Iknow some of you are probably getting tired of me talking about rain, but I have one more discussion left in me before we move on to other weather topics. Maybe we’ll eventually get to discuss the perfect summer weather we are going to have!
I’ve received a number of emails and have heard several people mention they think our springs are getting wetter. So I figured I would poke around in the rainfall data and see just what is up. Now, the best way to look at weather data is to visually plot it out, and that is exactly what I did.
I took the period of 1970-2010 and graphed out the monthly rainfall totals for April, May and June, along with the total for those three months. When I first looked at the graph I found it confirmed what I was thinking all along: spring rainfalls, in general, have not been increasing in amount. If we look at the total line we see a fair bit of variability from year to year, but over the past 40 years there does not seem to be any trend toward wetter springs.
That was my first impression. Then I started to take a closer look at the data – in particular, pattern over the past 40 years. June rainfalls, just like the other months, are extremely variable from year to year, but to me the data looks fairly random.
So now if we go back and look at the total rainfall for this whole period (April to June), while we haven’t seen an increase in the total amount of precipitation (we saw wetter springs in the ’70s) there does seem to be an increase in the number of wet years starting around 1996. If we take out 2006, every year since 1996 has seen over 150 mm of rainfall during these three months.
Have the springs been getting wetter? I would have to say, overall, no. What seems to be happening is that Aprils seem a little more stable and dry, May seems to be getting wetter, and overall we’re seeing more springs in a row that are wet, with very few dry springs in between.
I have to point out as I finish up this week that this is simply a snapshot and general interpretation of the data. Will these possible trends continue? Who knows? What is driving these possible changes? Again, we don’t know, but at least now if you find yourself in a discussion about whether springs are getting wetter in southern Manitoba, you have a little bit of evidence to help you argue either way.