New Delhi: Predictions that India is on track for its driest August in a century are turning out to be quite the irony for the Himalayan states of Himachal Pradesh and Uttarakhand, where heavy rains have unleashed devastating landslides. So, what explains the apparent paradox between a dry spell in some states and a deluge in others? The answer lies in the complex interplay of weather patterns and unplanned human development.
Much of the blame goes to El Niño, officials of the Indian Meteorological Department (IMD) told ThePrint. This phenomenon, characterised by warmer-than-average sea surface temperatures in the Pacific Ocean, influences weather patterns globally. In India, it affects the monsoon system, leading to reduced rainfall in some parts of the country and a deluge in others.
But what has exacerbated the ongoing damage in the hill states is the proliferation of human settlements encroaching on ecologically vulnerable areas, experts said.
According to reports, over 80 people have died in rain-related incidents in Uttarakhand and Himachal Pradesh and many more have been displaced, in addition to significant damage to property and infrastructure.
The events in these states have also highlighted that general predictions are sometimes at odds with localised weather patterns. Notably, meteorologists have also pointed out that climate change has made it more difficult to accurately predict extreme weather events.
ThePrint spoke to experts to understand the factors that led to the prevailing situation in Himachal Pradesh and Uttarakhand.
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Understanding the Indian monsoon trough
The juxtaposition of dry conditions and extreme rainfall, as currently seen in northern India, is a not unusual consequence of El Niño. While the weather phenomenon is generally associated with a weak monsoon in India, it can have the opposite effect in certain parts.
To grasp this puzzle, we need to first understand a semi-permanent feature of the Indian monsoon system— the monsoon trough. This is a low-pressure area, which extends from over Pakistan to the Bay of Bengal.
This trough is shaped by the geography of the region as well as the Earth’s rotation on its axis.
If the Earth didn’t spin on its axis, winds would flow straight from the equator to the poles. But because of the planet’s rotation, these winds blow westwards, creating south-westerly winds, explained D Sivananda Pai, head of the IMD Environment Monitoring and Research Center (EMRC). “Due to the presence of the Himalayas and the hotter land mass towards Rajasthan, the winds turn towards the west,” he added.
This leads to the formation of the monsoon trough. It is like a corridor in the sky that facilitates the movement of moist, warm ocean air to land areas.
As this humid air meets cooler air, it condenses into clouds. These cloud droplets gradually accumulate, becoming heavier and heavier until they eventually fall as rain.
“Winds will be westerly south of the trough, but easterly in the north. This wind pattern causes moisture convergence and thus leads to rainfall,” said Madhavan Nair Rajeevan, former secretary of the Ministry of Earth Sciences and Distinguished Scientist at the National Centre for Earth Science Studies, Thiruvananthapuram.
The accumulation of winds in this area means that the air constantly gets pushed up, creating a low-pressure area— which further attracts more moisture-laden winds.
Although this is a semi-permanent feature of the Indian monsoon, the position of the trough oscillates every year depending on the atmospheric systems influencing it.
Pai explained this by comparing the Indian monsoon circulation system to a cork floating in the ocean.
“The atmosphere is like a vast ocean. Wind patterns, heat, and changes in humidity at the global level cause disturbances in the system, causing the monsoon trough to oscillate, sometimes southwards and sometimes northwards,” Pai said.
Rajeevan added that when the monsoon weakens— that is, there is less rainfall— a high-pressure system is created over central India that pushes the trough northward.
And when this shift northwards happens, winds rush towards the trough. Instead of the rainfall getting distributed evenly across central India, it instead gets concentrated over the Himalayas, resulting in heavy rains along the foothills.
Pai added that even though humidity builds up over central India, the atmospheric conditions that allow this moisture to rise and condensate are absent.
“When rain stops over central India during the months of July and August — when active monsoon is expected — for more than three to four days, the IMD calls it a monsoon break,” Pai said.
This year, the break monsoon conditions have lasted longer than usual because of the atmospheric conditions that forced the trough to remain along the Himalayas.
El Niño & human factors— a dangerous combination
According to Rajeevan, while monsoon breaks are a regular occurrence, they become prolonged in El Niño years, which typically occur every three to five years.
As defined by the World Meteorological Organization (WMO), a UN agency, the El Niño/La Niña Southern Oscillation (ENSO) “has a major influence on climate patterns in various parts of the world. This naturally occurring phenomenon involves fluctuating ocean temperatures in the central and eastern equatorial Pacific, coupled with changes in the atmosphere”.
Right now, the tropical Pacific Ocean is experiencing El Niño conditions due to “rapid and substantial changes in oceanic conditions” over the last several months, according to the WMO. The agency has also predicted that there is a 90 percent probability of El Niño continuing during the second half of 2023.
One of the effects of El Niño is the weakening of eastward winds, which, in turn, impacts the Indian monsoon system by pushing the monsoon trough northward.
While climate change intensifies the effects of El Niño, such as increased heat or rainfall, it is still uncertain whether climate change is altering the fundamental patterns of El Niño itself.
Pai said that the effect of climate change on the monsoon trough system is also not directly understood.
“At the end of the day, it is not the weather patterns or climate change that cause disasters – it is the unprecedented growth of human settlements in historically vulnerable areas,” he pointed out. “If the same rainfall were happening in an untouched forest, no one would care. But we need to think more about how to improve infrastructure in vulnerable areas like the Himalayas.”
(Edited by Asavari Singh)
Also Read: Over 2,700 died in 2022 due to extreme weather conditions — IMD’s state-wise annual climate report