In the comments last week, Joe mentioned that the reason the Blatchford data becomes unreliable in the mid-1990s might be because Environment Canada started using a different weather station at that time. And he's right, and a few months ago I even wrote a boring post about the different Blatchford stations, and the overlapping data that is available for some years.
From March 1995 through January 2005 both stations were in operation, and so there are two sets of data. When I had first looked at this I was mostly interested in temperature, so I compared that for the two stations:
Today I'm interested in precipitation, so here is how the monthly numbers compare over time:
It's more variable than I would have thought. Since the new Blatchford station's yearly data was low, I just assumed that it was missing data for some days. But if things were that simple, then the older station would always have higher numbers, and the chart would always be positive. Instead, we see quite a few dips into the negative, and the older station has more precipitation only about two-thirds of the time. On the whole though, over those 10 years the older station recorded 200mm more precipitation than the new one.
Comparing the two Blatchford stations to the other local stations really makes things clear though:
This shows the two Blatchford stations, as well as the International, UofA and Stony Plain.
My concern last week was the huge dip in the Blatchford numbers from 1995-2000, and we can see that the alternate data from the older station is much more consistent with the other local stations. All of the stations saw significant drops in the 2000-2002 range, but the newer Blatchford stations is hundreds of mm's lower than all the others.
That's definitive enough to make me go back to redo some of the charts from last week, with the data from the older Blatchford station replacing the unreliable newer one.
It's not a huge difference, but things don't fall off a cliff in 2000 the way they originally did. 2002 is still a dry year, but it rises from last place up to third last.
Original - new Blatchford Station
Updated - older Blatchford Station
And again, it's not a huge change. But it is nice to have a slightly cleaner version of this chart, and one that I can have a little bit more faith in.
Using this alternate data still doesn't change the fact that the Blatchford data is unreliable for 2007 onward, but at least now it looks pretty good for 1880 through about 2005. For any recent precipitation numbers I will still be relying on the Edmonton International.
No comments:
Post a Comment