activity : indicator-start-of-spring-process-2018



Data for this indicator were analyzed using methods described by Schwartz et al. (2013):
Schwartz, M.D., T.R. Ault, and J.L. Betancourt. 2013. Spring onset variations and trends in the continental United States: Past and regional assessment using temperature-based indices. Int. J. Climatol. 33:2917–2922.

* 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.
* 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 (1) 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, and (2) daily minimum and maximum temperatures measured at weather stations.
* The annual start of spring can be estimated for any location where daily minimum and maximum temperatures are recorded.

* Data were plotted as an anomaly time series bar graph (relative to the 1901-2000 average)
* Data were plotted in blue for positive values (later spring) and green for negative values (earlier spring)
* Labels were added to the y-axis to indicate later spring or earlier spring and the zero line was labeled as the "1901-2000 average"

Methodology Contact: Mark D. Schwartz (University of Wisconsin-Milwaukee)


How the source was modified: Leaf and bloom observations were derived from the USA National Phenology Network "Extended Spring Indices" dataset. These data were combined with GHCN-Daily temperature data from NOAA NCEI to estimate the annual start of spring across the contiguous United States.

Data Bounding

The input object was time bounded starting from January 01, 1900 (00:00 AM)

The input object was time bounded ending at December 31, 2017 (00:00 AM)

The input object was bounded spatially:

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