Winter rain and snow in Western Himalayas could vary by almost 50 per cent depending on the air pressure gradient over the Atlantic Ocean between the Azores and Iceland, which could have an impact on India’s food and water supply. This was revealed by a new study led by the University of Reading.
“Despite being several thousand miles apart, we have known that pressure patterns over the North Atlantic have some influence over winter weather in the western Himalayas. However, making sense of that link and how strong it is has puzzled scientists for years,” said lead author
Dr Kieran Hunt.
“The link we have found could be incredibly useful for states and rural communities in north-west India that rely on winter rain and snow for supplies of food and water. Advance notice of any shift towards wetter or drier weather from observing the North Atlantic could be a lifeline in preparing for water shortages, or even flooding,” said Hunt, who is a research scientist in tropical meteorology at the University of Reading.
ATLANTIC AIR; COORELATION
The new study focused on the correlation between fluctuating phases of the North Atlantic Oscillation (NAO) and winter rain and snow in the western Himalayan region. They said that
the strong contrast between high pressure around the Azores and low pressure around Iceland forces the North Atlantic jet stream northwards during a positive NAO phase. This in turn causes more instability in the subtropical jet stream that runs over Africa towards India, they added.
The additional disturbances in the subtropical jet are carried as storms to north-west India. The study pointed out that winter storms in the region were on average 20 per cent more frequent and seven per more intense during a positive NAO phase. This increased to 31 per cent more frequent winter storms in areas that already see them most often, they concluded. This led to 40 per cent more moisture being carried along the subtropical jet on average, which means 45 per cent more rain and snow in the western Himalayas in winter months during a positive NAO phase
ATLANTIC AIR; STORM INCREASE
The increase in storms in north-west India is likely to affect states such as Jammu and Kashmir, Punjab, Gujarat and southern Pakistan. These are mostly rural areas but do contain cities such as Srinagar, Peshawar, Jodhpur, Hyderabad and Karachi.
ATLANTIC AIR; METHOD
For the study, the researchers used 70 years of data from the Reading-based European Centre for Medium-range Weather Forecastsand other organisations, as well as rainfall gauge data from the western Himalayan region provided by the Indian Meteorological Department.
The authors said that they came across correlation was strongest within the 2-3 and 12-16 year cycles in NAO variation. The slow variations in NAO offers scope for improving the forecasting of wetter or drier-than-average north-west Indian winter weather up to three months in advance, they added.
Dr Hunt said: “Climate change may also have a hand in the amount of winter rain and snow seen in north-west India in future, as the shape and position of the North Atlantic jet stream and the strength of the subtropical jet are expected to be affected as the planet warms. This has potential implications for the jet stream that fuels storms in India.”
The study provides evidence that could lead to better forecasting of winter precipitation levels in India, months in advance. The results could also be used to improve yields of crops, such as wheat and barley, and to help manage vital water supplies in the country.