We have had a challenging late winter here in the Winterbournes, and those of who live close to the river have had an anxious few weeks.
We are frequently being told to expect more “extreme weather events” as a result of climate change, but it is difficult sometimes to put this into a local context. We recently had an excellent presentation by Robert Grace on the science behind climate change which I for one found very useful and informative. I think we always feel more comfortable if we understand the reasons behind events.
With thanks to George Shepherd for the local Hurdcott meteorological data, and Clare Dunster for the Winterbourne Dauntsey groundwater data, we can begin to explain just how the wildly variable rainfall (from season to season and year to year) affects local flood risk. This flood risk seems to take three forms: flash floods, where very heavy rainfall washes down the hill in a short lived torrent; river flooding, when the river overflows the banks; and groundwater flooding where the water table rises to create springs, puddles and even small lakes! These are of course interrelated – the higher the groundwater, the more likely we are to get flash floods and river flooding as the ground can’t absorb any more. Of note is that the one and only Environment Agency Flood Warning we had for the Winterbournes this winter was of groundwater flooding.
Hurdcott weather data for 2019 show typical seasonal rain variation. Overlayed on the graph are the monthly averages for groundwater. Not surprising they align!
However, the data also show how individual peaks of rainfall can quickly lift the groundwater levels. The second graph shows the daily groundwater readings, with the additional thicker bars showing some individual (very wet day) rain fall readings.
The groundwater levels rise each time! In winter these periods of high rain were often associated with named storms (Erik in February, Freya and Gareth in March, Hannah in April, Miguel in June, Atiyah in December.
And to whet your appetite for the report next year, this is what happened in the first 6 weeks of this year………
Charles Penn, Clare Dunster, George Shepherd
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