Introduction

Planet earth- rightly termed as blue planet because of enormous quantity of water enveloping the earth, is unique in harbouring life on earth as we know today. The term hydrosphere represents this part of the earth.

For millions of years, the intricate balance between hydrosphere and atmosphere has resulted in the observed global pattern of seasons, cycle of snow and rainfall, summers and winters, droughts and floods. This has consequences on life in a myriad mystifying ways. Over a period of last two hundred years, man has been exercising enormous influence on climate primarily through his activity. The carbon dioxide content in the atmosphere is now steadily increasing. There is a forty percent decline in arctic ice thickness in recent history. It is estimated that the global mean sea level has already increased by ten to twenty centimeters.

The frequency of floods and droughts has increased enormously. The increase of global surface temperature will result in alteration of hydrological cycle changing rainfall, runoff and consequent frequency of floods.

Available water resources in India

Of the total precipitation, only forty seven percent is available for any practical purpose. The rest goes in evapo-transpiration, runoff, and percolation losses.

The surface water forms a mere 17 percent and ground water is about 10 percent. Yet, ground water is used for fifty percent of the irrigated agriculture!! Eighty percent of rural and fifty percent of urban population depend on ground water for their domestic needs. In a global warming context, the increase in surface temperature alters regimes of groundwater recharge as well. This has serious implications for a country like India where two fifths of Indian agriculture out put is contributed from areas irrigated by ground water.

Three-fourth of the total annual rain fall happens between just four months between June and September. The spatial and temporal variation in the quantity and distribution of water in various parts of the country creates and maintains the extraordinary diverse biological diversity of the country. Nearly 40 percent of the biodiversity lives in water and the remaining life forms survive supported by water.

Aquatic ecosystems cover a variety of habitats in the form of inland, coastal and marine systems encompassing rivers, ponds, lakes, reservoirs, marshes, estuaries, lagoons, mangroves, marine habitats and so on. Life originated in water and no life can exist without water.