Scientists from the Walker Institute at the University of Reading have helped to explain why heavy snowfall over the Himalayas in winter and spring can lead to drought over India, especially in the early part of the summer monsoon. This work forms part of the Climate Programme of the National Centre for Atmospheric Science (NCAS).
As far back as the 1880s scientists have known that increased snow over the Himalayas can be linked with weaker summer monsoon rains over India. However, the mechanisms explaining this link have never been properly understood.
The new research, published this week in Climate Dynamics, studies the mechanisms using the Met Office/Hadley Centre climate model. It shows that greater snowfall reflects more sunlight and produces a cooling over the Himalayas. This in turn means a weakening of the monsoon winds that bring rain to India. The relationship is strongest in the absence of warm (El Nino) or cold (La Nina) conditions in the tropical Pacific, because these are normally the dominant control over Indian rains.
Dr Andy Turner, lead author of the research, says "Our work shows how, in the absence of a strong influence from the tropical Pacific, snow conditions over the Himalayas and Tibetan Plateau could be used to help forecast seasonal monsoon rainfall for India, particularly over northern India during the onset month of June. The onset timing of the monsoon is very important for agriculture; a lack of rainfall early in the growing season can have a devastating impact on crops."
Previous studies have also found links between snowfall over a much larger area of northern Eurasia, but this study suggests that the Himalayan region has a stronger influence on Indian rainfall.
The monsoon rains over India and the rest of South and East Asia are relied on by more than a third of the world's population.
This research is based on a large number of experiments with the Met Office/Hadley Centre climate model which have been used to show robust relationships between the monsoon and winter/spring snow. This study shows in detail the mechanisms linking heavy snowfall over the Himalayas and Tibet in winter and spring with summer monsoon drought, particularly in the early part of the season (June).
- A. G. Turner, J. M. Slingo. Using idealized snow forcing to test teleconnections with the Indian summer monsoon in the Hadley Centre GCM. Climate Dynamics, 2010; DOI: 10.1007/s00382-010-0805-3
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