The North Atlantic Ocean and Western Himalayas may be thousands of kilometers apart but they are linked with each other. A research study has said that the amount of winter rain and snow in the Indian side could vary by almost 50 per cent depending on the air pressure gradient over the Atlantic Ocean between the Azores and Iceland.

The researchers from the University of Reading, said that 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 in India's western Himalayas. They said that keeping a tab could also be useful to improve yields of important crops, such as wheat and barley, and to help manage vital water supplies in the country.

The researchers used 70 years of data from the Reading-based European Centre for Medium-range Weather Forecasts and other organisations, as well as rainfall gauge data from the western Himalayan region provided by the Indian Meteorological Department.

The authors found the correlation was strongest within the 2-3 and 12-16 year cycles in North Atlantic Oscillation (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. Scientists had spent decades trying to establish the causes of a link between the two regions. This new study provides important evidence that could lead to better forecasting of winter precipitation levels in India, months in advance.

Dr Kieran Hunt, a research scientist in tropical meteorology at the University of Reading and lead author of the study, said: “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. “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.” The new research, published in Climate Dynamics, focused on the correlation between the fluctuating phases of the North Atlantic Oscillation (NAO) and winter rain and snow in the western Himalayan region.

During a positive NAO phase, the strong contrast between high pressure around the Azores and low pressure around Iceland forces the North Atlantic jet stream northwards, which in turn causes more instability in the subtropical jet stream that runs over Africa towards India.

The additional disturbances in the subtropical jet are carried as storms to north-west India. The research showed that winter storms in the region were on average 20 per cent more frequent and 7 per cent more intense during a positive NAO phase, compared to a negative phase. This increased to 31 per cent more frequent winter storms in areas that already see them most often.

This resulted in 40 per cent more moisture being carried along the subtropical jet on average, and therefore 45 per cent more rain and snow in the western Himalayas in winter months during a positive NAO phase.

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.