When does spring start?
Well it’s March 1st according to the Met Office, traditionalists go with the date of the spring equinox which falls on the 20th or 21st March. I suspect, though, that a lot of us have a personal, natural sign that we look out for each year that reassures us that spring is on the way. There is a science (phenology) to do with the dates when natural things happen and the UK government has an “official” Spring Index that is based on the occurrence of certain natural phenomena. The index is one of the UK Biodiversity Indicators and is, to quote,
.. calculated from the annual mean observation date of the following four biological events: first flowering of hawthorn (Crataegus monogyna), first flowering of horse chestnut (Aesculus hippocastanum), first recorded flight of an orange-tip butterfly (Anthocharis cardamines) and first sighting of a swallow (Hirundo rustica).
Now in some years, as we all know, spring is early and some years it’s late, and not surprisingly this is do with the weather:
When March and April are warm spring is early and when it is cold spring is late. No real surprise there but phenology is an old science in the UK and scientists have noticed that spring is getting, on average, earlier.
If you want to work out your own Spring Index you can type your four sighting dates in this spreadsheet and it will work it out for you.
If you are interested in knowing more about phenology and helping them to record many more aspects of when natural events happen have a look at the Nature’s Calendar website run by the Woodland Trust.
Published by: Robin Sutton
Wednesday, February 3, 2016