Overview

Adjusted and homogenized Canadian climate data (AHCCD) consist of daily, monthly, seasonal and annual totals of daily adjusted rain, snow and total precipitation (millimetres) for 467 locations in Canada. The time periods of the data vary by location. Data availability over most of the Canadian Arctic is restricted to the mid-1940s to 2017. AHCCD was developed for use in climate research, including climate change studies as the assessment of long-term trends in Canada’s climate.

Provider's contact information

Environment and Climate Change Canada

Contact info.cccs-ccsc@canada.ca for information related to monthly, seasonal and annual data.

Contact ec.dccah-ahccd.ec@canada.ca for information relate do daily data.

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.

Citation:

Variable name and units:

Rain (mm),

Snowfall (mm)

Total precipitation (mm)

Spatial coverage and resolution:

Canada, point location.

Temporal coverage and resolution:

Time period varies per station with data for most stations in the North starting in mid-40’s or 50’s and ending in 2017.

The data is available at daily, monthly, seasonal, annual time steps.

The data will continue to be updated regularly.

Information about observations (number, homogeneity)

The following table presents the number of stations per region and daily variable:

The figure below show the position of the stations for northern Canada.

Note: A larger set with daily data (3346 stations instead of 467 stations across Canada) exist at http://open.canada.ca/data/en/dataset/d8616c52-a812-44ad-8754-7bcc0d8de305. This dataset is not part of AHCCD product because it was produced without joining of stations, however, it is using the same adjustments/corrections as the AHCCD precipitation data.

Methodology

The daily AHCCD station data are derived from observations made at the weather stations from the Meteorological Service of Canada (MSC) and use the same ID as MSC stations; this allows users to compare the raw station data to adjusted data. The AHCCD dataset was developed for use in climate research, including climate change studies that needs long-term data records. Also several variables were processed, the method used to adjust and homogenize station data differs for each variable. Adjusted precipitation datasets accounts for a number of known errors in precipitation measurements. The methods to adjust daily rainfall and snowfall are described in Mekis and Vincent (2011).

The adjustment of rain and snow was done separately (allowing the correction of known problems such as instrument deficiencies and changes in observing procedures) and used just measurements that were made by observers (they do not include any automatic measurements).

First, rain gauge measurements of precipitation are known to underestimate amount of actual precipitation due to the loss of rain water from the instruments during periods of high intensity rainfall. Field experiments have been undertaken at various locations to quantify these biases and correct them for the types of rain gauges used by the MSC.

Second, ruler measurements have been used historically to measure snow depth and an assumed density of 100 kg m-3 was used to convert snow depth to snow water equivalent. However, AHCCD data use more accurate density estimates that vary geographically across the country. Snow tends to be denser in the east and north of the country, and less dense in the west. Also, daily precipitation amounts below a minimum measurable amount were set to a value of zero in the past. However, the accumulated impact of these trace amounts can become significant, especially in areas like the Arctic where precipitation amounts are low. Adjustments were applied to account for this underestimation by assigning a value to these trace days: 0.1 mm was applied for rain, whereas for snow the adjustment factor ranged from 0.03 to 0.07 mm depending on the station location.

Finally, nearby observations were sometimes joined and adjustments were applied based on a simple ratio computed using available periods of overlapping data. For more information, please see Mekis and Vincent (2011).

Daily total precipitation was calculated by adding the station’s adjusted daily rain gauge and snow ruler observations together. Monthly rain, snow and total precipitation were calculated by adding the station’s daily rain gauge, snow ruler and total precipitation observations, over the month. A monthly value is missing if more than 3 consecutive days or more than 5 random days are missing in the month; a seasonal/annual value is missing if at least one month is missing in the respective season/year.

Information about the technical and scientific quality

The data were quality controlled (information is provided in Mekis and Vincent 2011). The dataset is accompanied by a technical documentation and a scientific paper.

Over the past decade, precipitation monitoring technology has evolved and Environment and Climate Change Canada and its partners implemented a transition from manual observations to using automatic precipitation gauges. The update of historical adjusted precipitation data has been on temporary hiatus since autumn 2017 to enable the data integration required to link the current precipitation observations from automatic precipitation gauges to the long-term historical manual observations. Updates will resume once this extensive data reconciliation effort is complete.

Limitations and strengths for application in North Canada

The data constitute the longest records at stations that were adjusted for known measurement issues such as wind undercatch, evaporation and wetting losses for each type of rain gauge, snow water equivalent from ruler measurements, trace observations and accumulated amounts from several days. As a result of adjustments, total rainfall amounts have increased by more than 20% in the Canadian Arctic, compared to the original observations, while the effect of the adjustments on snowfall was larger and more variable throughout the country. Observations from nearby stations were sometimes combined to create time series that are longer; hence, making them more useful for trend studies. This dataset is usually used to validate other historical datasets estimated using various models or methodologies.

The major limitation for applications in the North is the number restrained of locations with a record. Also, the data availability over most of the Canadian Arctic is restricted to the mid-1940s to 2017. As any data at stations, it has missing values, which may vary by variable, station and time. The missing values in daily records were taken into account when monthly, seasonal and annual data was developed (see methodology section).

References to documents describing the methodology or/and the dataset

Mekis, E. and L.A. Vincent, 2011: An overview of the second generation adjusted daily precipitation dataset for trend analysis in Canada. Atmosphere-Ocean, 49(2), 163-177.

Xu (2012) Homogenization of Canadian in-situ precipitation data, Final Report of Contract KM040-09-1134.

Technical documentation:

http://crd-data-donnees-rdc.ec.gc.ca/CDAS/products/EC_data/AHCCD_daily/Adj_Precipitation_Documentation_Daily.doc

Link to download the data and format of data:

For daily data:

The large set with daily data (3346 stations instead of 467 stations across Canada) without joining of stations: http://open.canada.ca/data/en/dataset/d8616c52-a812-44ad-8754-7bcc0d8de305

The second generation of daily data with joining of stations:

http://crd-data-donnees-rdc.ec.gc.ca/CDAS/products/AHCCD_daily/ (.txt on CRD/ECCC webpage)

https://climatedata.ca/download/#ahccd-download (this will be available in the following months)

For monthly, seasonal and annual data (second generation of daily data with joining of stations):

https://climate-change.canada.ca/climate-data/#/adjusted-station-data (GeoJSON and CSV on CCCS/ECCC webpage)

http://crd-data-donnees-rdc.ec.gc.ca/CDAS/products/AHCCD/ (.txt on CRD/ECCC webpage)

On MSC Datamart at https://dd.weather.gc.ca/climate/ahccd/geojson/historical/ (GeoJSON)

Publications including dataset evaluation or comparison with other data in northern Canada.

This dataset is usually used as reference in the evaluation of climate variables from other datasets.

Adjusted precipitation was used in a number of climate trends studies including the trends in annual and seasonal temperature and precipitation in Canada (Vincent et al., 2015, Zhang et al., 2000), changes in temperature and precipitation daily indices (Vincent et al., 2018, Vincent and Mekis, 2006 and Mekis and Vincent, 2011) and global changes in daily and extreme temperature and precipitation (Alexander et al., 2006).