Behind the Wayanad landslides: Extremely heavy rain, fragile ecology, a steady rise in population

Wayanad district received more than 140 mm of rainfall in the 24 hours between the mornings of Monday and Tuesday, about five times more than what is expected, data from India Meteorological Department (IMD) showed. Within the Wayanad district, several areas reported more than 300 mm of rainfall during this period.

Heavy rains during the monsoon season trigger landslides in Kerala almost every year. The whole of western Kerala, which is a hilly terrain with sharp slopes, is susceptible to landslides. There were major landslides during and after the 2018 flooding event, including in Wayanad. The district also saw a few smaller landslides in 2019.

“But this is possibly the worst landslide-related disaster in the state ever,” said K S Sajinkumar, an assistant professor of Geology at the University of Kerala.

“The terrain here has two distinctive layers, a layer of soil sitting atop hard rocks. When a lot of rain happens, the soil gets saturated with moisture and water reaches the rocks and flows between the soil and the rock layers. This weakens the force that binds the soil to the rocks and triggers the movement. This is what seems to have happened in this instance as well,” Sajinkumar said.

Nearly 17,000 sq km of area in Kerala, most of it on the western side of the Western Ghats, is mapped as landslide prone.

“We have to have strict restrictions on land use in these areas. Cultivation or other activities cannot be allowed. I am not suggesting these activities have triggered this landslide because we are still to make the assessments, but in general the regulations required, considering the local ecology, are not implemented,” G Sankar, a former scientist with Thiruvananthapuram-based National Centre for Earth Science Studies.

Incidentally, the possibility of these landslides, in view of the expected rains, had been predicted by the IMD a couple of days ahead of the event. But as Sajinkumar said, there is little that can be done in the absence of a good mitigation plan.

“There are two things needed. We need to assess how much rains result in saturation of the soil level in different areas. We can then define rainfall thresholds for landslides. Then we need to map out the routes that landslides are likely to take after they have been triggered. We have susceptibility maps, but haven’t drawn up the route maps, which is a much more difficult exercise. With route maps, we would be able to mark out areas which should be out of bounds for settlements or any activities,” Sajinkumar said.