Storm surge, an abnormal rise in water associated with tropical cyclones and severe storms, poses a significant threat to coastal communities. It can cause extensive damage and risk lives and property. Understanding its causes and effects is important for coastal residents and emergency planners.
Defining Storm Surge
Storm surge is an abnormal rise of water generated by a storm, occurring above predicted astronomical tides. It differs from heavy rainfall or typical high tides. The primary forces are the storm’s strong winds pushing water towards the shore and low atmospheric pressure within its center. This combination creates a dome of water that moves inland as the storm approaches the coast. Unlike predictable regular tides, storm surge is a temporary, rapid increase in sea level directly linked to severe weather.
The Science Behind Storm Surge
Storm surge height and impact are influenced by meteorological and geographical factors. A storm’s powerful winds are a primary driver, physically pushing seawater towards the coast. The speed and duration of these winds directly affect water accumulation, with stronger, larger storms generally producing higher surges.
Atmospheric pressure within the storm is another contributing factor. The extremely low pressure at the storm’s core causes the sea surface to bulge upwards slightly, an effect known as the “inverse barometer effect.” While this accounts for a smaller portion of the total surge, typically about 5% of the water rise, it adds to the overall water elevation.
Coastal geography also plays a role. Shallow, gently sloping seabeds (bathymetry) allow water to pile up more easily, amplifying surge height. Concave coastlines, like bays or inlets, can funnel water, concentrating the surge and leading to higher levels. The storm’s arrival timing relative to the normal tidal cycle can alter the total water level, as a surge coinciding with high tide results in a higher “storm tide.”
Storm Surge vs. Other Water Hazards
Storm surge must be distinguished from other water-related coastal flooding phenomena. Storm surge refers specifically to the rise in water level caused solely by the storm’s forces. In contrast, “storm tide” is the total observed seawater level during a storm, combining storm surge and the astronomical tide (the normal, predictable rise and fall of ocean water). For example, a 5-foot storm surge at a 3-foot high tide results in an 8-foot storm tide.
Storm surge is distinct from a tsunami. Storm surge is meteorological, driven by wind and pressure from weather systems like hurricanes. Tsunamis, however, are geological phenomena, typically caused by sudden underwater disturbances like earthquakes, volcanic eruptions, or landslides. Unlike storm surge, which is a mound of water pushed inland, tsunamis involve a series of powerful waves that can travel across entire ocean basins.
Storm surge also differs from riverine or rainfall flooding. Storm surge involves ocean water pushed inland from the coast. Rainfall flooding occurs when excessive precipitation overwhelms drainage systems or causes rivers to overflow, leading to freshwater inundation. While a severe storm might bring both heavy rain and storm surge, their mechanisms and water sources are different.
Consequences of Storm Surge
Storm surge impacts are devastating, posing threats to coastal environments and communities. Coastal inundation is a primary consequence, leading to widespread flooding of homes, businesses, and critical infrastructure. The volume of water can submerge entire communities, making areas impassable and trapping residents.
The force of surging water causes severe erosion along beaches and damages natural coastal barriers like dunes. This erosion can undermine foundations, leaving structures vulnerable even after water recedes. Pressure and currents within the surge can inflict significant structural damage to buildings, breaking windows, collapsing walls, and carrying away debris.
Storm surge is frequently the leading cause of fatalities during severe coastal storms and hurricanes. The rapid rise of water, combined with strong currents and floating debris, creates hazardous conditions. This makes escape difficult and often impossible for those caught in its path.