The grass got its first trim on the year today. But not until I rewired the plug - I felt really manly. I also got my strimmer out and tidied up the edges. Then I got out my bottle of Asda brand weed 'n' feed and treated the lawn to some chemical care. Then I read that the stuff doesn't work very well if you apply it within three days of cutting the grass. Oh well.
I felt I better seize this opportunity to cut the grass as it has been so wet lately. While I was pushing the mower around I got to thinking how it is that we have had lots and lots of rain, but there is some sort of water shortage going on. This seems somehow inconsistent. But then I remembered weatherman Shafernacker saying that only 4 months in the last two years have had above average rainfall. That factoid stuck with me, cos to me it is a clear indication of climate change. As I was pushing the mower around I made lots of assumptions about statistics and then concluded that the chances of only four months out of the previous 24 having above average rainfall were very low indeed. I decided it should be "24 choose 4". Which I then calculated to be one in 198. Being a grumpy old fart I concluded that all this rain may have caused floods and killed somebody, and made my roof leak, but the long term effect of climate change is a hosepipe ban in many English counties. I then applied my weed 'n' feed with a watering can.
The chances of any one month having above average rainfall is fifty-fifty. Maybe. Maybe not. Did Thomasz mean the median average? If he did then I think my maths was fine. I get to assume the months are independent and recall the binomial distribution from A-level maths. On the other hand who actually uses median averages these days? It if more than likely that the statistic reported on the TV was the mean average, in which case I am not sure what it says about anything. You can't relate the two averages without knowing more about the distribution of values.
Consider the "monsoon" pattern of rainfall. (One of the two things I learnt in GSCE Geography. The other was that Rotterdam is a big container port with a "hinterland".) In India or wherever they get monsoons it only rains for one or two months of the year. All their rainfall comes all at once, and it doesn't rain in the other months. You could say that this climate has 10 or 11 months every year with "below average" rainfall. But this pattern of rainfall has been happening for millennia, and only some very poor statistical analysis will link it to climate change.
