Changes in monsoon-time sea conditions under the influence of El Niño have made swell surges a frequent feature along the country’s western coast, prompting repeated alerts during the southwest monsoon — a shift from previous years, when such warnings were largely confined to the pre-monsoon period.

The Indian National Centre for Ocean Information Services (INCOIS), under the Ministry of Earth Sciences, has sounded a red alert for swell surge for two days along the entire coastal belt of Kerala and the southern stretch of Tamil Nadu since Saturday. On Monday, the alert was further extended till late night, with the State Disaster Management Authority asking people along the coast to remain vigilant against strong waves, sea erosion, coastal flooding and the washing away of fishing vessels. INCOIS has issued an orange alert for swell surge along coastal Karnataka since Saturday.

Swell surge is caused by waves formed by an ocean swell, which occurs due to distant storms like hurricanes or long periods of fierce gale winds. During such storms, huge energy transfer takes place from the air into the water, leading to the formation of very high waves. Such waves can travel thousands of kilometres from the storm centre until they strike the shore.

Story continues below.
Subscribe to see fewer ads.

Usually, swell surge is a consequence of strong winds in the southern part of the Indian Ocean, where an ocean swell is generated, with the waves then travelling north to reach the coast in two or three days.

Since the onset of the southwest monsoon this year, the Kerala coast has had 14 alerts against swell surge, also known as kallakadal in fishermen’s parlance. Two of the alerts were red alerts. On Sunday, the coastal belt of Alappuzha district experienced heavy waves, leading to flooding of coastal roads and disrupting traffic. Coastal areas remain on alert against huge waves at a time when mainland Kerala has reported a 28% deficit in the southwest monsoon season.

According to INCOIS director Dr T M Balakrishnan Nair, with the southwest monsoon expected to withdraw by the end of September, it remains to be seen whether swell-surge events will continue into the post-monsoon period under the prevailing El Niño conditions. “Until this monsoon season, alerts against swell surges were generally issued during the pre-monsoon period. However, this monsoon was marked by INCOIS issuing repeated warnings against swell surge.”

The INCOIS director said: “The El Niño phenomenon has influenced the sea conditions, with the usual monsoon waves and winds largely missing. The sea remains relatively calm due to the El Niño effect. At the same time, powerful swell waves, which originate from 1000 to 2000 kms away, have become very evident, leading to repeated episodes of swell surge along the coast”.

Story continues below this ad

He said the calm sea has also encouraged fishing and other activities, as the normal rough-sea conditions associated with the monsoon have been largely missing. “In previous years, the combination of monsoon waves and swell waves would produce rough and heavy seas, making it difficult to distinguish the contribution of swell surges separately. Consequently, there was no need for specific alerts against swell surges, as both phenomena contributed to huge waves hitting the coast and flooding. When the sea remains calm, fishing activities will also go up. Hence, we have to be alert against swell surges,” he said.

On swell surge incidents being more frequent along India’s western coast, Dr Balakrishnan said the powerful waves travelling from the southern ocean first hit southern Kerala and the Kanyakumari region of Tamil Nadu. The deep sea in that region also allows the swell waves to retain their energy and hit the coast strongly.

Following a red alert for swell surge from INCOIS, the KSDMA has warned fishermen against launching small vessels into the sea or beaching them during the alert period. It also warned that entertainment and leisure activities along the beaches and sea should be avoided during the period.