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Peak rainfall climate change allowances have been updated

Peak rainfall climate change allowances have been updated


The Environment Agency has updated the peak rainfall intensity climate change allowances throughout England. The work uses a high-resolution climate model, which simulates local rainfall patterns better.

Instead of a national approach, England has now been divided into 92 Management Catchments, and the Hydrology Data Explorer has been updated to provide allowances for each catchment individually.




When do I need to consider the new peak rainfall intensity allowances?

If you are undertaking an assessment or modelling that uses peak rainfall intensity as an input or boundary condition, then it’s likely the new allowances will apply.

The new guidance states that peak intensity allowances should be used for urbanised catchments or rural catchments of less than 5sqkm. However, different hydrological responses in larger rural catchments (e.g. initial losses) mean that peak river flow allowances should be used instead.


How do new peak rainfall allowances compare with the previous version?

Management Catchments see a reduction in peak rainfall allowances from the previous version. In fact, peak rainfall allowances may have increased up to 50% for the 1%AEP upper-end allowance, as shown in the figure below.



The impact of the new upper-end allowances will mostly be felt in the South of England, North of England and parts of the West. 


Does the new rainfall intensity guidance address the type of development?

Yes. Rainfall allowances are divided by epochs, and depending on the lifetime of your development, you will have to assess which best applies. The guidance goes further and states that residential developments should have a minimum lifetime of 100 years, meaning that the 2070’s epochs should apply.


How can we help?

Should you be unsure how best to incorporate the latest climate change allowances in your design, we are here to help. M-EC has a dedicated team of flood risk and drainage experts with a vast experience in the water industry, covering the full project lifecycle from planning to construction.


Contact Us

  Joao Gill - Associate Flood Risk Engineer

  01530 264753