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The Last Beginning of Spring

By: Dr. Ricky Rood, 4:20 AM GMT on April 13, 2008

Getting Ready for Spring (5):

First I want to apologize for such a long absence. Thanks for keeping some discussion going. Slammed with classes. I have not even been able to keep up with my class web site. For those of you who go there, look in the next week for the rest of the lectures. There are some good new references. Speaking of good and new, and I know this will excite the people of this blog, at least the commenters, here’s something new about hurricanes from Kerry Emanuel. This from the New York Times. I expect Jeff will talk about it. (If it is old news ... sorry.)

This is the last of the series on the changing springtime. This one is a little more in the spirit of doing science. At the time of the equinox NPR did a story on the beginning of spring. It featured Kirsten de Beurs from Virginia Tech. Here is the audio link from the radio. The article talked about the cherry blossoms at the Tidal Basin in Washington. (If you are ever in Washington at cherry blossom time, it is a first tier event.) I contacted Kirsten and she put together a plot from satellite data for me. Here is the link on her web page, with a more detailed description than the one I give below.

Figure 1: from Kirsten de Beurs: Normalized Difference Vegetation Index ( NDVI from the Advanced Very High Resolution Radiometer AVHRR satellite . Left 1982, Right 2006.

I want to write about these two “snap shots” from 24 years apart. First, I want to say that these two figures by themselves do not establish a trend. They are interesting figures because they show the type of details that must be addressed when trying to determine trends. This figure specifically shows when the NDVI is halfway to its yearly maximum – this could be called the time of fastest “greening.” (I always find the term greening a little confusing and you see a map with so much red, but as drawn, my ultimate point will focus on 2006 being less red! Thanks Kirsten.) This maximum increase is used to indicate the start of season. What the figure shows, then, is the date that the start of the season occurs, as defined by this satellite observation.

I have marked A, B, and C on the figures. A is in Indiana, and this region is red, showing a very late start of season. This is agricultural land and the time of maximum greening is determined by when, in this case, a whole lot of corn is planted. The point B, down in North Carolina (Weren’t we ALL disappointed in the NC-Kansas game, but you knew the emotion would be with Kansas?), and shows an alarmingly late spring in 1982. This is not a late spring as much as this was a year with sustained cloud cover over this part of the country. Clouds are notorious confounders of satellite observations, and often satellite observations are composites of cloud-free images. In 1982, apparently not much cloud-free time there.

Up in area C, in eastern Canada, is where there is evidence of a large difference in the onset of spring between the two years. (Note a discrepancy in Nova Scotia, which I know nothing about.) In area C, there are more yellows and greens, less red, as the start of the season has gotten earlier. It is the persistent signal of early spring in the recent years that is consistent with the warming temperatures.

This series of blogs started with the phenology, the onset of spring. I talked about how seeing a change in the transition from winter to spring and fall to winter, a lengthening of the warm season, would be a robust indicator of a general warming trend. The basic idea was that the random-aspect of weather would be averaged out. This would reveal a tendency in the seasonal transition. We started with birds and trees, looked at change in snow cover, and satellite data of vegetative activity. I want to bring it back to the birds and trees.

Steve Bloom in the comments of the first blog in the series and Kirsten de Beurs both pointed out this citizens science website , Project Budburst. Here is a link to the U.S. National Phenology Network, which gives guidance for how to observe. Like, siting a weather station, you don’t want to observe next to the heating vent. And from the National Sustainable Agriculture Information Service, a lot of information on flowers, birds, and butterflies.

Welcome to spring.


Blogs on spring getting earlier:

Getting Ready for Spring (1)
Getting Ready for Spring (2)
Getting Ready for Spring (3)
Getting Ready for Spring (4)
Jeff Masters blog on snowy winters

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.