Winter rain and snow in the western Himalayas could vary by almost 50%, due to the effects of atmospheric conditions in the North Atlantic

A study conducted by the University of Reading found that the amount of winter rain and snowfall in the Western Himalayas can vary by nearly 50 % as a function of the atmospheric pressure gradient above the Atlantic Ocean between the Azores and Iceland.

Scientists have 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 predictions of winter rainfall levels in India months in advance. The results could be used to improve yields of important crops, such as wheat and barley, and to help manage vital water supplies in the country.

The Dr Kieran Hunt, tropical meteorology researcher at the University of Reading through and lead author of the study, said: “Despite being several thousand miles apart, we know that the pressure patterns above the North Atlantic have some influence on winter weather in the However, making sense of this link and its direction has puzzled scientists for years.

“The link which we found could be extremely useful for states and rural communities in northwest India that depend on winter rains and snow for food and water supplies. Advance notice of any change to wetter or drier weather from the North Atlantic sighting could be a lifesaver in preparing for water shortages or even flooding.”

The new research, published in Weather Dynamics, focused on the correlation between fluctuating phases of the North Atlantic Oscillation (NAO) and winter rain and snow in the western region of the Atlantic. Himalayas.

During an optimistic NAO phase, the strong contrast between the high pressure around the Azores and the low pressure around Iceland power the jet stream from the ‘North Atlantic northward, which in turn causes greater instability of the subtropical jet stream that crosses Africa towards India.

Additional disturbances in the jet subtropical are transported as storms to northwest India. The research showed that winter storms in the region were on average 20% more frequent and 7% more intense during a good stage of NAO, per compared to a negative stage. This has risen to 31% more frequent winter storms in areas that already see them most often.

This resulted in an average of 31% more moisture than the length of the subtropical jet, and therefore 45% more rain and snow in the western Himalayas during the winter months during a positive NAO phase.

Increased storms in northwest India are expected to affect states such as Jammu and Casmir, Punjab, Gujarat and southern Pakistan . These are mainly rural areas but contain cities such as Srinagar, Peshawar, Jodhpur, Hyderabad and Karachi.

The study used 70 years of data from the European Center for Medium-Range Weather Forecasts based in Reading and other organizations, as well as rainfall data from the Western Himalayan region provided by the Indian Meteorological Department.

The authors found that the correlation was strongest in cycles of 2-3 and 12-16 years in the variation of the NAO. The slow versions of the NAO improve the prediction of a wetter or drier than average winter in northwest India up to three months in advance.

In addition to the winter rains that support crops grown during this period, the snow that falls on the Himalayas melts to feed rivers in the spring, making it an important part of water security in India.

Further work is needed to further investigate the correlation identified by this study, why the rate at which the NAO affects rainfall in the Western Himalayas varies from zero to six months, and whether there is an influence on the winter monsoon in southern India and the Sri Lanka.

Dr Hunt said: “Climate change could also affect the amount of winter rain and snowfall seen in North West India. e in the future, as the shape and placement of the North Atlantic jet stream and the power of the subtropical jet are expected to be affected as the planet warms. This has potential implications for the jet stream that powers storms in India.

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