Historical and Homogenized Temperatures for Canada
Update to December 2008
Background
A database of homogenized and long-term temperature time series has been specifically designed
for climate change analyses over Canada. The data consist of daily maximum, minimum and
mean temperatures for 210 locations across the country. Series extend back to 1895 where
possible: however, data availability over most of the Canadian Arctic is restricted to the mid1940s to present. The original data includes daily station temperatures extracted from the
National Climate Data Archive of Environment Canada. It was necessary in some cases to join
short-term station segments to create long-term series; the list of the joined stations can be
obtained from the author. Using a technique based on regression models (Vincent, 1998), annual
maximum and minimum temperature series were tested for “relative homogeneity” with respect
to surrounding stations. The methodology involves the identification of inhomogeneities in the
temperature series, which are often non-climatic steps due to station alterations including changes
in site exposure, location, instrumentation, observer, observing program, or a combination of the
above. Monthly adjustments were derived from the regression models, and adjustments were
applied to bring each homogeneous segment into agreement with the most recent homogenous
part of the series (Vincent and Gullett, 1999). Daily adjustments were derived from an
interpolation technique using the monthly adjustments (Vincent et al. 2002). Whenever possible,
the main causes of the identified inhomogeneities were retrieved through historical evidence such
as the inspector reports. For more information, please contact Lucie Vincent at
Lucie.Vincent@ec.gc.ca.
Naming convention and file format for monthly homogenized temperatures
Filenames are mx9999999.txt, mn9999999.txt and mm9999999.txt for monthly maximum,
minimum and mean temperatures respectively and 9999999 represents the 7-digits station
identification number. These files are grouped together by province and territories following the
naming convention tx_mly_zz.zip, tn_mly_zz.zip, tm_mly_zz.zip for monthly mean maximum,
minimum and mean temperatures respectively where “zz” is the abbreviation for the province or
territory.
Within each file, the first line outlines the station characteristics (identification number, name,
province, station joined or not, element, unit, last update). The second line identifies the content
of each column (Year, Jan to Dec, Annual, Winter, Spring, Summer, Autumn). Each temperature
value is followed by its respective flags. The record format is: i4,1x,17(f7.1,1x,a1,1x). The data
are in a comma-delimited format, which can easily be retrieved by packages such as Excel.
Missing values are identified as "-9999.9". The data flags are as follows: "M" indicates a missing
value, "E" a value that has been estimated during the archiving process, "e" a value that has been
estimated using the neighbouring stations, and "a" a value that has been adjusted due to
homogeneity assessment. The absence of a flag indicates an original, unaltered value.
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Naming convention and file format for daily homogenized temperatures
Filenames are dx9999999.txt, dn9999999.txt and dm9999999.txt for daily maximum, minimum
and mean temperatures respectively and 9999999 represents the 7-digits station identification
number. These files are grouped together by province and territories following the naming
convention tx_dly_zz.zip, tn_dly_zz.zip, tm_dly_zz.zip for daily maximum, minimum and mean
temperatures respectively where “zz” is the abbreviation for the province or territory.
Within each file, the first line outlines the station characteristics (identification number, name,
province, station joined or not, element, unit, last update). The data appear as year and month
followed by 31 daily values with their flags. The record format is i4,1x,i2,1x,31(f7.1,a1). Missing
values are identified by "-9999.9". The data flags are as follows: "M" indicates a missing value,
"E" a value that has been estimated during the archiving process, "e" a value that has been
estimated using the neighbouring stations, and "a" a value that has been adjusted due to
homogeneity assessment. The absence of a flag with any datum indicates an original and
unaltered value.
REFERENCES
Vincent, L.A., X. Zhang, B.R. Bonsal and W.D. Hogg, 2002: Homogenization of daily
temperatures over Canada. Journal of Climate, 15, 1322-1334.
Vincent, L.A., and D.W. Gullett, 1999: Canadian historical and homogeneous temperature
datasets for climate change analyses. International Journal of Climatology, 19, 1375-1388.
Vincent, L.A., 1998: A technique for the identification of inhomogeneities in Canadian
temperature series. Journal of Climate, 11, 1094-1104.
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