Scientists Link Trend to Global Warming
Baltimore, MD—Nearly a year after Tropical Storm Irene and other powerful storms led to record flooding that devastated many areas of Maryland, a new Environment Maryland Research & Policy Center report confirms that extreme rainstorms and snowstorms are happening 55 percent more frequently in the Mid-Atlantic region than in 1948.
“As the old saying goes, when it rains, it pours—especially in recent years as bigger storms have hit Maryland more often. We need to heed scientists’ warnings that this dangerous trend is linked to global warming and do everything we can to cut carbon pollution today,” said Tommy Landers, director of Environment Maryland.
The group was joined by Congressman John Sarbanes (MD-3), who represents parts of Baltimore and nearby counties all of which have seen damaging extreme precipitation events.
“Climate change is occurring at a rate that is alarming and unsustainable. We must pursue policies that will not only protect public health and the environment, but will also promote clean energy innovation and prepare our economy for success in the future,” said Congressman Sarbanes, a member of the House Energy & Commerce Committee, which has jurisdiction over federal climate change policy.
State Senator James Rosapepe (District 21) of Prince George’s County also participated and addressed how Maryland should respond to the reality of increased extreme precipitation.
“This reports documents what every Marylander knows from days of derecho-soaked power failures – climate change means more economically-damaging storms. It’s time for BGE and PEPCO to accept reality and invest in the electricity reliability that our 21st century economy requires,” said Sen. Rosapepe.
Based on an analysis of state data from the National Climatic Data Center, the new report found that heavy downpours or snowstorms that used to happen once every 12 months on average in the Mid-Atlantic region now happen every 7.7 months on average. Moreover, the biggest storms are getting bigger. The largest annual storms in the Mid-Atlantic now produce 23 percent more precipitation on average than they did 64 years ago.
Scientists have concluded that the rise in the frequency and severity of heavy rainstorms and snowstorms are linked to global warming. Warming increases evaporation and enables the atmosphere to hold more water, providing more fuel for extreme rainstorms and heavy snowstorms.
“The increase in frequency and intensity of extreme precipitation events is consistent with the expected effects of global warming: warmer air holds more moisture, and that moisture is fuel for storms. It won’t necessarily rain more often. But when it does rain, it’s more likely that the rain will come as a high energy, intense downpour,” said Dr. Ben Zaitchik, Assistant Professor of Earth & Planetary Sciences at the Johns Hopkins University.
In August of 2011, Tropical Storm Irene hammered the East Coast, bringing high winds and torrential rain that downed trees and power lines, flooded streets and homes, and caused widespread destruction. The storm tore through Maryland, leaving 700,000 residents without power. Due to flooding and fallen trees, over 180 roads were shut down across the state, and for the first time in state history the first day of school was cancelled. At least one fatality was reported when a house collapsed in on a woman.
The new Environment Maryland Research & Policy Center report, “When It Rains, It Pours: Global Warming and the Increase in Extreme Precipitation from 1948 to 2011,” examines trends in the frequency of and the total amount of precipitation produced by extreme rain and snow storms across the contiguous United States from 1948 to 2011. Using data from 3,700 weather stations and a methodology originally developed by scientists at the National Climatic Data Center and the Illinois State Water Survey, the report identifies storms with the greatest 24-hour precipitation totals at each weather station, and analyzes when those storms occurred. The report also examines trends in the amount of precipitation produced by the largest annual storm at each weather station.
Nationally, the report found that storms with extreme precipitation increased in frequency by 30 percent across the contiguous United States from 1948 to 2011. Moreover, the largest annual storms produced 10 percent more precipitation, on average. At the state level, 43 states show a significant trend toward more frequent storms with extreme precipitation, while only one state (Oregon) shows a significant decline.
Key findings for Maryland and the Mid-Atlantic include:
- Extreme rainstorms and snowstorms are becoming more frequent. The Mid-Atlantic region experienced a 55 percent increase in the frequency of extreme rainstorms and snowstorms from 1948 to 2011. In other words, heavy downpours or snowstorms that happened once every 12 months on average in 1948 now happen every 7.7 months on average. 
- The Mid-Atlantic region ranks second nationwide for the largest increase in the frequency of storms with heavy precipitation.
- The biggest rainstorms and snowstorms are getting bigger. The amount of precipitation released by the largest annual storms in Maryland increased by 14 percent from 1948 to 2011.
Landers was careful to note that an increase in the frequency and severity of extreme rainstorms does not mean more water will be available for human use. Hotter temperatures fuel extreme rainstorms by increasing rates of evaporation. At the same time, however, that evaporation increases soil dryness. Moreover, scientists expect that, as global warming intensifies, longer periods with relatively little precipitation will tend to mark the periods between heavy rainstorms. As a result, droughts are likely to become more frequent and severe in some regions of the United States. Currently, more than half of the lower United States is suffering through prolonged drought, aggravated by the fact that the last six months have been the hottest January–June period on record.
According to the most recent science, the United States must reduce its total global warming emissions by at least 35 percent below 2005 levels by 2020 and by at least 85 percent by 2050 in order to prevent the most devastating consequences of global warming. Environment Maryland highlighted two proposals from the Obama administration—carbon pollution and fuel efficiency standards for cars and light trucks through model year 2025, and the first ever carbon pollution standards for new power plants—as critical steps toward meeting these pollution reduction targets.
At the state level, Maryland officials have drafted a comprehensive statewide plan to reduce greenhouse gas emissions. They are also working with neighboring states to find ways to improve the Regional Greenhouse Gas Initiative (RGGI), the first-in-the-nation cap on carbon pollution from the power sector that sells permits for carbon emissions and has led to nearly $1 billion in investments in energy efficiency and clean energy solutions in the region.
“How serious this problem gets is largely within our control – but only if we act boldly to reduce the pollution that fuels global warming. Maryland officials can build on the progress we have made reducing emissions by seeing this critical statewide plan to the finish line, and by strengthening the Regional Greenhouse Gas Initiative, which has been a key part of our strategy to reduce pollution and shift to clean energy,” Landers said.
 For Maryland alone, the report found a 91% likelihood of an increase in the frequency of extreme precipitation events. In Maryland the data came from relatively few weather stations – 17. In contrast, Pennsylvania had 75 and New York had 84. So, the relatively low number of weather stations influenced our ability to detect a statistically significant trend. For Maryland in particular, then, the most telling data are the 55% increase in the frequency of extreme events in the Mid-Atlantic, and the 14 percent increase in the amount of precipitation from those events in Maryland.