Himalayas wettest, warmest on record: Researcher

Recent decades have been the wettest and warmest on record in the Himalayas, say researchers who are alarmed that a "warming signature" has led to an overall rise in mercury levels and the retreat of glaciers.

They warn that the impact of global warming is clearly evident over the northwestern Himalayas in the form of rising maximum and mean temperatures in the last 25 years.

"An overall warming signature was observed with the maximum, minimum and mean temperatures experiencing rising trends," say the climate researchers with the Snow and Avalanche Study Establishment (SASE), a Defence Research and Development Organisation (DRDO) laboratory based in Chandigarh.

The maximum, minimum and mean temperatures in the Himalayas saw a total increase of 0.9 degree, 0.19 degree and 0.65 degree, respectively, over a quarter of a century.

However, the warming was not consistent across the Himalayas, with the minimum temperature in the Lower Himalayas showing an anomalous cooling by 0.83 degree Celsius (statistically significant) during this period.

The highest rise in mean temperature was observed in the Greater Himalayas at 0.87 degree Celsius (1991-2015), followed by the Karakoram Himalayas at 0.56 degree Celsius.

The rise in mercury is in agreement with observations of the comparatively higher rate of glacier retreat in the Greater Himalayas than in the Karakoram Himalayas, as reported in several studies, says the SASE study titled "Recent Wintertime Climatic Variability Over the North West Himalayan Cryosphere", published in the recent edition of Current Science journal.

It says the total precipitation -- both rainfall and snowfall -- has increased. However, snowfall was found to have decreased with a concurrent and significant increase in rainfall in all zones of the northwestern Himalayas.

The "spatiotemporal winter climatic variations" support the impact on recently reported findings on Himalayan snow cover and glacier variations at different durations.

"This (climatic variations) could have resulted from increased aerosol emissions by anthropogenic activities as aerosols, by virtue of their absorbing nature, do not allow much of incoming solar radiation to reach earth's surface, thereby leading to cooling," say authors H.S. Negi, Neha Kanda, M.S. Shekhar and A. Ganju.

Blaming high rainfall and less snowfall for the flooding in Kashmir in April 2017, they say the increase in liquid precipitation over seasonal snow in winter has induced enhanced melting and resulted in the flood situation.

Such rising trends in liquid precipitation over snowfall have a negative influence on the Himalayan glaciers. In addition, the frequency of hazards like avalanches and landslides is expected to increase during late winter, they warn.

The higher rate of warming in the Greater Himalayas compared to the Karakoram Himalayas partly explains the observance of higher glacier retreat rates over the former than the latter.

Precipitation, solid and liquid, has increased in all zones of the northwestern Himalayas, though a significant increase has been reported in the Lower Himalayas only in the past 25 years.

The precipitation in all zones, except the Lower Himalayas, follows decreasing trends in the past 15 years, which signals significant climatic change, especially after 2000.