The Risk of Seagull Poop



I was standing at a pedestrian crossing in a city recently waiting for the light to change to cross. Two gentlemen, also waiting to cross, were talking about their favourite weather apps. One said the one he used wasn’t very accurate, but that he liked it because it always overestimated the chance of nice sunny weather and it made him feel happier.

It got me thinking about my own use of weather apps. Do you have one on your smart phone? I’ve been talking about devices and systems we use to give us certainty, and weather apps are another great example.

Despite the fact that I use them a lot, I’m always entertained by their use of probability for rainfall. The image below is from the Met Office weather app, saying the chance of rain each hour for that day.

What exactly does a 5% risk of rain look like? When it comes to rain surely it either does or it doesn’t.

The Met Office explain their ‘probability of precipitation’ as a more useful opinion of the risk of rain:

“PoP allows you to make the decisions that matter to you. For example, if you are just hanging out your sheets that you need next week you might take the risk at 40% probability of precipitation, whereas if you are drying your best shirt that you need for an important dinner this evening then you might not hang it out at more than 10% probability.”

Because of course we all make decisions this way.

For me the greatest risk my bed linen faces when it’s hung outside to dry is not from rain, but from seagull poop. Back home in North Wales I live by the coast, and there are lots of seagulls. At certain times each year when their chicks are huge and annoying, they become extra aggressive and poop on everything.

I want someone to come up with an algorithm that determines the percentage chance of seagull poop in any given hour where I live. And then the question I would have to ask myself is what is my threshold limit now? Will I still accept 15%, 5%...