Storms and floods

Key takeaways

• The Northeast U.S. (NEUS) has experienced a strong increase in the frequency and intensity of storms.
• The NEUS is especially vulnerable to northward-moving tropical storms that expand in size while retaining high moisture content and strong winds.
• Tropical storms cause significant coastal wind damage and widespread flooding across the NEUS, compounded by rising sea levels.
• Remnants of tropical storms have caused significant flooding and damage in the NEUS.
• Projected increases in winter rainfall are expected to increase surface runoff and peak river flows, causing flooding.

Storms in Summer and Fall

Large storms originating in the tropics, referred to as hurricanes in the Atlantic Ocean, bring abundant moisture and heavy rainfall to the NEUS. The impact of oceanic and atmospheric warming on the frequency and intensity of hurricanes is an active area of research. While there is no long-term trend in the frequency of landfalling hurricanes in the smaller domain of the U.S. (Marvel et al., 2023), recent research does suggest a significant increase in the rapid intensification of hurricanes due to anthropogenic warming (Bhatia et al., 2022).

Tropical Storms

Tropical storms can cause significant wind damage along the coast as well as flooding across the NEUS, which is compounded by rising sea levels (see Douglas and Kirshen, 2022 and references therein). The NEUS is especially vulnerable to tropical storms moving northward, as they increase in size considerably while still retaining their tropical characteristics such as high moisture content and strong winds. Two events with significant impacts on the coastal NEUS in the last two decades include Hurricane Irene in 2011 and Hurricane Sandy in 2012. Both systems caused severe flooding in parts of the coastal NEUS. Extreme precipitation events in the NEUS also occur from the remnants of tropical storms. Significant flooding and damage in New York City in late September 2023 caused by the remnants of tropical storm Ophelia and flooding in New Jersey in 2021 caused by the remnants of Hurricane Ida are notable examples of remnants of tropical systems affecting the NEUS.

Winter Storms

A projected increase in winter precipitation in the future will result in more rainfall and less snowfall due to atmospheric warming. This leads to model projections indicating a decrease in snowfall frequency in the NEUS in the future (Zarzycki, 2018). This, however, does not discount the likelihood of individual high-impact snowfall events. In fact, during sufficiently cold conditions, snowstorms in the future can drop more snow because of the ability of the warmer atmosphere to hold more moisture (Zarzycki, 2018). In fact, the frequency of heavy snowfall in the NEUS has increased over the past three decades (Whitehead et al., 2023), which is likely caused by interactions between warming in the western Atlantic Ocean and frequent Arctic air outbreaks (Cohen et al., 2018). Higher winter warming will result in an overall increase in days and nights with temperatures above freezing, leading to decreases in snow cover as well as snow depth (Burkowski et al., 2022). These changes are likely to impact coastal and southern regions of the NEUS first, with high elevation regions remaining more resilient (Burkowski et al., 2022). A projected increase in winter precipitation in the form of rainfall is also projected to increase surface runoff and peak river flows in winter in the future (Siddique and Palmer, 2021; Siddique et al., 2020).

Extreme Precipitation and Flooding

Over the past several decades, the NEUS has experienced a strong increase in the frequency and intensity of extreme precipitation events. Regional increases in heavy precipitation events exceed that of the rest of the United States with a 74% increase in the heaviest 1% of all precipitation events since 1958. Flood events have risen in association with increases in precipitation, particularly extreme events. This puts fish, wildlife, and their habitats at increased risk to direct impacts, such as physical damage, displacement, and mortality, as well as indirect impacts that result from increased inputs of sediments, nutrients, and pollution to aquatic systems.
The largest increases in heavy precipitation extremes are projected to occur in the northern, coastal, and mountainous areas of the NEUS. Some locations in Massachusetts, such as the eastern region, have shown an increasing trend in the number of days with two inches of precipitation or more since 1970. Annual maximum daily precipitation (the maximum amount of precipitation that fell within a 24-hour period over the course of a year) in coastal Massachusetts and the greater northern New England region has also increased by 1 to 2 inches since 1970. In addition, the Connecticut River basin has experienced more than a doubling of heavy rainfall events over the last 60 years. Regionally, the majority of heavy precipitation events occurred during the summer months of May through September.