New Hampshire can experience any natural disaster that can occur anywhere in the world, with one exception: The state has no active volcanoes.
Natural disasters have historically not occurred as frequently in New Hampshire as in other parts of the world, but the state has had its share. Since 2005 it has experienced a destructive series of events, including floods, a major tornado and the most serious ice storm in its history.
Following is a brief overview of natural disasters that are most likely to threaten New Hampshire.
- Tornadoes and Severe Winds
- Severe Winter Storms
- Ice Storms
- Wildland Fires
The most common hazard in New Hampshire is flooding. Every year some part of the state experiences flash flooding, main stem river flooding, coastal flooding or a combination of the three.
The most recent series of floods began in October 2005 with a flood that primarily affected the southwest corner of the state and devastated the town of Alstead. The flood killed seven people. It was followed by floods in May 2006 and April 2007 and a series of floods during the late summer and early fall of 2008.
These floods all had one thing in common – continuous heavy rain caused by two or more weather systems that stalled over the state. Because of the state’s rough topography, its many small rivers and streams can quickly overflow their banks during heavy, continuous rain. There is no place for the excess water to go except onto roads and fields and into populated areas.
Historically, the state’s two largest floods occurred in 1936 and 1938. The 1936 flood was associated with snow melt and heavy precipitation. The 1938 flooding was caused by the Great New England Hurricane of 1938. Those floods prompted the construction of a series of flood control dams, built in the 1950s and ‘60s. They continue to be operated by the US Army Corps of Engineers.
The threat of flooding is most common in the spring from a combination of snow melt and rain. But floods may strike the state at any time of the year.
All coastal states from Texas to Maine are at risk from hurricanes and New Hampshire is no exception. The primary threats associated with hurricanes come from flooding due to a coastal storm surge, inland flooding due to heavy precipitation and severe winds. Hurricanes are known for their high winds and the damage they can cause, but about 80 percent of deaths during hurricanes are due to drowning.
The largest recorded hurricane to strike New Hampshire was the Great New England Hurricane of 1938, which caused $22 million (in 1938 dollars) in direct damage and killed 13 people. A repeat of this event today would be devastating. The state’s population has more than doubled since 1938 and much of that population growth has been in areas near the coast or inland waterways. There are many more people in harm’s way today. New Hampshire also lacks a statewide building code to enforce wind-resistant construction standards.
Hurricane Bob dealt New Hampshire a glancing blow in 1991 yet still was responsible for $2.5 million in damage and three deaths. It is important to note that tropical storms below hurricane intensity have been responsible for some of the worst inland flooding experienced in the Northeast. Moving slowly and carrying lots of moisture, tropical storms can produce rain of several inches per hour. Even though hurricanes tend to lose intensity and their winds diminish as they move north, the heavy rain they bring can still be dangerous.
Tornadoes and Severe Winds
One or two tornadoes are reported in New Hampshire a year. Most of these and small and only cause localized damage. The state is generally not associated with the huge tornados that occur in the Midwest and South. But, on July 24, 2008, a large thunderstorm system spawned a tornado that touched down in Epsom and Northwood just before noon. This EF-2 tornado, with winds up to 157 mph, tore through the middle of the state, and headed northeast to Ossipee. It killed one person, destroyed or damaged 60 structures and damaged thousands of acres of forest. It was the worst tornado in New Hampshire history and resulted in a Presidential Disaster Declaration for the affected counties.
Previously, the most significant tornado to strike New Hampshire occurred in September 1821. That tornado had a path half a mile wide, killed six, injured hundreds and left thousands homeless.
The southwestern portion of the state is considered a special wind hazard area as demonstrated by the high proportion of tornadoes and severe wind events that are experienced there annually. On July 3, 1997 several tornadoes struck this section of the state. An EF-1 tornado caused severe tree loss in Swanzey, destroying a building and damaged the stables at the Cheshire Fairgrounds. At the same time an EF-2 tornado struck Greenfield, causing damage to a summer camp, the recycling center and completely destroying a lumber facility. No deaths resulted from these events.
A microburst is a severe localized wind blasting down from a thunderstorm. These "straight line" winds are distinguishable from a tornado’s circular pattern of destruction and debris.
Depending on the size and location of these events, the destruction to property may be devastating. Microbursts have produced winds as strong as 175 mph. Winds of this intensity can cause severe damage to forests and structures, and are certainly life threatening.
Microbursts have severely damaged several areas of New Hampshire. On Aug. 18, 1991, five people were killed and 11 injured in Stratham. This downburst also caused almost $2.5 million in damage. In 1994, a microburst left a path one-half mile wide and 4-6 miles long in the town of Moultonborough. On July 6, 1999, two people were killed when a microburst struck central New Hampshire.
Severe Winter Storms
Though snowstorms are taken in stride in New Hampshire and are a source of income to the state though the ski and snowmobile industries, they can cause severe damage and death. Heavy wet snow has caused widespread power outages and the collapse of buildings. Ice storms (see below) also cause power outages and create extremely hazardous conditions for motorists.
The safest thing to do during a severe winter storm is to stay home and enjoy the day off. Schools and many businesses close during heavy snow storms and it is easier for plows to get the roads cleared if traffic doesn’t get in the way. But if the power goes out for an extended period people may need to seek shelter outside the home. Local officials will provide information on shelter locations and services if that becomes necessary.
Utility crews begin work on power restoration immediately and most outages last only a few hours. But if the damage to power lines, poles and other equipment is widespread it may take days or weeks to restore service. Anytime there is a power outage associated with a major storm, people should assume it will last more than a couple of days. They should seek warm shelter and take other appropriate measure to protect themselves.
When a mass of warm moist air collides with a mass of cold arctic air, the less dense warm air will rise and the moisture may precipitate out in the form of rain. When this rain falls through the colder, more dense air and comes in contact with cold surfaces, the latent heat of fusion is removed by convective and evaporative cooling. Ice forms on these cold surfaces and may continue to form until the ice is quite deep, as much as several inches.
The buildup of radial ice may strain branches of trees, power lines and even transmission towers to the breaking point. One inch of radial ice will bring down tree limbs onto power line. Two inches or radial ice on power lines with bring the lines down because of their own weight, usually taking poles and transformers with them. Either way, ice storms cause widespread power outages.
Debris from downed trees and wires makes roads impassible and makes emergency access, repair and cleanup extremely difficult. Sawyer crews have to clear the way before line crew can begin restoring power.
The state’s largest ice storm occurred in December 2008. The National Weather Service had been predicting a major ice storm, but actually arrived was about twice what was expected. More than half of the state’s electric utility customers, which included about two-thirds of the population, were out of power. Some for as long as two weeks. All four of the state’s electric utilities were overwhelmed and brought in extra sawyer and line crews from as far away was the Midwest and Canada.
An earlier ice storm, in January 1998, also caused power outages around the state as well as significant damage to the state’s forests.
It is for good reasons that lightening is called the "Underrated Killer"! New Hampshire is ranks 16th in the nation for casualties from lightning strikes. Nationally lightning kills and injures over 400 people a year, some sources believe this number to be twice as large.
Lightning is most common - and most deadly - in the summertime, when people are outdoors and engaged in recreational activity. Any thunderstorm can generate deadly lightning. Anyone who can hear thunder is in danger of being struck. People should seek shelter in a sturdy building if a thunderstorm approaches.
New Hampshire is considered to be an area of moderate seismic hazard. This means that the state could experience large (6.5-7.0 magnitude) earthquakes, but they are not likely to occur as frequently as in a high hazard area like California. The state typically experiences one or two earthquakes per year registering magnitude 2.0 to 3.5.
According to the NH Division of Homeland Security and Emergency Management and the US Geological Survey, the overall earthquake risk to the state is high. This is because of the built environment of New Hampshire. That is, many structures in the state (e.g., buildings, homes, bridges, and highways) are old or not built to modern earthquake standards. Hence, they are unable to withstand quakes. Additionally, due to the unique geology of New Hampshire, earthquake propagation waves travel up to 40 times further than they do in the western United States. This means the area of damage could be larger.
Recognizing the significant danger posed by seismic activity in the New England region, the US Geological Survey is presently installing the Advanced National Seismic System in Boston and New York City to provide emergency responders with real-time earthquake information.
Large wildland fires are typically associated with the western states, although they are possible in New Hampshire. Historically, New Hampshire’s large wildfires run in 50-year cycles. With some of the state’s largest wildfires occurring in the late 1940’s many people believe we are overdue for the next bad fire season.
Local five departments and the state Division of Forests and Lands post fire dangers levels during the fire season. The threat is greatest during dry periods and in spring when the land has begun to dry out after winter snow has melted, but new leaves have not grown out.
Permits are required in New Hampshire for outdoor burning at anytime that the ground is not covered with snow. Property owners should check with local forest fire wardens about local restrictions.