rain could affect ground conditions causing instability, particularly where the underlying geology is clay-based. Many areas of Hertfordshire lie on London Clay and could therefore be affected. Building foundations could be compromised leading to structural damage of the building from subsidence and heave. Heavy rain could also cause landslips, potentially damaging properties, roads and other infrastructure.

Pressure on water resources

What is the impact?

Drier summers will put pressure on the availability of water in Hertfordshire for drinking, washing and irrigation as groundwater resources, such as aquifers, decline whilst at the same time being subjected to increased demand for potable water to supply new and future housing in Hertfordshire. We are already seeing periodic limitations on water use through hosepipe bans in the summer months. Periodic limitations like this are likely to become more frequent and extensive as summers get warmer.

Although summers will be drier and warmer, we will still experience short, intensive bouts of heavy rainfall. Following a prolonged period of dry weather, the ground’s inability to absorb intense rainfall fast enough could lead to excess water directly entering a nearby watercourse, such as rivers, stream and lakes.

Usually soil acts as a natural form of filter and enables any contaminated water to be slowly ‘cleaned’ before finally reaching the groundwater reserve. Without this process there could be implications for natural water resources in terms of reduced quality, particularly if the water entering the watercourse is from potentially contaminated land, such as a car parks or industrial areas. Drainage networks may also find it difficult to cope with flash flooding, further compromising the quality of our water resources.

Additionally, as patterns of annual rainfall become more unpredictable, there will be increasing uncertainty regarding the availability and recharge of Hertfordshire’s groundwater resource.

What are some of the possible consequences for not adapting the built environment to climate change?

  • There will be an increased demand for mains water:

For domestic use to water gardens and for consumption.

For business use to irrigate landscaped areas. For irrigating public parks, garden and other green spaces (further exacerbated by increased demand for green spaces for shading/urban cooling).

  • This will increase pressure on groundwater reserves and further increase the need for energy-intensive water treatment and transportation.
  • Heavy rainfall may result in increased surface water runoff and overflow from struggling drainage networks, which could cause contamination of waterways and groundwater sources. This will exacerbate the need for water treatment.
  • Freezing conditions during severe weather events, and reduced ground stability after heavy rainfall, could damage water distribution networks further reducing the availability of water.

Ground conditions

What is the impact?

Ground conditions can be affected by periods of drought and excess water conditions. Clay soils, as found throughout Hertfordshire, are particularly susceptible to shrinking and swelling (known as ‘shrink-swell’) that can cause structural damage to buildings and infrastructure.

What are some of the possible consequences for not adapting the built environment to climate change?

  • Prolonged periods of heavy rain could affect ground conditions causing instability, particularly where the underlying geology is clay-based. Many areas of Hertfordshire lie on London Clay and could therefore be affected. Building foundations could be compromised leading to structural damage of the building from subsidence and heave.
  • Heavy rain could also cause landslip, potentially damaging properties, roads and other infrastructure. 
  • Soils that contain clay minerals, such as London Clay, absorb water when wet (making them swell), and lose water as they dry (making them shrink). This shrink-swell behaviour is controlled by seasonal changes in the soil moisture content (related to rainfall and local drainage). Whilst cracking is an obvious surface effect, it is not always realised that the fissures may penetrate to a depth of 3 metres, and exceptionally, can reach 10 metres below the ground surface. This can have severe consequences for building foundations, causing subsidence and resulting in structural damage, as well as transport infrastructure.
  • As more buildings and infrastructure suffer from structural damage, the amount of insurance claims will increase. This will lead to increased insurance premiums making it more and more.