This blog protests why I will be using only 15 stations from across Canada to get a trend. So let's put that to bed right off.
The surface records at Environment Canada are at best pathetic. The number of stations peaked in the mid 1980's. This is the count of stations' starting years:
This graph shows the same trend, except this time the years are on the Y-Axis with the station count in the X-Axis.
Thus if you want 50 stations in the analysis it would have to start in year 1911 to prevent the lower number of stations before that data skewing the results. If you wanted 100 stations, it would have to start in 1930.
Recall that the warming trend that the AGW proponents says is happening is increasing in temps from 1850 to 1945, then a drop until 1975, then an increase since 1975. So starting the analysis too far from 1900 will not show a proper over all trend. Especially if, as we have seen in some of the stations, the warmest and coldest years were in the mid 1920's
Thus there is a trade off. The earliest is best, but that restricts us to 15 records.
The following analysis will look at 15 stations only, those that start in 1900 and have a good set of records. Not all of the stations that start in 1900 have continuous records, some have gaps, but it is the closest we will get to as long a recordset as possible. These 15 are the earliest with the most number of records (few gaps).
The 15 stations are from a wide range of stations across southern Ontario. Station data from the far north is so little so late that, if one wants to make claims of trends, one must put that in context of the duration of the records.
For example, Sach's Harbour, way up in the NWT doesn't have records before the mid 1950's. Hence any claim that the trend is increasing (it hasn't since 1970) is ONLY from the mid 1950's. With no prior data there is no way anyone can know what the over all trend is from 1900. Half that data range is no measure of trends.
This is the 15 stations used for the rest of these posts:
|2205||CALGARY INT'L A||Alberta|
|3328||SASKATOON DIEFENBAKER INT'L A||Saskatchewan|
|380||BELLA COOLA||British Columbia|
|588||FORT ST JAMES||British Columbia|
The other interesting problem that arises is which months to use. The ideal would be to use just July or August. But hot temps occur in other months, and depending on the method used to define a heat wave or hot day will be influenced by the months selected.
This is Station 5325's TMax range for all years:
Red line is the hottest record setting day (highest TMax in 109 years), the blue line is the minimum TMax, and the black is the average TMax. Notice the crest is mid July, but with a few above 30C prior to and after that.
Two of the tests in the next posts will be choosing a threshold temperature by a relative means. One will be the top 10% of hot records, the other being those above the upper second standard deviation. But including TMaxs from month's prior to the crest will lower the threshold.
Using this station as an example, using all the months the top 10% hottest records will return 1582 records (from a total of 15,812). The month distribution of those records looks like this:
However, looking at this from the percent of days in each month we get this:
So the top 10% of the hottest records will have 20% of those records from July. This isn't really the top 10% as it will get dominated by July temps that are actually below the 10% for July.
The other option is to pick just July for the top 10%. Take the lowest temp found in that, and use any days above that low TMax regardless of the month. If we do that we get the lowest temp at 28.3C, so any records above that value regardless of the month. This reduces the records significantly to 164 records. July still dominates at 75% of the records, but it produces a much closer definition of what constitutes a "hot" day for that location.
The other option is to use the top 10% for EACH MONTH so they are all equally weighed. The problem with that is that in May and Sept the top 10% hottest days aren't when compared to mid summer days.
So the best approach to determine what is a "hot" day is to use July as the baseline to find the lowest temp of the top 10% of July's hottest days, and use that lowest threshold to get all those hot days for that location. This process will also be used to get those temps above the upper second standard deviation.