Historical Adjusted Precipitation for Canada
Update to December 2008
Background
Long-term historical adjusted precipitation time series has been specifically designed for
climate change analyses over Canada. The data consist of rainfall, snowfall and total precipitation
for 462 locations across the country. Series extend back as much as possible: however, data
availability over most of the Canadian Arctic is restricted to the mid-1940s to present. The
original data includes daily station rainfall and snowfall extracted from the National Climate Data
Archive of Environment Canada.
The methodology follows the steps described in Mekis and Hogg (1999). Adjustments
were applied on daily values for rain and snow separately. For each rain gauge type, corrections
to account for wind undercatch, evaporation, and gauge specific wetting losses were
implemented. The details of rain gauge corrections are further explained in Devine and Mekis
(2008). For snowfall, density corrections based upon coincident ruler and Nipher measurements
were applied to all snow ruler measurements (Mekis and Hopkinson, 2004).
In Canada, when a station is relocated, a new identification number is often given to the
new location and the two station’s observations can be combined in order to create longer time
series. Adjustments obtained from standardized ratios between the tested site and neighbours or
overlapping observations were applied for the joining of observations from several stations
(Vincent and Mekis, 2009). The list of the joined segments by stations along with the joining
dates and applied adjustments can be obtained from the author.
Trace observations are important especially on the Canadian Arctic. The measurement of
trace precipitation in Canada went through several phases over time. Great care was given to
properly account the trace observation (Mekis, 2005). Two versions are provided for the user
community: stations with all adjustments including trace correction and stations with all
adjustment not including the trace adjustment. For more information, please contact Eva Mekis at
Eva.Mekis@ec.gc.ca.
Naming convention and file format for monthly adjusted precipitation
Filenames defined as mr9999999.txt, ms9999999.txt and mt9999999.txt for monthly rain,
snow and total precipitation respectively where 9999999 represents the 7-digits station
identification number. These files are grouped together by province and territories following the
naming convention art_mly_zz.zip, ast_mly_zz.zip, apt_mly_zz.zip for adjusted monthly rain,
snow and total precipitation with trace corrections respectively, where “zz” is the abbreviation for
the province or territory. Similarly the ar_mly_zz.zip, as_mly_zz.zip and ap_mly_zz.zip stands
for the adjusted monthly rain, snow and total precipitation without trace corrections.
Within each file, the first line contains 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). The
seasons are defined as: Winter: DJF, Spring: MAM, Summer: JJA and Autumn: SON; the first
winter is always missing (-10.0). Each precipitation value is followed by its respective flags.
Since the monthly value is the total of the daily values, no flag displayed. For further information
on flags, please go to the original daily values. The record format is: i4,1x,17(f8.1,1x,a1,1x). The
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data are in a comma-delimited format, which can easily be retrieved by packages such as Excel.
Missing values are identified as "-9999.9" with the flag "M".
Naming convention and file format for daily adjusted precipitation
Filenames defined as dr9999999.txt, ds9999999.txt and dt9999999.txt for daily rain, snow
and total precipitation respectively where 9999999 represents the 7-digits station identification
number. These files are grouped together by province and territories following the naming
convention art_dly_zz.zip, ast_dly_zz.zip, apt_dly_zz.zip for adjusted daily rain, snow and total
precipitation with trace corrections respectively, where “zz” is the abbreviation for the province
or territory. Similarly the ar_dly_zz.zip, as_dly_zz.zip and ap_dly_zz.zip stands for the adjusted
daily rain, snow and total precipitation without trace corrections.
Within each file, the first line contains 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(f8.2,a1).
The data are in a comma-delimited format, which can easily be retrieved by packages such as
Excel. Each precipitation value is followed by its respective flags. The list of flags applied:
'X'
'Y'
'Z'
'M'
'T'
'A'
'C'
'F'
'L'
Joined station, earlier record was adjusted to match the later record using
standardized ratios based on annual values
Joined station, earlier record was adjusted to match the later record using
standardized ratios based on long series
Joined station, earlier record was adjusted to match the later record using
standardized ratios based on monthly values
Missing data
Trace event; precipitation occurred but less than measurable amount. Original
archive value is 0.
Accumulated amount; previous value must be flagged C or L (i.e. period of
accumulation)
Precipitation occurred, amount uncertain; value = 0
Accumulated and estimated
Precipitation may or may not have occurred; amount uncertain; value = 0
REFERENCES:
Devine, K.A. and É. Mekis, 2008: Field accuracy of Canadian rain measurements. AtmosphereOcean 46 (2), 213–227.
Mekis É. and W.D. Hogg, 1999: Rehabilitation and analysis of Canadian daily precipitation time
series. Atmosphere-Ocean 37(1), 53-85.
Mekis, É. and R. Hopkinson, 2004: Derivation of an improved snow water equivalent adjustment
factor map for application on snowfall ruler measurements in Canada. 14th Conf. on
Applied Climatology, Seattle, USA. 7.12.
Mekis, É., 2005: J3.7 Adjustments for trace measurements in Canada. 15th Conference on
Applied Climatology, Savannah, Georgia, USA, 20-24 June 2005,
Vincent, L.A. and É. Mekis, 2009: Discontinuities due to joining precipitation station
observations in Canada, Journal of Applied Meteorology and Climatology, Vol. 48, No. 1,
156–166.
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