The rivers originating in the Himalayas carry a lot of sediment and cause erosion of the banks in the upper reaches and over-topping in the lower segments. The most flood-prone areas are the Brahmaputra and Gangetic basins in the Indo-Gangetic plains.
The other flood-prone areas are the north-west region with the rivers Narmada and Tapti, Central India and the Deccan region with rivers like the Mahanadi, Krishna and Kauveri.
The floods in Bihar in 2008 were one of the worst the country has seen. Floods in urban areas are rare. Streets do fill up with water, but drainage systems are usually in place to take care of excessive water logging.
However, in July 2006, the county’s business hub, the city of Mumbai, was rendered completely chaotic for several days as 942mm of rain lashed down. As with most ‘natural’ disasters, in this one too, man had a role to play.
The rapid and constant development of the city and the flouting of rules and regulations caused blockage and choking of the Mithi river that flows through a part of the city and used to carry off excess water to the sea.
Violations of coastal regulation zone rules, development on green and no- development zones, building on areas marked for parks and open spaces all of this ensured that what little open space the city now had was not enough to absorb heavy rain. An ancient and badly maintained drainage system added to the problem.
In 2001, more than eight states suffered the impact of severe drought. Analysis of rainfall behaviour in the past 100 years reveals that the frequency of below-normal rainfall in arid, semi-arid, and sub-humid areas is 54 to 57%, while severe and rare droughts occur once every eight to nine years in arid and semi-arid zones.
The drought of 2002 was officially acknowledged by the India Meteorological Department (IMD) as the ‘first-ever all- India drought year’, since 1987.
The aggregate rainfall received by the country as a whole during the year’s monsoon season from June to September 2002, at 735.9 mm, was 19.35 % below the historical long period average (LPA) of 912.5 mm for this period. In July 2002, rainfall deficiency dropped to 51%, surpassing all previous droughts.
The drought impacted 56% of the land mass and threatened the livelihoods of 300 million people across 18 states.
The states most exposed to cyclone-related hazards, including strong winds, floods and storm surges, are West Bengal, Orissa, Andhra Pradesh and Tamil Nadu along the Bay of Bengal.
The impact of these cyclones is confined to the coastal districts, the maximum destruction being within 100 km from the centre of the cyclone and on either side of the storm track.
The worst devastation takes place when and where the peak surge occurs at the time of the high tide.
Stretches along the Bay of Bengal coastline have the world’s shallowest waters, but the relatively dense population and poor economic condition complicate the situation. The population density in some of the coastal districts is as high as 670 persons per square km.
Cyclones have a devastating effect on the economy and lives of the people in the affected districts. A very large population in the affected districts loose its source of livelihood. Public infrastructure suffers extensive damage. The economy of the state suffers a serious setback. This has an adverse impact on the development of the state.
During the International Decade of Natural Disaster Reduction (IDNDR), India suffered the adverse impact of several earthquakes, the most significant being in Uttarkashi, Latur and Jabalpur.
Some of the most devastating earthquakes in India in the past include the Kashmir earthquake in 2005, the Kutch earthquakes 1819 and 2001, the Shillong earthquake of 1897, the Kangra earthquake of 1905, the Bihar-Nepal earthquake of 1934, the North-East and Assam earthquake of 1950, the Anjar earthquake in Gujarat of1956, etc.
The Seismic Zonation Map of India shows the north-eastern states, the Kutch region of Gujarat and Uttarakhand as most vulnerable.
What made the earthquake more tragic was that many parts of the state were reeling under a drought for the second successive year.
Kutch was facing drinking water and fodder scarcity. Men had migrated for work leaving women and children behind. Thus it was the poorest and the most vulnerable who were affected.
The peninsular part of India comprises continental crust regions, which are considered stable as they are far from the tectonic activity of the boundaries.
Although these regions were considered seismically least active, an earthquake that occurred in Latur in Maharashtra on September 30, 1993, measuring 6.4 on the Richter scale caused substantial loss of life and damage to infrastructure.
One of the most devastating disasters of the 21st century was the Asian tsunami that wreaked havoc in 11 countries on December 26. 2004. A tsunami is a series of ocean waves generated by sudden disturbances in the sea floor, landslides, or volcanic activity.
In the ocean, the tsunami wave may only be a few inches high (typically 30-60 cm), but as they race onto shallow water regions their speed diminishes which results in increase in the height of the wave.
Typical speeds in the open ocean are of the order of 600 to 800 km/hr. The tsunami’s energy flux, which is dependent on both its wave speed and wave height, remains nearly constant. When it finally reaches the coast, a tsunami may appear as a series of massive breaking waves.
Experts warn that as a consequence of climate change, natural disasters like floods from rising sea levels, droughts and heavy rainfall will increase, impacting peoples and economies more dramatically than before.
Developing countries that do not have proper preventive and coping strategies in place will suffer the most.