New Delhi | An accurate early warning system that correlates rainfall and the potential for landslides. That is the imperative, say experts as rains create havoc in hills across India and the toll mounts in Kerala's Wayanad slopes where landslides buried entire homesteads and possibly hundreds of people.

On Thursday, cloudbursts in Himachal Pradesh led to houses, bridges and roads being washed away with five people dying and 50 missing. In Uttarakhand, heavy rain triggered floods and house collapses with at least 14 people killed. The rain scripted tragedies in the hill states came just two days after extremely heavy rain – more than 570 mm over 48 hours – triggered the disaster in Wayanad, leaving at least 195 people dead.

Given the scenario of erratic rain, extreme weather events, changing climatic conditions and the fragile hills – both in the north and in the south – an accurate early warning system (EWS) based on empirical rainfall thresholds followed by a systematic evacuation protocol is essential.

“EWS is important to understand what are the vulnerable areas and which are the vulnerable communities. EWS will use the areas and the potentialities of the threat, the extent and timing of the threat so it can establish the mitigation measures, including evacuation,” Nilmadhab Prusty from the Centre for Development and Disaster Management Support Services told PTI.

As of now, there are no granular studies or EWS for landslide forecasts in the country.

In Kerala, for instance, the Geological Survey of India (GSI) did give a forecast on July 29 for two days but not a sense of what was in store – the landslides hit early morning on July 30.

The Kerala State Disaster Management Authority (KSDMA) gets forecasts for landslides in four categories -- very high possibility, high possibility, moderate and low possibility.

“The ‘Experimental Rainfall Induced Landslide Forecast Bulletin' for Wayanad district forecast only this -- ‘A low possibility of occurrences of landslides: A few small landslides may occur.' There was no information from the central agency that there would be widespread or even moderate landslides,” P M Manoj, press secretary of the KSDMA, told PTI.

Kerala had approved three pilot projects for state-specific landslide early warning systems in 2020. But none is complete yet.

According to the GSI website, about 0.42 million square km (covering nearly 12.6 per cent of India's land area) is prone to landslides. This includes all the Himalayan states, sub-Himalayan terrain of the northeast and the Eastern and Western Ghats states.

There is also the question of evacuation.

The KSDMA, for instance, does have a wide network of locally trained DM personnel and adequate mechanisms to disseminate the early warning messages. But that is only part of the picture.

On July 29, the KSDMA asked people from hilly areas to go to relief camps but people did not leave as “they had not expected the intensity of the disaster to be this massive”, Manoj said.

In December 2017, the National Disaster Management Authority (NDMA) launched a pilot project for a ‘Low-Cost Landslide Monitoring Solutions'. But that was restricted only to Himalayan states and nothing much has been done after that, an official said.

A community-run effort at EWS in Maharashtra is hoping to make a difference with Satark, a project that issues landslide alerts.

Started by the Pune-based non-profit Centre for Citizen Science (CCS) in August 2015, it ensures awareness about and issues alerts for landslides in the Sahyadri ranges (as the Western Ghats are known in Maharashtra).

The group's work started a year after the Malin village landslide in Pune district that left 151 dead. The group members poured over data from over the past few decades, from government agencies, local information sources and newspaper reports. “That gave us an idea about the correlation between the rainfall quantum and what is the time that a possible landslide can happen in any given location,” Mayuresh Prabhune, one of the founding members of CCS, told PTI.

The CCS has mapped all landslide incidents over the last 20-25 years in the Sahyadri ranges and monitors rains every day during monsoon. At places where there was no government data, either through manual rain gauges or automatic rain gauges (ARG), the CCS gave manual rain gauges to local citizens.

“Each region along the Western Ghats has a different saturation level. When we monitor continuous rains, get data from all the stations, that at least gives an idea what the soil saturation level is and also what the minimum threshold level (for any location) is,” Prabhune said.

For example, the CCS data shows that in the case of Mahabaleshwar, landslides happen after 600 mm rains. So, in case of continuous rainfall there, the group keeps a tab on daily accumulated rainfall and takes steps accordingly.

“The landslide may happen on day four or day five, depending on how much rain has fallen before,” he added.

The group issues notifications at three levels: Watch, Alert and Warning. “Third is a specific village level alert. After the second step, we start monitoring it 24X7 and use radar images for the third step,” Prabhune said.

A March 2022 study published in the journal Land, an international and cross-disciplinary, peer-reviewed, open access journal, said the Satark model showed 76.5 per cent success in landslide prediction one day in advance.

Although local administration takes help from CCS at times, the Maharashtra government has not yet agreed to a formal tie up.

The minimum threshold level that CCS talks of was exactly what was pointed by a 2020 study by four researchers from Indore, Italy and Australia for Wayanad after conducting a detailed study of the recurring landslides in Wayanad between 2018 and 2019.

The study, published in the journal Water concluded that 24 mm of rainfall a day is enough to trigger landslides in Wayanad.

Way back in June 2009, the NDMA released the ‘Guidelines on Management of Landslides and Snow Avalanches' which laid down the national policy for the management of landslides and related activities in the country.

A ‘Landslide Risk Mitigation Scheme' (LRMS) followed in 2014 and was highlighted in the National Disaster Management Plan of 2016, updated in 2019.

According to an official from the NDMA, the existing landslide monitoring and early warning technologies cost crores of rupees and the need for a low-cost landslide early warning system (EWS) has been long recognised.

However, in the absence of any guideline or protocol for landslide mitigation at the national level, it is incumbent on the states to manage the disaster at their end.

The official in charge of mitigation at the NDMA did not respond to PTI's queries on the matter.

“Early warning system has two parts. One is an accurate generation of the alert, which our scientific agencies are doing in a fairly good way and then, taking it effectively to the relevant people,” explained Sanjay Srivastava, a member of the Experts Group of the NDMA.