USA NPN National Phenology Network

Taking the Pulse of Our Planet

You are here

Accumulated growing degree days can be used to predict life cycle transitions in plants and insects.

Image credit:
Sara N. Schaffer

Accumulated Growing Degree Day Products

Heat accumulation in the spring is commonly used to predict the timing of phenological transitions in plants and animals. This accumulation is typically reported in Growing Degree Days. The USA-NPN is currently generating daily Accumulated Growing Degree Day (AGDD) maps using a January 1 start date and two base temperatures, 32°F and 50°F. The map at right shows the accumulation of Growing Degree Days since Jan 1, 2016 using a 32°F base temperature. 

What are Growing Degrees?

In many plants and animals, phenological transitions – especially those in spring - happen when enough warmth has accumulated. This warmth is often measured using growing degree days (GDDs). Growing degrees days are defined as the number of degrees the average daily temperature exceeds a base temperature, or the temperature below which the organism will remain in dormancy. Growing Degree Days are calculated as:

GDD = ((Tmax + Tmin)/2) - Tbase

If the average temperature for a day is lower than the base temperature, then no Growing Degree Days are counted.

Growing Degrees are accumulated daily, following a specified start date, by adding each day’s total to all previous days’ totals.

What is the value of Growing Degree Day calculations?

For many plants and animals, there is a specific number of growing degree days that must be accumulated to trigger a change in phenological status such as budburst in plants or egg hatching in insects. These are referred to as growing degree thresholds. If a growing degree threshold for a phenological transition in a particular organism is known, it is possible to assess how soon that transition is likely to be reached, by calculating accumulated growing degree days (AGDDs) over the course of the season.

Learn More

Daily Accumulated Growing Degree Day and Spring Index Maps information sheet

Available Growing Degree Day Products 

The USA-NPN is currently generating provisional daily Accumulated Growing Degree Day (AGDD) maps using a January 1 start date and two base temperatures, 32°F and 50°F.

Accumulated Growing Degree Day maps can be explored in the USA-NPN Visualization Tool.

Download map images (.png, .gif, .pdf, etc) or raster data files from the Geoserver Request Builder page.

Raster data files can also be accessed via the USA-NPN Geoserver instance. Available products include:

  • Contemporary (daily, current year) and 6-day forecast maps of Accumulated Growing Degree Days (AGDD) - available for 2016 and 2017
  • Daily anomaly maps of AGDD, generated by comparing current day maps to 30-year (1981-2010) averages
  • Daily 30-year (1981-2010) average temperature accumulations
  • Daily Tmin and Tmax values for the current year

Geoserver Documentation

Map Products Documentation: Crimmins, T.M., R.L. Marsh, J. Switzer, M.A. Crimmins, K.L. Gerst, A.H. Rosemartin, and J.F. Weltzin. 2016. USA National Phenology Network gridded products documentation. U.S. Geological Survey Open-File Report 2017–1003.  DOI: 10.3133/ofr20171003.

How to Cite Map Products

USA National Phenology Network. Year of dataset access. Name of data product, USA-NPN, Tucson, Arizona, USA. Data set accessed YYYY-MM-DD at

USA-NPN Data Use Policy

Estimating Uncertainty in AGDD Products

The USA-NPN is committed to reporting measures of uncertainty, where possible, to support the use of these data products in decision making. 

To assess the level of uncertainty in the USA-NPN AGDD products, we compare our URMA/RTMA-based calculations of Accumulated Growing Degree Days to those made using measurements from U.S. Climate Reference Network stations, accessed via the Applied Climate Information System, in the AGDD Uncertainty Assessment Dashboard.