Early warm weather could spell trouble later

In the venue of predicting spring, there is the groundhog, the Old Farmer's Almanac ... and then there is the science of when plants usually get first leaves.

Here in much of Delaware, spring, based on early leaf-out, is about 20 days ahead of schedule, according to new maps produced by the USA National Phenology Network. 

Phenology looks at seasonal changes in plants and animals from year to year, such as when migrating songbirds first show up, when waterfowl head south for the winter or when daffodils bloom or certain insects reappear. The timing can be influenced by weather and climate. Think of it as nature's calendar.

The maps show just how far ahead an area is when it comes to spring leaf-out of three indicator species: common lilac and two species of honeysuckle.

The last time there was a really early spring was in 2012, said Alyssa Rosemartin, with the USA National Phenology Network.

This spring is shaping up to be even earlier, she said.

“While these earlier springs might not seem like a big deal – and who among us doesn’t appreciate a balmy day or a break in dreary winter weather – it poses significant challenges for planning and managing important issues that affect our economy and our society,” said Dr. Jake Weltzin, a U.S. Geological Survey ecologist and the executive director of the phenology network.

The timing of spring can have a big impact on everything from when disease-causing insects like ticks and mosquitoes start to bite to reduced crop yields.

Last year in Delaware, there was an early warm spell, and the thousands of peach trees in the state were in full flower when a killing frost hit. Depending on the species, there was a reduction in crop harvest of as much as 85 percent. Nature can also get out of sync. Plants may flower early or insects arrive before birds show up to eat them. For land managers, it can mean an earlier start to controlling invasive species or protecting the rare ones from disturbance.

Weltzin said plant leafing models used to produce this data are the foundation for a study that found spring is arriving earlier than ever in 3 out of 4 national parks. Half of these parks had very early onset of spring compared with the previous century.

Maybe it shouldn't come as a surprise to weather watchers. The hottest year on record globally was 2016. Last year was the third record year in a row, and 16 of the 17 hottest years on record have been since 2000.

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Here in Delaware this week, two record high temperatures were recorded at New Castle Airport: 71 degrees on Sunday and 73 degrees on Thursday. The average temperature for the month to date is 7 degrees higher than normal. It was even warmer in Georgetown, where records were shattered on Thursday and Friday. The Thursday high was 75, breaking the record of 67 set in 1990. Friday's high was 76, breaking the record 72 set in 1961.

In Lewes, flowering quince trees are in bloom, and in some places, daffodils are already open. In Wilmington, crocuses are up and in flower.

"Clearly this is abnormally early," said Susan Barton, associate professor and extension specialist at the University of Delaware.

For gardeners, it could mean an early show of spring flowers, and because it seems to be warming up fast, the display may not last as long as it would in a longer, cooler spring, she said.

Sycamore trees, which are among the first to leaf out, can survive even if the leaves get zapped by a hard frost and prolonged cold. Those early leaves might drop, she said, but "the trees just leaf out again."

The biggest issue comes with fruiting trees. If the flowers come too early and there is a freeze, the crop is often lost, she said.

A warm spring isn't a bad thing with those flowering bulbs.

"It's just a matter of enjoying them early," she said.

The team that built the spring index maps created models that were based on field observations collected across the country. The team members calculated how much heat has to build before leaves start to open on lilacs and honeysuckle plants. Both are common and are sensitive to temperature.

They also looked at heat and temperature data from the National Oceanic and Atmospheric Administration, including National Weather Service data. In addition, they collected historic temperature data from an Oregon State University database.

By comparing daily maps with historic ones – all created using the same data sets – they projected how this spring differs from the average between 1981 and 2010.

Plants, for instance, won't grow if it is 32 degrees or lower, so by looking at daily temperatures they could start to project accumulated growing degree days, Rosemartin said.

Contact Molly Murray at (302) 463-3334 or mmurray@delawareonline.com. Follow her on Twitter @MollyMurraytnj.