USA NPN National Phenology Network

Taking the Pulse of Our Planet

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Status of Spring

The USA-NPN is tracking the start of the spring season across the country using models called the Spring Leaf and Bloom Indices. 

How does this year stack up against the recent past?


In 2017, we see very large anomalies in the southeastern United States on the Spring Leaf Index map, where the Index was met up to three weeks earlier than what is typical for these locations. 

The timing of leaf-out, migration, flowering and other seasonal phenomena in many species is closely tied to local weather conditions and broad climatic patterns. The Spring Index maps and Accumulated Growing Degree Day Maps offered by USA-NPN shed light on plant and animal phenology, based on local weather and climate conditions.

Spring Indices: Indicators of phenological activity


How do you know when spring has begun? Is it the appearance of the first tiny leaves on the trees, or the first crocus plants peeping through the snow? The Spring Leaf Index is a synthetic measure of these early season events in plants, based on recent temperature conditions. This model allows us to track the progression of spring onset across the country.

The map at right shows locations that have reached the requirements for the Spring Leaf Index model (based on NOAA National Centers for Environmental Prediction Real-Time Mesoscale Analysis temperature products).

Learn more about the Extended Spring Indices and the data products available.

Accumulated temperature: A driver of spring phenology


Heat accumulation in the spring is also 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. 

Learn more about Accumulated Growing Degree Day maps and the data products available.

Access Phenology Map Products

The Spring Index First Leaf and First Bloom maps and Accumulated Growing Degree Day maps can be explored in the USA-NPN Visualization Tool.

Raster data files (layers used in geospatial analysis software like GIS packages) can also be accessed via the USA-NPN Geoserver (online spatial data map server). Learn more about the data layers available and how to access the USA-NPN Geoserver on the Accumulated Growing Degree Day Products and Extended Spring Indices pages.