www.usanpn.org
a project of the USA-NPN
National Climate Indicator System
Seasonal Timing & Phenology
Patterns and Sources of Seasonal Timing
Variability in Hydroclimate and Phenology
Across the American West and U.S.
1. Spring onset using weather algorithms
validated with long-term lilac observations
(USA NPN)
2. Boreal bird irruptions across the U.S. using
citizen science data (Project FeederWatch)
Part 1: Spring Indices
Weather-based algorithms of plant
development calibrated & validated
with lilac & honeysuckle observations
COLLABORATORS
Mark Schwartz, UWMilwaukee
Toby Ault, Cornell
Greg McCabe, USGS
Greg Pederson, USGS
Ben Cook, NASA
Ali Macalady, UAz
Raul Zurita-Milla, U
Twente, Netherlands
Jake Weltzin, USGS/
NPN
Lilac Observation Sites 1956-2014
Schwartz Spring Indices
SI - chilling requirements included
SI-x - skip chilling, start counting Jan 1
Model tallies up chilling hours (e.g.,
hrs spent <−2.2◦C) until
requirements met
After chilling satisfied, model starts
recording accumulation of recent
growing-degree hours and number
of “high-energy synoptic events.”
At daily time steps, model checks if
requirements for spring onset met,
at which point the event (First Leaf
or First Bloom) is assumed to have
occurred.
Time series of 3-day growing
degree hour accumulations
SI Suite of Indices
First Leaf, First Bloom, Damage index value
(Difference in days between FL and last freeze)
• Can be generated at
any location with
daily Tmax/Tmin or
Reanalysis Data
• Output consistent
over all areas
• Well validated
• “sees” only the
atmosphere, (i.e.,
free of local
biological effects)
Interannual Variations in Spring Onset 1950-2010
Courtesy of Toby Ault
Calendar Day of Year
SI-x Variances
1981-2010
First Leaf
Last Freeze
Damage Index
(FL – LF)
Regional SI-x
variations & trends
Schwartz, Ault &
Betancourt (2012)
Intl. J. Climatology
Autocorrelation Function
Autocorrelation Function
Risk of early modeled first leaf date based on ENSO & PDO
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
10
20
30
10
20
30
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
Lag in months
McCabe et al. (2011)
Int. J. Climat.
Correlation of regional SI-x and crop flowering
Long-Range Forecasts of Seasonal
Transitions in the Climate System and Their
Relevance for Management and Adaptation