New and Noteworthy: 2023 Adjusted and Homogenized Canadian Climate Data (AHCCD) Now Available

Historical climate data are crucial for researchers, policymakers, and anyone interested in analyzing long-term past climate trends. Did you know that ClimateData.ca offers a range of historical datasets? This blog introduces the newly released 2023 Adjusted and Homogenized Canadian Climate Data (AHCCD), an important update for anyone studying historical climate trends and patterns in Canada, and guides readers through the various other historical datasets available on the site.

New AHCCD Data Now Available!

ClimateData.ca has just updated its platform with the latest 2023 AHCCD temperature data. This dataset is valuable for anyone interested in studying historical climate trends.

The AHCCD consists of climate station data that have been adjusted to account for non-climatic factors, which can influence the recorded data but are unrelated to the weather conditions that actually took place. For example, climate data records can be affected by changes in recording instruments, observing procedures, station relocation, or alterations in the surrounding environment (e.g., tree growth creating shade). These non-climatic changes are detected and adjustments are made using statistical procedures to reduce their influence on the data. Additionally, some data are corrected for measurement techniques that are known to possibly lead to underestimates or overestimates. In addition, data from nearby stations are sometimes combined to create longer time series.

Ready to explore the new data? Download them now on ClimateData.ca.

If you want to learn more about the AHCCD data, we suggest reading this article. In it, you’ll find links to research papers and technical documents.

ClimateData.ca’s AHCCD in action

The Okanagan Basin Water Board (OBWB) utilized the Adjusted and Homogenized Canadian Climate Data (AHCCD) from ClimateData.ca to develop the Okanagan Indicators Dashboard. This tool allows users to explore how weather patterns and water quality in the Okanagan Valley have shifted over time. The AHCCD dataset is particularly vital for understanding long-term trends in temperature and precipitation, especially given the challenges of inconsistent historical records in the region. The dashboard features over 30 climate change indicators, including temperature, precipitation, lake inflows, and streamflow categories, all based on direct, physically measured observations. This is especially important for regions like the Okanagan, where historical data is sparse. Sandra Schira, one of the lead developers of the project notes, “the ability to present these changes with data from actual thermometers, rather than models, has been instrumental in communicating the realities of climate change to local decision-makers and residents.” By focusing on accessible data presentation, the dashboard aims to make this critical information available to a broad audience, without requiring users to engage in complex statistical analysis.

Historical Data on ClimateData.ca

In addition to AHCCD, ClimateData.ca provides access to many other types of historical climate data:

  1. Observed Station Data: These are raw weather observations collected by surface weather stations. They are ideal for examining past conditions recorded by meteorological instruments and include temperature, wind, dew point, humidity, and more. You can download station data through ClimateData.ca by visiting the Download page.
  2. Gridded Historical Data (ANUSPLIN): This dataset (also known as NRCANmet) has been created by using statistical interpolation techniques and observed station data to derive gridded estimates of temperature and precipitation across Canada. These techniques consider elevation as well as the location of the weather stations and result in a comprehensive spatial representation (at a resolution of ~ 6 km x 10 km) of the historical climate of Canada. These gridded temperature and precipitation datasets have been used to derive many of the climate indices available on ClimateData.ca. You can download ANUSPLIN data from ClimateData.ca’s Interactive Map page. On the map, first choose a variable of interest, then zoom in and click on a grid cell. In the menu above the time series plot, select “Annual Values” from the Options menu and then click on GRIDDED HISTORICAL DATA in the legend above the chart. Use the Download option to obtain the chart data in csv format – if the GRIDDED HISTORICAL DATA option has been selected, the csv file will contain the ANUSPLIN data.
  3. Climate Normals: Climate Normals describe the average climate conditions of a particular location over a 30-year period (e.g., 1971-2000, 1981-2010, 1991-2020). At the end of each decade, Environment and Climate Change Canada calculates a new set of Climate Normals using station observations from that decade. All member countries of the World Meteorological Organization calculate Climate Normals. Because they describe the most recent average climate conditions for a location, they are often used to put extreme events into context. You can view Climate Normals data on ClimateData.ca’s Interactive Map page, or download them directly from the Download page.
  4. Modeled Historical Simulations: This dataset has been created using global climate models – these mathematical models simulate the Earth’s climate system by integrating the physical processes of the atmosphere, oceans, land surface, and ice. These models provide a representation of historical climate conditions by running simulations over a defined historical period using the observed atmospheric composition over that time period (e.g., greenhouse gas and aerosol concentrations). These data are bias corrected using the gridded historical data listed above, and will be quite similar to that data on average. It is made available for use in conjunction with future climate projections. You can Download both historical and future climate model projections (referred to as ‘Variable Data’ on ClimateData.ca) from the Download page.
  5. Adjusted and Homogenized Canadian Climate Data (AHCCD): This dataset consists of climate station data that have been adjusted to correct for non-climatic factors that influence observations, such as changes in instruments, observing procedures, or station relocations. These adjustments help remove errors introduced by such factors, ensuring that the data more accurately reflect actual climate trends. The AHCCD dataset is particularly valuable for analyzing long-term climate trends, as it removes the effects unrelated to climate from the data for variables like temperature and precipitation. By homogenizing the data, the AHCCD enables more accurate trend analysis and climate research. You can download AHCCD (temperature and precipitation only) from the Download page.

Need some more help choosing a dataset?

The article Which Historical Data Set Should I Use? on ClimateData.ca’s Learning Zone provides a detailed guide to help users choose the appropriate historical climate dataset for their needs.