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Preparing for UK water extremes: flooding and drought

This blog introduces the first two of four research projects commissioned by the Adaptation Sub-Committee to inform the 2017 UK Climate Change Risk Assessment. Here’s an extended summary  of the findings of all four projects. 

Climate change is set to increase the probability of flooding and put pressure on water availability in the UK. Periods of too much or too little rainfall are both likely symptoms of increasing global temperatures. These could happen back to back, as was the case in the first six months of 2012, the so-called “wettest drought on record”.

In this blog, we consider the potential impacts of climate change on flooding and water availability in the UK, based on new research commissioned by the Adaptation Sub-Committee (ASC) as part of our work to inform the Government’s next climate change risk assessment. Both sets of water-related projections address uncertainty by considering a range of possible scenarios, based on differing levels of climate change, population growth, and adaptation effort.

First, flooding. A new study ‘Projections of future flood risk in the UK’ by Sayers and Partners finds that by the 2050s nearly half a million more homes are projected to be at a significant risk of flooding (at a 1 in 75 or greater chance of flooding in any given year). This takes into account current approaches to flood risk management and assumes these continue. In more extreme climate change scenarios, if global temperatures increase by 4°C rather than 2°C by the 2080s, and if population growth is high, then this figure increases to more than a million additional homes.

Additional investment in maintaining and enhancing flood defences and much wider uptake of property-level protection measures and sustainable drainage systems (SuDS) would be needed to fully offset the increase in risk expected under a 2°C climate projection. Under a 4°C projection, not even this enhanced level of adaptation would be sufficient to completely offset the increase in risk.

Separate analysis considers the consequences should coastal defences, as they exist now, fail as sea levels rise. A 0.5 to 1 metre rise in sea levels – plausible by the end of the century – would make around 200km of coastal defences (20 per cent) highly vulnerable to failure. This would lead to 200,000 hectares of land and 400,000 properties being at risk of a 1-in-200 year tidal surge, as experienced in January 1953 and December 2013. Localities with the highest number of properties at risk in this scenario include Cleethorpes, Fleetwood, Weston-Super-Mare, Eastbourne, Burnham-on-Sea, Bognor Regis, Worthing, Bridgewater and New Romney.

The key message from the study is clear: avoiding significantly more flood damage means keeping global increases in temperature to no more than 2°C, while also investing in and delivering stronger flood risk management policies and plans across the country.

Next, water availability. In a second research study for the ASC, led by consultancy HR Wallingford, existing projections of water availability have been updated using the latest datasets from government agencies and water companies across the UK.

In terms of public water supplies, the UK currently has 10 per cent more water than we need to supply homes and businesses; a supply-demand balance surplus of around 2,000,000,000 litres per day (2,000 Ml/d). However, this is for the UK as a whole. Modest deficits exist in some water resource zones that water companies are currently addressing.

This picture is projected to change as global temperatures increase and the UK population grows. Increases in demand for water are expected to be accompanied by decreases in water availability due to climate change. Supply-demand deficits are projected to be widespread by the 2050s, with water demand exceeding supply by around 800 to 3,200 Ml/d (5-16 per cent of the total demand for water at that time) under high population and high climate change projections. This assumes current water resource management plans are delivered by water companies between now and the 2030s.

HR Wallingford also carried out additional analysis to incorporate water demands from agriculture, energy generation and industry. These sectors require additional water to that supplied by water companies, and abstract what they need from rivers, lakes and groundwater. To balance the demand for abstraction with the needs of the natural environment, the Environment Agency maintains a minimum ‘environmental flow rate’ for rivers. Relaxing the current environmental flow rates would create more water for human use, but risks causing severe harm to ecosystems. As the ASC recommended in its first statutory progress report to Parliament in June, reforming the water abstraction licencing regime is necessary to ensure water is allocated efficiently between different industries and sectors whilst safeguarding the natural environment.

Overall, further adaptation is needed to offset the projected increases in risk from both flooding and water scarcity even under a 2°C temperature rise scenario. At the moment these water-related risks are considered in isolation (too much, or too little water), but there are clearly co-benefits in addressing them together in some parts of the country. For example, approaches to natural flood management, such as peatland restoration, can help store rainwater in upland areas and help recharge aquifers. SuDS in urban areas slow down and capture rainwater, allowing it to filter into the ground, rather than add to river levels or sewer overspills and be flushed out to sea. Water companies will need to work more closely with the flood risk authorities and seek opportunities to manage water at the catchment scale as an increasingly valuable, and scarce, resource.