Horn Point Laboratory

Climate change already affecting Chesapeake Bay region

Scientists find evidence of hotter summers, seasonal shifts

The task was simple; the potential payoff, massive.

Guests of the 2015 Horn Point Laboratory Open House were asked to find their birthdate on a chart that indicated the biggest rain events and hottest days since 1930. The goal was to help those guests visualize how much climate in the Chesapeake Bay region has changed in their lifetime.

At the end of the exercise, one thing was clear—many of the most extreme weather events happened in the past 20 years.

Victoria Coles, associate research professor

Victoria Coles and Raleigh Hood, two scientists from University of Maryland Center for Environmental Science’s Horn Point Laboratory, have spent the past two years working with a postdoctoral scholar Kari St.Laurent, compiling data and using it to tell a story of climate change in the region that people can understand.

“Our point here was to talk more about what we’ve been seeing in a way that might convince people to take actions that would increase their own personal and community resilience,” Coles said.

The project is a collaborative research effort with the National Estuarine Research Reserves, a division of the National Oceanic and Atmospheric Administration; UMCES; Chesapeake Environmental Communications; and NOAA’s National Centers for Coastal Ocean Science, which also funded the effort.

The overall goal was to help residents of the Bay region understand what’s happening in their backyard, as well as governing officials to help drive policy and action.

With Coles’ experience working on the state’s climate assessment and Hood’s expertise in nutrient cycling in the Bay, both got to work compiling information. They paired some historical data, such as about annual rainfall in the Chesapeake Bay region, with new data, and they compared predictions with actual events to make new predictions going forward.

Among their findings they learned:

●    The number of days where the maximum temperature is higher than 77 degrees is growing with the southern Chesapeake Bay experiencing almost 40 more summer days each year than it did 100 years ago.
●    There are fewer days in the year when the low temperature is less than 0 degrees.
●    The Bay region is seeing more precipitation with each passing decade, receiving 2 to 7 more inches of precipitation per year than it did a century ago, in the northern and southern Bay respectively.
●    Over 100 years, growing seasons have lengthened by 20 days in the northern Bay, and 40 days in the southern Bay.
The group made graphics to help visualize the data, which painted a direct picture of climate change in the Bay area.

“It’s really brought home in the most tangible way how much climate change is impacting this region,” Hood said.

Graphics by Chesapeake Environmental Communications

They wanted to measure extremes and variability—how much of a month’s rainfall was really extreme versus light rain, how many warm nights were there, what was the coldest temperature in a month—because that resonates well in people’s memories.

“Organisms and people feel weather; they don’t really feel climate,” Coles said. “Climate dictates what your annual average fuel bill is maybe, but it’s the weather events that you’re actually experiencing and those weather events are changing. Those are things that people notice.”

With each finding came an explanation. More summer days means more money spent on air-conditioning, for example, and warmer winters could leave room for new agricultural pests and diseases. Coles, Hood, and their collaborators on the project wanted to tell a story with the data that would not only show evidence of climate change, but also help people understand its personal impact. They ended up with four stories.

1. Pathogens live for longer during summer

The first story showed longer summers could increase someone’s exposure to human pathogens that naturally occur in the Bay. Humans are at risk of contracting vibrio vulnificus, if they have a wound or infection, but can also get infected through shellfish that would also be more at risk of a lengthened exposure time, Hood said.

According to the Centers for Disease Control and Prevention, Vibrio bacteria live in higher concentrations between May and October when water temperatures are warmer. About a dozen Vibrio species can cause human illness, known as vibriosis, which causes an estimated 80,000 illnesses and 100 deaths in the United States every year.

2. Water temperatures on the rise

One story from their findings involved submerged aquatic vegetation (SAV), or grasses that act as key nursery areas for crabs and young fish.

“A lot of our grasses are at the southern limit of their range, so if temperatures are increasing, they’re going to be thermally stressed,” Coles said.

Stress can lead to massive die offs with subsequent consequences for nursery areas for crabs and fish. Key nursery areas also feel stress from nutrients and cloudiness in the water. Matching historical data with past high temperature swings, the researchers found high temperatures occurred at the same time as losses of SAV. They used this to make a model of how high temperature events affected SAV over the past century.

“Thermal stress wasn’t an issue over the past century except a few times in the past 15 years,” Coles said of the model. "It may be at this tipping point where it’s really becoming more of a stressor.”

3. Seasonal shifts confuse wildlife

Another story focuses on the timing of spring and fall, and the mismatch that results from the shift.

“Everything’s sort of greening up earlier,” Hood said.

The shift in the timing of the spring bloom affects species that depend on the bloom for food. Seasonal shifts also impact wildlife that rely on environmental cues, for example, to know when to migrate.

“Just because it’s generally warmer in the fall doesn’t mean you won’t have a dip down to freezing, so what we see are these cold stuns where fish that should have migrated out didn’t migrate out because it was warm. Then the temperature plummets 20 degrees in a day and then suddenly you have stunned or dead fish everywhere,” Coles said.

This has happened, too, with brown pelicans. Some of the juveniles don’t migrate because it’s staying warm later, and they aren’t as prepared for winter when it comes.

4. Knowing when a hard rain will fall

The last story regards nutrient loading in the Bay and changes in precipitation, including how it falls—heavily, moderately, or lightly.

During their research in the Bay, they found an increase of very wet days, little or no change in moderately wet days, and a small decline in mildly wet days in the northern part of the Bay while there was a small increase in the southern half, signaling regional differences over the past century.

“Overall, there has been an increase in heavy precipitation over the past century consistent with what other studies at larger spatial scales have shown,” Coles said. “We don’t have the information to go down to storm scale, but basically, more precipitation is being delivered in large events.”

How much it rains matters, Coles explained, because nutrient management strategies are dependent on how intense the rainfall is. If it’s coming in large events, then stormwater management system upgrades could be critical compared to relying on a sewer system, for example, she said. If it’s coming in light or moderate events, then maybe rain gardens could be useful. Not being prepared could be environmentally and financially costly, Hood added.

Along with their partners, Coles and Hood developed an iBook on the Chesapeake Bay with a chapter on climate change, written papers and blogs, and created a website with their findings, Detecting Climate Change in Chesapeake Bay.

The UMCES team hopes the project will help individuals understand how the climate is changing and how they have a responsibility to help the environment.

“Let’s face it, addressing climate change ultimately has to happen at the individual level. We all are going to have to reduce our emissions. We all need to understand that we have to go to alternative energy sources,” Hood said. “That’s why it’s important to show how our weather and climate extremes are changing right here in our communities, we want people to understand that their own lives are impacted by changing climate.”

Banner photo credit: Integration and Application Network/Jane Hawkey