Western Ghats witnessed 6,970 landslides in August 2018Updated: Sep 20, 2019 00:19 IST
Intense and excess rainfall in the Western Ghats region of Kerala, Karnataka and Tamil Nadu resulted in thousands of landslides last year, an analysis by Hyderabad-based National Remote Sensing Centre (NRSC), which is a centre of the Indian Space Research Organisation.
Using Isro’s satellite resources with satellites that are part of the International Charter Space and Major Disasters, the five-member team mapped a total of 6,970 landslides covering 22.6sqkms in the Western Ghats in August 2018 of which 83.2% were triggered by very high rainfall. Very high rainfall resulted in 14.9% landslides even though slopes are moderate, mainly in the Kodagu district of Karnataka.
Researchers, in addition to excessive rain, attributed a combination of factors – sliced up hills and valleys, changes in land use, agricultural practices, and tea and coffee plantations – to the large amount of landslides in the three states.
VS Vijayan, chairperson of the Salim Ali Foundation in Kerala, and member of the Western Ghats Ecology Expert Panel (WGEEP) led by ecologist Madhav Gadgil said development that is not eco-friendly and non-sustainable practices are a threat to the Western Ghats that run across six states.
“Extensive quarrying in the Ghats, changes in land use, increase in rubber and other plantations and tourism where structures are being built on the slopes was responsible for landslides,” said Vijayan who was not involved in the mapping exercise.
Vijayan added, “We submitted WGEEP report in 2012 where we had marked out landslide-prone areas in the Western Ghats. Many of these areas recorded landslides last year. Had our report been implemented, the impact of last year’s heavy rain that triggered landslides would have been less.”
Studies have shown that Western Ghats, with its steep slope and thick soil cover, makes it second most landslide-prone region after the Himalayas in the country.
“The Western Ghats region of peninsular India received excess rainfall due to a low pressure system in the Arabian Sea. This resulted in the worst floods in the state of Kerala during the last century,” stated the paper that was published in Current Science, a peer-reviewed journal of the Indian Academy of Sciences, last week.
Landslides were mapped for 23 districts across the three states covering an area of 98,356sqkms. Pulak Guhathakurta, head of the climate application and user interface, climate research and services, IMD Pune, said that extreme rainfall events have increased over states in the Western Ghats as compared to the northeast.
Kerala which recorded abnormally high rainfall – 164% above normal between August 1 and August 19 and worst even since 1924 – which caused the death of 483 persons and large-scale loss of property witnessed the maximum 5,191 landslides. From June 1 to August 19, Kerala received 2346.6mm rainfall as against the expected 1649.5mm – that’s 42% above normal – which led to severe flooding in 13 of its 14 districts, as per data from the India Meteorological Department.
With 3% above normal rainfall, the analysis found that 993 landslides had occurred in Karnataka, followed by 606 in Tamil Nadu that witnessed 4% below normal rainfall. Of all the 23 hilly districts, Idukki in Kerala logged the highest number of landslides (1632), followed by Kodagu in Karnataka (771) and Coimbatore in Tamil Nadu (447).
While “highly dissected hills and valleys and thick top soil are mainly responsible for maximum occurrence of landslides in Kerala, those in Kodagu district was also due to thick soil cover that has resulted in dominant agricultural land-use practices.
“Plantations and croplands (especially coffee) are predominant. The thick soil cover in the region has mostly encouraged the agricultural land-use practice and in turn has resulted in more number of landslides in the area due increase in pore water pressure after excessive rainfall,” stated the study.
It’s a similar situation that led to the landslides in Coimbatore concentrated towards the south of the district. “Regionally, the most pervasive land-use practice in the area is croplands with coffee/tea plantations along the hill slope. Along with the high dissection of the hill slopes, the agricultural pattern may have loosened the topsoil resulting in more landslides being triggered in the area,” the paper stated.
Other reasons for landslides
Kerala: Toe cutting by rivers due to sudden release of excess water accelerated landslides and subsequent damage. Debris flows with long run-out zones were mapped in Palakkad and Wayanad districts of Kerala. For instance, the run-out length of one such debris flow recorded in Wayanad district is 3.1kms.
Karnataka: Largest landslide and largest total area of the landslide at Kodagu district – it comprises moderately dissected hills of the Western Ghats – largely owing to debris flow from multiple crowns merging in the main valley.
First Published: Sep 20, 2019 00:19 IST