The enormous havoc and dislocation caused by natural and man made disasters have become a great burden particularly on the highly populated and poverty stricken developing countries causing perpetual misery to thousands of lives and livestock. Over the past 20 years alone, these extreme natural disasters have resulted in the loss of life of more than 3 million people and have affected over 800 million people all over the world, causing damage to property to the tune of 50–100 billion dollars, 50 per cent of which is due to floods and cyclones. Over 60 per cent of all the major disasters have occurred in the developing countries, two-thirds of which have been in the developing Asian regions (Rao 1995a; World Resources Institute 1992). Even though extreme natural events such as floods, drought, cyclones and earthquakes are not totally under human control, prediction of occurrence of some of these events with a good degree of certainty is possible, thanks to the developments in space technology. Instead of collectively taking up the challenge of preventing or at least mitigating the effects of such disasters, providing aids after the events which are both inadequate and untimely has only resulted in perpetuating the misery of the worst affected, silently suffering victims of disasters.

An effective disaster management system consists of four main components — disaster prediction, disaster warning, disaster management and disaster relief. Disaster warning is a basic prerequisite for ensuring disaster preparedness and in some cases to help in the prevention of disaster itself. Clearly the most important application of satellites is in detecting, predicting and delivering early warning of impending disasters such as flood, drought, cyclone and even forest fires (Rao et al. 1987; Heath 1994). Continuous monitoring by both geostationary and low earth orbiting weather satellites like GOES, INSAT, METEOSAT and NOAA is capable of providing early warning on cyclones and floods. Forest fires, environmental hazards, volcanic eruptions and even propagation of desert locust phenomena can be detected well in time by remote sensing satellites like, LANDSAT, SPOT and IRS. Sustainable development strategy must address this important issue in order to provide stability and reasonable security to the vulnerable rural population in these countries. Remote sensing information are now operationally used to regularly monitor flood conditions, volume of water flow and damage assessment. From such a database collected over years, it is possible to identify different risk zones in the flood prone area based on the severity index for flood proneness of each zone. Optimal treatment of each zone on a long term basis, depending on the severity, can then be attempted to achieve reduction in flood damage without impairing environmental integrity (Rao 1993) (Fig. 9).

Data relay and communication satellites have the ability not only to deliver early warnings on various disasters but also in disseminating requisite information on hazard awareness and educating the local people in preparing themselves to face such hazards. Locale specific unattended Disaster Warning Systems (DWS) installed by India along the vulnerable eastern coast of the country, using communication and meteorological capability of INSAT multipurpose satellites, have proven their immense value in providing timely warning on cyclone and flood disasters over the last 10 years. Most dramatic use of DWS, consisting of over 150 disaster warning receivers was during the cyclone that hit the eastern coast of India in May 1990, enabling the civic authorities to evacuate over 170,000 people from the cyclone affected area, which saved thousands of lives and livestock. But for the operation of DWS, analysis of cyclone events which occurred in the pre INSAT era indicates that the total human death toll would have been at least 20,000 during this event, as against only 800 deaths recorded (Rao 1995a; 1995b).

Drought is a complex phenomena, the causes for which are many involving both natural and induced factors such as atmospheric perturbation, climatic variability, sea surface temperature changes and human intervention, ranging from deforestation and poor land management to destabilization of green house effect. While it is difficult to identify the exact onset and the end of drought because of its slow creeping nature, remote sensing derived Vegetation Index (VI) has been very effective in monitoring drought conditions on a real time basis, often helping the decision makers to initiate appropriate strategies for recovery by changing crop patterns and practices. The use of meteorological satellite data to assess spatial and temporal inadequacies of rainfall at critical crop stages and subsequent assessment of the crop condition status based on VI analysis provide an excellent drought monitoring mechanism. Comparison of the temporal changes in the bi-weekly VI indices with the corresponding figures in a normal year can easily provide advance information on the onset of drought conditions in any given region (Fig. 10). Under the National Agricultural Drought Assessment and Monitoring System (NADAMS), bi-weekly drought bulletins are issued, almost on real time, to all the drought prone districts in India to enable decision makers to assess the severity of drought and take appropriate remedial measures (Rao 1995c).