This indicator tracks the start of spring each year. The start of spring occurs on the date when enough heat has accumulated to initiate growth (leafing and flowering) in temperature-sensitive plants.
The bars on the graph show the number of days by which the start of spring differs from the average start of spring during the last century.
Start of Spring Is Changing in the U.S.
On average, the start of spring has occured earlier in the contiguous United States since 1984. A trend toward earlier springs could have significant implications for agriculture, natural resource and hazard management, and recreation.
About Start of Spring
This indicator estimates the annual start of spring on the basis of when growth can begin for temperature-sensitive native and cultivated plants. It can be used to monitor, assess, and predict variations and trends in spring timing at the national scale.
The annual start of spring can be estimated for any location where daily minimum and maximum temperatures are recorded. The modeled values correlate well with observed leafing and flowering in a number of native and cultivated species, such as winter wheat, pear, and peach varieties.
These values are calculated from a numerical model that simulates the accumulation of heat needed to bring plants out of winter dormancy and into vegetative and reproductive growth. The model is based on:
Long-term observations of lilac and honeysuckle first-leaf and first-bloom, collected by citizen science volunteers at hundreds of sites across the contiguous United States
Daily minimum and maximum temperatures measured at weather stations