In 2018, Kerala experienced its worst floods in a century, affecting 13 out of 14 districts. Such was the impact that the rate of soil erosion in the state has increased by 80 per cent, which means that the amount of soil loss is anywhere between 31 to 56 metric tonnes per hectare per year, as per a recent study analysing soil erosion in the state before and after the floods with the help of satellite imaging.
Idukki district reported the sharpest spike in soil erosion, an increase by 220 per cent, stated the latest joint study by experts from IIT-B, College of Engineering Pune and Rural Data Research and Analysis.
Incessant rain last month triggered a landslide in Pettimudi, located at 20 km from Idukki’s famous hill station Munnar, crushing over 60 tea plantation workers to death and destroying their homes.
Applying geographic information system (GIS) techniques, experts put together the state’s rainfall data, land use maps and satellite imageries to understand the role of floodwater in triggering soil erosion after the 2018 deluge.
While Kerala lies in an ecologically sensitive zone, some districts have to directly bear the brunt. One of them is Idukki, followed by Ernakulam.
“For districts like Idukki, which lie along the Western Ghats, high rainfall and elevation play contributory factors in pushing the rate of soil erosion in comparison to other districts like Thiruvananthapuram. This, besides the changing land use, land cover, and vegetation add to the overall erosion,” said lead author Pennan Chinnasamy from IIT-B.
Kerala receives an annual rainfall of 3000 mm and experiences summer as well as winter monsoons. According to a special report released by Ministry of Earth Sciences, Kerala recorded 42 per cent excess rain between June and August 19, 2018. But it was the extremely heavy spell between August 1 and 19 that caused the destruction, when the state recorded 164 per cent above normal rain.
Steeper the slope, greater was the rainwater run-off and soil erosion, making hilly districts particularly vulnerable, stated the study published in the Journal of the Indian Society of Remote Sensing.
“Once eroded, the leftover surface gets exposed and remains vulnerable for further erosion. Formation of new layers of soil could take years and this is where better planning is needed post an event of flood,” added Chinnasamy.
As a result, land in the state is at 63 per cent increased risk of soil erosion in the coming years, the study concluded.
A special report by the Kerala government on this flood also stated that nearly 71 per cent total area had eroded due to these massive floods, including 94 per cent from Idukki district alone.
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