The climes they are a-changin'

I was talking to my parents last night and they were bemoaning the amount of rain they have had the past month.  These are the same parents who can best be described as climate change skeptics. 

Really they pay little attention to things like climate change other than my father making an off-hand remark on a bad weather day, like a warm day in January, or snowy in May, 'Must be that climate change thing you're always talking about.'

I never talk about climate change around my dad.

Anyways, I decided to take a look at the precipitation totals at BWI airport for a few reasons:

1. To see if there's a noticeable trend.
2. To see if I could use data to make a case to my parents that climate change might just be something worth talking about.  It's always good to try to change a 75 year old's mind, right?

Why BWI to ask?  Well, I grew up, and my parents still live, two miles from BWI as the planes fly (if you draw a straight line from one of the runways, south eastward, you go right through my parents backyard).  Here's proof:

OK, that's not really proof, but you'll just have to trust me, planes fly over that house all day, and all night...all year...nonstop. I blocked out the address to prevent the paparazzi from hounding my parents when the brilliance of this post leaks out.

Where was I?

Oh yeah, definitive proof of climate change so I can stick it to my parents. 

Here's a graph of official annual precipitation readings at BWI from 1951-2017. Here's a link to the data.  The blue dots are rainfall in inches.  The black line is a simple linear regression line to show the trend (we all like simple linear regressions, right)?

There you have it.  Definitive proof that...well..proof of something.  Take that mom and dad!

I'm not an expert at statistics or anything (ok, maybe I am), but that looks like rainfall totals have been trending upward at BWI since 1951.  

"But wait!," you say, "it looks like 1999 was screwy and couldn't that be pulling the slope of that fake regression line upward?"

That's mighty astute of you.  Yes it could.  And not only that, this graph doesn't control for month-to-month variations that may affect annual totals.  I'll bet you didn't think of that, oh-astute-reader, did you? 

So let's look at the year-over-year monthly trend in rainfall at BWI from 1951-2017:

A couple of observations:

1. The screwy 1999 number seems to be driven by a weird observation in October of 1999--Did BWI really get over 40 inches of rain in October of 1999?  I'll look into that for you.
2. 75% of the months (9 out of 12) show an upward trend in rainfall totals from 1951-2017.  Three do not (February, March and November).  February isn't a real month so we can throw that out (how do you count an extra day once every 4 years?).  The trends in March and November look pretty flat.

So there you have it.

Conclusive proof that my parents need to stop telling their friends that I "Still believe in that climate change hoax."