Over the past 20 years, rainfall, flooding and sea level have increased across Maryland, according to data collected from the National Oceanic and Atmospheric Administration (NOAA).

From 2000 to 2020, precipitation in Maryland increased by 2.63 inches per decade, according to NOAA. The administration also found the Northeast Atlantic region saw 100 to 150 percent more flood days in 2020 than in 2000. The Maryland Sea Grant College at the University of Maryland projected sea level in the Chesapeake Bay will rise up to 2.1 feet by 2050 in a 2013 report. 

INCREASED PRECIPITATION

Across the northeast United States, precipitation has become more frequent and heavier, a trend that is projected to continue throughout the 21st century, according to the 2017 Climate Science Special Report

Typically, summer months — June, July and August — appear to have higher numbers of thunderstorms and tropical storm activity that can account for much of the Northeast’s annual precipitation levels, Greg Carbin, the chief of forecast operations at the National Weather Service’s Weather Prediction Center, said. This makes sense, he said, because warmer global temperatures and a more moist atmosphere are supporting larger amounts of rain over larger areas.

“There’s a lot of moving parts to this,” Carbin said. “The stage is set to support very heavy precip[itation]. Similar to what we saw … in the New York City area with the remains of Hurricane Ida, rainfall rates of three, four inches an hour, there’s very few cities that can sustain an event like that without having some impact.”

Precipitation is especially heavy in counties surrounding the Chesapeake Bay. When evaluating precipitation by year, coastal counties were consistently among those with the most precipitation over a 20-year period, according to CNS analysis of data from NOAA. In 2018, Baltimore City had the highest annual precipitation in Maryland over the course of 20 years with 73.84 inches.

Increasing precipitation can also be seen over a larger period of time. Within 125 years, data from NOAA shows that the five wettest years in Maryland occurred after 1970, with precipitation falling between 55 and 65 inches. The five driest years were between 1925 and 1965, with between 23 and 35 inches of precipitation.

Hurricane Isabel in 2003 — the second wettest year in Maryland since 1895 — hit North Carolina primarily, but Maryland and other states were heavily affected as well. In the upper Chesapeake Bay, water surged six to eight feet above normal levels. Rainfall ranged from four to seven inches across the state. The Category 5 hurricane killed 17 people in total — one in Maryland — and racked up $410 million dollars of damage in the state, $1.685 billion total. 

Since 1980, flooding, severe storms, tropical cyclones and winter storms have made up 78 percent of the cost of Maryland’s billion-dollar extreme weather events, according to NOAA. These events have cost Maryland between $9.1 billion and $20.25 billion.

RISING SEA LEVELS & FLOODING

But severe weather events aren’t always so dramatic. Rising sea levels have increased the number of “nuisance floods,” or tidal floods that cause minor impacts, by five to 10 times since the 1960s in numerous U.S. coastal cities, according to the 2017 Climate Science Special Report.

Annapolis, located on the Chesapeake Bay, is a city that is regularly affected by flooding.

Being right on the Bay and containing several peninsulas, flooding is something that the city’s Deputy Director of Emergency Management Dave Mandell is always prepared for. Still, the flood of the 2019 Annapolis Boat Shows caught him unaware.

Though the day started sunny, a coastal flood soon hit. When the dock floods downtown, the water level is typically around 3.1 feet, Mandell said. That day it hit about 4.1 feet. Deputy City Manager Jaqueline Guild said she was wading through knee-deep water. It was the worst coastal flood the city had seen in almost five years, although flooding is a regular occurrence.

“That’s what surprises a lot of people that aren’t exposed to a lot of what we do in Annapolis is the daylight today, it’s sunny out, it’s not raining and … there’ll be water and they’ll think ‘Oh, did it rain?’” Mandell said. “It didn’t rain at all. It’s just the winds and the tides and the combination can cause it.”

According to NOAA, high-tide flooding in the U.S. happens more than twice as often today as in 2000. By 2030, the U.S. will likely see an increase in annual floods from seven to 15 times a year and by 2050, certain areas could experience up to 75 high tide floods per year. 

Rising sea levels are also a concern. In Annapolis, subsidence — the gradual sinking of land — exacerbates the increasing sea level. Between January 2000 and December 2020, data from NOAA showed that the sea level rose 0.33 millimeters.

Baltimore’s sea level has also been steadily on the rise. In Jan. 2000, the average sea level was -0.12 millimeters. In December 2020, it increased to 0.16 millimeters, establishing a 0.28 millimeter difference. Looking at the linear trend — a comprehensible average of all the values — we see a steady increase of 0.07 millimeters over the past 20 years.

But that isn’t the only cause for concern.

Sea level gauge measurements at Fort McHenry have risen 12 inches since 1900, according to Lisa McNeilly, the director of sustainability in Baltimore City. Tidal gauges are one way scientists measure rising sea level by using sensors to measure the water level around the world.

“We have a lot of concern around a range of different locations and causes of flooding,” McNeilly said.

Scientists have been measuring sea level with tide gauges since 1851, and satellite altimeters since the 1990’s. According to NOAA, satellite altimeters measure sea level “by measuring the time it takes a radar pulse to make a round-trip from the satellite to the sea surface and back.”

In 2019, sea level had risen 87.6 millimeters since satellite recording began in 1993.

However, Maryland state climatologist Dr. Alfredo Ruiz-Barradas cautioned that it’s important to consider how natural phenomena also have the ability to affect the earth’s climate over the course of millennia.

“Any decadal change we may be tempted to label as man-made has to be placed in context of these natural phenomena that have the capability to induce changes in these [time] scales,” Ruiz-Barradas said in an email.

To combat the more extreme precipitation and flooding of recent years, people need to think about building more resilient, robust systems that can mitigate the damage, according to the National Weather Service’s Greg Carbin. New Orleans, with its major storms, and the Netherlands, where elevation is low, are just two examples of areas that deal with significant flooding. However, they’ve spent the money to successfully keep the water damage at bay, he said.

“If you build back better, or you build for resilience in your systems to try to account for some of these extremes, you’re most likely gonna save a little bit of money in the long run, as opposed to thinking that the climate is static,” Carbin said.

This article was originally published on CNSMaryland.org on Wednesday, October 13, 2021.


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