The cyclone originated as a “depression” in the Gulf of Thailand, near east of Port Blair, on 25 October 1999 and gradually moved in a northwestward direction. It intensified into a supercyclone and hit the area between Erasama and Balikuda in Odisha on 29 October at 10.30 a.m. The supercyclone swept the entire coast of Odisha including the cities of Bhubaneshwar and Cuttack and 28 coastal towns. About 13 million people were affected. A large number of livestock were killed. Standing crops of paddy, vegetables and fruits were heavily damaged. Due to salinisation caused by tidal surge, large tracts of agricultural land have turned infertile. Large tracts of sal, teak and bamboo plantations have disappeared. The mangrove forests between Paradeep and Konark vanished. Moisture Cold When water evaporates from land and different air Warm water bodies, it becomes water vapour. Moisture air in the air at any time, is known as humidity. When the air is full of water vapour we call it a humid day. As the air gets warmer, its capacity to hold the water vapour increases and so it becomes more and more humid. On a humid Cyclonic Rainfall day, clothes take longer to dry and sweat from our body does not evaporate easily, making us feel very uncomfortable. When the water vapour rises, it starts cooling. The water vapour condenses causing formation Moist air of droplets of water. Clouds are just masses of such water droplets. When these droplets of water become too heavy to float in air, then they come down as precipitation. Jet planes flying in the sky leave a white trail behind them. The moisture from their engines Relief (Orographic) Rainfall condenses. We see trails of this condensed moisture for some time when there is no air movement to disturb it. Precipitation that comes down to the earth in liquid form is called rain. Most of the ground water comes from rainwater. Plants help preserve water. When trees on hill sides are cut, rainwater Warm flows down the bare mountains and can causeair flooding of low lying areas. On the basis of mechanism, there are three types of rainfall: the Convectional Rainfall convectional rainfall, the orographic rainfall and Fig. 4.5: Types of Rainfall the cyclonic rainfall (Fig. 4.5). 26 OUR ENVIRONMENT

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