Global warming is reshaping the world’s highest and youngest mountain range and its interaction with the region’s weather systems
The cloudbursts and torrential rains experienced by the western Himalayas and Sikkim in 2023 are curtain raisers to a future that is already upon us, and will become more pronounced with every passing year of excessive fossil fuel consumption. Being a minor contributor to the global greenhouse gas emissions, there is very little that India can do to arrest global warming and thereby, the changes taking place in the Himalayas. All that the future governments can do is to adapt to the changes and minimise the damages. For this, we need to understand just how global warming has begun to affect the climate in and around the Himalayas.
The impact of global warming on the southwest monsoon is not immediately apparent. In 2023, the southwest monsoons arrived early, covered the entire country a fortnight ahead of time and lasted a whole week longer than usual. The precipitation in India, for the entire monsoon season, was 7 per cent below the long-term average, which is well within the boundaries of normality. But it was the pattern of rainfall distribution that was anything but normal, for the monsoon was punctuated by some of the worst extreme weather events that South Asia has experienced in living memory.
What’s more, 2023 was the second consecutive year of such extreme departures from the norm; the intense monsoon surges in 2022 also caused widespread landslides across Pakistan, flooding one-third of the country.
Till 2021, most such deviations in the southwest monsoon winds had occurred in the southern half of the sub-continent—two unprecedented floods in Tamil Nadu, two equally unprecedented cyclones in the Arabian Sea, and a 14-month-long drought across the Deccan peninsula, all caused by the failure of the northeast stream of monsoon, also known as the retreating monsoon. But in the last two years, such deviations have mostly taken place in the Indo-Gangetic plain.
In July 2023, when the southwest monsoon was at its peak, rainfall was excessive in the arid and semi-arid western half of the country, but heavily deficient in the eastern half of the Indo-Gangetic plain and the whole of the northeast India and the coastal areas (see ‘Clear shift’). This is a reversal of the rainfall pattern that has existed since time immemorial, in which precipitation is highest in the east, and declines gradually as the clouds move up the Indo-Gangetic plain to the northwest.
Further analysis of the rainfall during the entire monsoon season shows that the area with an excess of rainfall stretched in a broad northeast to southwest swathe, from the cold desert of Ladakh through Jammu and Kashmir, Punjab, Haryana, western Rajasthan and western Uttar Pradesh, to Gujarat and the Saurashtra peninsula. And this was balanced by a similar departure from the norm in the opposite direction in the eastern part of the country. The paucity of rain was highest in Manipur (46 per cent), followed by Jharkhand (27 per cent), Bihar (21 per cent) and Assam (18 per cent). Uttar Pradesh recorded a deficit rainfall in the eastern part of the state, while its northwestern districts adjoining Punjab and Haryana received a surplus (see ‘Drying wet lands’).
These changes in the monsoon pattern, particularly the sharp reversal between the two parts of Uttar Pradesh, alert us that these are not aberrations, but products of what may be a permanent change in the orography of the Himalayas. Orography deals with the interaction between mountain ranges and other uplands, with moisture bearing winds and temperature changes. This interaction determines not only the micro-climate at different altitudes on the mountain slopes and in the valleys between them, but the weather in the river basins and plains into which the rivers debouch.
We now need to keep a close watch on the next few southwest monsoons to be sure that we are seeing the birth of a new pattern in the southwest monsoon, within which its northern stream, which used to be the weakest, has become the strongest.
The possibility of a new pattern in the southwest monsoon also cannot be ruled out because the temperature of the uppermost layer of the Arabian Sea has risen by 1.2°C to 1.4°C in the four decades from 1982 till 2019, against the average temperature rise of 0.8-0.9°C for all the oceans of the world. This has created far more evaporation for the clouds to pick up. What’s more, since the northern stream has to travel the longest distance over the Arabian Sea before making landfall, it is not surprising that it picks up the maximum amount of water vapour and releases it when pushed upwards by the towering ranges of the Himalayas. This shift of the southwest monsoon is likely to become more evident as the atmosphere grows warmer.
The abnormal warming of the Arabian Sea is also stoking more cyclonic storms. Between 2001 and 2019, there has been a 50 per cent increase in the frequency of cyclones in the Arabian Sea. About half of these dissipate before they land. So far, most of the remainder have moved westwards and made landfall on the Arabian coast and in Yemen. But this pattern has also begun to change. Cyclones were virtually unknown along the west coast of India until very recently because the Arabian Sea was cooler than the Bay of Bengal. But this has changed in the past two decades. The first cyclone from the Arabian Sea to hit the Indian west coast was cyclone Tauktae in May 2021. It caused relatively little damage, but the second, Biparjoy, which hit the Gujarat coast on June 15, 2023 caused massive damage.
The abnormally high surface temperatures in the sea rapidly intensified this cyclone. It remained a Category 1 cyclone with winds stronger than 120 km per hour for 114 hours—the longest duration recorded by an Arabian Sea cyclone. About 100,000 persons had to be evacuated to shelters. The cyclone brought in its wake heavy rainfall that flooded the hot deserts of Saurashtra, Kutch and Rajasthan. Saurashtra received rainfall that exceeded the long-period average during the post-cyclonic period by 5,696 per cent, Gujarat by 4,938 per cent, Rayalseema by 456 per cent, eastern Rajasthan by 374 per cent and west Madhya Pradesh by 370 per cent. These events in the last two years, once again, indicate that while monsoon precipitation will continue to fluctuate under the various impacts of El Nino, La Nina and other such influences, the southwest monsoon as a whole is likely to continue shifting westwards, as global warming continues.
At the other side of the subcontinent, there has been a gradual, but secular decline in rainfall. Cherrapunji (now Sohra) in Meghalaya was long considered the wettest place on Earth, because it had experienced a record precipitation of 2,297 cm in August 1880-1881. As recently as 1974, Cherrpunji set another world record of 2,455 cm. But since then the annual precipitation has dropped rapidly till it was averaging only 800 to 900 cm a year in the pre-COVID decade. Today it is a drought-prone area for good parts of the year in which drinking water is sold for up to Rs 24 a litre.
Why did the excess rainfall in western India cause so much damage? There has been a dramatic rise in the incidence of excess rainfall and cloudbursts. Had the excess rainfall been evenly spread across July and August, the months of maximum precipitation, it would have caused a fraction of the damage that it did. But not only did a disproportionate amount of the rain fell in July, but most of it came in a single week at the beginning of the month from July 8 to 12 (see ‘When it rains it pours’).
This catastrophe can be traced directly to the warming of the atmosphere in the Himalayan region. The average warming here has been 1.6°C, against the average of 1°C temperature rise in India as a whole, and 1.1°C for the globe. This level of warming has created what can only be described as an orographic nightmare in the Himalayas.
More ominous than the increase in the number of cloudbursts in the Himalayas is their accelerating frequency. The raging torrents created by the rise in their frequency and ferocity, have caused a series of calamities in the downstream plains of Punjab, Haryana and sub-mountainous parts of Uttar Pradesh, which were already failing to cope with higher rainfall and the debris and flood water received from the upstream valleys. Floods in the Ravi river, which divides India from Pakistan in Punjab, reached the danger level, breeched its banks and inundated scores of villages in the corridor on both sides of it. Further east the Ghagghar, a river that had dwindled to a stream decades ago and seen a massive urbanisation on its floodplain, became a raging torrent, breeching its banks at many places and sweeping away thousands of dwellings. The inundation spread to many villages downstream. Still further east, another small river the Hindon that originates in the Shivalik foothills of the Himalayas and flows right into Delhi, flooded after 48 years and inundated fields, factories and houses built in the floodplains in Delhi’s eastern suburbs of Noida and Ghaziabad, and their surrounding areas, before emptying itself into the Yamuna river downstream of Delhi.
This suggests that the world is not only growing warmer, but that in the Himalayan region we have already crossed one or more “tipping points”, critical thresholds that, when crossed, lead to accelerating and irreversible change in the climate system.
Cloudbursts are not just intense rain showers, but a genetically different form of rain. Even in heavy showers, the raindrops are usually about 2 mm in diameter. Their size grows to between 4 and 6 mm during severe thunderstorms and cloudbursts. Being heavier, these raindrops fall faster. Their terminal velocity is about 10 metres per second as against 7 m per second in the case of normal raindrops. Thus they trigger landslides with their tremendous pounding power.
If the temperature gradient within the cloud is steep enough, the larger raindrops congeal into hail. The overall intensity of precipitation then frequently rises to 100 mm of rain per hour. This is the intense pounding of the soil that triggers erosions, landslides and muddy runoffs. If the orographic gradient—the rapidity with which clouds cool as they rise—is steep enough, the intensity of precipitation can rise to 250 mm per hour! This was the actual intensity of the storms that have been reported in Leh and Ladakh and one can imagine the devastation they caused. Against this, the normal intensity of precipitation is 33 mm/hour. Even a 70-80 mm/hour rate of precipitation is a rare event in the foothills of the Himalayas. Number of the thunderstorms, cloudbursts and hailstorms has increased from between two and four per annum during the four decades between 1970-2010, to 53 in Himachal Pradesh alone in 2023 (see ‘Sharp rise’).
In July 2023, westerly disturbances over Ladakh and the mountain ranges of Himachal Pradesh collided with the moisture-laden warm winds of the southwest monsoon immediately to the southeast of this region. This resulted in heavy rains between July 7 and 13, both in the cold desert of Ladakh, and the hot deserts of Rajasthan, Saurashtra and Kutch in Gujarat. The rainfall that occurred was four times the long-period average (LPA) for Himachal Pradesh, and twice the LPA in western Rajasthan and the Saurashtra and Kutch regions of Gujarat.
The worst long-term damage is, however, being recorded in the upper reaches of the Himalayas, and unlike the floods caused by the monsoons, it is relentless. The rise in average surface temperatures in the Himalayas has exceeded 1.6°C and is causing the Himalayan glaciers to melt rapidly, which are then retreating at an accelerating rate (see ‘Himalayan meltdown’). The ice-melt from the glaciers is forming glacial lakes across the Himalayan range. The number of such lakes in Uttarakhand and east of Himachal Pradesh, has increased from 127 in 2005 to 365 in 2015. The increasing frequency and ferocity of cloudbursts is causing these lakes to overflow or burst their banks and cause havoc downstream. The raging torrents they have unleashed have cut short thousands of lives, drowned tens of thousands of sheep, goats and other livestock, and swept away thousands of homes and public buildings.
The first such catastrophe occurred in 2013, above Kedarnath, one of the holiest pilgrimage spots in India. The torrent that raged down the Bhagirathi claimed, officially, 6,074 lives, mostly of pilgrims; but many bodies were never recovered. A similar “lakeburst” occurred at Chamoli in Uttarakhand in February 2021; it caused havoc to infrastructure along the Alaknanda for a hundred kilometres downstream of the town. In February of 2023, the township of Joshimath, also on the Alaknanda river, started sinking as its topsoil had been fatally loosened by the rising incidence and ferocity of cloudbursts, indiscriminate construction along the banks of the river and the disturbance of the Earth’s crust by a hydropower project of the National Thermal Power Corporation (NTPC).
The most recent glacial lake burst occurred in Sikkim on October 4, 2023, and claimed more than 400 lives.
In the west of Himachal Pradesh and Ladakh, glaciers are receding in the Hindu Kush Himalayan range by 5.9 to 6.7 m every year (see ‘Beating retreat’).
Overall, the Himalayas have already lost more than 40 per cent of their ice, and are likely to lose up to 75 per cent by the end of this century. This is making the vegetation line in the Himalayas shift upwards at the rate of 11 to 54 m per decade. With 90 per cent of Himalayan agriculture being rainfed, this will make it impossible to sustain the livelihoods of the people who now inhabit the Himalayan region, and endanger the lives of those in the plains who depend on its waters.
The accuracy, precision and reliability of meteorological services in India have improved a great deal in recent years. The need now is for additional budgetary provisions to monitor glaciers and glacial lakes, for the early draining of excessive water, and much better forecasting and forewarning of impending landslides and “lake bursts”, so that preventive measures can be taken and timely evacuation, relief, and resettlement and rehabilitation can be started. However, these will only limit the damage that runaway global warming is going to inflict. Only reducing the demand for fossil fuels and rapidly replacing the energy source with renewables, can save the Himalayas and thereby prevent much of northern India from eventual desertification.
Jagir Singh Samra is the Director of the Centre for Rural and Industrial Development, Chandigarh. Prem Shankar Jha is a visiting Fellow at The Centre for Science and Environment, Harvard University
This was first published in the State of India's Environment 2024
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