Extreme Rainfalls And Dry Spells Define the Northeast Climate In The Age Of Global Warming

Heavy downpours send huge amounts of water tainted with chemicals and nutrients from road, lawns and farm fields into ponds like Mill Pond in Water Mill, often sparking algae blooms. Dana Shaw

Marine scientists have sounded new alarms over the effects of a warming climate on marine life on the South Fork in the months since a massive die-off of bay scallops in the Peconic Estuary.

While the effects may seem subtle in the scale of human memory, a national study that tracks weather events has revealed that the general warming of the atmosphere has already had a major impact on weather patterns in the Northeast — one that is likely contributing substantially to the problems with algae blooms on the East End.

In the last 30 years, what meteorologists call extreme rainfall events — resulting in two inches or more of rainfall in a 36 hour period — have increased by 71 percent just in the Northeast.

Very heavy rain events have been increasing nationwide in that same time period — and rainfall overall is increasing in the United States — but the spike in our region is nearly double that of the next highest increase, in the Midwest.

More rain in itself isn’t necessarily problematic, but the emerging pattern of more extreme rain amounts, in more focused events, has played perfectly into the set of conditions that algae blooms use to thrive.

In August 2014, Long Island set the state record for rainfall in one day at nearly 16 inches, and more than 20 inches fell over a 36-hour period. The week following that event saw explosions of algae blooms throughout the South Fork’s bays and ponds and widespread closures of beaches and shellfishing grounds because of spiking bacteria levels.

The emergence of harmful algae blooms like the “brown tide” of the 1980s and 1990s to the several variations of red or blue-green algae that now blossom in local bays — killing fish, shellfish and, in at least one case, a family pet — has been pegged to the gradual seepage of nutrient-saturated waste from the bathrooms of thousands of homes with failing septic systems that sit in the watersheds of local harbors. But while that steady stream of nitrogen and phosphorous may be the fuel that feeds the simmering fire of algae blooms over decades, extreme rainfall events are a dousing of gasoline that can set off a raging conflagration.

Dr. Christopher Gobler has led the most prominent team of researchers tracking and studying algae blooms over the last two decades. He has spotlighted the shifting patterns of very heavy rains in his frequent talks on the conditions in Long Island’s waters as a key driver of the most destructive events.

“When you get rainfall spread out more or less evenly throughout a month or a season, much of the water gets absorbed into the ground or runs into a vegetated area, so there’s uptake of nutrients and certainly all of the phosphorous gets removed when it goes through the ground,” Dr. Gobler, a marine science professor at Stony Brook University’s School of Marine and Atmospheric Sciences said recently. “But when you get these heavy rainfalls, you very quickly saturate the surface soils and you get a situation where … everything just starts running directly into surface waters. You don’t get any seepage, so it is much more potent and more likely to be having a direct stimulating effect on algae blooms.”

Rain storms that dump more than 2 inches of water in a 36 hour period have been on the increase nationwide in recent decades, but the Northeast has seen the largest spike by far. National Climate Assessment

Along with nutrients, the same effects of heavy rainfalls also spike levels of bacteria. Researchers have shown that the DNA in high bacteria levels that often force closures of beaches or shellfishing areas come largely from mammals, like pets and deer, whose feces and urine left on roadways and lawns is washed into bays or ponds after heavy rains.

The forces behind the shift in rainfall patterns can be many, but researchers say that the uniform underlying magnifier is quite obviously the slow warming of the Earth’s atmosphere.

Stony Brook University professor Dr. Kevin Reed has been studying the way climate change is impacting the development of tropical cyclones like hurricanes. In two papers published this year, his findings have shown that the warming climate is likely to result in fewer hurricanes overall, but more severe ones.

He plans to turn his research to examine whether similar impacts may be seen with other storm systems, like the nor’easters and storm fronts that account for most of the severe weather in the Northeast.

“As temperatures increase, the amount of moisture in the atmosphere increases, which means the amount of water available for precipitation increases,” Dr. Reed explained.
One of the conditions that has also been seen as the number of extreme rainfall events has increased, is also longer stretches without rain, the scientist said.

“You can also see periods of drought because the time between events can be increasing,” Dr. Reed said. “We can go two or three weeks without any rainfall at all, and all of a sudden we get 3 inches at once. There’s a reason for that.

The spring of 2020 was a prime example on Long Island. The National Oceanographic and Atmospheric administration and U.S. Geological Survey drought monitoring showed that Long Island was in a marginally abnormal dry spell going into the height of summer and portions of Connecticut, Vermont and Massachusetts were nearing an official drought. Then on July 10, the remnants of Tropical Storm Fay swept through the region, dumping more than 2 to 3 inches of rain on much of the island — though the South Fork saw little of that — and more in areas west of the city.

Dr. Reed says that the very conditions that can drive tropical storms like Fay to generate such extreme rainfalls, can also account for longer periods between rains.

“If you have an atmosphere that has more moisture, you will get stronger storms, but when you have an event that is more efficient at removing moisture from the atmosphere — which is essentially what a storm is — the atmosphere that is left behind is drier,” he said.

The effect also carries over, Dr. Reed says, on a global scale. Places that are seeing more rainfall overall, and much more of that in extreme storms, but the other side of the coin is that other regions of the world are seeing steep declines in rainfall — an effect that carries expansive implications on human populations.

“The wet get wetter and the dry get drier,” he said.

And our region’s rollercoaster of dry spells followed by heavy downpours only serves to magnify the effects of the heavy rain on algae blooms and water quality in general. When rain doesn’t fall for long periods, the contaminants that a coming storm will carry with in its runoff when it does come build up.

“When it hasn’t rained in a while, you get all sorts of things accumulating on surfaces,” Dr. Gobler said. “Then the heavy rain comes, it pushes it all in at once. It’s that first flush, which is really an appropriate term for it.”