If hope springs eternal with spring, then how should we define when the season of spring has, well, sprung? If you were to ask an astronomer, they would tell you that spring begins in the northern hemisphere after the March 20 vernal equinox, bringing earlier sunrises and later sunsets. But this change in daytime may not be as defining of spring as the sprouting plants that longer and warmer days bring.
To answer this burning question enter the USA National Phenology Network (USA-NPN), a monitoring and research initiative focused on collecting, organizing, and delivering phenological data to a wide range of audiences. According to the Merriam-Webster Dictionary, phenology is the “branch of science dealing with the relations between climate and periodic biological phenomena (such as bird migration or plant flowering).” Thus the USA-NPN has developed two models to measure and identify the arrival of spring: The First Leaf Index and the First Bloom Index.
First Leaf Index
The First Leaf Index is computed based on when the leaves of lilacs and honeysuckles begin to show. These two species of plant were chosen based on their frequent appearance in many environments across the United States, as well as their tendency to leaf earlier than other plants. According to this First Leaf model, the Atlanta region saw its first leaves start to sprout in late February.
First Bloom Index
Much like the First Leaf Index, the First Bloom Index model strives to forecast when the first lilac and honeysuckle flowers will bloom across the United States based on temperature and weather events, of which data is collected from NOAA’s National Centers for Environmental Prediction Real-Time Mesoscale Analysis. According to the First Bloom model, the Atlanta region should have experienced its first bloom in early March this year.
Finally, you may be wondering: How do these estimates compare to previous springs? Check out the USA-NPN’s Phenology Visualization Tool, and then get outside when you can to enjoy spring!