JOIN USIn Kerala, people shift from resistance to adherence
Over the last century, more than 50% of the land in southern India has been converted to monoculture plantations and agriculture fields from tropical forests and grasslands. This has made the terrain more vulnerable to landslides. A steady rise in the population, road construction and mining activities further exacerbated the risks.
In the same hundred years, India’s weather pattern too changed with an increase in the frequency of extreme weather events. When a heavy downpour hits the earth, the rainwater run-off overwhelms streams, drains and rivers, carrying with it soil particles and huge boulders. These factors largely contributed to the south Karnataka and Kerala floods and landslides in the recent years.
For the third year in a row Kerala witnessed major natural calamities, especially landslides on the Western Ghats claiming many lives. While nearly 500 lives were lost in 2018, the number dropped 125 in 2019. This year, around 70 lives including those killed in Munnar, were lost so far and the monsoon season is far from being over.
Most of the studies on the causes of the calamities came to almost similar conclusions. One of the most comprehensive studies was carried out by a committee chaired by K P Sudheer, executive vice president of Kerala State Council for Science, Technology and Environment.
In the report presented in December 2019, the panel reported that steep sloped areas having slope more than 33% were more vulnerable to landslides. Majority of the landslides in 2018 and 2019 occurred in these terrains. Anthropogenic activities for agricultural expansion and water conservation such as terracing, blocking and diversion of stormwater channels and alteration of natural vegetation patterns amplified the landslide susceptibility of these regions.
Idukki district was the worst-hit. An analysis by a team of civil engineers from Indian Institute of Technology, Indore shows that between 2010 and 2018, there were 225 landslide events in the district. The state government records show 143 major landslides in 2018 in Idukki, which has an elevation of nearly 3,000 mt with slopes that can go up to 80 degrees at some place.
While the expert committee in its report recommended slope stabilisation measures like increasing vegetation cover, removing roots of trees felled, proper selection of crop and adequate engineering design in road construction at unstable slopes, Sudheer said quick implementation of long-term measures could not be expected since it required involvement of multiple government departments.
Godwin Vasanth Bosco, an ecologist working on restoration of forests and grasslands of the Nilgiri Highlands and Western Ghats, said the immediate step required was to stop road expansion activities as it was the commonest triggering factor.
Changing pattern of the south east monsoon leading to extreme rainfall events is the primary reason behind the calamity. But weather scientists have made it clear that such a change is a reality that one has to live with and be prepared for.
“Nearly 200 landslides occurred in Kerala in 2018. That's not only because of rains but also the way we have changed the land - through mining, construction and agriculture,” said Roxy Mathew Koll, a weather scientist at Indian Institute of Tropical Meteorology, Pune.
Heavy rainfall in August, two months after the onset of monsoon, had been one common phenomenon that preceded the landslides in the last three years. While normal rain expected in Kerala for August was 427 mm, the state received 476 mm only in the first 10 days of August this year.
M G Manoj, a scientist at the Advanced Centre for Atmospheric Radar Research of Cochin University of Science and Technology, said had the high intensity rain happened in July, the disaster would not have been so intense as the soil would have had more water-holding capacity.
However, the former director of Indian Meteorological Department's Thiruvananthapuram Centre S Sudevan said that the monsoon was highly variable. A long-term analysis of the data of 150 years has shown a declining trend in June, July rains and a slight increasing trend in August.
In the last three years, Kerala witnessed a huge amount of excess rainfall in August. Compared to the normal rainfall of 419.5 mm in August, the state received 821.9 mm in 2018 and 951.4 mm in 2019 – nearly 100% more in both years. In 2018, when the state experienced the catastrophe, the rainfall was 164% more in the first three weeks of August. And going by the early trends, August 2020 will end up as an excess rainfall year too. Post 2018 disaster, the University of Reading, UK in a research paper showed the state required 34% more reservoir capacity to accommodate all the rainfall of August 2018. Analysis of river stream flow at all 62 dams in the state showed that climate change would have the strongest impact in the south of the state.
The Western Ghats can be divided into two segments, north and south, separated by the Gap of Palghat. Deep-seated landslides are reported in the northern segment and the eastern flank while the southern segment mostly experiences shallow landslides. Idukki belongs to the southern part and is prone to shallow landslides.
In an effort to find out a landslide alert system for Idukki, the IT team has shown that a rainfall of 70.6 mm over a period of 10 days and 229.8 mm over a period of 40 days can trigger a landslide event. But more research needs to be conducted to find out similar thresholds for other landslide prone districts of Kerala and Karnataka.
On the positive side, what has changed in the last three years in Kerala is people’s attitude. A high level of compliance towards alerts, fresh assessment of calamity prone areas and permanent shifting of around 3,000 families from vulnerable areas resulted in a decline in the number of casualties this year despite widespread minor landslides and landslips.
"Earlier there used to be a high level of resistance from people to shift from calamity prone areas despite alerts. In view of the bitter experiences of the last two years, now there is a high level of adherence," said Kerala State Disaster Management Authority member secretary Sekhar L Kuriakose.