WHAT ARE STORM SURGES?
A storm surge is the abnormal rise of the water levels near the coast or near large lakes.
The onset of a storm surge is not sudden. Therefore, with existing tools of prediction, prior warnings can be made available to the people residing near the coastline so they can make appropriate preparations.
A storm surge should not be confused for a tsunami. Storm surges happen frequently and are basically the effect of tropical cyclones, hurricanes or typhoons. They are caused due to high winds and pressure, and occur right along the coastlines. History is witness to the major impacts caused by storm surges around the globe. In fact, they can be life-threatening to the people and infrastructure along the coastline, though not always. Tsunamis, on the other hand, happen less frequently, originate from earthquakes or seismologic activity, and can reach thousands of miles. They also bring with them much more loss of life and damage than storm surges.
The Indian coast is surrounded by the Arabian Sea on the Western coast and by the Bay of Bengal on the Eastern Coast which is categorized into 4 zones based on surge height. For surge heights greater than 5m, a zone is considered Very High Risk (VHRZ) whereas for surge heights between 3-5m, a zone is categorized as a High Risk Zone (HRZ). Moderate Risk Zones are zones with surge heights between 1.5 to 3m.
The coastal areas and off-shore islands of Bengal along with adjoining Bangladesh are the most storm-surge prone, with storm surge heights reaching up to 13m. Hence, they are categorized as Very High Risk Zones (VHRZ). The East Coast of India is subjected to a large number of cyclones every year, particularly between Paradip and Balasore in Odisha, which sees storm surges of heights between ~5 & 7m (VHRZ). In the south, the estuaries of two major rivers, Krishna and Godavari lie on the Andhra coast between Bapatla and Kakinada. They hold storm surges of heights ~5-7m (VHRZ). The coastline between Pamban and Nagapattinam in Tamil Nadu are subjected to storm surges of height ~3-5m, making this a High Risk Zone (HRZ). Gujarat, along the west coast of India experiences storm surges of height ~2-3m, and is therefore designated a Moderate Risk Zone (MRZ).
Over the years, several storm surge models have been developed. A number of numerical software such as SPLASH, SLOSH etc., have also been adopted and implemented. They help forecast storm surges by use of powerful supercomputers that utilise meteorological satellites and sensors as verification tools. The major challenges to forecasting are sudden variations in tropical cyclone track and intensity, the need for a complete study on the consequences of storm surges, and the effects of climate change on risk estimation. By employing several numerical models as well as advanced observational and computational tools and skills, routine operational forecasting is possible. However, at present, only forecasts of 50 nautical miles accuracy in track with an intensity of 5 m/s within a 24-hour validity period is possible. The surge elevation can be within 50 cm along with a 12-hour validity time interval on average. In order to cope with variability of tropical cyclone in track and intensity, further research in this area is needed. The risk analysis should consider the integrated research on tropical cyclones, ocean waves, heavy precipitation, inundation, estuarine block, salty invasion and most importantly, the effects of climate change. Establishing an efficient warning system and reducing vulnerability to storm surge disasters should be the priority of coastal zone management (Li and Nie 2017).