29 February 2016
Further to the catastrophic floods in the north of England in December 2015 the Environment Agency (EA) has reviewed the climate change allowances to be considered in conjunction with the planning process in England. The new guidance can be seen here.
Climate change has always been considered in the preparation of Flood Risk Assessments (FRA) submitted to support Local Plans and individual planning applications (as required by the NPPF Chapter 10). The new allowances represent a significant change in approach and incorporate outputs from the latest climate change models.
The new data in respect of future river flows introduces ‘allowance factors’ based on climate change model prediction ‘percentiles’. These are applied according to River Basin Management Plan (RBMP) areas and also vary according to the location of a site relative to the EA designated flood zone and the vulnerability classification of the development under consideration.
When considering climate change over the next 100 years in relation to residential developments, the new methodology introduces a very significant increase in extreme event river flows. Where the old guidance required checks on a presumed 20% increase, the recent update indicates that the ‘upper end allowance’ to be considered is in the range 45 - 105%, depending on the RBMP area. However, river model data for the specific extreme event flow necessary to apply the new ‘allowance factors’ is unlikely to be immediately available.
Additionally, there are other, less significant, changes in ‘allowance factors’ that should be included in the planning and development process. Rainfall intensities used in the design of site surface water drainage could potentially increase from 30 to 40 per cent and, where applicable, consideration needs to be given to coastal conditions such as wind speed and extreme wave heights.
The new guidance is applicable as of 19th February 2016. Though there are transitional arrangements in respect of development plans already submitted for examination and for validated planning applications, where the EA consider that flood risk is a particularly sensitive issue the new allowances will be applied.
For further information or assistance in managing the consequences of this new guidance please contact Matthew Elliott on 0113 219 2554 (firstname.lastname@example.org) or Tom Beavis 0113 219 2292 (email@example.com).