The deadly landslides in Kerala's ecologically fragile Wayanad district were triggered by a heavy burst of rainfall, made 10 per cent heavier by climate change, according to a new rapid attribution study by a global team of scientists.
The team of 24 researchers from India, Sweden, the US and the UK said that more than 140 mm of rainfall fell in a single day on soils highly saturated by two months of monsoon precipitation, triggering catastrophic landslides and floods that killed at least 231 people in Wayanad.
"The rainfall that triggered the landslides occurred in a region of Wayanad that has the highest landslide risk in the state. Even heavier downpours are expected as the climate warms, which underscores the urgency to prepare for similar landslides in northern Kerala," Maja Vahlberg, a climate risk consultant at the Red Cross Red Crescent Climate Centre, said.
To measure the impact of human-caused climate change, the scientists from the World Weather Attribution (WWA) group analysed climate models with high enough resolution to accurately reflect rainfall in the relatively small study area.
The models indicated that the intensity of rainfall has increased by 10 per cent due to climate change, they said.
The models also predict a further four per cent increase in rainfall intensity if the average global temperature rises by two degrees Celsius compared to the 1850-1900 average.
The scientists, however, said there is a "high level of uncertainty" in the model results as the study area is small and mountainous with complex rainfall-climate dynamics.
Having said that, the increase in heavy one-day rainfall events aligns with a growing body of scientific evidence on extreme rainfall in a warming world, including in India, and the understanding that a warmer atmosphere holds more moisture, leading to heavier downpours.
According to scientists, the atmosphere's capacity to hold moisture increases by about 7 per cent for every one-degree Celsius rise in global temperature.
The earth's global surface temperature has already increased by around 1.3 degrees Celsius due to the rapidly rising concentration of greenhouse gases, primarily Carbon Dioxide and Methane. Scientists say this is the reason behind worsening extreme weather events, such as droughts, heatwaves and floods worldwide.
The WWA scientists said that while the relationship between land cover, land use changes and landslide risk in Wayanad is not fully clear from existing studies, factors, such as quarrying for building materials and a 62 per cent reduction in forest cover may have increased the slopes' susceptibility to landslides during heavy rainfall.
Other researchers have also linked the Wayanad landslides to a combination of forest cover loss, mining in fragile terrain and prolonged rain followed by heavy precipitation.
S Abhilash, the director of the Advanced Centre for Atmospheric Radar Research at Cochin University of Science and Technology (CUSAT), had earlier told PTI that the warming of the Arabian Sea is leading to the formation of deep cloud systems, resulting in extremely heavy rainfall in Kerala in a short period and increasing the risk of landslides.
"Our research found that the southeast Arabian Sea is becoming warmer, causing the atmosphere above Kerala to become thermodynamically unstable. This instability is allowing the formation of deep clouds," he had said.
According to the landslide atlas released by ISRO's National Remote Sensing Centre last year, 10 out of the top 30 landslide-prone districts in India are in Kerala, with Wayanad ranked at the 13th spot.
A study published by Springer in 2021 said all landslide hotspots in Kerala are in the Western Ghats region and are concentrated in Idukki, Ernakulam, Kottayam, Wayanad, Kozhikode and Malappuram districts.
It said about 59 per cent of total landslides in Kerala have occurred in plantation areas.
A 2022 study on depleting forest cover in Wayanad showed that 62 per cent of forests in the district disappeared between 1950 and 2018, while plantation cover rose by around 1,800 per cent.
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