A detailed national inventory of wetlands has been prepared on the basis of satellite imagery by ISRO, highlighting areas of critical ecological significance and those which are facing extreme threat due to developmental activities.

This is for the first time in India that the city-based Space Application Centre (SAC), a part of ISRO, has prepared such an inventory and atlas of all the wetlands that are existing in the country.

"Wetlands are the most productive ecosystems which play crucial role in hydrological cycle like helping in storm and flood control, water supply, providing food, fibre and raw materials and in recreational benefits," said SAC Director Dr Ranganth R Navalgund.

They also support lakhs of migratory birds coming from colder regions of the world in summers, apart from diverse local flora and fauna.

"However, the very existence of these unique resources is under threat due to developmental activities and population pressure. This calls for long-term planning for preservation and conservation of these resources," Navalgund said.

"Creating an updated and accurate database that supports research and decision making is the first step towards this. SAC took up this challenging task under the project National Wetland Inventory and Assessment (NWIA) sponsored by Ministry of Environment and Forests," he said.

"Two-date, satellite data acquired during pre and post-monsoon seasons are used for inventory of wet and dry season hydrology of wetlands. They have been categorised in 19 classes and mapped following standard map projection. The map outputs include status of water spread, aquatic vegetation and turbidity," Navalgund said. .

As per the finding of SAC study, excluding rivers, wetlands cover some 10 million hectares, or a little over three percent of the country's geographical area. Of this 10 million hectares, reservoirs account for about 2.5 million hectares, inter-tidal mud flats for 2.4 million hectares, tanks for 1.3 million hectares, lakes/ponds for 0.70 million hectares, mangroves for some 0.47 million hectares and corals for about 0.14 million hectares.

The main objective of the project were wetland mapping and inventory at 1:50,000 scale resolution by analysis of digital satellite data of post and pre-monsoon seasons, creation of digital database in GIS environment and preparation of state-wise wetland atlases.

State wise distribution of wetlands showed that Lakshadweep has 96.12 per cent of geographic area under wetlands followed by Andamand and Nicobar Islands (18.52 per cent), Damand and Diu (18.46 per cent) and Gujarat (17.56 per cent) have highest extent of wetlands.

Puducherry (12.88 per cent), West Bengal (12.48 per cent), Assam (9.74 per cent) are wetland rich states. States like Mizoram, Haryana, Delhi Sikkim, Nagaland and Meghalaya the extents of wetland is less than 1.5 per cent.

The inventory said, India has long coast line and large area under coastal wetlands like inter-tidal, mudflat, lagoon and creek.

The inventory has also mapped high altitude lakes lying above 3,000 meter elevation. The Indian Himalayas cover almost 18 per cent of India?s land surface and is spread over six states, which have 4703 lakes above 3,000 meter elevation.

This includes 1996 small lakes. The total area of these lakes is 1.26 lakh hectares.