Subscribe
The heavy rainfall that triggered the disastrous landslides in Wayanad district of Kerala on July 30 was made 10.8 per cent heavier due to the warming since the pre industrial era fuelled by fossil fuel emissions, according to the World Weather Attribution (WWA).
WWA is a global consortium of climate scientists who analyse weather observations and climate models to understand and quantify the role played by global warming in the occurrence, frequency and intensity of extreme weather events.
The heavy rainfall was one among many reasons for the devastation, apart from land cover and land use changes in the form of deforestation and quarrying. The series of landslides in the district, mainly in the villages of Mundakkai and Chooralmala, have killed more than 400 people with many more missing.
While the total rainfall on Wayanad between the mornings of July 29 and July 30 was 140 millimetres, a rain gauge located in nearby Puthumala maintained by the Hume Centre for Ecology and Wildlife Biology measured 572 mm of rainfall in 48 hours, leading to the landslides.
Since June 22, there was also continuous rainfall in Wayanad with short breaks. At the Kalladi weather station located 5 km from Mundakkai, 1,830 mm of rainfall has been recorded in the previous 30 days.
WWA scientists from India, Sweden, United States and United Kingdom got one day maximum rainfall data for the past century for north Kerala, which received heavy rainfall on July 29 and July 30 from the India Meteorological Department (IMD).
The scientists investigated historical trends of extreme rainfall in the area. They found that the occurrence of one day heavy rainfall events has become 17 per cent more intense in the last 45 years and during the same period when Earth’s climate has warmed by 0.85°C.
The researchers also checked and analysed 25 climate models for accurate representation of the event and to analyse the role of warming in the event. They found that 16 models showed good results, 11 of which could make projections into the future.
The study finds that in today’s climate that is warmer than the pre-industrial era by 1.3°C, an event of this magnitude is expected to occur once in 50 years. The event is also the third-highest single-day rainfall event after 1924 and 2019 and surpasses the single-day rainfall that occurred during the once-in-a-century floods in 2018.
With future warming of around 2°C, the single-day rainfall events are going to become around four per cent more intense, it added.
“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,” said WWA in its scientific report of the study.
In terms of early warnings, the study pointed out that the IMD had issued an ‘orange’ alert for the district on July 29 and changed it to ‘red’ after the first landslide already occurred. Slope-specific landslide early warning systems are extremely expensive and difficult to implement but they also provide the best opportunity for saving lives that could be possibly lost due to such events, the authors noted.
Wayanad has the highest risk of landslides among all the districts of Kerala, the scientists highlighted.
“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 per cent reduction in forest cover, may have contributed to the increased susceptibility of the slopes to landslides when the heavy rain fell,” said WWA in its scientific report.
“The soils in the hilly Wayanad district are among the loosest and most erodible in Kerala, with high risk of landslides during the monsoon season. More stringent assessments of landslides, restricting construction in hillside areas and minimising deforestation and quarrying are needed to avoid similar disasters in the future,” the scientists pointed out in a WWA press release.