The long-range forecast for the Chesapeake region calls for slightly warmer and wetter conditions, with an increasing chance of thunderstorms. The prediction could be bleak for many types of waterfowl on the Bay. Meanwhile, up in the watershed, the fishing outlook is good for smallmouth bass, but poor for trout — brook trout in particular.

But don’t trade in the binoculars or fly fishing gear just yet. The long-range outlook, in this case, isn’t for next week or next month — it’s for the next century. It is the likely scenario for future conditions produced by Penn State scientists and others who recently completed the first detailed study of potential climate change impacts for the Mid-Atlantic region, including the entire Bay watershed.

They admit their crystal ball is foggy at best. “We’re not trying to project what the future actually will be,” cautioned Ann Fisher, of Penn State’s Environmental Resources Research Institute, who is coordinating the effort. “We don’t think we know enough about that. But we think we know enough to say — given what we know about the physics of the climate and how it might evolve over the time — what might be likely to happen in the Mid-Atlantic region.”

A team of scientists have worked nearly two years on the Mid-Atlantic Regional Assessment, one of a series of regional studies sponsored by the EPA to assess potential long-term impacts of climate change in different parts of the country. Their recently published report, “Preparing for a Changing Climate: The Potential Consequences of Climate Variability and Change,” paints a mixed picture for the region.

Forest production may increase from more carbon dioxide in the atmosphere, but the species of trees may change. Some agricultural crops may benefit, while others could suffer. Human health could suffer from increased heat-related stress and illness; at the same time, illnesses stemming from cold conditions would decline. But ecosystems, including the Bay, could prove less adaptable, the report suggests.

The scientists derived regional climate estimates from two highly regarded computer models, one from the Hadley Centre for Climate Prediction and Research in Great Britain, and one from the Canadian Centre for Climate Modeling. Both have shown an ability to accurately reproduce climate patterns over the past century.

The models indicate that temperature increases of 2 degrees by 2030 “are likely” with an additional increase of 3 to 8 degrees possible by the end of the century. Also, the report says, there is a “high likelihood” that the average annual precipitation will increase, possibly in the range of 3–10 inches a year.

For comparison, the average temperature in the Mid-Atlantic region over the last century, has been about 52 degrees, and rainfall has averaged about 41 inches. During that period, the temperature increased about 1 degree, and precipitation increased about 10 percent.

While there would be an overall warming trend, it would not necessarily be constant, the report notes. Regional weather patterns, and major weather-influencing events such as El Niño and La Niña tend to overpower long-term trends. Some years would still be colder than normal, but the trend would be toward slightly warmer conditions.

Not only would the air gradually warm, but the seasonal patterns for precipitation could change. Both models suggest an increase in winter storms, and the Hadley model predicts wetter springs as well. Both suggest drier summers. Also, scientists suggest storms may become more intense: Increased heat would also increase evaporation. That adds up to more water in the atmosphere which, in turn, leads to more thunderstorms. So, it’s possible that the increased rain would be in sudden bursts rather than soaking drizzles.

One of the most certain outlooks for the future, according to the report, is sea level rise. Water expands as it is heated, and glaciers melt. Sea levels in the Mid-Atlantic could rise 24 inches or more along the coast by the end of the century, inundating many coastal wetlands. Higher water will increase storm surges, causing more damage to coastal infrastructure such as buildings, roads and wastewater treatment facilities. “The cost of protecting valued infrastructure or natural areas could be quite high,” the report cautions. Even if storms do not become more frequent or severe, the raised water level will mean storms causing the equivalent damage of today’s “100-year” storms will occur every 25 or 30 years.

The loss of coastal wetlands could impact a long list of species that depend upon them for food or shelter during different life stages, such as weakfish, black sea bass, striped bass, herring, spot, blue crab and horseshoe crabs. The inundation of coastal areas could also affect migratory shorebirds: Chesapeake and Delaware bays are home to two of the largest concentrations of migratory shorebirds in the Western Hemisphere.

Because the models don’t agree on future precipitation patterns, streamflow changes into the Bay are less certain, according to the report. If streamflow increases significantly, especially in the spring, as projected by the Hadley model, it could greatly impact the Chesapeake’s water quality. Increased flows would also increase stratification in the Bay, preventing the oxygen-rich layer of top water to mix with deeper water. That would cause the bottom water in the Bay to become an oxygen-depleted “dead zone.”

If the Hadley model is correct, the report said the amount of oxygen-depleted water in the Bay could increase, perhaps by 30 percent. But if the CCC model is correct in projecting a smaller increase in rainfall occurring mostly in winter, the amount of oxygen-depleted water could actually decrease, the report said. Complicating the water quality picture is the potential that a warmer climate would lead to more severe storms. That would increase sediment, nutrient and chemical pollution from farms and other land uses because a hard rain drives more runoff into streams than a gentle rain.

Waterfowl in the Bay may be at particular risk from climate change, the report suggested. Many ducks that winter on the Bay breed in the Prairie Pothole Region of the north-central United States and south-central Canada. This area, known as the continent’s “duck factory,” is expected to undergo warmer and drier conditions, reducing the pothole wetlands needed by the ducks. According to the report, some scientists project the number of ducks breeding in that region could decline 20-40 percent by the 2030s. That could decrease the numbers of mallard, northern pintail, American wigeon, canvasback, redhead, lesser scaup, common goldeneye, ruddy duck and bufflehead in the Bay. In addition, warmer temperatures and possible streamflow increases could affect water quality causing the Bay’s underwater grass beds — an important food for many ducks — to decline.

Climate change would also affect life in the streams that feed the Bay. Not surprisingly, the number of warm water streams would increase, and the number of cold water streams would likely decrease, the report said.

Some of the worst news is for the brook trout, which requires clean, cold water. The brook trout range has gradually withdrawn to higher, more remote streams over time, and that range contraction is likely to continue and perhaps accelerate. In addition, brook trout throughout the region will face increasing competition from the larger, more aggressive brown and rainbow trout, which are less sensitive to temperature fluctuations. “Brook trout might be lost from many [Mid-Atlantic region] streams,” the report said.

Not all the news is bad, especially for anglers who like warm water species such as largemouth bass, smallmouth bass, catfish, carp and panfish. As temperatures increase and trout habitat shrinks in lower elevations, bass habitat will likely increase, the report said. And some species, such as smallmouth bass populations, would not even be bothered by reduced stream flows that might occur in the summer — it’s the condition they prefer. Studies in the Susquehanna River have shown that smallmouth bass populations benefit during low flows while above-normal flows produce the smallest populations.

But the prediction for smallmouth bass and other warm water fish is not without its clouds. More thunderstorms would drive more sediment and other pollutants into streams. Also, because warmer water holds less oxygen, dissolved oxygen levels would decrease as lakes and streams warm. Those impacts could stress not only fish populations, but freshwater ecosystems as a whole, the report said, raising concerns about the future of mussels and other rare species. But, those impacts are also harder to predict, the scientists noted.

In the Mid-Atlantic region, ecosystems may be particularly vulnerable to impacts from climate change. Unlike forestry, agriculture — and even humans — many ecosystem components may not be able to adapt as rapidly as the climate changes. Many of the poorly studied species which require a narrow range of habitat conditions — such as some freshwater fish and mussels — could be threatened. Because many ecosystems are poorly studied, the report said it is difficult to say what will happen as some species thrive in the altered future climate and others are crowded out.

“Although some desired species might become more abundant, the overall result is likely to be a reduction in biodiversity,” the report said. That could have ripple effects, such as harming species important for purifying water or pollinating crops. But more research is needed before such impacts could be predicted, the report said.

At this point, in fact, uncertainty seems to be one of the most certain predictions for regional climate change impacts. Even as scientists agree the climate is changing, they acknowledge that future projections are highly variable. Regional and seasonal projections are more uncertain than global projections. As a result, the Mid-Atlantic report says its findings don’t suggest that new actions be taken just because of threats from global warming.

Instead, it says climate change merely provides additional reasons to do things that already make sense: promoting runoff controls such as forest buffers for agriculture and other land uses, and improving watershed planning to protect water quality and supply. Some impacts from rising sea level can be avoided by better managing development in coastal areas, the report said, while incentives promoting development or agriculture in lands that may be subject to flooding should be eliminated. Said Fisher: “This just gives you one more reason to be taking actions that are beneficial, and cost-effective anyway.”
The report is available on the Mid- Atlantic Regional Assessment’s web site: Hard copies are available by calling 814-865-3143.

For information about climate change and the Chesapeake Bay, see “Warming trend would put heat on Bay Recovery efforts,” and related articles in the January-February 1999 Bay Journal.