Mike's musings

Getting rained on

Today has been a beautiful hot day, with temperatures at least above 20 degrees Celsius. I took Buster for a walk at lunchtime, and as we'd been moving rather fast, and he was pretty hot, I let him have a swim in a lake nearby. I stood under a large willow tree - around 20m tall - and was somewhat surprised to find that I was being rained on.

There was a gentle, but steady, fall of drops from the tree under which I was standing - I've never come across anything like it. I went out of the shade of the tree, and it stopped: it was definitely coming from the tree. I wondered if it was respiration (which produces water) or some condensation from the air (though it didn't feel that humid). In the end, I sent this SMS to AQA (Any Question Answered):

I was just standing under a large (20m+) willow tree by a small lake. Although the temperature is in the high 20s Celsius under a clear blue sky, and it's nearly 2pm, the tree was dripping water on me, like light rain. Why? Condensation, respiration, or other reason?

I got the following helpful answer back a few minutes later:

AQA: The tree was losing water by the process of "transpiration" through it's (sic) leaves. On a hot day a large willow tree can lose up to 5,000 gallons of water.

That's nearly 19,000 litres of water, folks! I suspect that I knew about this when I did biology at school, but it was good to learn something nearly new.

Labels: walk, weather