The year is 1996. In January, severe "100-year" floods rip through the watershed, gouging out costly stream restoration projects built just the year before.
Heavy rains wash record amounts of nutrients off the land and into the Bay. Algae concentrations hit record highs in the spring. And, aided by strong river flows, the oxygen-depleted "dead zone" is one of the largest ever recorded in the Bay.
Then came the first six months of 1998. Flows into the Bay passed the record set only two years before for the same period. Again, the "dead zone" hit record proportions. In two earlier years, 1993 and 1994, the high flow story was strikingly similar.
To some, those events may be history.
But to others, they may be a glimpse of the future - a slightly warmer, but much wetter period that could be in store for the region as a consequence of global climate change. With the 1990s shaping up as the wettest decade on record for the Chesapeake watershed, some suggest it may be a future that is already taking form.
No one can say for sure. Yet it is a cause for concern: Of all the potential consequences of global climate change, increased flow would pose one of the big-gest challenges for Bay restoration. It could require clean-up efforts - such as nutrient reductions - which go far be-yond those presently envisioned. Other impacts, such as sea level rise, which destroys coastal marshes and low-lying habitat, and temperature increases, would complicate the picture even further.
Still, it would not make the job impossible, scientists say. "I still think that much of this is in our hands," said Donald Boesch, president of the University of Maryland Center for Environmental Science. "It's going to make the job a bit more difficult, but it is not going to be so overwhelming to make it impossible."
Concerns about the many potential impacts of climate change have grown for more than a decade as global-scale models have predicted a gradual warming of the Earth as levels of heat-trapping "greenhouse" gases build up in the atmosphere. The global average temperature is already thought to be warmer than at any time in more than 1,000 years - perhaps warmer than any time since the last ice age. While warmer temperatures may have been experienced in northern Europe during the Middle Ages, this appears to have been a regional, rather than a global phenomenon.
In 1995, the United Nation's Intergovernmental Panel on Climate Change issued a report saying that the Earth had warmed about 1 degree Fahrenheit in the past century, and would likely increase another 2 to 6.5 degrees in the next century, with the most likely forecast being about 3.5 degrees.
"I'd be a liar if I said we are certain of everything," said Brent Yarnal, a geography professor at Pennsylvania State University who is working on climate change issues. "But this is simple physics. We know that more greenhouse gases should warm the atmosphere."
Still, such forecasts are global in scale. In reality, some areas will warm more than others; some areas may even cool. Air over oceans is expected to heat less than air over land.
In an attempt to clarify the picture for the mid-Atlantic, Yarnal and other Penn State scientists have begun looking at potential regional consequences of climate change. Using bits of information from global models, they are trying to determine what may be in store when the amount of carbon dioxide in the atmosphere is doubled from pre-industrial levels - something expected to take place after 2050.
They expect a modest warming in the region, but it may be felt mainly at night and during the winter - the "snow season" may be shorter. But the more significant change, from the Chesapeake perspective, is what could be in store for precipitation.
"We think it's going to get wetter," Yarnal said. In fact, it could get a lot wetter. One model being used predicts a 20 percent precipitation increase, primarily in the winter and spring. Another predicts a 30 percent increase in the spring and summer.
That doesn't mean every year will be wetter than normal. Global climate changes will not overwhelm local weather patterns or other regional factors that affect the weather. Some years would still be cool, some warmer. But the overall trend - over many years - would be toward warmer, wetter conditions.
In fact, when it's not wet, it may be drier than normal. When regional weather patterns set up in ways not conducive to rain, warmer temperatures would lead to more evaporation, potentially pushing dry conditions toward drought. "The possibility is that you are going to be either really wet, or really dry," Yarnal said.
Already, this region has been getting more than its share of rain. While global precipitation has been relatively low since about 1980, overall precipitation in North America has averaged about 5 percent more than normal since 1970. While some parts of the nation have experienced near-drought conditions, the northern part of the Bay drainage has received some of the largest precipitation increases.
At the same time, scientists working for the National Oceanic and Atmospheric Administration's National Climatic Data Center reviewed precipitation records for the past century and found that not only has it been getting wetter, more of that rain is coming in "extreme 1-day precipitation events" - a 24-hour period where it rains more than 2 inches.
Yarnal said that trend applies to the mid-Atlantic as well, because more moisture in the atmosphere usually leads to more severe weather. "We're talking about more frequent severe rains, and more intense severe rain."
He cautioned against reading too much into the specifics of regional precipitation forecasts extrapolated from small pieces of huge computer models that were designed to give global - not local - predictions. "These are just two model runs," Yarnal cautioned.
Boesch also cautioned against relying solely on computer projections, but said a more compelling case emerges as those forecasts are combined with a growing scientific consensus on climate change and observed trends. "I think there is a compelling reason that we need to begin taking these changes into account as we plan our future."
Many recent years appear strikingly similar to what is predicted regionally. So far this decade, five years have been wetter than normal, with extremely high flows occurring in early 1993, 1994, 1996 and 1998. Also, 1996 was the wettest year on record; 1998 had the wettest first six months on record. In 1997 and the second half of 1998, there were droughts.
No one can say for sure whether that is a signal of global climate change. But some are beginning to question whether the standard explanation - that weather changes from year-to-year - can adequately explain the severity of such extreme fluctuations in recent years.
"I've had too many conversations with people who are at the point of saying, 'Maybe this isn't just a question of a few wet years, that we may be moving into, for whatever reason, a period of wetter years,'" said Mike Hirshfield, vice president of the Chesapeake Bay Foundation.
An altered climate that includes a trend toward increased precipitation - particularly if that rain comes in severe storms - would fundamentally challenge the current Bay restoration effort.
Here's why: The Bay restoration is based on the premise that reducing the amount of nutrients entering the Chesapeake will improve water quality. Nutrients cause excessive algae blooms. When there's more algae than can be consumed by predators, the excess die, sink to the bottom and are decomposed by bacteria in a process that depletes the water of oxygen. This results in "dead zones" which can't be used by fish, crabs and other aquatic species. In addition, the blooms cloud the water, preventing underwater grasses - which provide food and habitat for waterfowl, fish, young crabs and other species - from receiving sunlight critical to survival.
The amount of nutrients entering the Bay is strongly tied to precipitation. Rains flush large amounts of nitrogen and phosphorus off fields, lawns, golf courses and other land and into waterways.
U.S. Geological Survey figures show just how strongly nutrients and flows go together. In 1985 - the "average" rainfall year used as a baseline for measuring Bay Program nutrient reductions - about 133 million pounds of nitrogen entered the Bay from the Susquehanna, as well as 5.5 million pounds of phosphorus.
But in 1996, the wettest year on record, more than 216 million pounds of nitrogen were flushed down the river, along with 7.1 million pounds of phosphorus, according to the USGS. Despite a decade of nutrient reduction efforts, 62 percent more nitrogen, and 29 percent more phosphorus were discharged from the Susquehanna River during 1996 than during 1985.
High flows present a sort of one-two punch to the Bay. They not only wash more nutrients in to feed algae blooms, they also increase the degree of "stratification" between freshwater on the surface, and heavier saltwater on the Bay bottom. That stratification prevents the top and bottom layers from mixing, meaning that when bottom oxygen is depleted, it is difficult for it to be replenished by the oxygen-rich surface waters.
Compounding the picture further is that flows into the Bay increase at a faster rate than rainfall. Here's why: Using the Susquehanna watershed as an example, about 40 inches of rain hits the ground in a typical year. As a rule of thumb, Mother Nature uses about half - or 20 inches - which is taken up by trees and plants, evaporates into the air, or is otherwise not passed on. That amount stays pretty constant - if 30 inches fall, Mother Nature still takes her 20 inches, or if 50 inches falls, she is still pretty content with the same 20.
What that means is that any increased rainfall from climate change will go straight to the Bay, unless the rate of evaporation increases dramatically. As a result, said Ray Najjar, an oceanographer at Penn State, a 10 percent increase in rainfall actually translates into a 20 percent increase in flow reaching the Bay. "It's a sensitive system," he said. "It's not going to take that large of a change to have noticeable effects."
If those factors were further complicated with a slight warming, which would accelerate the entire biological process of algae production and decomposition, the oxygen situation would be further compounded. "I don't want to be a Jeremiah here," Boesch said, "but it is a sobering thought that those trends might conspire against us to make the job more difficult."
Increased rain could pose a variety of other problems as well.
Not only would the Bay suffer from more low oxygen problems, so could many of the rivers and streams that feed it. Increased flows that deliver more nutrients, and warmer temperatures that speed biological processes, could combine to lower dissolved oxygen levels in many waterways, said Greg Knight, a Penn State geography professor who is studying the impact of climate change on water quality. At the same time, those impacts could be mitigated somewhat by the fact that there would be more water in the rivers. "There are a complex set of tradeoffs," he said.
Of even more concern to stream habitat, Knight noted, could be periodic droughts which might become more severe in the future. Not only would they decrease water in rivers, but warmer temperatures would create more demand by utilities and others - from farmers to golf courses - who depend on water. The net result could be more severe impacts on stream habitats during low-flow periods, he said.
In the Bay, meanwhile, flows would not only contribute to increases in algae, they may also change the makeup of the phytoplankton communities. In recent high-flow years, scientists have noticed a disturbing trend toward increased blooms of "blue-green" algae, a troublesome species that has virtually no food value for predators.
"While you can readily predict there would be quantitative changes in phytoplankton with changes in flow regimes, I think the qualitative changes are also very interesting and pose some interesting potential repercussions as well," said Richard Lacouture, a biologist with the Academy of Natural Sciences' Benedict Estuarine Research Center.
Meanwhile, Claire Buchanan, a biologist with the Interstate Commission on the Potomac River Basin, said the Bay Program's monitoring effort in recent years has documented a decline in the levels of mesozooplankton - microscopic animals preferred as food by many small fish - in parts of the Bay. Smaller microzooplankton, which are less desired as food, have been holding steady. Such changes may not be strictly caused by a higher volume of water, she said, but may be related to changes in water quality and other factors affected by flow, such as turbidity, dissolved oxygen, salinity and temperature.
One concern is that after a series of high flow years, different species could come to dominate the plankton community and - with changes that could ripple through the entire food chain - the Chesapeake would not "bounce back" to its former species composition even during years of lower flows.
THERE is little the Bay Program, or the Bay states, can do about flow. But the good news is that continued efforts to reduce nutrients can help offset some of the impact of higher flows, scientists say. The bad news is, those nutrient reductions may have to be far greater than those under way today.
Until the mid-1980s, there was a close correlation between flows and the amount of hypoxia - low oxygen water - in the Chesapeake. But since the mid-1980s, the connection is not as tight, according to Bill Boicourt, an oceanographer at the University of Maryland Center for Environmental Science Horn Point Laboratory.
"Some kind of threshold seemed to have occurred where there was increased duration and an increased spatial extent of hypoxia, so that conditions were worse, in general, from year to year, regardless of the freshwater inflow," Boicourt said. The reason, he said, appears to be that the huge amount of nutrients that enter the Bay have become more important to hypoxia, relative to flow.
The message, Boicourt said, is that while increased flows will "work against us," it is still likely that water quality can be improved even if higher flows become the norm. But it will take a greater level of nutrient reduction, both to offset the increased amount of nutrients that would be washed off the land, and to offset the effect of increased stratification. "There is no question that we have to work extremely hard," he said.
Whether the recent high flows are a result of global climate change or other factors, Rich Batiuk, associate director for science with the EPA's Bay Program Office, said the recent years provide the Bay Program with a "wake-up call" for Bay management. "It's telling us that we can't manage on the median," he said. "You have got to start looking at some of the extremes."
Instead of having nutrient reductions based on "average" flows, he said reductions in the future may need to protect the Bay against high flow years, though not necessarily "worst case" scenarios.
He and others suggested that could also force a rethinking of some runoff control practices. For example, the design of best management practices may need to be re-examined to make sure they could hold back water - and nutrients - in the face of the potential for more frequent, stronger storms.
More emphasis may need to be placed on restoring forests and other natural systems, which can buffer waterways by slowing down runoff. "The way to deal with water from the sky is to have relatively well-forested, well-vegetated land that it is falling on," said CBF's Mike Hirshfield. "If it is true that the wet years are going to be more the norm than the exception, actions like minimizing impervious surfaces and having real buffers - the things that you want to do anyway to deal with nutrients - are going to be that much more important."
Knight, of Penn State, said that while nothing is certain about future climate changes, the potential implications warrant the pursuit of such "no regret" strategies to mitigate potential impacts - ranging from the promotion of more vegetative buffers to energy conservation practices that save money while reducing greenhouse gas emissions.
"At this point, one can begin to make reasonable conclusions about potential directions of change if certain things happen," Knight said. "We're certainly far from being able to say that those things will happen, but on the other hand, everything we learn suggests that to the extent to which our society has 'no regret' strategies to contribute to the abatement of this global warming, we ought to be taking them and then worry about the details later on."
But, Knight said, he doesn't see that happening. "In some ways we are going in exactly the opposite direction that we should be going. I don't think people see the connection between continued ex-urbanization, sport utility vehicles and the general energy intensity of what we do as being equally threatening, in a way, to critical resources."