Extreme rainfall event in the Eastern Himalayas: 04/05Oct20205 (Part II - 'The damage and fatalities in Nepal and Bhutan')

The October 2025 rains (see previous blog) were among the most intense to strike Eastern Nepal, the Darjeeling Himalayas, and Bhutan in recent years. The storm system, which crept in from northern Uttar Pradesh and Bihar, tracked east-northeast, impacting Eastern Nepal — including Kathmandu — first. The devastation it caused has been extensively covered by the media. Below, we’ve compiled a selection of key excerpts:

Nepal

Rainfall data (mm): Kathmandu 145, Rautahat 330, Ilam 330mm (reported 37 fatalities)

Fatalities, damage and cost:
a. 66 fatalities have been reported, 69 people are missing. 37 people died in Ilam district.
b. Huge damage on development infrastructure like roads, bridges and drinking water projects across Koshi province amounting to Nepalese Rs2.06 billion. Road projects worth about Rs190 million have been lost in Ilam alone.Bridges worth an additional Rs385 million have been destroyed. 226 homes were reported submerged in Kathmandu and a total of 4,059 households affected (ReliefWeb / GDACS summary of national reports).
c. Across Panchthar, Taplejung, Sankhuwasabha, Solukhumbu and Okhaldhunga, dozens of rural roads have been blocked or buried under landslides. Of the 73 roads, 44 still remain completely obstructed, while 12 of 23 motorable bridges have been totally destroyed. A total of 20 suspension bridges remain impassable due to flood damage.

Bhutan

Bhutan lies directly to the east of Kalimpong district (West Bengal) and Sikkim. As the powerful October 2025 storm swept across the Darjeeling–Sikkim Himalayas, it reached Bhutan on 5 October, bringing with it widespread devastation. The rainfall recorded during the event is shown in the map above.
Like Nepal, Bhutan is crisscrossed by several major rivers — Jaldhaka, Diana, Torsa, Sunkosh, Raidak, Jayanti, and Kaljani — which flow from its mountains into the fertile plains of North Bengal and Assam. These rivers are lifelines for irrigation and agriculture in the region. However, intense rainfall in Bhutan’s highlands often translates into dangerous flooding in the plains downstream.

Fatalities and damage reported

As per The Bhutanese, '3 people are likely dead as two persons are reported missing in Haa Dzongkhag due to flash floods in Sertena, Gakiling Gewog and one was washed away in Kazhi in Wangduephodrang. 1 body from Haa was recovered on 6 October 2025 from Cooch Bihar'.
Further '17 bailey bridges, six suspension bridges, three culvert bridges, three wooden bridges and three private bailey bridges were washed away'. Details of the damage are available here.
According to Kuensel, Bhutan’s national newspaper, “across Bhutan, numerous roadblocks, landslides, and washed-out bridges have cut off several communities. The southern and western highways have reported significant disruptions, and several homes have been damaged or flooded.”

One of the most critical impacts was on the country’s extensive hydropower infrastructure. Authorities in North Bengal were placed on high alert after a technical failure at the Tala Hydropower Dam caused it to overflow, sparking fears of downstream flooding in the Dooars region.
In response to the severe weather, five major hydel projects — Tala, Suchhu, Dagachhu, Punatsangchhu, and Chhuka — were temporarily shut down. This unprecedented situation not only disrupted power generation but also highlighted the growing vulnerability of Himalayan infrastructure to extreme weather events.

Further details on the damage to Bhutan’s dams can be found here.

Praful Rao,
SaveTheHills
savethehills@gmail.com
9475033744

Amidst earthquakes, now landslides : Nepal (11June2015)

Sadly the grim predictions (see 1 & 2) are coming true. Even as Nepal continues to be rocked by aftershocks (map) landslides triggered by rains have killed more than 41 people in the north east of the country.
The worst part is the rains are not due to the SW monsoons which are yet to arrive over the region and are caused by the numerous western disturbances which have been sweeping down the Himalayas.
I have been tracking these rain clouds daily, wondering in helpless bewilderment when the misery of millions affected by the quakes and now the landslides, in Nepal will end.

Praful Rao,
Kalimpong,
Dist Darjeeling

The 12May2015 Nepal Quake : An expert's view

Dr Malay Mukul of IIT Mumbai (Dept of Earth Sciences) hails from Kalimpong and has contributed numerous articles to this blog. After yesterday's quakes which rattled much of India, I posed him this question :
'What the hell is happening in our region?'
His reply is placed below :-
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The 12May2015, 7.3 earthquake in eastern Nepal was not completely unexpected. When we had the December 2004, 9.1 Indian Ocean Earthquake, there was similar 8.6 shock in March 2005. There were also two 8+ events in 2007. So once the beast wakes up, it will take its own time to settle down. We can do precious little to change this except either to get out of the way and live in safer places in peninsular India or, if that is not an option, to live in houses that will not kill us during a great earthquake (magnitude 8 and above).
Today's 7.3 earthquake appears to be identical to the 7.8 event. Same fault plane at almost identical depths. The fault that got active is the basal decollement fault of the Himalaya called the Main Himalayan Thrust. This is a fault that is present at the base of the Himalaya and extends from Kashmir to Arunachal Pradesh. Obviously, it is present below us in the Darjeeling-Sikkim Himalaya too.
All the GPS work people have been doing in the Himalaya tells us how much this fault is slipping per year in different parts of the Himalaya. It was about 18 mm/year in the Nepal Himalaya and looks like it is about 16 mm/yr in Darjeeling-Sikkim.
Imagine a beaker filling up with water at this rate. So the question is when will the beaker completely fill up? Once it does, nature empties it out in an event like the Nepal 7.9 earthquake.After that it starts filling up again.
Two scenarios can arise because of this:
1.The 7.9 event also causes a southward lurch of the Himalaya. In the 7.9 event, the Himalaya lurched south by about 4m at 15km depth which was effectively about 1m at the surface. This lurch would also add strain (or water in our example to the beaker that is filling up nearby)to the whole
system. If this sudden addition causes the beaker to fill up in an adjacent region,another event would occur. Strictly speaking it is not an aftershock and a separate event by itself with its own aftershocks.
However, it is an event that is triggered by the main event.
2. The beaker did not empty completely during the 7.9 event. In that case the beaker simply empties itself in two events rather that one. This is definitely better than having a single bigger event. Two 7+ earthquakes are better than one 9 event!
The aftershocks of the 7.9 event showed that the earthquake rupture was propagating east. In fact today's event was very close to the region where we saw a 6.7 aftershock earlier. Would it trigger an event in Darjeeling-Sikkim? It could, if we think the first scenario was operational.
Yes! I totally agree with you, having an earthquake on the decollement or the Main Himalayan Thrust in the Darjeeling-Sikkim Himalaya would be our worst nightmare. We have been very lucky. Nature has given us three warnings!  September 2011 and the 2015 Nepal events.
All projections seem to point to us and say that we could be next. We need to get our act straight! The NIMBY (not in my backyard) syndrome may no longer be applicable to us!
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Comment by Praful Rao

The writing on the wall is writ large and clear.
Increasingly and every year, disasters in and around the Himalayas (hydrological and geo) are taking a huge toll both in terms of human lives and economic losses. Yet, despite 'the three warnings' Prof Mukul talks about or the recent Kashmir and Uttarakhand disasters I am sure nothing much will change and we will continue our 'normal activities' as if nothing ever happened.

Praful Rao,
Kalimpong,
Dist Darjeeling

12May2015 : New Quakes in Nepal

Source : USGS/IMD/CNN

Nepal 7.9R Earthquake (25Apr2015) : 96 Aftershocks (in two weeks) and still counting...

Placed above is a record of aftershocks (source) following the 7.9R earthquake which devastated large parts of Nepal on 25Apr2015. There have been 96 aftershocks till date (including the induced 5.1R quake which was epicentred around Mirik.
In order to generate awareness about quakes especially amongst the people of the Himalayas, I posed several questions to experts.
The questions and answers (in this case given by Dr Malay Mukul, of IIT Mumbai, Dept of Earth Sciences) are placed below :-
Q. Regarding the Nepal quake, why are there so many aftershocks WITHIN a short time frame - 96 within a time span of 2 weeks? The 6.8R (18Sep2011) Sikkim earthquake which we experienced never generated so many aftershocks.
A. This is normal. If you just see the aftershock records for the Bhuj earthquake,you will find that they continued for months after the main shock. You would see is a gradual decrease in the aftershock magnitude as well as number of events. Now we are mostly getting 3s and 4s.
The aftershock activity is also a function of the magnitude and depth of the main earthquake. Shallower and large magnitude main shocks create more intense aftershock activity.
The Sikkim earthquake was much lower in magnitude as well as deeper.
Q. Are the continuous rattling (aftershocks) dangerous for installations and structures already weakened by previous tremors? I know that 2 hydel projects in Darjeeling district suffered some damage during the recent quake.
A. Yes! Aftershocks tend to add to the damage created by the main shock and in many cases topple structures that were still standing at the end of the main shock. So if your building has suffered structural damage you need to make sure you either fix it or stay away from it.

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Comment by Praful Rao
My thanks to Dr Malay Mukul for his prompt answers. 
Two major earthquakes have shaken in this region within the last 4 years, (6.8RSikkim and the recent Nepal one), yet we continue to flout all regulations regarding building codes and continue to construct thousands of 8-9storey buildings on these fragile mountains. I also wonder whether the numerous dams that we have constructed or are constructing  are safe?


Praful Rao,
Kalimpong,
Dist Darjeeling

Earthquake induced landslides and the onset of the SW monsoons 2015

Placed above is a preliminary map of Earthquake Induced Landslides in Nepal (read Dr Dave Petley's report here). I am aware of a similar study being carried out by a team from the GSI in the Darjeeling-Sikkim region.
With the SW monsoons knocking at our doorsteps and almost 3000mm of rain ahead (for Darjeeling district) in the next 5months, my biggest fear is how our injured mountains will bear up with this onslaught... and don't forget that 'developmental activities' such as road building and construction work including those of dams have gone ahead over the years, at breakneck speed in this entire region, with little regard to the environment.
In this regard, placed below is an article by Ranit Chatterjee, a graduate of TISS and now a student at Kyoto University(Japan):-

A STITCH IN TIME SAVES NINE

In the back drop of the recent earthquake in Nepal followed by temblor in the hills with epicentre located in Mirik and keeping in mind the approaching monsoon season ,the area may get hit badly by landslide in the coming months. The occurrence of earthquakes in steep landslide-prone areas greatly increases the likelihood that landslides will occur, either because of ground shaking or shaking-caused dilation of soil materials, which allows rapid infiltration of water. The second condition is more serious for Darjeeling considering the soil and rock conditions. The Darjeeling area may see an increase in landslides as an after effect of the series of recent earthquakes and onset of rainy season. Interestingly, it has been noticed that the rainfall pattern has changed in the region. The annual rainfall though has not changed much but the rainfall pattern is no longer uniformly spread over five months but happen in concentrated pockets over a short span of time mainly in July and August. This increases the runoff and chances of landslides increases.

In order to increase the level of awareness and preparedness at both institutional and personal level following measures can reduce the risk to a certain extent.  

1. Early warning system especially for heavy rainfall, landslide is an effective measure for saving lives. In the hills due to very spread out settlements it is important to set up a mechanism to transmit message across to villages. The banging of electric poles  can be used effectively to alert people when power supply is down and SMS is not available.

2. Identify safe locations for each area and the knowledge of safe location should be communicated to the community. A general system needs to be practiced where community leaders can guide them to the safe house. Like practiced in Japan once a year a real time mock drill for evacuation may be useful to put down a protocol and understand the evacuation process.

3. In case of houses, which have been damaged in the recent earthquake or aftershocks. It is recommended to get a structural safety check done by a qualified structural engineer or Civil engineer. Architects are trained in design and basics of structures and can handle up to 4 storied buildings unless he or she has a specialization in structures. Draftsman and masons are equivalent to quacks please avoid their advise on design and structural safety.

5.  Check for possible signs of landslides like tilting of trees, fences, and electric poles. Cracks in the lintel and sill of doors and windows.

6. Observe the weather closely everyday on your smart phone or Internet. A good practice is to keep a check on the weather forecast and warnings for the day.

7. Know the emergency contact numbers of the local fire service, police, disaster management department, ambulance etc.

8. Keep important documents inside plastic packet to protect from damage by water. Laminating important document is another of protecting the documents.

9. Preparation of an emergency kit at household level.

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Praful Rao,
Kalimpong,
Dist Darjeeling