Natural hazards are severe natural phenomena or events, broadly classified in two categories: hydro-meteorological and geological hazards. Tropical cyclones, heavy rainfall, severe thunderstorms, floods and drought are hydro-meteorological hazards whereas earthquakes and volcanic eruptions are grouped under geological hazards. Landslides and avalanches are caused by a combination of geological and hydro-meteorological factors.
Occurring at different scales and across varying durations, hydro-meteorological hazards can range from seconds to several years and cover a localised area or thousands of kilometers (Fig 1). During 1980-2010, hydro-meteorological hazards accounted for 90 per cent of the total number of disasters, 70 per cent of causalities and 75 per cent of total economic losses (World Meteorological Organisation, 2006). Globally, 7870 hydro-meteorological related disasters were reported from 1970 to 2009, causing the loss of 1.9 million lives and economic damages amounting to 1.9 trillion USD (Fig 2) (WMO Bulletin 2013).
While economic losses associated with hydro-meteorological hazards have increased in the last five decades, there has been a significant decline in loss of lives because of real time monitoring and early warning systems with effective communication and emergency preparedness at the national and local levels (Fig. 3 a & b).
End to end early warning system (EWS) has emerged as core component of disaster risk reduction and preparedness. It consists of monitoring hazards, risk assessment, impact based warning generation and warning dissemination, aimed at alerting decision-makers and the general public to impending hazardous weather conditions. It also serves as a source of advice on how to avoid negative outcomes associated with weather extremes, thus reducing deaths, injuries, property losses and other risks.
Continuous monitoring of hazard parameters and precursors is essential to generate accurate warning in timely fashion. For this, EWS has to have a sound scientific basis for prediction and has to be continuously operational. In the recent years, proliferation of multi-sensor observing systems, real time data communication, high speed processing using super computers and advanced numerical models have led to significant improvements in the skills of weather forecasts.
Cyclone Warning Division of the India Meteorological Department (IMD) also functions as the World Meteorological Organizations’ (WMO) Regional Specialised Meteorological Centre (RSMC) for tropical cyclones for the North Indian Ocean region providing advice and guidance (Tyagi, Bandyopadhyay and Mohapatra, 2010).
Improved observing and forecasting systems
Steady improvements in observing system over ocean and coastal areas with real time availability of satellite imageries and data from buoys have been of great help in monitoring genesis, intensification and movement of storms over the ocean. IMD has installed 10 radars having a range of 400 km covering the entire Indian coast.
Real time satellite picture and radar images of cyclonic storms are used by forecasters to monitor the location and intensity of cyclonic disturbance. Digital satellite and radar data are used in data assimilation of numerical weather prediction models—a significant development that has contributed to improvement in forecasting in the last five years (Fig 4). This was amply demonstrated in the case of the very severe cyclonic storm Phailin (2012) and Hud Hud (2013) and the recent cyclone Vardah (2016).
Lead time in providing warnings has a crucial role in disaster preparedness. IMD provides cyclone warnings to central and state government officials in four stages—pre-cyclone watch; cyclone alert; cyclone warning; and post land fall outlook. The first stage warning is issued 72 hours in advance containing early warning about the development of a cyclonic disturbance in the north Indian Ocean, its likely intensification into a tropical cyclone and the coastal belt likely to experience adverse weather. The second stage warning is issued at least 48 hours in advance of the expected commencement of adverse weather over the coastal areas. It contains information on the location, intensity of the storm, likely direction of its movement, intensification, coastal districts likely to experience adverse weather and advice to fishermen, general public, media and disaster managers. The third stage warning is issued at least 24 hours in advance prior to the expected commencement of adverse weather over the coastal areas. Landfall point is forecast at this stage. These warnings are issued at 3 hourly intervals, giving the latest position of cyclone and its intensity, likely point and time of landfall, associated heavy rainfall, strong wind and storm surge along with their impact and advice to general public, media, fishermen and disaster managers. The fourth stage of warning is issued by at least 12 hours in advance of expected time of landfall. It gives likely direction of movement of the cyclone after its landfall and adverse weather expected to be experienced in the interior areas. Fourth stage warning system has proved very effective in providing adequate lead time for necessary preparations.
There has been a paradigm shift in disaster risk management from disaster response to disaster preparedness. Improved EWS and better disaster preparedness in cyclone-prone areas have led to drastic reduction in loss of lives, speedy recovery and rehabilitation. It has thus not only contributed to financial savings in terms of compensation to the families with casualties, but also evacuation costs that have considerably reduced due to accurate land fall location warning.
Although, significant improvements have been made in short and medium range forecasts of cyclones and heavy rainfall, the same skills have not been achieved in respect of localised hazards such as cloud burst, flash floods, urban floods and landslide etc. Since these phenomena are primarily localised and short-lived, they require real time monitoring, warning and instant response mechanism. It needs observing network of radars, automatic weather stations, radiometers, lightening detectors etc. and very short range (<6hr) forecasting capability. As on date, these systems are unavailable in hilly and remote areas.
Climate change is another major challenge to cope with in future. Climate projections indicate increase in extreme weather events such as floods, droughts, heat waves and intensity of rains and storms. Improvements in climate models provide hope that in coming years climate projections will have less uncertainty and can be used in decision making. India made a systematic beginning in climate modelling by establishing Center for Climate Change Research (CCCR) at Indian Institute of Tropical Meteorology, Pune in 2008. The CCCR is working on Earth System Model which will provide model projections to IPCC VI and will be useful in the planning and implementing mitigation and adaptation measures to counter adverse impact of climate change.
There has been significant improvement in early warning of cyclones with a paradigm shift in risk management of disasters—from response to preparedness. This has led to reduction in loss of lives, speedy recovery and rehabilitation of affected people. The early warning systems are providing better results with improved observations over both land and ocean, along with precise model development. This prowess needs to be extended to localised and short-lived hazards which at present continue to elude us, specially over the mountainous areas.
Regional Specialised Meteorological Centre. 2013. Report on cyclonic disturbances over north Indian Ocean during 2012 published by Cyclone Warning Division. India Meteorological Department, New Delhi.
Tyagi A., B. K.Bandyopadhyay and M. Mohapatra. 2010. Monitoring and Prediction of Cyclonic Disturbances over North Indian Ocean by Regional Specialized Meteorological Centre, New Delhi: Problems and Prospective. YasinCharabi and Salim Al Hatrushi (EDs). Springer. pp 93-104.
World Meteorological Organisation Bulletin (2013), Reducing and Managing Risks of Disasters in Changing Climate: pp- 62-63.
Author is Air Vice Marshal (Retd.) and Former Director General, India Meteorological Department. firstname.lastname@example.org