A flooded town high street.

Flooding in a changing world environment

The Property Care Association takes a look at why flooding is becoming worse and more frequent and how we can mitigate this risk.

The volume of water on our planet has not changed for eons. Water may change its form from a solid to a liquid to vapour. It cannot be added to or taken away and is therefore a closed system. Flood events globally have evidently become more frequent, but the alarming aspect is the volume and intensity of the flood water is increasing. According to studies, both flash floods and prolonged flooding have become more common, impacting both urban and rural communities. The changing climate exacerbates extreme weather patterns, with more frequent and intense rainfall events, rising sea levels, and altered seasonal patterns that make certain regions more prone to flooding. Urban expansion, with inadequate drainage systems and reduced green spaces, also amplifies flood risks.

There are several significant factors behind the increased flooding.

Global temperature rise

As global temperatures increase, so does the rate at which polar ice melts, contributing to rising sea levels. Coastal and low-lying areas are at higher risk of experiencing severe flooding due to sea level rise, which also contributes to more intense storm surges during hurricanes and typhoons. 

Arctic amplification 

The Arctic is warming about twice as fast as the global average, a phenomenon known as Arctic amplification. This rapid warming reduces the temperature difference between the colder polar regions and warmer mid-latitudes. This impacts on the air pressure at higher atmospheric levels.

Jet stream

The jet stream’s strength depends on the temperature contrast between the poles and mid-latitudes. With a smaller gradient due to Arctic warming, the jet stream weakens and slows down. Jet streams that meander due to reducing temperature contrast can lead to blocking patterns that can trap a weather system in place for extended periods. Low pressure trapped systems are often linked to a flood event. Conversely, a persistent high-pressure ridge can result in prolonged heatwaves and drought conditions. The jet stream’s variability can lead to unusual seasonal weather patterns. Spring can sometimes be colder than usual, or summer can start late in some areas, impacting agriculture, ecosystems, and local economies.

Changes in sea level pressure

The warming of ocean surface waters influences sea level pressure (SLP). For example, a warmer ocean surface lowers the sea level pressure above it, which can lead to more intense low-pressure systems over oceans. This change has implications for storm formation, particularly tropical cyclones (hurricanes and typhoons), 

which develop over low-pressure areas with warm, moist air. Warmer sea surfaces are thus linked to more intense storms with lower central pressures and stronger winds.

 

Enhanced storm intensity

Lower barometric pressures in tropical systems (due to warmer sea surface temperatures) can intensify storms, leading to more destructive hurricanes and typhoons. Lower pressure in these systems allows more air to converge and rise, fuelling the storm, increasing wind speeds and rainfall intensity.

The balance of global weather patterns has changed in a relativity brief period. This means that the natural water cycle begins to stutter. Increasing evaporation rates due to higher temperatures and greater surface areas of bodies of water mean that the warmer air holds significantly more water vapour, so when condensation occurs over land, the volume of precipitation and lower air pressures can very quickly overwhelm natural geographical pathways and drainage systems, leading to the flooding of coastlines, inland rivers and waterways (fluvial)Increasingly, because of urbanisation, flash flooding (pluvial) is a now a major concern.

Internationally, governments are attempting to lower the global temperatures through various organisations and committees. However, their attempts to agree and reduce our current position will take many years to reverse and return global temperatures to an acceptable level. So, in the meantime, we must mitigate against the impacts of flooding and flood events. This does not just mean rebuilding or restoring buildings and construction after an event but, we need to protect our communities by providing them with earlier warning of a potential flood to allow building owners time to provide planned protection to their property prior to an event to minimise damage and therefore reduce recovery time after flood water has subsided. Also in areas of high risk of flooding, safe evacuation needs to be addressed and delivered to the emergency services.

Mitigation of flood risk assessment and strategies

An assessment of flood risk is therefore critical to understanding the potential impact to vulnerable high-risk areas within known flood zones. This is addressed at present through various authorities and organisations but needs to be extended to an individual property level. This would provide the property owner solutions to make their buildings more resilient and provide faster recovery time after a flood. The FloodRe second quinquennial report indicated that there is a shortage of competent surveyors in this field and more are required.

A competent flood risk assessor should be able to analyse historical data and predictive modelling: reviewing historical flood data helps to predict future risks. Advanced predictive models, which factor in climate change projections, are essential for understanding how flooding may occur.

They should be able to map flood zones: identifying areas prone to flooding (both coastal and fluvial and pluvial) can help in proactive planning. These maps are vital for city planners, developers, and policymakers in designing infrastructure and land use that account for potential flood scenarios.

A flood risk assessor should carry out a vulnerability assessment: this assesses which areas, communities, and infrastructures are most vulnerable to flooding based on geographic, economic, and social factors. Identifying vulnerable populations, such as those in low-income areas or with limited access to emergency resources, is essential for effective disaster planning.

Property controlling measures – resistance, resilience, and recovery 

Analysing the risk potential would then lead to a mitigating design for property resilience against an anticipated flood event. This would need to incorporate the following framework.

Resistance: this focuses on preventing flood water from entering a structure or area. Examples include building flood barriers, levees, and dams, as well as raising building foundations above expected flood levels. Creating water-retentive urban infrastructure, like green roofs and permeable pavements, can help in flood resistance.

Resilience: resilience involves designing infrastructure and landscapes that can endure flooding with minimal long-term impact. For 

instance, flood-resilient building materials and flood-proof utilities can allow for quicker restoration. Resilience also extends to creating community preparedness programs and ensuring rapid access to emergency services during flood events.

Recovery: recovery strategies focus on the aftermath of a flood, aiming to return the community to normal as quickly as possible. This includes fast-tracking repairs and reconstruction, providing financial aid to affected individuals, and restoring essential services like water, power, and healthcare. Community support systems and governmental relief efforts are key for effective flood recovery.

Implementing such a comprehensive flood risk analysis and building design strategy statement emphasising communities can enable better adaption to increasing flood risks before a flood occurrence.  

The government has implemented a significant building strategy. Planning authorities will be under pressure to allow these homes to be built in ever increasing flood zones. By assessing a buildings flood risk at a design construction stage, these homes can be constructed with resilience. 

The probability of flooding and flood events is likely to increases over the next decade. If nothing is done, property owners will face the full costs of restoring their homes as insurers are less likely to cover the rising costs of building repairs in areas of high risk of flood occurrence. 

Around the country, we have a number of flood projects which are doing brilliant work to minimise the effects of flooding in flood zones. However a more coordinated informative and planned approach through trained building assessors accessing the all the guidance and resources developed by these projects will minimise the initial impact damage on a property, reduce restoration costs through resilience and lessen the devastating and frightening effects of flood water to communities and individuals.

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