The Himalayas are warming more rapidly than the rest of the globe. Researchers have found that the average annual mean temperature during the 25-year period from 1982 to 2006 increased by 1.5°C, with an average increase of 0.06°C per year. This is about three times greater than the global average of temperature rise in the same time period.
This has had an effect on rainfall too. The average annual precipitation during the same period has increased by 163mm or 6.52mm per year in the Himalayas.
The findings are from a study conducted by researchers associated with the University of Massachusetts, Boston and the Bangalore-based Ashoka Trust for Research in Ecology and the Environment (ATREE). The results were published on Tuesday.
The principal author of the study, Uttam Babu Shrestha of the University of Massachusetts, said, “Our study reaffirmed that the Himalayas region is indeed experiencing rapid climate and associated changes in the various ecoregions."
The study, Shrestha claimed, vindicates the observations of communities. He said, “Local people have been noticing changes in the growing patterns of plants, and our study confirms such changes.” In fact, the average start of the growing season seems to have advanced by 4.7 days in the Himalayas in the 25-year period from 1982 to 2006.
While most of the recent debate about climate change in the Himalayas has been dominated by glacial melting, this study demonstrate significant changes in temperature and precipitation in the Himalayas—greater than the upper bounds predicted by the Intergovernmental Panel on Climate Change (IPCC) and recent Indian assessments.
The Brahmaputra Valley semi-evergreen forest ecoregion has experienced the greatest rate of warming, 2.0°C (0.08°C per year), and the Northern Triangle temperate forest ecoregion (a temperate broadleaf and mixed forest ecoregion of thick forest covering the mountains of northern Myanmar), the least, 0.25°C (0.01°C per year).
It is the change in rainfall pattern that is more alarming. While earlier researchers had found both increasing and decreasing precipitation trends in the Eastern Himalayas, lack of a consistent trend in the Central Himalayas, and decreasing trends in the Western Himalayas, this study has found a consistent trend of increasing average precipitation in the Himalayas as a whole.
The pattern of increase in annual precipitation is consistent in all ecoregions except the Northern Triangle ecoregion. The Brahmaputra Valley semi-evergreen forest ecoregion registered the greatest increase, 269.25mm (10.77mm per year), whereas the Northern Triangle temperate forest had the greatest decrease, 130.5mm (5.22mm per year)
Even more alarming are changes in phenology (study of periodic plant and animal life cycle events and how these are influenced by seasonal and inter-annual variations in climate). The average start of growing season (termed, SOS) has advanced in some regions, and been delayed in others. However, the frequency of the significant negative trends (advancement) of SOS is much greater than that of positive trends (delay).
Moreover, a larger proportion of local people at higher elevations are experiencing climate change than people at lower elevations. The study argues that the relationship between temperature and SOS might be location dependent.
