Overview
Canadian gridded temperature and precipitation anomalies (CANGRD) are datasets of historical gridded temperature and precipitation anomalies, interpolated from AHCCD at a 50 km resolution across Canada. This document is describing the precipitation data. Total precipitation anomalies represent the departure from a mean reference period (1961-1990) expressed as percentage change (%) from the mean reference period. Trends of relative total precipitation change (%) for 1948-2012 are also available for download.
Provider's contact information
Environment and Climate Change Canada (Contact the Climate Services Support Desk)
Electronic Mail Address at CRD: ec.ccds.info-info.dscc.ec@canada.ca
Licensing and citation
Open Government Licence - Canada.
The end-user licence for Environment and Climate Change Canada's data servers specifies the conditions of use of this data.
Variable name and units:
Total precipitation (mm)
Spatial coverage and resolution:
Canada, 50 km spatial resolution, polar stereographic grid.
Temporal coverage and resolution:
Precipitation anomalies: 1954-2014
Data is available at monthly, seasonal and annual time steps.
Information about observations (number, homogeneity)
CANGRD data is based on the AHCCD data and are available from 1948 for all of Canada, and from 1900 for southern Canada (south of 60°N). AHCCD has a small number of stations in North Canada, and the distance between stations is large. The AHCCD and CANGRD are usually updated annually in the spring.
Methodology
The monthly, seasonal and annual total precipitation anomalies are computed at each observing station and for each year by subtracting the relevant baseline average (defined as average over 1961-1990 reference period) from the relevant monthly, seasonal, and annual values. They are then normalized by dividing by the mean reference period and expressed in percentage to produce normalized precipitation departures. The anomalies are interpolated to the evenly spaced (50 km) grid in polar stereographic projection using the Gandin’s Optimal Interpolation. Values for grid boxes over large bodies of water such as Hudson Bay are excluded. The grid is a 125 (columns) by 95 (rows) matrix, where the SW corner (0,0) is at 40.0451°N latitude and 129.8530°W longitude. The projection is true at 60.0°N and centered on 110.0°W.
Information about the technical and scientific quality
A positive aspect of this dataset is the use of adjusted and/or homogenised data from the AHCCD (adjusted precipitation data). This station-based dataset has undergone rigorous quality control, and have been adjusted for identified inhomogeneities caused by station relocation, changes in instrumentation and in observing practices and are corrected for undercatch and regional variation in snowfall density following Mekis and Vincent (2011)
The dataset uses classical methods for the interpolation. In general, results from the interpolation of anomalies are better than those from actual values because anomalies vary less in space.
Data is available in .grd format on the CRD webpage. This format is not a standard format. Less advanced users should use the CCCS webpage to download GeoTIFF format. CCCS webpage offers the possibility to download the data in NetCDF format as well, but this is also not in the standard form (uses bands instead of time coordinate; this should be corrected by the end of August 2021).
The dataset is accompanied by a technical report.
Limitations and strengths for application in North Canada
The data was constructed to describe large-scale climate change over Canada and for national-scale assessments. Interpolation errors are expected to increase with the distance between stations. Because there is a small number of stations available in Northern Canada (most of them in coastal and valley locations), interpolation errors in inland regions and in Yukon high elevation regions can be significant. Consequently, the result should be interpreted as a mean change over a large region (e.g., the mean change over the North or a territory), and it is not recommended to be used for local applications.
Because it provides anomalies, not actual temperature values, it cannot be used to compute other climate indices.
Some users may find the data in .grd difficult to use because of its custom projection and format.
References to documents describing the methodology or/and the dataset
Environment and Climate Change Canada (2018). Canadian Gridded Temperature and Precipitation Anomalies CANGRD.
Milewska, E. and W.D. Hogg, 2001: Spatial representativeness of a long-term climate network in Canada. Atmosphere-Ocean 39(2): 145–161.
Milewska, E., R.F. Hopkinson and A. Niitsoo, 2005: Evaluation of Geo-Referenced Grids of 1961 – 1990 Canadian Temperature and Precipitation Normals. Atmosphere-Ocean 43 (1): 49-75.
Link to download the data and format of data:
https://climate-change.canada.ca/climate-data/#/historical-gridded-data (GeoTIFF and NetCDF on CCCS/ECCC webpage)
GeoTIFF data available on the MSC Datamart
http://crd-data-donnees-rdc.ec.gc.ca/CDAS/products/EC_data/CANGRD/ (gridded data .grd on CRD/ECCC webpage)
Publications including dataset evaluation or comparison with other data in northern Canada
Rapaić, M., R. Brown, M. Markovic, D. Chaumont, 2015: An evaluation of temperature and precipitation surface-based and reanalysis datasets for the Canadian Arctic, 1950–2010. Atmosphere-Ocean 53(3): 283–303. https://doi.org/10.1080/07055900.2015.1045825 (The paper compares CANGRD to several other gridded datasets and other coarse-resolution reanalysis)