This can have long-term effects on food and water security in north India
This year, extreme weather has come early to the Himalayas. The mountainous states of Jammu and Kashmir, Himachal Pradesh, and Uttarakhand experienced bouts of heavy rainfall, thunderstorms, flash floods, and landslides in March and April, much ahead of the disastrous monsoon season when such events usually happen.
Meteorologists attribute this to a combination of rising temperatures and shifting patterns of western disturbances — a non-monsoonal precipitation pattern originating from the Mediterranean.
During summer, western disturbances usually travel beyond the foothills to higher mountain regions, confining snow and rainfall to the Himalayas’ upper reaches. But instead, they are causing extreme rainfall in the Himalayas’ lower regions. This change in behavioural patterns of western disturbances is caused by human-induced climate change, claim experts.
Potential for more extreme weather
This fundamental shift can have potentially devastating consequences. A split in the travelling pattern of western disturbances can cause more rainfall and snow in the Himalayan foothills. Also, all western disturbances do not naturally lead to rainfall, while rainfall is occurring on days when it’s not supposed to.
Incessant warming across Arabian Sea and Bay of Bengal infuses moisture in abundance in the atmosphere. Thus, the slightest rise in temperatures when combined with high levels of moisture, leads to rainfall.
“After remaining insignificant till January, western disturbances picked up frequency from late January onwards and have been affecting western Himalayas at regular intervals. The influence of western disturbances has been growing significantly over Jammu and Kashmir, Himachal Pradesh and Uttarakhand. They have been dumping more rainfall over the Himalayan region, which is directly related to climate change,” said Dr. K J Ramesh, former director general of Meteorology, India Meteorological Department.
Western disturbances usually cause rainfall during winter months across northwest India, and is part of the larger weather system. They are embedded in the fast-flowing, high altitude wind current known as the subtropical westerly jet that lies over the Indian Himalayan region. Climate change has led to the widening of the jet stream, which now leaves more space for these western disturbances to oscillate.
This, in turn, leads to the unpredictability of western disturbances.
This year, weather patterns largely show a different trend, according to Dr. Ramesh.
“Global warming has led to rapid warming of the Arabian Sea, which then emits more moisture northwards. Now, when the amplitude of western disturbances extends up to the north Arabian Sea, more moisture is fed into the system, resulting in intense weather activity over the hills,” he said.
Rise in heat stress to continue to alter western disturbances
According to scientists, changes in the behavioural patterns will only exacerbate if temperatures keep rising. With this, Himalayan states need to be prepared for more extreme weather events during the year.
“Growing evidence shows that western disturbances are impacting weather outside the winter season, leading to extreme precipitation events. There is no doubt that increasing heat stress is the basis of everything, as it is generating more energy and at the same time pushing moisture upwards,” said Professor A P Dimri, director at the Indian Institute of Geomagnetism.
Western disturbances play a critical role in maintaining critical mass balance of the Himalayan glaciers — freshwater source for agricultural plains in India and Pakistan. They replenish snow reserves and provide freshwater through rain during winter, while the snowmelt during summer feeds crops just before monsoon. So, food and water security is dependent on western disturbances playing their part, normally. Climate change is putting that at risk.
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