Cyclone Dana: Why Bay of Bengal gets more, deadlier tropical cyclones?

Cyclone Dana is expected to hit coastal areas of the Bay of Bengal on Friday, bringing heavy downpours and strong winds. Data suggests the Bay has a higher number of and deadlier cyclones than the Arabian Sea – India’s other western oceanic flank.

Cyclone Dana will hit coastal areas of Odisha and West Bengal with wind speeds up to 120km/h and storm surges as tall as a two-storey building on Friday, October 25. (Photo: India Today)

But why is the Bay of Bengal more prone to cyclones?
With a coastline of 8,041 kilometres, the Indian subcontinent is one of the worst regions affected by cyclonic storms. Nearly 10% of the world’s tropical cyclones occur in this region.
The Bay of Bengal sees as many as four times the number of cyclones as the Arabian Sea, as per the National Disaster Management Authority (NDMA). Its analysis of the frequency of cyclones on the east and west coasts of India between 1891 and 1990 shows that nearly 262 cyclones occurred in a 50 km wide strip above the east coast.
Of this number, 92 cyclones on the East Coast were “severe,” while the Arabian Sea saw just 19 storms of this category.
More than 500 million people live on the coastal rim of the Bay of Bengal. As per US-based weather journal Weather Underground, 26 out of the 35 deadliest recorded tropical cyclones have occurred in this region.

As per the India Meteorological Department, Cyclone Dana will severely impact Jagatsinghpur, Kendrapara, Bhadrak, and Balasore districts in Odisha. (Photo: India Today)

Storm surges are most severe in shallow, concave bays where water, driven by the strong winds of tropical cyclones, funnels and concentrates as the storm advances. The Bay of Bengal is shaped like a trough that makes it more conducive for storms to gain force – thus a ‘textbook example’ of this type of geography.
What makes matters worse are high sea surface temperatures in the Bay of Bengal, which can trigger extremely strong cyclones. The threshold value for surface temperatures of the sea for the formation of cyclones is 28°C, but it is 30°C-32°C over the Bay of Bengal.
Additionally, the Bay gets more rainfall with sluggish winds and warm air currents around it that keep temperatures relatively high all year. The influx of warm water from perennial rivers like the Brahmaputra and the Ganges makes it further impossible to mix with the cooler water below.
As per an analysis by the Ministry of Earth Sciences, the lack of landmass between the Pacific Ocean and the Bay of Bengal causes cyclonic winds to move into the coastal areas, causing heavy rainfall. The absence of air movements from north-western India towards the Bay in the post-monsoon phase is also another reason for the increased chances of cyclones in the Bay of Bengal.
More than 60% of cyclones in this region make landfall in various parts of India’s east coast, 30% experience recurvature and landfall over Bangladesh and Myanmar, while 10% dissipate over the oceanic regions, according to the ‘Assessment of Climate Change over the Indian Region’ project.
There are other coastlines around the world which are vulnerable to surging storms, the Gulf Coast of Louisiana, USA, for example. But India’s north coast is more prone to catastrophic surges than anywhere on Earth. The highly populous coastline also exacerbates the threat: one in four people in the world live in a country that borders the Bay.