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[NEW DELHI] Snow has started melting even in winter in some areas of the Himalayas, which could influence regional river patterns, Indian satellite data has revealed.

Using data from the Indian remote sensing satellite RESOURCESAT-1, scientists from the Ahmedabad-based Space Applications Centre (SAC) — part of the Indian Space Research Organisation (ISRO) — analysed changes in snow cover in the central and western Himalayas.

The data shows that snow has started to melt during winter too, which could affect river patterns in the Himalayan river basins.

Rivers originating in the Himalayas depend on melting snow during the crucial summer months.

The team, writing in the February issue of Annals of Glaciology, monitored 28 basins in the Ganges and Indus river systems every five to ten, between October and June for three years from 2004.

In low altitude basins of 4,000 metres or below, even in the middle of winter the snow cover area was reduced from 90 per cent to 55 per cent in 2004–05. Similar trends were observed in ensuing years.

Even in colder high-altitude basins of more than 6,000 metres, snow melt was observed in early winter (December).

Annual changes in snow cover patterns reflect immediate responses to climate change, compared with changes in glaciers that respond slowly, over decades, Anil Kulkarni, coordinator of the research, told SciDev.Net.

"This [change in snow cover patterns] has the potential to influence run-off patterns of numerous Himalayan streams," Kulkarni said.

According to a 2009 ISRO bulletin, Kulkarni's team have also analysed 'glacier retreat' — when a glacier recedes or appears to move backwards because the rate of snow accumulation is slower than the pace at which snow melts.

They combined data from two Indian remote sensing satellites, IRS-P6 and IRS-1D, with field observations. Their analysis of 1,317 glaciers in the Indian Himalayas reveals the total glacier area has decreased from 5,866 square kilometres in 1962, to 4921 square kilometres in 2004, which represents a "16 per cent deglaciation".

The annual rate of loss of the Indian Himalayan glaciers is 0.39 per cent per year, reported Kulkarni and colleagues. This is compared to 1.1 per cent in Kilimanjaro, Tanzania; almost 0.6 percent in the Swiss Alps; and about 0.5 percent in Tien Shan, China.