A tsunami early warning system is devised to detect tsunamis well in advance and issue timely warnings to prevent loss of life and damage. A tsunami early warning system is made up of two components, a network of sensors to detect tsunamis and a communication infrastructure to disseminate timely alarms for evacuation of people from coastal and low lying areas.
The December 26, 2004 earthquake and the subsequent tsunami exposed the vulnerability of the Indian coastline to oceanic hazards. Following the event, India started its own interim tsunami warning center in the first quarter of 2005 to issue tsunami bulletins generated from seismic information. The interim services were succeeded by setting up of a state-of-the-art Indian Tsunami Early Warning System (ITEWS) at the Indian National Centre for Ocean Information Services (INCOIS), Hyderabad, under the Earth System Sciences Organisation (ESSO), Government of India.
Modelling studies indicate that for tsunamigenic earthquakes occurring close to the Andaman and Nicobar Islands, the water arrival time is less than 30 minutes and for the Indian mainland the water arrival time is more than four hours. This means that the criteria to be adopted for issue of warnings need to be different for the islands and for the mainland.
Since immediate warnings need to be issued for Andaman and Nicobar islands, without enough time for confirmation of water levels, this might lead to false alarms. However, in the case of mainland, warnings are issued only upon confirmation of water levels. Hence, there is little chance of any false alarm.
Implemented in phases, the system became fully operational in October 2007. The warning system has seismic inputs from the India Meteorological Department (IMD), bottom pressure recorders from the National Institute of Ocean Technology (NIOT), tide gauges from the Survey of India (SoI), communication inputs from the Indian Space Research Organisation (ISRO), modelling inputs from Integrated Coastal and Marine Area Management (ICMAM) and INCOIS. ITEWS is thus a good example of a coordinated effort by different government agencies to establish a world class facility to monitor and provide alerts.
ITEWS is responsible for providing tsunami advisories to the Indian mainland and island regions, while acting as one of the regional tsunami advisory service providers (RTSPs) for the Indian Ocean Region. ITEWS also provides tsunami advisories to the Indian Ocean rim countries, besides Australia and Indonesia.
Components of the Indian tsunami early warning system
The ITEWS comprises a real-time network of seismic stations, bottom pressure recorders (BPR), tide gauges and 24×7 operational warning centres to detect tsunamigenic earthquakes, to monitor tsunamis and provide timely advisories as per the standard operating procedure (SOP) to vulnerable communities by means of latest communication methods with the back-end support of a pre-run model scenario database and decision support system (DSS). The Warning Centre is capable of issuing tsunami bulletins in less than 10 minutes after any major earthquake in the Indian Ocean thus allowing response/lead time of about 10-20 minutes for near source regions in the Andaman and Nicobar and a few hours in the case of the mainland.
The ITEWS information is disseminated to the National Disaster Management Authority (NDMA), Ministry of Home Affairs (MHA), local disaster management officers, district administrators and the public through the website, e-mail, short message service (SMS), fax, voice over internet protocol (VoIP) and global telecommunication system (GTS).
The ITEWS not only serves as National Tsunami Warning Centre (NTWC) but also as Tsunami Service Provider (TSP) to the Indian Ocean rim countries. The UNESCO’s Intergovernmental Oceanographic Commission (IOC) formed the international coordination group for the tsunami warning system in the Indian Ocean (ICG/IOTWS) on July 2005, as a coordinated international response to the 2004 tsunami event. The ICG/IOTWS works as a ‘system of systems’ with operational robustness achieved through a number of TSPs, which communicate with the NTWCs of the Indian Ocean countries.
ITEWS has been established with all the necessary capabilities to serve as one of the TSP for the Indian Ocean. The TSP operations of ITEWS (along with TSP-Australia and TSP-Indonesia) were operationalised on October 12, 2011 during the tsunami mock drill, IOWave11 exercise, with the Director General of IOC/UNESCO congratulating the TSPs for achieving this capability.
The last Indian Ocean wide mock tsunami drill was conducted on September 9-10, 2014 . The drill not only emphasised the testing of communications from warning centre to its stakeholders, but also provided an opportunity for testing national/state/local chains of command and decision-making, including the alerting and evacuation of people from selected coastal communities. They also provided a prospect to promote emergency response plans and tsunami preparedness. The next Indian Ocean wide mock tsunami drill is scheduled for September 7-8, 2016.