Bengaluru: Climate change made the rainfall that triggered the recent Wayanad landslides in north Kerala 10% heavier, as per a rapid study published by scientists of the World Weather Attribution (WWA) group on Wednesday (August 14). More such landslides are likely to occur, per the report. It also added that minimising deforestation and quarrying, while also improving early warning and evacuation systems, will help protect people in northern Kerala from future landslides and floods.
The multiple landslides in Meppadi panchayat in Wayanad district on July 30 claimed the lives of at least 231 people as per a recent statement by a state minister. More than 100 people are still missing, and rescue teams have retrieved 205 body parts from the area, including from the waters and banks downstream of rivers that flow through here.
Signatures of climate change in Wayanad landslides
In the aftermath of this tragedy, scientists with the WWA conducted a preliminary, rapid study of whether human-induced climate change had worsened the rainfall that triggered the landslides. The WWA is an initiative by scientists across the world to study if recent extreme weather events were caused or made more probable by it. They have also provided such preliminary immediate studies for several extreme weather events in India and Asia, including the heatwaves of 2023 and 2024.
The team of 24 researchers, including six scientists from India, studied North Kerala (districts north of Ernakulam, including Wayanad), and analysed the one-day maximum rainfall during the monsoon season here from June to September. For this, the team used a combination of both observation data across years (including data provided by the India Meteorological Department and the US’s National Oceanic and Atmospheric Administration) and climate modelling (25 models across three separate modelling experiments).
Their report, published on August 14, found that climate change – a warming of 1.3°C since the pre-industrial era – has made single-day monsoon downpours in Wayanad about 10.8% heavier. This may sound small, but it marks a significant contribution of climate change to the event, the authors clarified.
Heavy rainfall is not uncommon during the monsoon season in Wayanad, noted Mariam Zachariah, one of the authors of the study, but “what set this time apart is the very heavy rainfall that fell on July 29 and 30,” she said, at the team’s virtual press conference on August 13. Zachariah is a researcher at the Grantham Institute, Climate Change and the Environment at Imperial College London, UK.
The IMD’s data shows the rainfall in north Kerala during this time was the third highest after the 1924 floods that the state witnessed, and in 2019. It even surpassed the rainfall that led to the 2018 floods in Kerala, she added.
Several factors may have contributed
Moreover, the heavy rain that fell on the already-saturated soil in the area – characterised by “loose, erodible soils” according to the study – was another crucial factor.
“The soils in Wayanad were highly saturated, which is common in the region during the rainy monsoon season, meaning the meteorological cause of the landslide was the heavy rainfall on the preceding day of the event,” the report summary said.
The report also highlighted the roles that deforestation and quarrying – the latter still continues in the district, the report quoted references as saying – may have caused in the event.
“While the linkage between land cover, 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 report said.
As per a study published in 2020, this sharp decrease in forest cover in Wayanad district occurred between 1950 and 2018; area under tea plantations increased by around 1800%. Incidentally, the area where the landslides occurred – including the village of Mundakkai, which was among the villages that bore the brunt of the landslides – is adjacent to tea estates.
“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 report noted. Over the last 45 years – when the climate has warmed by 0.85°C – such heavy one-day rainfall events have become about 17% more intense, the study also said.
The need for better early warning systems
More such landslides can occur, the rapid study by the WWA has warned.
According to the report, such one-day bursts of monsoon rainfall will continue to become even heavier, risking even deadlier landslides. With Wayanad being one of the districts in Kerala that studies show is among the most susceptible to the risk of landslides, this calls for developing better early warning systems so that people can be quickly evacuated out of harm’s way, the authors said at the press conference. However, the report also noted how “notoriously difficult” landslides are to predict, and that India’s early warning systems are still in their infancy.
“While early warning of extreme rainfall and the potential for landslides was shared by the IMD, the information was not tailored or specific to the places that would eventually see the landslides,” the report added. “These state-level warnings are often ineffective because they do not specify which particular slopes are most at risk and cover thousands of people, making it difficult to encourage early action.”
Though India’s Union minister for home affairs Amit Shah said that the IMD had warned Kerala would witness heavy rainfall, Kerala’s chief minister Pinarayi Vijayan has refuted the claim. The IMD’s press releases also show that even on July 29 (the landslides occurred between 1 and 6 am on July 30), it only gave an orange alert for Kerala which translates to “Be Prepared”. The red “Take Action” alert for the state came after the landslides occurred, Vijayan said. IMD press releases also confirm this.
Interestingly, all press releases on weather updates provided by the IMD after August 1 say that “Action may be taken based on ORANGE AND RED COLOUR warnings” (stressed in capitals in the press releases) and that “Vulnerable regions likely urban and hilly areas action may be initiated for heavy rainfall warning”.
The WWA report highlighted that the Wayanad disaster shows the “need for a more robust and localised early warning system that can provide accurate, timely, and actionable alerts”. These warnings should also be “understandable to all and contain precise advice on actions to take” after receiving the warning, the report noted. “This requires not only technological enhancements but also improved coordination between government agencies and local communities to ensure that early warnings translate into effective early actions, ultimately saving lives.”
Towards a system that works
Attribution is an important component of climate change studies and the WWA report is interesting, said Jagdish Krishnaswamy, Dean of the School of Environment and Sustainability at the Indian Institute for Human Settlements, Bengaluru. Krishnaswamy was not involved in the WWA rapid study.
“I really appreciate that the attribution to climate change study also gave a nice summary of the factors that go into landslide generation,” he told The Wire.
However, it would have been nice to have an integration of rainfall intensity related to climate change with the measured hydrologic response (such as the way water flows and circulates) which eco-hydrologists in the Western Ghats, working in instrumented catchments, have studied, he added.
For example, it would have been good to integrate the knowledge about water infiltration rates in soils in the Western Ghats ecosystems in relation to rain intensities, how headwater streams (streams, even really small ones, at higher elevations) respond to high rainfall intensities, and build up of soil moisture – types of data and evidence published from the Western Ghats, he said.
Krishnaswamy and his colleagues have worked for more than three decades on different aspects of the hydrology of the Western Ghats, and have long-term monitoring stations.
A study by Krishnaswamy and other scientists in 2017 found that subsurface watershed residence time – a measure that provides information about the storage, flow pathways, and source of water under the earth’s surface, including the average time that rainwater falling in a catchment takes to reach a stream – decreases in specific ways as mean rainfall intensity rises. Current model systems, however, do not capture this well, per the study, and the predicted increases in rainfall intensity (as climate change science predicts will happen in future) could make river floods in such areas more likely.
“So shallow subsurface flow pathways [water flowing immediately below the ground] are an important part of the hydrology of the Western Ghats, and very specifically responds to high rainfall intensity,” Krishnaswamy told The Wire.
Additionally, attribution of landslides to land use change has to be done cautiously and with evidence, Krishnaswamy added.
“Of course the impact is much higher downstream because of the type of land use…we are exposing a lot of people and infrastructure to the hazard by building houses or expanding infrastructure in particular locations. But you can have some landslides originating in forested areas, even in this particular case, the landslide started in a forested area. A few years ago, the forested sites his team worked in, in the Upper Nilgiris — not far from Wayanad — was also affected by a landslide.
“Adaptation has to be very local,” he told The Wire. For example, in the wet seasons, authorities in collaboration with civil society may want to consider evacuating people from certain high risk areas and have them come back to the region in the non-monsoonal months to eke a livelihood out of those places, he said. This is something Krishnaswamy also spoke about in detail during an interview he gave to Asianet News after the Wayanad landslides.
“That is something that needs to be thought of very creatively,” Krishnaswamy said. “Also in terms of temporary shelters for people who can move out of these areas during the monsoon and come back later.”
Odisha is a good example to consider in this context, said Krishnaswamy. After the 1999 super cyclone in Odisha, responses to subsequent cyclones have improved greatly; early evacuation systems have been in place and there has hardly been any mortality.
“However, the conditions and the terrain in the Western Ghats are different so we have to design it accordingly. But we can come up with a system which will work,” he said.
