Comparison of two different methods for adjusting Canadian precipitation, snowfall and rainfall data

1. Method: Source: NOAA National Climatic Data Center (NCDC), USA
Reference: TD-9816 "Canadian Monthly Precipitation", Groisman 1998
2. Method: Source: Meteorological Service of Canada, Climate Research Branch
Reference: Rehabilitation of Canadian Daily Precipitation Time Series, Mekis and Hogg, 1999 Historical Canadian Climate Database


1. Method

2. Method

Number of stations


495 best quality stations

Length of data


-1999, updated annually

Correction time-step



Rain correction




Type B rain gauge installation date

The same date (1975) is used for each station

Exact installation date is used for each station (starts in 1971 - see Figure 1)


Number of measurements per day

Mean value or surrounding station information is used

Varies with the type of station:

Climate stations: 2x

Synoptic stations: 4x


Trace correction


0.1 mm for each trace event. TOR (Trace Occurrence Ratio) is used to determine the number of measurements per day for the stations [see Mekis & Hogg, 1999]

Snow correction




Snow ruler and Nipher data were used

Only snow ruler data was adjusted (see comment 1 below.)


Snow ruler correction.

10:1 ratio + RAT values (Climatological Ratios) are computed on monthly level

Location specific snow density ratio is determined based on coincident snow ruler and adjusted Nipher gauge measurements [see Metcalfe et al. & Mekis & Hogg].


Trace correction


Correction depends on type (snow or ice crystal trace) and gradually decreases towards the North

.Correction also depends on measurement frequency [for details see Mekis & Hogg + metadata requirements listed below]



Station joining


186 stations are joined (out of 495)


Mekis, Éva and William D. Hogg, 1999: Rehabilitation And Analysis Of Canadian Daily Precipitation Time Series. Atmosphere-Ocean 37(1) 1999, 53-85.

Metcalfe, J.R., S. Ishida and B.E. Goodison, 1994: A corrected precipitation archive for the Northwest Territories. Environment Canada - Mackenzie Basin Impact Study, Interim Report #2, 110-117.

Groisman, P.Y. 1998. National Climatic Data Center Data Documentation for TD-9816, Canadian Monthly Precipitation. National Climatic Data Center 151 Patton Ave., Asheville, NC. pp. 21,

Figure 1. Distribution of the Type B installation year for the rehabilitated 495 precipitation locations

Figure 1.</B> Distribution of the Type B installation year for the rehabilitated 495 precipitation locations

Comment 1. : Decision was made that for century long climate change detection purposes the snow ruler data will be used to avoid the inhomogeneities -(introduced by the installation of the Nipher gauges) within and between the stations.

Metadata requirements for Method 2: