How will new climate change allowances impact development proposals?

The Environment Agency (EA) have published new guidance on climate change allowances for flood risk assessments and strategic flood risk assessments. These were published on 19th February 2016, which can be found here.  The EA have produced these new guidelines based on the most recent climate change projections for the UK (UKCP09).

The new guidance will include updates to the allowances that should be factored into assessments. Including the impact of climate change on peak river flow, peak rainfall intensity, sea level rise, offshore wind speed and extreme wave height.  A range of allowances have been provided depending on the type of development, regional location and time period.  Whilst guidelines are included to determine which allowance to use. Early consultation with statutory consultees have to be key in order to agree the most suitable allowance.


Perhaps the biggest change is in the allowances for peak river flows. The previous guidance recommended the use of a flat 20% increase in flows across the whole of England.  The guidelines have now broken down into different river basin districts to reflect how climate change will impact different types of catchment.  Upper allowances vary from 45% to 105%.

The EA’s Flood Zones are based on ‘existing’ scenarios. Therefore, it seems unlikely that there will be any changes to the Flood Map or site allocations. However, the higher allowances for climate change will have a result in higher design flood levels. Which could have an impact on the viability of some schemes when appropriate mitigation and resilience measures are taken into account.

Allowances for peak rainfall have increased from 20-30% to 30-40%. These increases will need to be accounted for in surface water drainage strategies.  This will increase the required storage volumes to meet planning policy. Which may require greater consideration to be given towards exceedance flowpaths.

Whilst the new guidance will come in with immediate effect. It is understood that valid planning applications submitted before the 19th February 2016 should be assessed against the previous guidance. But that all new submissions should have to take this latest guidance into account.

Our Work

RMA currently work with clients and statutory consultees to ensure that all of our projects appropriately apply the new guidance.  If you have any queries or require expert advice on flood risk please do not hesitate to contact us.