As the raging warmth of the Indian Ocean due to climate change is leading to more and more cyclones ravaging South Asia, we wonder why and which part of it has crucial role to play in formation of these air containing giants.
Though Indian Ocean is second in terms of total number of storms, after the Pacific, but increasing frequency and intensity of Cyclones with each passing year is troublesome and worth investigating.
This year has been exceptional. With countries in South Asia groped with the Covid-19 crisis and allied worries, these weather events have only multiplied the plight of millions.
But these extreme weather events have no longer been exceptional for Indian ocean waters and people living on their periphery.
Last year Amphan and Nisarga hit the Indian Subcontinent taking birth from Bay of Bengal within 2 weeks of each other.
Temperatures in the Bay of Bengal were between 30-33 degrees Celsius when Cyclone Amphan got formed in mid-May and surface temperatures of the Arabian Sea were 30-32 degrees before the weather depression evolved into Cyclone Nisarga.
Further, to add to our woes, rising sea water levels due to global warming can bake higher storm surges reaching farther inland areas. And higher temperatures can form cyclones much faster than anticipated.
According to a Scientist at Divecha Centre for Climate Change, Indian Institute of Science: “This year both Arabian Sea and Bay of Bengal were about 1 degree warmer than normal (in early May) and hence the conditions were conducive to increasing the strength of the cyclones.”
“A warmer ocean does not automatically mean there will be more cyclones, but if the cyclones are born, they will become stronger on account of a warmer sea.”
Indian Ocean has been the warmest of all five oceans, partly attributed to the African-Asian landmasses obstructing the entry of cold water from the Arctic.
The north Indian Ocean composing of the Arabian Sea and the Bay of Bengal alone, generates about 7% of the world’s cyclones.
Which is more furious and why?
Currently, the cyclone Yaas is making a landfall in Odisha. While just a week back cyclone Tauktae originated in the Arabian sea claiming lives in Maharashtra and Gujarat.
If we compare the two of these Cyclones, Tauktae spent several days looming in the Arabian Sea where it could draw the required heat and moisture, reaching peak intensity of more than 220 km/hr.
While for Yaas, taking birth in Bay of Bengal, the travel distance to landfall becomes shorter. As a result, it did not get a longer period over the waters to exhibit the intensity of Tauktae.
However, the Bay of Bengal is a comparatively more active basin than the Arabian Sea for instigating cyclonic storms in its waters.
12 cyclones have formed in BOB for last 4 years, indicating an anomalous behavior. Several reasons for a boisterous BOB are as follows:
The shape of water: The bay that forms of the coastal body, gives birth to a concave or shallow where the strong winds tend to push water, finally concentrating as a storm. As it is shaped like a trough it makes a more hospitable place for storms to gain force and grow.
Even depth (measured in Bathymetry) varies for both these waters increasing vulnerability of BOB to get higher frequency of storms and cyclones over the basin.
Rainfall and Salinity: BOB gets more rainfall with slow winds and warm air currents enclosing it keeping the temperatures relatively high throughout the year (thinking why fisheries are good around BOB).
Fresh warm water from the perineal rivers like Brahmaputra, Ganga keeps consistently refilling the bay, making it impossible to mix with colder water below. This keeps a check on salinity of the bay than on any other basins.
Even the geographical design of Pacific Ocean and Bay of Bengal cause these fast-circulating winds to move inwards of coastal areas causing heavy rainfall.
Plus, in BOB, overall precipitation exceeds evaporation whereas evaporation exceeds precipitation in case of Arabian Sea. BOB receives more than 1-3m annual rainfall (even more than that in Andaman Sea) while Arabian Sea receives barely around 1m rainfall.
Additionally, Arabian sea too enjoy a greater advantage: lack of any fresh-water source allows the water to relatively mix with each other, the gushing winds coming in from Pacific Ocean will hit the western ghats etc. first cutting down the prevailing intensities.
With increasing warming around the world, it becomes our imperative to understand what makes India vulnerable and its waters unsustainable to live around.
With sheer understanding will come the need and urge to mitigate in best possible ways. Afterall, risk aversion is best possible strategy in the market.