Extreme Weather Indices
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A suite of extreme weather indices has been created to help with agricultural decision-making. The indices are short-term weekly forecasts (for up to a month ahead) that predict risks to agricultural production from extreme weather factors related to temperature, precipitation, heat, and wind. New users may want to start with the Learn About link below. More experienced users may want to go directly to View the Maps and Downlod Data links.
Click on any of the four sections below to:
- Learn about the Extreme Weather Indices
- View the Extreme Weather Indices and Probability maps
- View the Map Production Schedule
- Download the Indices Datasets
Learn about the Extreme Weather Indices
Air temperature is a key factor affecting the development, yield and quality of field crops. How crops respond to temperature is characterized by three cardinal temperature indices which describe the minimum, maximum, and optimum temperatures for plants to start, stop, and advance development.
see Additional Terminology for crop definitions referred to below
- Frost Free Days:
The number of days in the forecast period with a minimum temperature above the threshold temperature at which frost damage occurs. This index has widely been used as an estimate for the length of a growing season.
The threshold temperature is −2°C for cool season crops, and 0°C for warm season crops.
- Cool Wave Days:
The number of days in the forecast period with a minimum temperature below the lowest threshold temperature at which crop growth will begin (cardinal minimum temperature).
The threshold temperature is 5°C for cool season crops and 10°C for warm season crops.
- Heat Wave Days:
The number of days in the forecast period with a maximum temperature above the threshold temperature at which crop growth ceases (cardinal maximum temperature).
The threshold temperature is 30°C for cool season crops, and 35°C for warm season crops.
- Ice Freeze Days:
The number of days in the forecast period with a minimum threshold temperature below the frost temperature:
- The threshold temperature is −2°C for herbaceous/woody crops during the growing season.
- The threshold temperature is −5°C for herbaceous crops and −10°C for woody crops (non-dormant over non-growing season).
- The threshold temperature is −15°C for herbaceous crops and −30°C for woody crops (dormant period).
Precipitation establishes yield potential and quality of field crops. Both extremely dry and extremely wet conditions have the ability to inhibit proper crop growth. The greatest daily precipitation index covers the risk of excessive precipitation in the short term.
Note that when selecting this indicator using the tool below users must also select the minimum precipitation threshold in millimetres for the accompanying probability map
- Greatest 10-day precipitation:
- The greatest 10-day precipitation total expected over 10 days.
- Greatest daily precipitation:
- The greatest daily precipitation over the forecast period.
- Total precipitation:
- The total precipitation over the forecast period.
Cumulative heat-energy is the fuel of crop growth and development and supports high yield and good quality of crop production.
- Effective Growing Degree Days:
The accumulated value of heat degrees that the daily average temperature is above a specified threshold temperature. This condition must be maintained for at least 5 consecutive days in order for effective growing degree days to be accumulated.
The threshold temperature is 5°C for cool season crops, and 10°C for warm season crops.
Winds can significantly influence crop growth and yield mainly due to: plant damage; greater plant water loss to the atmosphere; and the distribution of pests and diseases in the field. The maximum wind speed and the number of strong wind days over the forecast period represent short term and extended strong wind events respectively.
Note that when selecting the maximum wind speed indicator using the tool below users must also select the maximum wind speed in km/hr for the accompanying probability map
- Number of strong wind days:
- The number of days during the forecast period with an average wind speed greater than 30 km/h.
- Maximum daily wind speed:
- The maximum wind speed during the forecast period.
- Number of Drying Days:
- The number of days during the forecast period with an average wind speed greater than 30 km/h and a maximum temperature above 30°C.
Collaboration with Environment and Climate Change Canada (ECCC)
Agriculture and Agri-Food Canada (AAFC) and Environment and Climate Change Canada (ECCC) have together developed a suite of extreme weather indices based on four main categories of weather factors significant to agriculture: temperature, precipitation, heat, and wind. The extreme weather indices are intended as short-term prediction tools and generated using ECCC’s medium range forecasts to create a weekly index product on a daily (week 1 & 2 products) and weekly (week 3 & 4 products) basis.
The daily forecasts of weekly indices are generated using Environment and Climate Change Canada’s Global Ensemble Prediction System (GEPS) with 20+1 ensemble members. In all cases, the probabilities are calculated at each point by counting the number of members which forecast the event in question during the forecast period and dividing this by the total number of members.
Environment and Climate Change Canada and Agriculture and Agri-food Canada have assessed the skill level (predictability) of each forecasted extreme weather index by calculating the Heidke Skill Score (HSS) which compares the proportion of correct forecasts to a no skill random forecast.
For a more comprehensive and detailed look at the methodology, please refer to the following published paper, "The Prediction of extreme agrometeorological indices using the Canadian Meteorological Centre’s medium range forecast (PDF)"
- Cool season crops
- Require a relatively low temperature condition. Typical examples include wheat, barley, canola, oat, rye, pea, and potato. These crops normally grow in late spring and summer, and mature between the end of summer and early fall in the southern agricultural areas of Canada. The optimum temperature for such crops is 25°C.
- Warm season crops
- Require a relatively warm temperature condition. Typical examples include bean, soybean, corn and sweet potato. These crops normally grow during the summer season and early fall, then ripen in late fall in southern Canada only. Other agricultural regions in Canada do not always experience sufficiently long growing seasons for these plants to achieve maturity. The optimum temperature for such crops is 30°C.
- Over-wintering crops
- Are biennial and perennial field crops such as herbaceous plants (strawberry, alfalfa, timothy, and many other forage crops) and woody fruit trees (apple, pear, peach, cherry, plum, apricot, chestnut, pecan, grape, etc.). These crops normally grow and develop in the growing season and become dormant in the non-growing season. However, extreme weather and climate events such as cold waves in the growing season and ice freezing events during the winter are a major constraint for their success of production and survival in Canada. The winter survival of these plants depends largely on agrometeorological conditions from late autumn to early spring, especially ice-freezing damage during the winter season. The optimum temperature for such crops is 25°C.
- Herbaceous crops
- Herbaceous crops include plants that have non-woody stems and their above-ground growth largely (roots and bulbs remain) or totally dies back in winter. Field crops are mainly herbaceous.
- Woody crops
- Woody crops plants that have wood stems and buds that survive above ground in winter. Fruit and berry crops are examples of woody crops.
View Extreme Weather Indices and Probability maps
The tool below allows you to choose from among a dozen extreme weather index forecasts and view maps of both where the forecast is expected, and the forecast confidence.
Make your choices using the drop down menus, and then view the selected forecasted index in the first map, and the confidence (probability) of that forecast being correct in the second map. Note that selection options change throughout the season; if a selection in the pull-down menu is grey it is currently not available, but it will be later in the season.
Printable PDF maps of your choices can be downloaded using the link above the maps.
View the Map Production Schedule
Refer to the schedule below to understand when each extreme weather index map is available on Drought Watch or Open Data. The availability of the indices changes throughout the year.
Extreme weather indices: production schedule
week 1 and week 2 forecasted maps produced daily
week 3 and week 4 forecasted maps produced each Thursday
- April 1 to October 31 (Growing Season)
- Frost-free days for warm season crops (> 0°C)
- Frost free days for cool season / overwintering crops (> −2°C)
- Cool wave days for warm season crops (< 10°C)
- Cool wave days for cool/overwintering season crops (< 5°C)
- Heat wave days for warm season crops (> 35°C)
- Heat wave days for cool season crops (> 30°C)
- Ice freeze days (woody or herbaceous crops) during growing season (< −2°C)
- November 1 to March 31 (Winter Season)
- Ice freeze days (herbaceous crops) in dormant period (< −15°C)
- Ice freeze days (woody crops) in dormant period (< −30°C)
- Ice freeze days (herbaceous crops) during non-growing season (< −5°C)
- Ice freeze days (woody crops) during non-growing season (< −10°C)
- April 1 to October 31 (Growing Season)
- Effective growing season degree days for warm season crops (Daily only, 2 week forecast)
- Effective growing season degree days for cool season crops (Daily only, 2 week forecast)
- September 1 to August 31 (Agricultural Year)
- Greatest daily precipitation
- Total precipitation
- Greatest 10-day precipitation (Daily only, 10-day forecast)
- September 1 to August 31 (Agricultural Year)
- Number of strong wind days
- Number of drying days
- Maximum wind speed
Download the Indices Datasets
This option allows you to download the digital datasets. Select the Extreme Weather category below to access Extreme Weather Indices products and metadata on Open Data.
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