Cyclones, tsunamis and early warning

The sea can turn dangerous suddenly. A cyclone is a huge rotating storm that forms over warm ocean water. A tsunami is a set of giant waves, usually set off by an undersea earthquake. We cannot stop them, but we can see them coming. Early warning systems work like giant alarms for the coast: they detect the danger, predict where it will strike, and warn people in time to evacuate.

Cyclones. India has cyclone warning services and marine weather services watching both the eastern and western coasts, all the time. Better technology now spots cyclones early, and this has saved many human and animal lives.

• The National Cyclone Risk Mitigation Project (NCRMP). Mitigation means reducing, so this project reduces cyclone risk: it builds cyclone shelters, makes warning systems stronger and improves emergency response in cyclone-prone States and UTs. It also has a Decision Support System (DSS) for disaster authorities.
• INCOIS, short for Indian National Centre for Ocean Information Services, and the IMD (India Meteorological Department) run the Storm Surge Early Warning System (SSEWS). It forecasts how far the sea will be pushed onto the land by a cyclone (the storm surge) and how much of the coast will flood.
• Names: names for North Indian Ocean cyclones are taken in turn from a list of 169 names sent by 13 member countries, including India. Recent ones: Biparjoy (2023) and Remal (2024). Names make warnings clear and easy to remember.

GEMINI, a safety device for fishermen. Out at sea there is no phone signal. GEMINI is a handheld navigation and information box for mariners, linked to the GAGAN satellite. It picks up the satellite's messages and passes them to the fisherman's phone by Bluetooth. An INCOIS app shows them in nine regional languages: high waves, strong winds, cyclone and tsunami alerts, where fish are likely to be, and maps of the sea floor (bathymetry).

• Today it reaches 50 nautical miles out to sea.
• An upgrade is planned that would reach 300 nautical miles and allow two-way messages, so fishermen could reply. Careful: that is the plan; today's device only receives.
• The Pradhan Mantri Matsya Sampada Yojana scheme (PMMSY) helps fishermen pay for it.

The 2004 tsunami. On 26 December 2004, a tsunami in the Indian Ocean killed about 2,30,000 people across many countries. In India, the Andaman and Nicobar Islands, Tamil Nadu, Puducherry, Andhra Pradesh and Keralam were badly hit. After this, many countries built tsunami warning systems. In India, the Indian Tsunami Early Warning Centre (ITEWC) set up a network of tsunami detection buoys. The system works in four steps (Fig. 1.15):

• Detection: seismic stations pick up an undersea earthquake at once.
• Confirmation: pressure recorders on the sea floor (OBPRs) feel the tsunami wave pass, confirming the danger.
• Tracking: tide gauges and radars on the coast watch the sea level rise.
• Warning: alerts go by satellite to the Government of India, which tells the state governments and rescue teams; people get them by SMS, email and coastal display boards.

People matter as much as machines. A warning only saves lives if people know what to do. That is why training and awareness matter. Old knowledge helps too: in 2004, people on the Indonesian island of Simeulue were largely spared, partly because their folk stories, passed down for generations, taught them the warning signs and to run at once.