New Hampshire experiences a diverse range of natural hazards influenced by its unique geography, including a mountainous interior, major river systems, and a small coastline. Its location in New England makes it a frequent target for powerful winter storms and a recipient of the residual effects of Atlantic tropical systems. These forces combine to create a distinct profile of risks, with the most common and impactful events centered on extreme weather.
Dominant Winter Hazards: Ice Storms and Nor’easters
Severe winter weather is one of the most frequent and costly hazards, with the state experiencing eleven billion-dollar winter storm events between 1980 and 2024. These events often manifest as Nor’easters, powerful low-pressure systems that move up the East Coast. Nor’easters bring heavy snowfall, blizzard conditions, and high winds, causing significant damage and widespread power outages, particularly in the interior and mountain regions.
Ice storms are destructive winter phenomena, occurring when rain freezes upon contact with objects near the surface. This freezing rain accumulates as a heavy glaze of ice on trees and power lines, leading to catastrophic infrastructure failure. The December 2008 ice storm, for example, led to a major disaster declaration due to widespread damage. The combination of intense cold and prolonged power loss during these events poses a significant threat to public safety.
Water-Based Risks: Flooding and Coastal Impacts
Flooding is the most common natural disaster in New Hampshire, occurring in multiple forms across the state’s varied landscape. Riverine flooding frequently affects inland communities, often triggered by prolonged, heavy rainfall or a rapid spring snowmelt that swells major river systems. The state has experienced multiple severe flooding events, including the extensive damage caused by the Mother’s Day storm of 2006.
Flash flooding is also a risk, particularly in mountainous regions where steep terrain accelerates runoff during intense downpours. The remnants of tropical systems, such as Tropical Storm Irene in 2011, contribute to inland flooding by delivering substantial rainfall. Although New Hampshire has a short shoreline, coastal areas face risks from storm surge and high astronomical tides, often exacerbated by powerful Nor’easters.
The coastal region is increasingly vulnerable to sea-level rise, which contributes to more extensive and frequent flooding. This rising baseline increases the severity of coastal flooding during major storm events. It also threatens infrastructure and historic sites near the ocean.
Severe Warm-Weather Events: Tornadoes and Thunderstorms
During the warmer months, the state experiences localized hazards primarily associated with severe thunderstorms. These storms frequently produce large hail and damaging straight-line winds, sometimes called microbursts, which can flatten trees and cause structural damage. While less frequent than in the Midwest, tornadoes do occur, averaging about 1.2 per year in the past decade, up from a historical average of 0.5 per year.
Tornadic activity generally peaks in July, and most recorded events are relatively weak, typically rating as EF0 or EF1 on the Enhanced Fujita scale. Despite their lower intensity compared to those in other regions, these events can still cause significant localized destruction to property and woodlands. The threat from these warm-weather events is highly localized, contrasting with the widespread impact of major winter storms.
Environmental and Geological Hazards
Slower-onset environmental conditions, like drought, pose a distinct hazard by increasing the risk of wildfires. Extended periods of low rainfall and low humidity dry out vegetation, creating abundant fuel for fires. This condition is particularly concerning when combined with steady winds, which can result in a “very high” wildfire danger rating.
Drought-stressed forests are also more susceptible to insect infestations and disease, which compromises the ecosystem. Furthermore, an estimated ninety percent of wildfires are attributed to human causes, meaning the risk is elevated during dry periods even without lightning strikes. The state experiences infrequent, low-magnitude seismic activity, with historical earthquakes recorded, though the threat from major geological events remains minimal.