A number of perennial Himalayan streams could turn seasonal as glaciers are retreating at a faster rate than some 50 years ago leading to water scarcity in the plains during summer months.

Scientists have also found that though the number of glaciers has increased in the Himalayan region the total area covered by them has reduced by 21 per cent in the last 50 years.

"Systematic and meticulous glacial inventory of 1962 and 2001 has now clearly demonstrated that the extent of fragmentation is much higher than realised earlier," Anil V Kulkarni, co-ordinator, Snow and Glacier Project at the Space Applications Centre Ahmedabad said.

A team of scientists led by Kulkarni estimated the glacial retreat for 466 glaciers in Chenab, Parbati and Baspa basins from 1962.

Expeditions to Chhota Shigri, Patsio and Samudra Tapu glaciers in Chenab basin, Parbati glacier in Parbati basin and Shaune Garang glacier in the Baspa basin were organised to identify and map the glacier terminus -- the lowest point of a glacier.

The study has shown an overall reduction in glacier area from 2077 sq km in 1962 to 1628 sq km at present, an overall deglaciation of 21 per cent, Kulkarni said.

"The glaciers are retreating at a fast rate and eventually this will reduce runoff of streams originating from these glaciers which can become seasonal," he said.

The three river basins, on which study were conducted, are important for Indian economy as a number power projects were under operation and construction.

Amid changes in glacial extent and their influence on river run-off are important to plan future strategies of power generation, the scientists said.

"In future, if additional global warming takes place, the process of glacial fragmentation and retreat will increase, which will have a profound effect on availability of water resources in the Himalayan region," Kulkarni said.

About 127 glaciarates and ice fields less than one square km have shown retreat of 38 per cent from 1962, the study found.

As the glaciers are retreating, as a response to global warming, it was expected that tributary glaciers will detach from the main glacial body and they will form independent glaciers.

The scientists found that the loss in glaciated area for large glaciers was 12 per cent as compared to 38 per cent for small glaciers.

The study suggests that small glaciers and ice fields were significantly affected due to global warming from the middle of last century.

The study was carried out using data from a number of Indian Remote Sensing satellites. Besides Kulkarni, his scientist colleagues M Bahuguna, B P Rathore and S K Singh, S S Randhawa and R K Sood from Himachal Pradesh Remote Sensing Cell and Sunil Dhar a geologist from government college, Dharamsala participated in the study.