Indicator Dictionary

This dictionary provides a high-level description of each indicator available through the Climate API.

Note

If you are trying to make an indicator REST API call, look up the indicator’s parameter details or follow how to make an indicator request.

In the explanations below, assume temperature and precipitation values are aggregated across all requested models for a specified period of time. For brevity, temperature refers to surface air temperature. Historic refers to 1950-2006.

Accumulated Freezing Degree Days

Accumulated Freezing Degree Days (AFDD) is calculated as the maximum consecutive sum of the difference from daily average temperature to freezing (0 °C). Because AFDD is minimally bounded at 0 during aggregation, the metric is somewhat resilient against warm outlier values. A higher AFDD suggests a colder period.

This indicator is a measure of the potential amount of freezing an area may experience during a specified period, and can be used to approximate maximum ice thickness. For more information on this use see Ice Engineering: Method to Estimate River Ice Thickness Based on Meteorological Data.

Average High Temperature

Average High Temperature is calculated by aggregating daily average high temperatures. It is an appropriate metric for probable long term temperature trends.

Average Low Temperature

Average Low Temperature is calculated by aggregating daily average low temperatures. It is an appropriate metric for probable long term temperature trends.

Cooling Degree Days

Cooling Degree Days (CDD) is the difference between a reference temperature and the daily average temperature for each day summed over some time span. For example, a day with average temperature of 80°F and a reference temperature of 65°F would equal 15 CDDs. CDD magnitude corresponds directly with warmth. CDD approximates air conditioning use, which accounts for roughly half of energy demand during the summer. The default reference temperature is 65°F.

Diurnal Temperature Range

Diurnal Temperature Range (DTR) is the average difference between the maximum temperature and minimum temperature in a day. It measures how much it heats or cools in a day. A decreasing DTR suggests a warming climatic trend but is only a rough measure as DTR can be skewed by many factors such as cloud cover, urban heat island effect, and aerosols.

Dry Spells

Dry Spells counts the total number of times per user-specified period that there are 5 or more consecutive days without precipitation. This indicator is useful to understand future drought patterns and inform resource planners of changes to prepare for.

Extreme Cold Events

Extreme Cold Events counts the total times the daily average minimum temperature is below some percentile of historic observations. The percentile defaults to 1, referring to the coldest percentile of historic daily temperatures. It is an appropriate indicator for understanding deviations from normal climatic extremes.

  • historic_range

    Optionally set the years used to define “historic” to an available consecutive period of 30 years, i.e. 1961-1990. Specify a time period by its start_year, historic_range=1951. Defaults to the most current time period available.

Extreme Heat Events

Extreme Heat Events counts the total times the daily average maximum temperature is above some percentile of historic observations. The percentile defaults to 99, referring to the hottest percentile of historic daily temperatures. It is an appropriate indicator for understanding deviations from normal climatic extremes. For example usage, see extreme cold events.

  • historic_range

    Optionally set the years used to define “historic” to an available consecutive period of 30 years, i.e. 1961-1990. Specify a time period by its start_year, historic_range=1951. Defaults to the most current time period available.

Extreme Precipitation Events

Extreme Precipitation Events counts the number of times total daily precipitation exceeds the specified percentile of total historic daily precipitation. The percentile defaults to 99. This indicator is useful to understand future heavy precipitation and inform resource planners of changes to prepare for.

  • historic_range

    Optionally set the years used to define “historic” to an available consecutive period of 30 years, i.e. 1961-1990. Specify a time period by its start_year, historic_range=1951. Defaults to the most current time period available.

Frost Days

Frost Days reports the number of days where the daily low temperature drops below 32˚F or 0˚C. The presence of, lack of, and schedule of frost days have strong impacts on growing seasons, permafrost, and heating demands, for example. While the freezing point of water varies slightly with local environmental conditions, for simplicity this indicator assumes a consistent 32˚F/0˚C. To customize freezing point, see the min temperature threshold indicator.

Heat Wave Duration Index

The Heat Wave Duration Index (HWDI) measures the maximum period of at least 5 consecutive days with daily high temperature greater than 5˚C above historic average high temperature norms. If the historic norm was 85˚F, a period of 6 consecutive days with maximum daily temperatures above 94˚F (5˚C = 9˚F) would register at 1 on the HWDI. This indicator provides a more specific and nuanced look at the extent and intensity of warming than average high temperature or even extreme heat events. It is closely related to heat wave incidents.

  • historic_range

    Optionally set the years used to define “historic” to an available consecutive period of 30 years, i.e. 1961-1990. Specify a time period by its start_year, historic_range=1951. Defaults to the most current time period available.

Heat Wave Incidents

Heat Wave Incidents counts the days the daily high temperature exceeds 5˚C above historic average high temperature norms for at least 5 consecutive days. This indicator is closely paired with heat wave duration index and, similarly, provides a concrete and palpable metric to the impacts of global warming. Frequency, duration, and intensity predictions of heat waves are very important for health and emergency services planning. See California’s comprehensive Impact assessment.

  • historic_range

    Optionally set the years used to define “historic” to an available consecutive period of 30 years, i.e. 1961-1990. Specify a time period by its start_year, historic_range=1951. Defaults to the most current time period available.

Heating Degree Days

Heating Degree Days (HDD) is the difference between the daily average temperature and a reference temperature summed for all days over some time span. For example, a day with average temperature of 40°F and a reference temperature of 60°F would equal 20 HDDs. HDD magnitude corresponds inversely with how cold it is. HDD can be used to approximate heat use in buildings. The default reference temperature is 65°F or the temperature below which a building would be heated.

Related to cooling degree days.

Max High Temperature

Max High Temperature reports the highest daily temperature generated across all requested models for the given period. While averages or percentiles may be more dependable measurements of regular climatic conditions, gauging potentially new maximum heat extremes is essential for proper emergency services preparation.

Max Temperature Threshold

Max Temperature Threshold counts the number of days in a user-specified time period where the daily high temperature meets a user-specified condition. The condition is required and includes a value and a comparison operator, such as “greater than” (gt). This indicator has broad applications depending on the user’s area of expertise, as it allows for the user to generate on-the-fly custom operations.

For example, you could generate a “Number of Extreme Heat Days” indicator by using the following options:

  • threshold=95
  • threshold_comparator=gt
  • threshold_units=F

Min Low Temperature

Min Low Temperature reports the lowest daily temperature generated across all requested models for the given period. While averages or percentiles may be more dependable measurements of regular climatic conditions, gauging potentially new minimum temperature extremes is essential for gauging the changing climate.

Min Temperature Threshold

Min Temperature Threshold counts the number of days in a user-specified time period where the daily low temperature meets a user-specified condition. The condition is required and includes a value and a comparison operator, such as “less than” (lt). This indicator has broad applications depending on the user’s area of expertise, as it allows for custom comparisons and provides a more general interface to other, more specific, indicators.

For example, the Frost Days indicator is the same as using this indicator with the following options set:

  • threshold=0
  • threshold_comparator=lt
  • threshold_units=C

Percentile High Temperature

Percentile High Temperature returns the high temperature value for a user-specified percentile and time period. This indicator can be used to help gather statistics about uncertainty in the climate model predictions for high temperature.

The defaults for this indicator return the 50th percentile (median) for each year in the source data.

Percentile Low Temperature

Percentile Low Temperature returns the low temperature value for a user-specified percentile and time period. This indicator can be used to help gather statistics about uncertainty in the climate model predictions for low temperature.

The defaults for this indicator return the 50th percentile (median) for each year in the source data.

Percentile Precipitation

Percentile Precipitation returns the daily average precipitation rate for a user-specified percentile and time period. This indicator can be used to help gather statistics about uncertainty in the climate model predictions for precipitation.

The defaults for this indicator return the 50th percentile (median) for each year in the source data.

Precipitation Threshold

Precipitation Threshold counts the number of days in a user-specified time period where the precipitation rate meets a user-specified condition. The condition is required and includes a value and a comparison operator, such as “less than or equal to” (lte). This indicator has broad applications depending on the user’s area of expertise, as it allows for the user to generate on-the-fly custom operations.

For example, you could generate a “Number of Dry Days” indicator by using the following options:

  • threshold=0
  • threshold_comparator=lte
  • threshold_units=in/day

Total Precipitation

Total Precipitation returns the summed precipitation volume ranging the user-specified period of time. It is an appropriate first-pass metric for probable long term precipitation trends. Total precipitation is broad because it waters down information on precipitation event intensity, particularly the longer the period of time. For a more thorough look, consider further analysis with yearly max consecutive dry days or extreme precipitation events.

Yearly Dry Spells

Deprecated since version 1.2: Use dry spells instead with the parameter time_aggregation=yearly.

Yearly Dry Spells counts the total number of times per user-specified period that there are 5 or more consecutive days without precipitation. This indicator is useful to understand future drought patterns and inform resource planners of changes to prepare for.

Yearly Max Consecutive Dry Days

Yearly Max Consecutive Dry Days (CDD) reports the maximum number of consecutive days with no precipitation during the given year. This indicator is a very specific metric of wetness and dryness. For a deeper study of CDD characterizing climatic conditions and climatic changes, see this study of Xinjian, China.