Autumn a Great Time of Year
Autumn is great time of year for change. There are changes pleasing to the eye as the plants show their autumn colours and the not so pleasing changeable weather when there is a storm sitting off the west coast of Ireland. Wetter weather at this time is expected but this year we had not only a very dry spell but quite cold conditions that got us thinking of turning on the central heating one month early.
Now the surprising thing is that the drier October did not stop the fungi appearing in my garden. Not only that, the soil exposed to the autumn sunshine just dried at the very most top surface where it had been roughed up by digging or hoeing. Every morning there was dew on the grass and an amazing amount of cob webs on the bushes shown up by dew.
So where did all this moisture come from?
From the air of course! But why? I explain this in more detail in my book A Wet Look At Climate Change and it’s all to do with the temperature. Clear skies that gave us the dry spell caused the night temperatures to fall. My own records over October showed a lowest temperature of 1.6°C and a lot of nights between 2 -5°C. As temperature falls, humidity has to increase, it’s a ’Law of Nature’. Air can only hold so much moisture as invisible water vapour and when the humidity reaches a particular high the water vapour condenses into water droplets. This high humidity point is not surprisingly called the “Dew Point”.
On the other hand, as temperature increases, humidity falls. You may have been out in the “Autumnal” sunshine without a coat. One afternoon I couldn’t resist taking a break from the keyboard and sat outside in a short sleeve shirt for about an hour. Pretty good for October in Ireland. On that day we had washing hanging out and with a very slight breeze it dried in no time. Radiated heat (infra-red) from the sun at this time of year is still strong enough that even though the actual air temperature may have only been around 15°C, you can feel the warmth.
That warming you feel heats things in direct sunlight and increases the temperature of the surrounding air. By our Law of Nature this lowers the humidity and at a certain point water can evaporate away from the surface of things. We commonly call this, drying.
Back to the fungi. In the shaded parts of my garden the high night time humidity responsible for the morning dew must have kept sufficient moisture in the soil for the fungi to growth and produce their magnificent fruiting heads.