The two most important hydrological extremes are floods and droughts. These events pose serious hazards to human populations in many parts of the world. These water related disasters are caused because of large diversity in climate and topography of the country. Climate change in future is expected to have severe implications on river flows in South Asia including India. Global climate change is likely to result in severe droughts and floods in India, with major impacts on human health and food supplies.

The contemporary trend of global warming is aptly highlighted in the IPCC report 2007. There is a strong consensus amongst scientists and planners today that the earth's climate is entering a warm episode, nudged primarily by human activities of fossil fuel burning and land use changes that inject steadily increasing amounts of CO2 into the atmosphere. It is also quite possible that the increased concentrations of atmospheric CO2 will also have a direct influence on productive systems of plant species in view of increasing rates of photosynthesis and improved water use efficiency.

The Himalayas possess one of the largest resources of snow and ice, which act as a huge freshwater reservoir. Monitoring the glaciers is important to assess the overall reservoir health. In this investigation, glacial retreat was estimated for 466 glaciers in Chenab, Parbati and Baspa basins from 1962.

The Arctic climate is changing. Permafrost is warming, hydrological processes are changing and biological and social systems are also evolving in response to these changing conditions. Knowing how the structure and function of arctic terrestrial ecosystems are responding to recent and persistent climate change is paramount to understanding the future state of the Earth system and how