AHCCD

1. Overview of AHCCD

  • Purpose: Adjusts historical climate station data to remove non-climatic factors such as station relocation, changes in instrumentation, or observer differences.

  • Developed for: Climate change studies, historical climate research, and policy-making.

  • Key Adjustments:

    • Correction of biases in precipitation measurements.

    • Integration of nearby station data to create longer time series.

    • Homogenization of temperature, precipitation, wind, and pressure records.

Key Features

Feature

Description

Time Coverage

1840 – 2019 (varies by station and variable)

Geographical Coverage

Point locations across Canada

Temporal Resolution

Monthly, seasonal, annual

Variables

Temperature, precipitation, wind speed, air pressure

Primary Use

Climate trend analysis, research, adaptation planning

2. Climate Variables and Data Formats

AHCCD provides homogenized and adjusted datasets for the following key climate variables:

2.1 Temperature Data

  • Maximum Temperature (°C): Highest daily value for each month/season.

  • Minimum Temperature (°C): Lowest daily value for each month/season.

  • Mean Temperature (°C): Average of max/min values.

  • Dataset Coverage: 780 locations across Canada.

  • Historical Range: Mid-1800s to present (varies by station).

2.2 Precipitation Data

  • Rainfall (mm): Total daily/monthly/seasonal rain accumulation.

  • Snowfall (mm): Snow water equivalent based on density correction.

  • Total Precipitation (mm): Sum of rainfall and snowfall.

  • Dataset Coverage: 467 locations across Canada.

  • Historical Range: 1880s to present.

2.3 Wind Speed Data

  • Measured at: 10-meter height (standardized).

  • Units: Kilometers per hour (km/h).

  • Dataset Coverage: 156 locations.

  • Historical Range: 1953 to present.

2.4 Pressure Data

  • Station Pressure (Pa): Surface-level pressure.

  • Sea Level Pressure (Pa): Pressure adjusted to mean sea level.

  • Dataset Coverage: 626 locations.

  • Historical Range: 1953 to present.

3. Data Homogenization & Adjustments

3.1 Temperature Adjustments

  • Objective: Remove non-climatic shifts caused by station relocation, observer changes, or instrument upgrades.

  • Method: Comparison with neighboring stations to detect discontinuities.

  • Technique Used: Quantile-Matching Adjustment to correct bias.

3.2 Precipitation Adjustments

  • Corrections for:

    • Wind undercatch (underestimation of snowfall).

    • Evaporation losses.

    • Trace precipitation underestimation (below measurement threshold).

  • Adjustment Methods:

    • Gauge-specific correction factors.

    • Density-based snow-to-water conversion adjustments.

    • Trace precipitation values assigned (e.g., 0.1 mm for rain, 0.03-0.07 mm for snow).

3.3 Wind Speed Adjustments

  • Correction for: Non-standard measurement heights.

  • Process:

    • Wind speeds adjusted to 10-meter reference height.

    • Comparison with model-based estimates to remove biases.

3.4 Pressure Data Adjustments

  • Corrections for:

    • Station relocation errors.

    • Incorrect elevation values used in past pressure reductions.

  • Adjustment Methods:

    • Historical metadata cross-referencing.

    • Identification of extreme or unrealistic values.

4. Methods for Climate Trend Calculation

  • Method Used: Theil-Sen Estimator (robust regression).

  • Conditions for Trend Calculation:

    • Time series must have <10% missing data.

    • Gaps longer than 5 years disqualify trend analysis.

  • Trend Products:

    • Seasonal and annual climate change trends for Canada.

    • Regional trend assessments.

5. Station List & Data Availability

5.1 Station Lists

  • Temperature: Link

  • Precipitation: Link

  • Wind Speed: Link

  • Pressure: Link

6. Applications & Use Cases

6.1 Climate Change Research

  • Monitoring long-term warming trends across Canada.

  • Evaluating regional temperature & precipitation anomalies.

  • Calibrating climate models for future projections.

6.2 Disaster Risk Reduction & Adaptation

  • Tracking changes in extreme weather (heatwaves, droughts).

  • Assessing regional flood & drought risk.

  • Informing infrastructure resilience planning.

6.3 Policy & Decision-Making

  • Supporting national climate adaptation policies.

  • Providing climate data for Canada’s carbon policy framework.

  • Guiding sustainable water & resource management strategies.

7. Limitations & Considerations

  • Data gaps may exist due to missing records.

  • AHCCD datasets are adjusted and should not be used as raw station data for legal applications.

  • For gridded (spatially interpolated) datasets, users should consult CANGRD (Canadian Gridded Climate Dataset).

8. Additional Resources & References

9. Conclusion

The Adjusted and Homogenized Canadian Climate Data (AHCCD) is a high-quality, long-term climate dataset that provides critical insights into Canada’s historical climate trends. By applying rigorous quality control and statistical adjustments, AHCCD ensures accurate, reliable climate records for research, policy-making, and environmental risk management.

It serves as an essential tool for tracking climate variability, assessing regional climate risks, and guiding adaptation strategies in Canada.

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