In 2022, heavy rains, floods and landslides claimed 835 lives in the country, according to the 2022 statement released by the India Meteorological Department. With a steady increase in the number of extreme weather events, especially heavy rainfall capable of triggering landslides and floods, the Indian Space Research Organization (ISRO) recently released the Landslide Atlas of India, a detailed guide to identifying landslide hotspots in the country.
What causes landslides?
Landslides are natural disasters that mainly occur in mountainous regions with favorable soil, rock, geology and slope conditions. The sudden movement of rocks, boulders, soil or debris down a slope is called a landslide. Natural factors that trigger this include heavy rains, earthquakes, snowmelt, and cuts down slopes caused by floods. Landslides can also be caused by anthropogenic activities such as mining, felling of hills and trees, excessive infrastructure development and overgrazing by livestock.
Considered among the most frequent natural disasters, landslides are extremely dangerous, threatening human and animal lives, damaging property, roads and bridges, disrupting communication lines and cutting power lines.
Some of the main factors affecting landslides are lithology, geological structures such as faults, hillslopes, drainage, geomorphology, land use and land cover, soil composition and depth, and weathering of rocks. All of these are factors when determining a landslide susceptibility zone for planning and forecasting.
In India, rainfall-induced landslides are more common.
How are landslides classified and mapped?
Landslides are broadly classified based on the type of material involved (rock, debris, soil, loose mud), the type of material movement (fall, topple, slide, rotational slide, or translational slide), and the type of material flow. Another category is landslides that spread laterally. Landslides mapped in the ISRO atlas are mainly event-based and seasonal.
ISRO’s National Remote Sensing Center (NRSC), Hyderabad, has developed a database of landslide-prone areas in India based on events from 1998 – 2022, primarily along the Himalayas and the Western Ghats. Apart from aerial images, high resolution satellite images captured using Indian Remote Sensing (IRS-1D) PAN + LISS-III, satellite ResourceSat-1 and 2, etc. cameras were used to study landslides during the last 25 years. The Pan-India Landslide Database classifies landslides – seasonal (2014, 2017 monsoon season), event-wise and route-wise (2000 – 2017).
How prone is India to landslides?
India is considered among the top five landslide-prone countries globally, with at least one death per 100 sq km reported due to landslides every year. Variability in rainfall patterns is the single biggest cause of landslides in the country, with the Himalayas and the Western Ghats highly vulnerable.
Excluding snow-covered areas, about 12.6 percent (0.42 million sq km) of the country’s geographical land area is prone to landslides. About 66.5 percent of the landslides were reported from the Northwest Himalayas, about 18.8 percent from the Northeast Himalayas and about 14.7 percent from the Western Ghats.
Almost half of the country’s landslide-prone area (0.18 sq km) lies in the states of Assam, Arunachal Pradesh, Sikkim, Meghalaya, Mizoram, Manipur, Tripura and Nagaland. Uttarakhand, Himachal Pradesh, Jammu and Kashmir cover 0.14 million sq km of total landslide-prone area, while Maharashtra, Goa, Karnataka, Kerala and Tamil Nadu account for 0.09 million sq km. A relatively small area (0.01 million sq km) in the Araku region of Andhra Pradesh along the Eastern Ghats also reports landslides.
In the Western Ghats, despite the low incidence, landslides have made residents significantly vulnerable to loss of life, particularly in Kerala.
What does the landslide atlas suggest?
Uttarakhand, Kerala, Jammu and Kashmir, Mizoram, Tripura, Nagaland and Arunachal Pradesh reported the highest number of landslides during 1998 – 2022.
Mizoram topped the list, recording 12,385 landslides in the last 25 years, of which 8,926 were recorded in 2017 alone. Similarly, out of a total of 2,132 landslides reported in Nagaland during this period, 2,071 incidents occurred during the 2017 monsoon season. A similar trend was observed in Manipur, where 5,494 landslides occurred during the 2017 monsoon season, including 4,559 landslides. Out of a total of 690, Tamil Nadu witnessed 603 landslides in 2018 alone.
Among all these states, alarming situation is emerging from Uttarakhand and Kerala.
While Uttarakhand’s fragility was recently exposed during landslide incidents reported from Joshimath to January, the Himalayan state has experienced the second highest number of landslides (11,219) since 1998, all occurring since 2000. The number of landslide incidents in the state during the year are: 2003 (32), 2010 (307), 2012 (473), 2013 (6,610), 2017 (1), 2021 (329) and 2022 (1).
The highest number of landslide-prone districts are Arunachal Pradesh (16), Kerala (14), Uttarakhand and Jammu and Kashmir (13 each), Himachal Pradesh, Assam and Maharashtra (11 each), Mizoram (8) and Nagaland (7).
Kerala has been continuously reporting massive landslides since 2018 when it was hit by the worst floods of the century. Here the landslide occurrences by year are 2018 (5,191), 2019 (756), 2020 (9) and 2021 (29).
From the facts and figures received, NRSC has ranked Rudraprayag in Uttarakhand as the top of the 147 vulnerable districts. It has the highest landslide density in the country along with the highest exposure to total population and number of households.
Anjali Mara is Science Communication and Outreach Manager at Raman Research Institute, Bangalore
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