Along coastlines and kilometres inland, storm surge is one of the biggest threats to lives and property during hurricanes and storms. Hurricane evacuations are primarily due to storm surge, they have cost millions of lives and hundreds of billions of dollars in damages over the last century.
|Storm surge from Hurricane Haiyan in the Philippines left buildings destroyed, trees up-rooted, cars piled on top of each other and many homeless. (Nov 2013 © UNICEF/Maitem|
In 1970, a massive storm surge left 300 000 people dead in the coastal wetlands of Bangladesh. In 2013, some 6 300 people lost their lives due to the Hurricane Haiyan/Yolanda storm surge at landfall in the Philippines. Improvements in forecasting and warning systems have significantly reduced the toll in human lives lost due to storm surge in recent years. However, even with the most effective warning systems available, the potential for large numbers of fatalities remains.
Population densities are increasing in coastal areas, sea level is rising and climate change is expected to heighten the frequency and intensity of the extreme weather events that cause storm surge – the lives and livelihoods of millions of people living in low-lying, highly populated areas are under threat.
Further findings show that overall, storm surge levels in Europe are projected to increase on average by around 15% by 2100 under a high-emissions scenario and that climate change will result in higher seas not only driven by sea level rise, but also by increased storminess. – Projections of extreme storm surge levels along Europe, Springer 2016
Mitigating the risks, increasing resilience, preparing populations and providing early warnings represent major challenges for meteorologists, hydrologists, oceanographers, emergency managers and policymakers.
What is a storm surge?
A storm surge is an abnormal rise of water generated by a storm. Strong winds in a tropical cyclone or a sever mid-latitude storm are their primary cause. However, ocean bottom topography, tides, waves and freshwater input from rivers affect the water level rise during a storm surge.
The depth of a storm surge can rise quickly — from centimetres to a meter or more in a matter of minutes. It can push an incredible distance beyond the coast. During Hurricane Ike, the surge moved nearly 50 kilometres (30 miles) inland in some locations. A storm surge can travel through bays and up rivers — basically any body of water on or near shore.
How to respond to storm surge?
Storm surge evacuation orders should be immediately heeded. Escape routes may be cut off when the storm hits – cars cannot be driven and the waters are rarely navigable. During a storm surge, the level of water flooding into a home can rise quickly — sometimes from a few centimetres to 2 to 3 metres in minutes.
One cubic metre of sea water (at 20°C) weighs 1 024 kilograms — over a ton. So a storm surge carrying tons of water at speeds typically from 15 to 25 kilometres an hour has tremendous power. A 50-centimetre storm surge can sweep a car off the road, and an adult would have difficulty standing in a 15-centimetre surge. Compounding the destructive power is the large amount of debris — trees and other objects — usually carried in the storm surge. These can act as battering rams, caving in buildings and structures that stand in their path.
Hurricane Katrina (2005) is a prime example of the damage and devastation that can be caused by surge. At least 1 500 persons lost their lives and many of those deaths occurred directly, or indirectly, as a result of storm surge. …It produced catastrophic damage — estimated at US$75 billion in the New Orleans area and along the Mississippi coast. Storm surge flooding of 25 to 28 feet (7.5 to 8.5 metres) above normal tide levels was associated with Katrina. – National Hurricane Center
WMO supports the National Meteorological Services in storm surge forecasting and warning by
- improving impact-based multi-hazard early warning systems
- strengthening technical supports for coastal services and disaster risk reduction
- coordinating and facilitating the provision of forecast services and related technical advice before, during and after storm surge events.
The WMO Coastal Inundation Forecasting Demonstration Project provides an example of cooperative work for building improved operational forecasting and warning capabilities for coastal inundation, combining extreme waves, surges and river flooding events.
The Joint WMO-IOC Technical Commission for Oceanography and Marine Meteorology regularly review and update of technical guides and publications on storm surge forecasting.