Frost-free days

[KathyLauren]

I put this in the Allotments Forum because frost-free days is usually something of concern to gardeners. This topic is also relevant to climate change.

I was looking at weather records for our little island to calculate the average frost-free period. When I graphed the data I had, it looked like there had been a considerable change over time. However, the records for this community are sporadic and were taken at at least three different locations, with the associated micro-climates. It was possible that I was seeing some other effect than climate change.

So, I retrieved the records for the nearest airport, 20 km away, which are continuous back to 1944. What I found confirmed my suspicion. The frost-free period in this area has changed more-or-less continuously from 170 days in 1945 to 220 days in 2003, the last year for which I have airport records. (My own local observations confirm that the trend continues.) That is about a 30% increase in 60 years.

Obviously, this has major implications for ecosystems both natural and horticultural.

I would be curious if anyone else has noticed similar changes over the years.

[Millymollymandy]

I've only been here for just over 5 years so I'll let you know in about 20 years!

[javaMan]

Have you noticed a shift in the distribution of the frosty days?

It's been scuppered of late, but I did notice a pattern for a few years where December would be relatively mild with a few frosty days particularly round Christmas. January gets very mild, but then a nasty, long cold snaps arrive in February and March. As opposed to an even distribution of frosty days. It's almost as if winter gets pushed further out into the year.

Angus