Over the 6th and 8th October 2023 my area was caught in a heavy rainfall event like many other parts of Scotland.
As I have a small weather station mounted in my garden that records weather data on an ongoing basis, I decided to estimate the statistical rainfall during the storm.
Storm Details
The storm started at 7:40 pm on the 6th October 2023 and continued uninterrupted until 11:50 pm on the 7th October 2023. A total of 27 hours 10 minutes. During this time there was a total of 49.2 mm of rainfall. This event had a maximum intensity of 4.8 mm/hour and the average intensity was 1.811 mm/hour.
There was a second storm event on the 8th October 2023. This lasted for a total of 23 hours and 20 minutes. During this event the maximum intensity was 3.6 mm/hour and the average intensity was 1.32 mm/hour. However, the total rainfall during this event was only 30.8 mm.
Annual Exceedance Probability
Based on the data it suggests that the storm event that occurred between the 6th October and the 7th October had an Annual Exceedance Probability (AEP) of 3.33% This means that there is only a 3.33% chance of a rainfall event being exceeded annually. Another way of explaining this is a 1 in 30 year rainfall event, although this does not suggest that this event will not occur for another 30 years.
Based on the storm event data of the 8th October the AEP would have been 20% or equivalent to a 1 in 5 year event.
For further reading, more information about flood estimation is available from the website below:
https://www.ceh.ac.uk/our-science/projects/flood-estimation-handbook
