Adjusted and Homogenized Canadian Climate Data - AHCCD

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Summary Description

The Adjusted and Homogenized Canadian Climate Data (AHCCD) are climate station datasets of quality-controlled and homogenized historical climate data from Environment and Climate Change Canada (ECCC). It provides long-term station-based observations for temperature, precipitation, wind and atmospheric pressure across Canada. The datasets incorporate adjustments to the historical station data for non-climatic factors (e.g., station relocations, site exposure, instrumentation changes, observer, observing procedures) to ensure consistency and reliability. AHCCD data was developed for climate research, climate change studies and trend analysis.

AHCCD_temperature_stations

AHCCD Temperature Stations with starting dates prior to 1990 (blue), starting dates from 1990 (green), and stations closed but more than 30 years of data (red).
(figure taken from Vincent et al. (2020))1

Dataset Characteristics

Key Strengths of AHCCD

Strength Description
Homogenized Time Series Adjustments remove artificial shifts due to non-climatic influences, enabling accurate trend analysis.
Long-Term Coverage. Many stations provide over 100 years of data for studying climate variability and change.
National Consistency Standardized methodologies applied across the Canadian network.
Data Source for ECCC’s Climate Indicators Used in the development of Canadian climate change indicators and official climate assessments.

Limitations of AHCCD

Limitation Description
Station Coverage Gaps Sparse in some northern or remote regions, limiting spatial completeness.
Point Locations Station-based data may not represent broader regional conditions, particularly in more northern station sparse areas where the next station my be far away and in complex terrain where local conditions change over short distances.
Varying temporal coverage The lenght of the data records vary by station. There may be gaps in the stations data or a station may have been retired. While the dataset is updated annually, the latest observation data may not have been processed.
Historical Instrumentation Issues Despite adjustments, some uncertainties remain from early observational practices.

Expert Guidance

Environment and Climate Change Canada (ECCC) produces the Adjusted and Homogenized Canadian Climate Data (AHCCD) for use in climate research and climate change studies and have been used in the production of climate trends2 ,3. The data are collected from Reference Climate Stations and some Canadian Aviation Weather Service stations. They are different from the official Meteorological Service of Canada (MSC) in situ records and should not be used for legal purposes. The AHCCD station IDs are the same as those of the MSC stations to facilitate comparison.

The data are point data and may not represent the climate values for a larger region. Althought the time series are quality controlled there may be missing values in the data, varying by variable station and time (see figure above).

In some instances AHCCD data from nearby stations may be merged to create a longer record. The length of the records for individual stations may vary significantly, and some records are from stations that have been closed.

The non-climatic shifts in tempertature data are identified by statistically comparing adjacent stations. Station metadata are investigated to understand non-climatic causes and determine a corrective measure if a shift has been identified. A recurring adjustment is related to the change in observing time at principal stations in 1961. The correction of the temperature record results in a slightly stronger warming in the homogenized dataset than the unadjusted data: For southern Canada this trend changed from 1.32° to 1.62°C for 1900–2018, with a smaller change for all of Canada.1

Precipitation data correction accounts for a number of known errors in precipitation measurements, such as underestimation of actually gauged precipitation and limits to the minimum measurable amount. Snow measurements adjust for varying snow density depending on geographical location. Updates of historical adjusted precipitation has been interrupted since Autumn 2017. This hiatus is related to the integration of manual observations to an increasingly automated station network. Updates are planned to be resumed, but no time has been specified.

For wind speed adjustements the key measures is the standardization of the measuring height at 10m above ground based on meta data and the measurement instrument setup. Furthermore, non-climatic causes of shifts in wind speed are identified by comparing monthly means at stations to modeled monthly means.

With respect to the sea level and station pressure data non-climatic shifts that AHCCD data are corrected for are related to station elevation, station relocation and errors during digitization of paper records. This process scans for example for unusually high or low values, sudden extremes or physically implausible pressure changes.

More details on the methodology can be found in the AHCCD Technical Documentation and the references therein.

Example Applications

links to Electricity Sector Applications

Variables available in AHCCD

For details click on variable group to uncollapse

Daily temperature values
  • Minimum temperature [˚C]
  • Maximum temperature [˚C]
  • Mean temperature [˚C]
  • >330 locations in Canada

For more details see the website on daily AHCCD data

Monthly, seasonal, and annual mean
  • Minimum temperature [˚C]
  • Maximum temperature [˚C]
  • Mean temperature [˚C]
  • 780 locations in Canada

For more details see the AHCCD Technical Documentation and the Adjusted and homogenized Canadian climate data web page for temperature data and references therein.

Daily precipitation values
  • Daily liquid precipitation (rain) [mm/period]
  • Daily solid precipitation (snow) [mm/period]
  • Daily total precipitation (rain and snow) [mm/period]
  • >460 locations in Canada

For more details see the website on daily AHCCD data

Monthly, seasonal, and annual mean
  • Liquid precipitation (rain) [mm/period]
  • Solid precipitation (snow) [mm/period]
  • Total precipitation (rain and snow) [mm/period]
  • 467 locations in Canada

For more details see the AHCCD Technical Documentation and the Adjusted and homogenized Canadian climate data web page for precipitation data and references therein.

Monthly, seasonal and annual means of hourly wind speed
  • Wind speed [m/s]
  • Evaluated at standard 10 metre level
  • 156 locations in Canada

For more details see the AHCCD Technical Documentation and the Adjusted and homogenized Canadian climate data web page for wind speed data and references therein.

Monthly, seasonal and annual means of hourly measurements
  • Station level pressure [Pa]
  • Sea Level pressure [Pa]
  • 626 locations in Canada

For more details see the AHCCD Technical Documentation and the Adjusted and homogenized Canadian climate data web page for wind speed data and references therein.

Data Access

Daily AHCCD station data can be found on ClimateData.ca or downloaded via the Climate Data Extraction Tool (Monthly, seasonal and annual AHCCD station data). A collection of all daily AHCCD station data in a single netCDF file is available on PAVICS.

References

1.
Vincent, L. A., Hartwell, M. M. & and, X. L. W. A third generation of homogenized temperature for trend analysis and monitoring changes in canada’s climate. Atmosphere-Ocean 58, 173–191 (2020).
2.
Vincent, L. A. et al. Observed trends in canada’s climate and influence of low-frequency variability modes. Journal of Climate 28, 4545–4560 (2015).
3.
Vincent, L. A., Zhang, X., Mekis, É., Wan, H. & and, E. J. B. Changes in canada’s climate: Trends in indices based on daily temperature and precipitation data. Atmosphere-Ocean 56, 332–349 (2018).
4.
Wan, H., Wang, X. L. & Swail, V. R. A quality assurance system for canadian hourly pressure data. Journal of Applied Meteorology and Climatology 46, 1804–1817 (2007).
5.
Wan, H., Wang, X. L. & Swail, V. R. Homogenization and trend analysis of canadian near-surface wind speeds. Journal of Climate 23, 1209–1225 (2010).
6.
Mekis, É. & Vincent, L. A. An overview of the second generation adjusted daily precipitation dataset for trend analysis in canada. Atmosphere-Ocean 49, 163–177 (2011).