'Frequency of landslides rising in Kerala due to land-use patterns, climate change'

Kerala was battered by a series of landslides and heavy floods following the torrential downpour which began last week. Kootickal, Plappali and Kavali panchayats of Kottayam district and Kokkayar of Idukki witnessed massive landslides, claiming 19 lives. An entire family was washed away. Several lost their homes in the flash of a second.

The unexpected calamity in the middle of October way past the arrival of monsoon brought back an important question- Is Kerala becoming increasingly prone to landslides in recent years?

According to a study by the Geological Society of India , 43 per cent of Kerala's total area is located in landslip or landslide-prone regions. The study also found that 74 per cent of Idukki and 51 per cent of Wayanad are located on hill slopes, prone to landslips.

According to a natural hazard proneness assessment by the National Centre for Earth Science Studies 1,848 square km (4.71 per cent geographic area) in Kerala, extending along the steep slopes of the Western Ghats (i.e., mostly in Wayanad, Kozhikode, Malappuram Idukki, Kottayam and Pathanamthitta districts), is highly prone to the occurrence of landslides.

In 2019, Kerala witnessed 80 landslides in eight districts over three days and the death toll crossed 120. In 2018, about 341 major landslides were reported from ten districts. Idukki district was ravaged by 143 landslides, resulting in 104 deaths.

Onmanorama speaks to Mr CK Vishnudas, Director of the Hume Centre of Ecology and Wildlife Biology, Wayanad, about the rising frequency of landslides in Kerala.

What were the key reasons for landslides in Wayanad in recent years?

Though landslides were reported in Wayanad earlier, they were not this frequent. Extreme rainfall in the past few years, however, made the slopes of Wayanad more susceptible to landslides.

For example, in 2019, the annual rainfall in Kurichyarmala region was around 4,000 mm, compared to the decadal average of 2200mm.

Meanwhile, the vegetation patterns were altered by the plantation activity. Though the tea plantations have been here for over a 100 years, the effect of the altered vegetation was felt when the heavy rainfall, spurred by climate change, took place. A rainfall of almost 800mm was received in 36 hours.

Climate change thus makes people living in hilly areas more prone to landslides.

Have you had a look at the terrain of the localities which reported landslides last week? Are the reasons similar?

The reasons are largely similar here as well. Extremely heavy rainfall coupled with land use patterns including construction.

The GSI study, which looked at the landslides of 2018-19, showed the areas prone to landslides are also increasing. What could be the reason for this?

Many of the landslides are occurring outside the hazard zones in the map prepared by the National Centre for Earth Studies a decade ago. The stable areas have become susceptible to landslides.

According to our study in the Vythiri region of Wayanad, 41% of the mudslips happened behind and around houses on slopes, 29% happened along roadways constructed by altering hill slopes,17% on commercial plots, 10% in plantation slopes and, 3% in forest area.

This shows that the primary reason for the expansion of susceptible zones is unsustainable, unscientific constructions.

Some experts have criticised the government for the land use patterns like quarrying and cutting down of rubber trees for the rise in landslides. Is there some credence to these charges?

Explosions, which go beyond a certain range, can affect the existing structure of the slopes and make it vulnerable. The cracks which appear on hills can provide pathways for water and pave way to landslides in the event of heavy rainfall.

Tall deep rooted trees on the mountain side binds the bed rock and keeps the top soil locked. Uprooting these trees can also increase the frequency of landslides.

Did water conservation methods such as rainpits, terracing, blocking/diversion of stormwater channels trigger landslides? And if yes, what is the scientific way of creating rainpits?

A couple of years ago, a farmer in Kurumbalakotta in Kottathara panchayat of Wayanad constructed many storm bunds on his plantation but the land couldn't hold the extreme load during rainfall. His entire plantation was washed away that year due to the weight of the water, stones from construction activity etc.

Prior to 2018, there was a deficit rainfall of around 40-50% in Wayanad. But in the years that followed there was extreme rainfall here and these structures proved harmful.

Rainwater conservation methods must be undertaken only in areas less susceptible to landslides and witness low levels of rainfall. It is also essential to ensure that excess water can run out of the hill slopes. The natural streams should not be blocked from taking its course and joining water bodies.

Rain gauges will help identify the intensity of rainfall. Water conservation can then be deployed accordingly.

What are the preventive measures to stabilise our slopes?

We should classify the zones with the help of landscape analysis and plan constructions accordingly. In Wayanad, we created a landscape susceptibility map. In high risk zones, constructions should be done in a cautious manner. In moderate zones, activity may be scaled up slightly and in low risk zones more construction activities could be permitted. This can be adopted at panchayat levels.

Planting of natural deep rooted trees can help. Rubber plantations should have some stretches of deep rooted trees to hold the soil together.

Many houses are located on hazard prone slopes and completely avoiding construction along these slopes is not viable. What are the options of sustainable housing in these areas?

Civil engineers used to level the plots and build huge boundary walls before constructing homes earlier. These constructions were not sustainable in the hill slopes.

However, if you observe tourist areas, resorts use pillars to construct their structures to capture the beauty of the area in its entirety. Some of those methods can be adopted for construction of houses as well. But due care must be taken to ensure that the top soil is not too deep in these areas.

We have hazard mapping and different warning systems in place. Are the present warning mechanisms sufficient when it comes to landslides?

In Wayanad, we installed rain gauges in many spots. When the rainfall crossed a threshold level in the area marked on our landslide susceptibility map, the warning was issued.

In 2020, we alerted the district authorities when Wayanad's Mundakkai continuously received rainfall for 3 days, crossing 900mm. A major landslide occurred in the area the next day. Fortunately, the DMA had shifted the residents by then.

Local warning systems must be in place to evacuate people when the need arises. Roping in the residents for measuring rainfall and educating them on the impending dangers of climate change is the need of the hour.