The challenge of integrated natural hazards for continued sustainable development in the Himalayas - Dr Malay Mukul, IIT Bombay

CURRENT SCIENCE, VOL. 127, NO. 9, 10 NOVEMBER 2024 1005
CURRENT SCIENCE
Volume 127 Number 9 10 November 2024
EDITORIAL

During the last decade, developmental activities have in-creased progressively in the Himalayas in response to the increase in population and the need for better infrastruc-ture. Defense requirements along the Indo-Tibetan border have also necessitated the improvement of road and rail connectivity in the Himalayas. Tourism has also flourished as more and more people travel to the Himalayas from the plains. Dams have been built on the Himalayan rivers to generate hydroelectricity to meet the increasing demand. All these essential developmental activities have strived to be sustainable. Nevertheless, there is a growing realization that natural processes can throw an unexpected spanner in the works of the most carefully thought-out development projects. Landslides, glacial lake outburst floods (GLOFs) and earthquakes can strike the Himalayas at any time and place, and understanding the Earth’s processes that trigger these natural hazards is crucial to preventing loss of life and property during these events. The Earth’s processes typically operate over geological time scales but have the potential to strike anytime they cross the tipping point. The focus has to shift from disaster management to disaster prevention to avert increasing loss of life and property.
Climate change has resulted in concentrated rainfall over short intervals from the earlier norm of distributed rainfall in time and space. This results in flash floods and slope failure that can combine to form devastating mud- and debris flows. The warming climate has also accelerated the melting of Himalayan glaciers, resulting in glacial retreat and the formation of large glacial lakes at their terminus. These lakes are surrounded by glacial moraines that can easily breach due to their low mechanical strength by excessive rain, slumping of moraine material into the lake, or even earthquakes. Any such event will result in an extreme debris-laden flash flood in the river valleys downstream destroying everything in its way. Two such events are fresh in our memory. First is the 4 October 2023, North Bengal–Sikkim extreme GLOF event that killed more than 100 people, changed the entire morphology of the Teesta River valley and destroyed a dam. Second is the 30 July 2024, rainfall-induced flash flood in Wayanad, Kerala. Although not in the Himalayas, the villages of Punchirimattam, Chooralmala and Mundakkai were destroyed killing more than 420 people during this event.
Landslides also accompany these events adding to the destruction inflicted by the flash flood. In the Himalayas, fluvial terraces and past landslide debris in the valley are soft targets for erosion by the flash floods because they consist of unconsolidated and incohesive material. River terraces are popular sites for the construction of buildings and camp sites as they offer flat top surfaces in sloping mountainous terrains. In extreme-event flash floods, these are the first to be destroyed, as evident from multiple videos on social media where riverside constructions topple and assimilate into the river. Toe erosion, or the erosion of the base of existing and previously stabilized landslides, dur-ing GLOF events can re-activate them.
Landslides exist as a separate, independent hazard in the Himalayas too. Steep slopes, weak rocks and high rainfall combined with human activities lead to multiple Himalayan landslides. Landslides can dam rivers and create lakes that can eventually burst through the dammed river and cause a flash flood downstream. Like the river terraces, the landslide debris spreads out in the valley and provides flat surfaces for construction. Therefore, they are frequently used to develop residential and commercial real estate or other essential infrastructure similar to the river terraces. Landslides or avalanches into glacial lakes filled to the brim due to retreating and melting glaciers also cause overflow of the glacial lakes and flash floods downstream. The 4 October 2023, North Bengal–Sikkim GLOF event was attributed to the landslide of a large chunk of lateral moraine into the South Lhonak Lake. Therefore, land-slides and GLOF flash flood events can also be integrated hazards and be the cause and the effect of the other.
The other looming hazard in the Himalayas is the seismic hazard. Decades of work have revealed the presence of a major fault under the Himalayas, the Main Himalayan fault, which extends from the Tibetan Plateau to the Gan-getic plains. The fault slopes north and transitions from a near-surface brittle deformation regime to a ductile regime at depths greater than ~15 km. As evident from the Global Positioning System (GPS) measurements, the Himalaya is being continuously transported from north to south along this fault. In the ductile regime, this motion does not cause earthquakes. At the brittle-ductile transition, this motion is arrested because of friction along the fault typically absent in the ductile regime. This causes strain accumulation in the region and is characterized by micro- to moderate-earthquakes and maximum vertical uplift. Bends in the Main Himalayan fault near the brittle-ductile transition also cause strain accumulation. This region is located in the central part of the Himalayas and is likely where large and great future earthquakes will originate. For example, the magnitude 7.3, 2015 Kathmandu earthquake originated in this region. Large and great earthquakes are also known to trigger multiple landslides. Studies also reveal that many Himalayan glacial lakes are full due to climate-change-induced enhanced melting of glaciers. Therefore, there is a high probability that future large and great earthquakes will also trigger coeval landslides and GLOF events.
Therefore, the worst-case natural hazard scenario in the Himalayas will involve coeval earthquakes, landslides and GLOF events. This is what we need to be aware of and prepare for. Himalayan natural hazard models must inte-grate seismic, landslides and GLOF hazards for any reali-stic forecast of disasters and disaster preparedness. The first step is the integration of all known information and scientific insights. For example, we know that large earth-quakes will originate in the central part of the Himalayas and affect the Higher Himalayan lakes initiating GLOF events. We can also identify the most vulnerable landslide-prone regions should these events occur. The disaster-pre-paration strategies should include the possibility of all three hazards occurring together in the Himalayas. Also, a purely statistical approach to hazard estimation may not be sufficient and realistic. For instance, the basis of seismic zonation in India is the frequency of large earthquakes. Zone 5, with the maximum frequency of large earthquakes, is recognized as the most hazardous. However, recent studies make Zone 4 more hazardous as strain has accumu-lated here since the last major seismic event but not been released. Similarly, the frequency of landslides separates more landslide-prone areas from others. However, no strategy exists to forecast the initial landslide occurrence in a region where no previous landslides have occurred. New studies and strategies that account for the Earth’s processes in addition to statistics must be evolved to understand and prevent loss of life and property in future natural disasters.
Sustainable development under such a scenario must recognize and understand the collective hazard to the fullest extent possible. A wealth of scientific data and insights relevant to these hazards are available. For instance, although earthquakes cannot be predicted in time, we know that the Himalayan earthquakes will originate in the central part of the Himalayas. This insight can help save lives if the buildings and infrastructure in that part of the Himalayas are designed or reinforced to withstand large earthquakes. Similarly, all Himalayan hydroelectric pro-jects must factor in the high seismic hazard and GLOF sce-narios. The Himalayas are also riddled with fault zones that concentrate weak rocks in them. These fault zones are also likely to nucleate landslides. Therefore, identifying such fault zones can potentially locate future landslides. Using existing scientific knowledge and insights to miti-gate or prevent future disasters is the key to sustainable development in the Himalayas. The most tragic disasters are those where red flags existed but no timely action was taken to prevent the disaster. The Himalayan seismic haz-ard is a potential example of such a situation. Studies over two decades have red-flagged several parts of the Himala-yas as areas where strain has accumulated over centuries without any release through large earthquakes. The next large earthquake in these areas will cause large-scale loss of life and property. The time to minimize or prevent this is now. We should not wait for the event to happen and merely disaster manage its aftermath.
Finally, the lessons of disasters that have already occurred must not be forgotten. For example, the extreme events in Wayanad and North Bengal–Sikkim have explicitly esta-blished the boundaries of the river basin. The river deposits associated with these events will be vegetated and provide flat surfaces where it might be tempting to build in the future. The river basin must be left alone and everything inside moved to higher and safer grounds. If these lessons are ignored, the disasters will keep repeating. The magnitude of the disasters will keep increasing as the population in-creases and more lives and infrastructure come in harm’s way. Our survival may ultimately depend on how well we recognize the multiple red flags in nature and get out of harm’s way when there is still time. Maintaining maxi-mum sync and harmony with nature during developmental activities is the only sustainable way forward. We must embrace this or be prepared to suffer the consequences.

Malay Mukul
Indian Institute of Technology-Bombay,
Mumbai 400 076, India
e-mail: malaymukul@iitb.ac.in

Published by
Praful Rao
SaveTheHills
savethehills@gmail.com
9475033744

Importance of real-time weather information in hydrological disasters: Need for more AWS

We, at SaveTheHills have long realized the importance of real-time weather inputs especially in the Himalayas where weather can change quickly and with devastating consequences.
In this regard, 'Hazard Alerts', our WhatsApp based social media group in this region, does precisely that - disburse verified information on weather and updates on forecast heavy rain, hazards such as landslides, road closures to the community in the quickest time and I am extremely happy to state that all three WhatsApp groups (Hazard Alerts 1,2, 3) and our other social media handles in Instagram, FB and so on, have today emerged as disciplined, powerful community driven platforms, which share such information and help each other using reports from individual members, satellite images of clouding, lightning app reports, social media posts and so on.

STH has also encouraged and helped in establishing a network of online AWS in this region so that real-time information from these stations is available to the community as well as disaster management people of this region:

I was keeping a track of Hurricane 'Milton' recently, and was able to monitor the rainfall data of several places around Tampa , Florida from my home in the Himalayan foothills as the storm wreaked havoc there. I accessed the weather in real-time on the Weatherlink app for Davis automatic weather stations in the area.

It is amazing to see how powerful technology is these days and I was particularly impressed to see the density of DAVIS AWS which are available at the Tampa bay area, probably because this area is prone to hurricanes and heavy rain/storm surges.

Real-time data on rainfall intensity and high-velocity winds can play a crucial role in warning communities about potential landslides and flooding. This allows for timely evacuations, prioritization of relief efforts, and ultimately, saving lives. It also allows preservation of valuable weather data of the region.

To maximize early warning systems, information from Automatic Weather Stations (AWS), satellite imagery, lightning reports from apps like Weatherbug and Damini, and even social media should be fully utilized. This is especially critical as climate change and warmer oceans are causing extreme weather events to become more intense, unpredictable, and accompanied by increased rainfall.

While I specifically mention DAVIS AWS, as we’ve successfully used this equipment for 6-7 years, there are undoubtedly many other reliable brands. The key requirement is that weather data must be available online with frequent updates.

For instance, the India Meteorological Department (IMD) has an AWS site that I found helpful during the 2024 monsoon season. However, the site’s updates are not as frequent, and parameters like rainfall intensity are missing. To address these gaps, private networks, such as the one in our region, can provide essential supplementary data.
STH strongly recommends building up on what is already available so as to make our early warning systems more robust and effective.

Praful Rao
SaveTheHills
savethehills@gmail.com
9475033744

Rainfall data of Sep 2024 of some towns in Sub-Himalayan W Bengal and Sikkim

Teesta river and bazar on 29Sep2024, a few days after heavy rain on 27/28Sep. The river had receded quite a bit yet it flowed nudging the bazar and the Darjeeling road at many places. The river is still swift and flows from one bank to the other.

Notice the way the heavy rain is all stacked up in the last week of the month with the first few weeks being deficient in rain.

A dramatic shift from deficient rain upto 25Sept followed by a large surplus thereafter.

The impact of the heavy rains in the month end has already been covered in a separate post here

 

Praful Rao
SaveTheHills
9475033744
savethehills@gmail.com

Commemorating the 'Teesta Valley GLOF of 04Oct2023' with photos of the event and its aftermath.

A woman washes the money she recovered while scavenging for lost property in a flood affected area of Rangpo (Sikkim) on 06Oct2023 - photo credit Praveen

As I write, it is very early morning on 04Oct2024 and it was exactly at this time last year that I was up at my home in Kalimpong, trying to contact and verify with people, mainly in Sikkim, about whether a GLOF had actually taken place in the Teesta valley.
In the meantime my cellphone was receiving images and videos of the floods as the wall of water tore down the valley. Just verifying what was happening in order to report and record it accurately  kept me engaged the entire day and next, while my young friend and photographer Praveen Chhetri visited Teesta Bazar which the GLOF hit around 4am. He recorded the impact of the GLOF as it happened.
I did not know then that this process of recording the GLOF and its impact would keep us busy for an entire year but it has - and has required numerous visits to many parts of the Teesta valley including one trip made in Nov2023 to Chungthang where the 1200mw Sikkim Urja hydroelectric dam was destroyed by the GLOF.
What we have in this blog is perhaps the most comprehensive photographic record of what was the largest GLOF which took place in the Himalayas. Praveen and I certainly have hundreds of images, many videos and voice recordings of the interviews of affected people that we did during the course of the year.

    Interviewing an affected person who had lost everything to the GLOF - Rangpo (Sikkim), 06Oct2023.

This post, where I publish some photos is only to commemorate that momentous event which changed the lives of so many
Lest we forget...

Army personnel recovering buried vehicles at Bardang (Sikkim) on 06Oct2023. 22 army persons who were a part of a convoy were swept away by the GLOF here

Landslide affected areas of Naga, a village between Mangan(district headquarters, North Sikkim) and Chungthang in Nov2023 (telephoto image from opposite hill). The village was almost entirely evacuated during the monsoons of 2024.

A man crosses the Teesta river on a bamboo bridge at Toong, North Sikkim in Nov2023. The bridge connecting Chunthang to Mangan was torn down by the GLOF

GLOF affected areas between Chungthang and Lachen town where there was no impact of the Sikkim Urja dam burst. The scale of the devastation caused by the GLOF alone is apparent in the photo - photo courtesy Dathup, Lachen.

GLOF eroded parts of NH10 between Teesta bazar and Melli in Oct 2023. With the Teesta river running 4-5m above the pre-GLOF levels, the erosion of NH10 increased remarkably in 2024.

Debris and vegetation which the GLOF had dumped on top of the NHPC Stage V 510MW dam at Dikchu, SIkkim. The Teesta river 'over toppled ' ie went over the dam at this site.

Tree stumps and debris inside the NHPC Stage VI dam at Sirwani, Singtam (Sikkim), Nov2023

Vehicles strewn around like battered toys, on the banks of the Teesta at Singtam (Sikkim).

Part of Teesta town (Krishnagram or Bhasuwa) literally sliding slowly into the river - Sep2024

A marooned COVID hospital on the banks of the Teesta and Rangeet rivers at Tribeni, (Darjeeling district) - Sep2024. There is no road access to the hospital with the Teesta river having kept large parts of the access road submerged after the GLOF.

Rangpo town in Sept24. One year after the GLOF, parts of the town are still trying to recover. The river still flows uncomfortably close to the town and the police checkpost (green roofed structure on the top left is literally tilting into the river.

Undoubtedly one of the most iconic images of a GLOF.

Drone image taken by Praveen at around 11.00am on 04Oct2023 from the Teesta bridge when the GLOF was passing thru the area. As can be seen much of the Teesta bazar was already submerged.

Documentation of parts of the above report was supported by Royal Enfield, as part of their Social Mission Initiative


With
Praveen Chhetri (9733185815)

Praful Rao
SaveTheHills
9475033744
savethehills@gmail.com

Extraordinary rains of September end 2024 (in the Darjeeling - Sikkim Himalaya).

Until the 23rd, the month of September 2024 for us in the Darjeeling-Sikkim Himalaya turned out to be very dry and inordinately hot, prompting a member of the SaveTheHill's What'sApp group 'Hazard Alerts' to write:

'What does it mean, no rain in Kalimpong, Sikkim or Darjeeling?? Paddy fields are drying, springs and streams have dried already, this year "MUL PHUTENA", meaning ground aquifers were not recharged completely. This situation warns of the chaotic food insurgency especially to those who wait for food from farmers. Poor farmers look at the sky, it looks blue, no cloud, and he screams for his hardships and crop failure. I'm a farmer, what option do I have now??'

Another member post this cartoon about the prevailing hot weather:

Then on 24Sep2024, another LOW pressure area, in a series of bumper to bumper lows which had formed in the Bay after 17July2024, developed as shown below:

IMD issued a number of press releases about the weather systems causing the heavy rain and likely weather which would ensue:

Based on IMD and other inputs, STH posted satellite imagery and weather updates continuously during the period in our WhatsApp groups 'Hazard Alerts, Hazard Alerts 2, Hazard Alerts 3' - we also used other social media handles to publicize the heavy rainfall warnings.

Rainfall data

On 29Sep2024, IMD gave us a GREEN (ie no warning after 3 days of RED warning and 1 day of orange warning in the above period) and we had a dry day after 5 days of non-stop rain.

The average monthly rainfall for September in Sub-Himalayan W Bengal and Sikkim is 388.1mm - the 5 day rainfall of Sept2024 end, as seen above came close to or in the case of many towns, exceeded the monthly average and thus we swung from a total deficiency of rain in the first three weeks of September to a gross excess of rain, all of the large volume of water coming at the end of the monsoons when the mountains are almost saturated with water. As such the impact of this unusual heavy rains was huge in the region.

IMPACT

Firstly and most importantly, there were no fatalities even though we did have many landslides and near misses.
Road Communications: NH10
The already poor state of road communications especially in the Teesta valley suffered further set backs.

Landslide on NH10 near Teesta bridge on 27Sep2024 (27 03 40.2 N 88 25 35.3 E)

Large landslide on NH10 near Melli (27.08388889N 88.45098611E)

Other places in the Teesta Valley

Flooded Darjeeling - Kalimpong road near Teesta bridge, 28Sep2024. The debris and sand deposits by the GLOF of Oct2023 had raised the level of the Teesta river by as much as 4-5m so heavy rain
always results in the river flooding this road.

Teesta Low Dam Project III at 27Mile and the flooded Bangay bazar bridge
(26°59´38.20´´N 88°26´32.83´´E)

Flood affected areas of Teesta bazar. As mentioned earlier, the GLOF of Oct2023 has pushed the riverbed levels up by 4-5m and as such the river runs perilously close to many densely populated areas - Melli, SIngtam and Rangpo to name a few. Heavy rain in the valley invariably results in flooding of these areas.

Melli town and stadium ( 27°05´23.03´´N 88°27´28.01´´). The stadium which was entirely covered by debris and sand by the GLOF in Oct2023 had been painstakingly cleaned by the town but it has been rendered unusable by the repeated flooding of the river.

The GTA Covid Hospital (27°04´48.63´´N 88°25´50.37´´E) lying derelict on the banks of the Rangeet river since the GLOF of Oct2023. Parts of the one lane road leading up to the hospital from Teesta Bazar has been under the river for a year now and the recent rains have inundated even more areas of the road.

Other parts of the Kalimpong and Darjeeling districts

Major landslide in the vicinity of Kalimpong town at the by-pass road, 7th mile (27 04 13.9 N 88 26 56.8 E). In Sep 2024, Kalimpong received less rain than Darjeeling and Kurseong and as such we never had as many landslides.This large landslide took place on 28Sep at around3.30pm.

Subsidence due to mountain stream erosion (jhora) in a densely populated area of Kalimpong municipality (27 03 47.0 N 88 27 45.8 E). The subsidence (seen here covered by plastic sheets to prevent water ingress) occurred during daytime on 28Sep2024 when the stream was gorged with runoff from upstream paved surfaces. My concern here is that this whole area is located above a landslide prone zone on which we have done a story in 2010.

Landslide in the Darjeeling Municipal area at Hooker Road, on 26Sep2024

Landslide at Lower Bhaktey bustee in Darjeeling

Sikkim received much less rainfall in late Sep2024 resulting in much less devastation and landslides.

I am sure there were many more unreported landslides and instances of flooding caused by the unusual heavy rains and we will keep updating this blog on the reports, when received. We will also be surveying the affected areas in due course of time.

My thanks to all HA members whose images and reports I have used liberally here and elsewhere - all with the intention of recording the event for posterity.

Documentation of parts of the above report was supported by Royal Enfield, as part of their Social Mission Initiative


Praful Rao
SaveTheHills
savethehills@gmail.com
9475033744

Rainfall data of August 2024 of some towns in Sub-Himalayan W Bengal and Sikkim

The National Highway 10 (NH10) which connects Siliguri to Gangtok and is the lifeline for Sikkim and Kalimpong district runs along the river valley almost hugging the banks of the river for almost 50 odd km. The monsoons extracted a heavy price for this closeness in Aug2024 - the highway was closed for almost 20 days due to landslides and erosion.

As per the above data:

• Darjeeling, Kalimpong (in West Bengal), Gangtok, Mangan, Damthang (in Sikkim) recd almost normal rainfall.
• Kalimpong, Siliguri, Jhallong, Alipur Duar (W Bengal) and Dentam in Sikkim recd went deficient in rainfall.
• Most of the rainfall occurred in the first half of the month (see below).
  
  This was undoubtedly due to the low pressure areas and depressions which formed in the Bay of Bengal and moved towards western India, which resulted in surplus rainfall in those parts towards the end of Aug2024 (see above).
  
  

  
  

  

  Major Landslide
  A major landslide occurred in Sikkim on 20Aug2024 at Dipu Dara, just above NHPC Stage V Power House at Baluatar.
  We have covered the entire incident in our previous blog report
  

  
  Documentation of a part of the above report was supported by Royal Enfield, as part of their Social Mission Initiative
  
  
  Praful Rao
  SaveTheHills
  savethehills@gmail.com
  9475033744