Cyclone Biparjoy: What is the ‘landfall’ of a cyclone?

The Gujarat government has so far shifted more than 94,000 people living in eight coastal districts to temporary shelters. It has also issued prohibitory orders, shut down public transport and advised people to remain indoors.

Two teams each of the National Disaster Response Force (NDRF) and the State Disaster Response Force (SDRF) have been deployed in Gujarat, while teams of the Army and Indian Air Force have also been kept on standby.

A deserted street in Devbhumi Dwarka, Thursday. Bhupendra Rana

What is the “landfall” of a cyclone?

Simply put, landfall is the event of a tropical cyclone coming onto land after being over water. As per the IMD, a tropical cyclone is said to have made a landfall when the center of the storm – or its eye – moves over the coast.

Crucially a landfall should not be confused with a ‘direct hit’, which refers to a situation where the core of high winds (or eyewall) comes onshore but the centre of the storm may stay remain offshore. As per the US’s National Oceanic and Atmospheric Administration (NOAA), because the strongest winds in a tropical cyclone are not located precisely at the centre, it is possible for a cyclone’s strongest winds to be experienced over land even if landfall does not occur.

What is the damage caused by a cyclone’s landfall?

The damage caused by the landfall will depend on the severity of the cyclone – marked by the speed of its winds. For Cyclone Biparjoy, classified by the IMD as a “very severe cyclonic storm”, the impact may include extensive damage to kutcha houses, partial disruption of power and communication lines, minor disruption of rail and road traffic, potential threat from flying debris and flooding of escape
routes.

The factors behind this kind of damage include extremely strong winds, heavy rainfall and the storm surge which cause devastating floods in the coast.

How long does a landfall last?

Landfalls can last for a few hours, with their exact duration depending on the speed of the winds and the size of the storm system. Cyclone Biparjoy’s land process is expected to last around five to six hours, with the cyclone almost completely dissipating over approximately the next 24 hours.

Officers of the Fire and Emergency Services of Dwarka evacuate a street dweller

Cyclones lose their intensity once they move over land because of sharp reduction of moisture supply and increase in surface friction. This means that while landfalls are often the most devastating moments of cyclones, they also mark the beginning of its end.

Click here for live updates on Cyclone Biparjoy.