The Environment Agency (EA) undertook a major overhaul of the climate change allowances back in 2016. This saw new climate change allowances for peak river flow and the creation of three bands: Central, Higher Central and Upper End to be applied differently depending on a development’s vulnerability classification and flood zone.
As of July 2020, a new High++ (H++) band was created. H++ is described as an extreme climate change scenario. In their guidance the EA say this climate change allowance should be used for nationally significant infrastructure projects and new settlements or urban extensions. The H++ allowance should be used as a sensitivity test.
This new guidance will require a new sensitivity test to determine the extent of flood zones in relation to large scale developments.
This new guidance hasn’t altered the requirement to consider climate change rates of 40% when undertaking drainage designs.