Why cyclones hit the east coast in October?

Context:

  • Last week, Cyclone Titli became the third major cyclone to hit the Odisha-Andhra coastal zone in the last five years, all in October. What explains the similar timing, and how effective are the mechanisms for prediction and disaster mitigation?

Season & frequency

  • Cyclones have always been frequent in the region. What has risen is is the “frequency of intense cyclones in the area”, say scientists with IIT-Bhubaneswar’s School of Earth, Ocean and Climate Science, citing their observations on the Bay of Bengal.
  • Adjacent to the northwest Pacific, which is one of the world’s most active basins for typhoons, the Bay of Bengal receives the remnants of major landfalls in the Philippines, China and South Asia. From these places come low-pressure systems that develop into a monsoon depression or a cyclone.
  • The reason that cyclones such as Titli, Phailin (2013) and Hudhud (2014) typically strike in October is that wind shear — the difference within wind speeds and direction at two different levels — is low during this time; low wind shear, when combined with surface sea temperatures greater than 26°C, raises the likelihood of cyclones.
  • In monsoon season, cyclones are rare because of high wind shear.

Hard to predict

  • The Odisha government has come under criticism for not being able to accurately anticipate the landfall of Cyclone Titli or the very heavy rainfall that brought large areas under water. Scientists say prediction is difficult because of budgetary and meteorological factors.
  • In the Atlantic basin, the US has dedicated aircraft that fly directly into the clouds to study moisture levels and gather various data on cyclone profile.
  • For Indian cyclones developing over the ocean, scientists say they have to largely rely on satellite images (a top view) that reveals little data on moisture content and intensity.
  • Indian scientists get a more detailed picture only when a cyclone is 300-400 km from the coast, which reduces preparation time; Cyclone Titli was additionally hard to read because it turned into a recurving cyclone (it changed direction). India acquires storm prediction models from the US and Europe but lacks the resources to upgrade the models regularly, IIT-Bhubaneswar scientists say.

How evacuation is done

  • Researchers classify evacuation exercises as preventive, vertical, and shelter-in-place. In preventive (or horizontal) evacuation, the impact area is meant to be completely evacuated, but this is a measure rarely taken in India because of poor roads and inadequate public transportation. Also, poor people rarely have the resources to find alternative accommodation.
  • Shelter-in-place evacuation involves fortification of existing houses and community buildings, which again required financial resources. In vertical evacuation, people are directed to specially designed buildings within the impact area. This strategy was largely followed during Cyclone Titli.

Source:IE