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On 30th July 2024, 2 days of record breaking rainfall triggered several landslides in the district of Wayanad, Kerala. The flow of material washed away houses in the villages downhill, killing more than 400 people with countless others injured, missing or displaced from their livelihoods. Was this a freak coincidence of weather conditions creating the perfect storm? was it made worse by global warming? Or was this altogether avoidable?
Gods Own Country
Gods Own Country
2018, Kerala, "God's own country" gears up for the blooming of the Neelakurunji flower, a plant that only reveals its purpleish blossoms once every 12 years, rhythmically turning the hillsides blue on a natural beat, giving them their name "The Neelgiris". However, all the doings of nature are not similarly kind or orderly, they seem to strike upon the lands on the whims of some very careless butterflies. That's what occurred in 2018 when the blossoming of the neelakurunji was preceded by anomalously high rainfall in the region causing large pieces of the land to falter and slide down the slope. This was repeated in 2019, and now again in 2024, every time with an unprecedented cost to human life.
A Slippery Slope
A Slippery Slope
The initiation point of a landslide in 2019, this is the same exact slope that experienced the 2024 landslide causing extensive damage and loss of many lives. Source: Google Earth Image.
The western coast of India is lined with ancient hills, nestled in this terrain is the state of Kerala. Demarcated by the ocean on one side and the Nilgiris separating it from the plains of Tamil Nadu on the other. Nearly 50% of the state's geography is undulating hills and plateaus that support a thriving tourism and tea industry that are major contributors to the state's economy. However, they also make most of the state exceptionally susceptible to landslides and other land mass movements.
On slopes, the ground is held together by the friction between the particles. When the friction at a certain level in the ground is reduced to a point where it can no longer support the weight of the ground above it, it leads to a landslide. This threat is greatest in the monsoon season, as the water seeps deep into the ground it fills up the spaces in between the ground particles. The more water there is underground the more pressure it exerts in those spaces, this is known as "pore pressure". As pore pressure increases, the buoyant forces literally lift the ground above, reducing the friction between planes of the slope and gravity does the rest.
Is it climate change?
Is it climate change?
The nearby weather station of Kalladi saw record highs of 200 and 372 mm of rainfall in the 2 days preceding the landslides on 30th July 2024. This is the highest recorded one day rainfall in IMD data, with the only exception being the 2019 season. After any extreme weather event, there is a lot of interest in understanding whether it was caused or made worse by climate change. The extent of damage caused in the 2024 landslides and in previous incidents in 2018 and 2019 have led to the inevitable question; Is this caused by climate change? The question is answered in what is known as an attribution study, like this one released by the World Weather Attribution organisation only 2 weeks after the landslides. The study employs observational and simulation datasets analysed by researchers from several IITs, Imperial College London and the IMD (Indian Meteorological Department). They estimate that global warming has caused rainfall in the region to be 10% more intense, the report has not yet been peer reviewed and all its claims must be taken with a grain of salt. This finding is in disagreement with studies that were done in response to the 2018 floods used different methodologies and focused more on sustained rain over a longer period of time and found that the 2018 event was not likely to be a result of global warming.
Rain recorded on 30th July 2024, with the Kalladi station marked out. Source: Government of Kerala, Irrigation Design and Research Board daily rainfall data. (note: Google maps was used to find the location the station. May not match the real location)
Interestingly, they found that in simulated scenarios with both no global warming and extreme global warming the state received greater rainfall than it does in present day scenario, revealing the highly nuanced nature of climate change variability. Still, other studies suggest that while the monsoon may have been weakened in the region due to climate change, it is accompanied by an increase in the frequency of heavy rainfall days in localised regions of the western coast. All this research has the same caveats, they are based on simulations and either sparse or reconstructed data. In reality, it is nearly impossible to fully separate the effects of global warming from natural climate variability. Most of these studies are also based on data from before 2018, as more studies come out that analyse more up to date datasets they might come to a different consensus. The 10% increase in rainfall intensity reported in the WWA report varied a lot based on which model was used, with some of the highest resolution and best fitting models actually showing a slight decrease in intensity. They also ignore pre 1979 IMD data that also showed a decrease in intensity by citing a strong consensus among models and large uncertainties in the observations. The differences in opinions show the complexity of studying the hydrological impacts of global warming, a state can have a drying up of the monsoon but increasing intensity of extreme rainfall, putting it at risk of both water shortages and natural disasters.
Is it Humans?
Is it Humans?
The landslides that occurred may have been unavoidable if the extreme rainfall was caused primarily due to natural climate variability. However, we can certainly avoid unregulated development on slopes without engineering consultation. Settlements built in an unscientific, unregulated manner can put those structures directly in the path of danger. Construction also inevitably leads to the alteration of drainage along the slope causing erosion of previously stable soil and collection of water at new places within the ground. Development of settlements and plantations also requires the clearing of natural forests or shrubland removing the stabilizing effect of vegetation from the soil.
A study done after the 2018 landslides in Kerala looked into the land use characteristics of regions that experienced landslides. They found that built-up regions saw the greatest density of landslides; 5% in moderately susceptible areas and 16% in highly susceptible areas. Agricultural land was the second worst offender in terms of landslide density. It was also noted that plantation forests had a significantly higher landslide density compared to natural forests (1.38 vs 0.35% in highly susceptible regions). The land use in the region went through periods of large scale deforestation followed by reforestation efforts in the form of plantation forests, this has been accompanied by an increasing amount of built-up area in regions susceptible to landslides.
The 2024 Choorlamal landslide is a striking example that demonstrates the need for Improved land use management in the region. As can be seen in the attached images, the region developed significantly in the last decade. In 2019 the slope suffered a landslide due to the record breaking rain in that season. 5 years later the the villages on that slope had re-established themselves. When another spell of record breaking rain fell on 30th July, Choorlamal once again had to watch several houses get washed away, claiming more than a 100 lives.
Images of the landslide affected region from 2012 and from earlier in 2024, notice that the 2019 landslide has not occurred in the 2012 image and much more of the region is now occupied by human in the 2024 image. Source: Google Earth image.
Another Orange Alert
Another Orange Alert
As I write this analysis piece on 23 August the state is coming out of another spell of orange rainfall alerts from 20th to 21st August. The rain gauge at Peermad, Idukki recorded another 17 cm of rain on the 20th of August. If these deluges are to be a regular occurrence in the state then significant resources need to be poured into the mapping of regions most at risk and securing unregulated construction in the region. This is the danger with all incoming changes due to global warming, significant resources that are required to achieve sustainable development and net 0 targets have to be diverted towards rebuilding and adaptation. The regions that lack these resources are going to continue to fall behind in reaching sustainability targets, prolonging the effects of global warming and incurring more damage with every passing year.
References
References
Impact of climate change on extreme rainfall events and flood risk in India
On the role of climate change in the 2018 flooding event in Kerala
Government of Kerala, Irrigation Design and Research Board daily rainfall data
Evaluating the relation between land use changes and the 2018 landslide disaster in Kerala, India
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