New Delhi: The increase in climate change-driven rainfall is likely to increase the potential number of landslides that could be triggered in the future, stated a study conducted by the World Weather Attribution (WWA) on the recent Wayanad landslide that killed more than 231 people.
The landslides in Wayanad resulted in devastating loss of life and occurred in a mountainous region with loose, erodible soils after 140mm of precipitation fell on saturated soils, it said.
“In today’s climate, which is 1.3°C warmer than it would have been at the beginning of the industrial period, an event of this magnitude is expected to occur about once every 50 years. The event is the third heaviest one-day rainfall event on record, with heavier spells in 2019 and in 1924, and surpasses the very heavy rainfall in 2018 that affected large regions of Kerala,” the findings of WWA’s study revealed.
The WWA is an international collaboration that analyses and communicates the possible influence of climate change on extreme weather events, such as storms, extreme rainfall, heatwaves, and droughts.
It stated that to assess if human-induced climate change influenced the heavy rainfall, “we first determine if there is a trend in the observations. Heavy one-day rainfall events have become about 17% more intense in the last 45 years, over a period when the climate has warmed by 0.85°C. Longer-term trends in the pre-satellite era are not clear, which may relate to lower quality weather data.”
To quantify the role of human-induced climate change, the study analysed climate models with high enough resolution to capture precipitation over the relatively small study region. “Overall, the available climate models indicate a 10% increase in intensity. Under a future warming scenario where the global temperature is 2°C higher than pre-industrial levels, climate models predict even heavier one-day rainfall events, with a further expected increase of about 4% in rainfall intensity,” it said.
The WWA findings said that given the small mountainous region with complex rainfall-climate dynamics, there is a high level of uncertainty in the model results. “However, the increase in heavy one-day rainfall events is in line with a large and growing body of scientific evidence on extreme rainfall in a warming world, including in India, and the physical understanding that a warmer atmosphere can hold more moisture, leading to heavier downpours,” it said.
The study also revealed that there was a lack of advance warning to the grassroot level at Wayanad. “While the extreme rainfall was well forecast by the Indian Meteorological Department (IMD) and warnings were issued, the information was at the state-level, making it difficult to discern which localities would be impacted by landslides and would therefore require evacuation. Slope-specific landslide early warning systems can be extremely costly and difficult to implement, but those would provide the best opportunity for effective early action. Given this, reducing exposure of people and assets to landslide-prone places may be a more effective strategy,” it said.
It said that while the linkage between land cover and land use changes and landslide risk in Wayanad is mixed in the limited existing studies, factors such as quarrying for building materials, and a 62% reduction in forest cover, may have contributed to the increased susceptibility of the slopes to landslides when the heavy rain fell.
“The Wayanad landslides is another catastrophic example of climate change playing out in real-time. The extreme burst of rain that dislodged an entire hillside and buried hundreds of people was intensified by human-caused warming. Until the world replaces fossil fuels with renewable energy, monsoon downpours will continue to intensify, bringing landslides, floods and misery to India,” said Mariam Zachariah, Researcher at the Grantham Institute - Climate Change and the Environment, Imperial College London.
The landslide at Wayanad followed an exceptional spell of monsoon rain that lashed the southern Indian state of Kerala on July 30. More than 140mm fell in a single day – equivalent to nearly a quarter of London’s annual rainfall.
The rain landed on soils that were already highly saturated, following two months of seasonal monsoon rains, triggering catastrophic landslides and floods in the Wayanad district. Boulders, mud and water buried several neighbourhoods in the early hours, killing at least 231 people. More than 100 people remain missing and recovery operations are ongoing.
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