Either too little, or too much water

In the first two episodes of this series, we looked at how climate breakdown has worsened the water shortage in eastern Nepal, with rains failing and springs going dry. 

But there is a flipside. In the monsoon, there is also the curse of too much rain leading to destructive landslides, floods driving people out. 

Analysing meteorological and hydrological data from the past half-a-century in eastern Nepal’s Tamor River basin, the big floods of 1963 and 1968 stand out with other less destructive monsoons in between. 

Nepal’s monsoons usually last 112 days from mid-June to mid-September, and its clockwork arrival and departure has inspired Nepali poetry and song.

But climate breakdown has disrupted the timetable, and there have been years with highly unusual monsoons and floods. In 1968, the monsoon delivered more rain than usual in some places and less than normal in others, and the big floods actually came after the monsoon is supposed to have retreated. 

The national news agency RSS reported a damaging flood in Sunsari, the district in the plains where the Kosi River disgorges into the plains after confluence of the Arun, Sun Kosi and Tamor.

Three days later, RSS reported that 500 cattle and 1,500 goats had drowned in Sunsari, and a child’s body had been found. And upstream in Leuti Khola, three people and seven houses were swept away.

A week later, RSS reported again that seven people and 14 livestock had been killed by floods, and bridges as well as paddy ready for harvest were swept away. Even upstream in Olangchung Gola, three people were killed.

Laxmi Prasad Siwakoti was a boy in 1968, and remembers enormous boulders thundering down rivers. One boulder the size of a house luckily was pushed to the banks before it could destroy a key bridge below Taplejung.

All this water created even more death and destruction in the inland delta of Sunsari, also washing down the bodies of people and livestock from upstream. The 1968 post-monsoon flow of the Kosi reached 23,106 cumecs – four times the volume in the 1963 flood.

Some researchers attributed the 1963 flood to the bursting of Tiptala Glacial Lake in the Kangchenjunga area, and that the 1968 flood was also caused by another moraine collapse on the same lake. 

But analysis of precipitation data of the Department of Hydrology and Meteorology shows that the reason for the catastrophic floods of 1968 was unusually heavy post-monsoon rainfall in the Tamor basin. Archival records of rainfall at Mulghat below Dhankuta shows that there was 162mm of rain on 3 October and another 158mm on 4 October. This meant that one-third of the total rainfall during four monsoon months fell in just two days.

Never had Mulghat recorded so much rain in such a short time, and in the 55 years since there has been that much rain only twice.

On 4-5 October 1968, Dhankuta received 300mm of rain. It had never received so much rain in the autumn before or since. Similarly, Taplejung recorded 231mm of rain in the same two days – it has never received so much rain in the post-monsoon since.

Hydro-meteorological stations across eastern Nepal in Panchthar, Taplejung, Dhankuta and Sankhusabha all show data of record-breaking post-monsoon precipitation on 3-4 October 1968. In fact data shows that except for northwestern Nepal, there was heavy unseasonal rain all over.

Dhulikhel near Kathmandu recorded 221mm rain that day, and even Jomsom in the trans-Himalayan rainshadow got 58% of its annual rainfall in just one week.

In a paper titled Heavy Monsoon Rainfall in Nepal, J L Nayava dug up an archival weather map from 1968 that showed a cyclone develop in the Bay of Bengal a week after the official retreat of the monsoon from Nepal in conjunction with a low pressure area over southern India. Both systems moved northwards, and it could have been the combination of the two that dumped the record rainfall in Nepal. 

Nayava notes: ‘On 29 September, a small low appeared over the Bay of Bengal at about 10°N, 90°E. During the next two days, the circulation of this low expanded as it moved north-eastwards into central India and intensified into a depression. By 3 October, Nepal and much of India had come within the circulation of this depression… During the next two days, a sharp 500mb trough passed through Nepal and central India and as the polar westerlies at 200mb intensified and moved equatorwards, bringing the subtropical westerly jetstreams ever closer to Nepal. As the depression moved north, the anticyclonic circulation at 200mb over the depression intensified and became orientated in a south-west-north-east direction. Associated with these developments, widespread rain fell in most parts of Nepal…’

It was not just eastern Nepal that suffered destruction, many people were killed in Bhojpur, Khotang and Solu to the west. If this was indeed a glacial lake outburst flood, the destruction would not have been so widespread.

The hydrological data of the Tamor of 3-5 October 1968 are also not commensurate with a flash flood triggered by a glacial lake burst. The Mulghat hydrological stations showed that on 4 October, there was 3,060 cumec of flow (volume of water never recorded before) which decreased only slightly over the next few days and returned to a more normal 636 cumecs only on 9 October. 

By the time the rains stopped that October, 60 people were dead in Kosi zone alone, thousands of livestock were killed and houses swept away. The new bridge over the Tamor and other suspension bridges were destroyed.

But that was not the end of the story. On 29 October 1968 came news that 91 people had been killed in Taplejung, 60 in Terathum, 30 in Panchthar and three in Dhankuta. Just in the Tamor watershed, 184 people were killed and thousands made homeless.

Nepalis have learnt over the years to be prepared for disasters during the monsoon, and to breathe a sigh of relief when the rains end. But the 1968 floods hit after the monsoon, when people felt safer.

Floods were nothing new in the Tamor. There was an unimaginable one five years earlier on 15 August 1963 that swept away 16 houses in Olangchung Gola, and this flood was different from the one in 1968.

Locals remember an air blast preceding the flash flood, and an approaching roar that shook the mountains like an earthquake. Houses shook, cattle cowered and goats ran for cover. Upstream, villagers saw clouds of dust and spray, and there was a smell of gunpowder in the air as enormous boulders collided with each other.

Although this was the monsoon period, the precipitation in the day preceding the debris flow was normal. This could not have been caused by a cloudburst. Alton C Byers, the American glaciologist who has researched historical glacial floods in the Kangchenjunga region, used satellite imagery and interviews with local villagers to pinpoint the flood to the bursting of Tiptala glacial lake at 4,900m.

“The gunpowder smell and the wind preceded the arrival of the debris flow,” remembers Nil Limbu of Chhiruwa of Taplejung, an eye witness of the 1963 event. “It destroyed everything, took away all the trees, left just rocks and boulders.”

The flood washed away the mule trail along the Tamor, and swept away the flat meadow along the river where there used to be a weekly market. Today, the trail is higher above the river, but for years later, there used to be rockfalls from above.

The debris flow raced downstream destroying houses, trails, bridges, farms, livestock. The flood made national news, and RSS reported that below Dhankuta, the Tamor destroyed the trail to Taplejung and washed away seven bridges.

The glacial lake outburst flood on the Tamor met the Arun and then the Kosi where the river flow spiked to 6,371 cumecs. Further downstream in the plains, the flood destroyed the western embankment of the Kosi Barrage, inundating villages in more than 1m of water.

A month later, the government released the death toll: 32 killed, unknown number of livestock, standing crops, and causing damage equivalent to 1.6% of Nepal’s annual budget that year. Nepal’s famous eye doctor Sanduk Ruit’s family also had to leave their home in Olangchung Gola after that flood and settled down in Dhankuta.

The combined result of the record rainfall-induced floods of 1968 as well as the glacial lake outburst flood of 1963 could have been early examples of climate-induced floods, which have become more frequent in recent years.

On 17 June 2023 Memeng station in Panchthar recorded 230mm rainfall in a 24 hour period, the highest rainfall ever recorded in that station (second highest was 148mm in July 2002). Nearby Dovan of Taplejung experienced 106mm on 18 June and 102mm on 19 June.

The basin-wide floods on the Tamor and its tributaries caused damage worth at least Rs8.5 billion on 30 hydropower plants in Sankhuwasabha, Taplejung and Panchthar. Eighteen workers were killed.

Half of these schemes were under construction, but plants generating 130MW were knocked out of action. Some, like the Upper Piluwa Khola 2 and Super Hewa Khola have still not been repaired.

While these were all caused by extreme rainfall events, on the Sikkim side of Kangchenjunga a post-monsoon disaster on 4 October 2023 washed away several hydropower plants on Teesta and its tributaries, and killed nearly 100 people downstream. The 1,200MW Chungthang Dam built at a cost of $1billion was destroyed.

It was later revealed that extreme rainfall on the South Lhonak Glacial Lake, north of Kangchenjunga, caused the collapse of a lateral moraine which allowed a wave to breach the terminal moraine. The lateral moraine could have been weakened by thawing permafrost, and collapsed during heavy rainfall on the night of 4 October. 

The Sikkim disaster was an important lesson for Nepal, which has invested heavily in infrastructure on this side of the border. More than a dozen medium and large hydropower plants have been built or are under construction along the Tamor alone. The 1960 Tiptala and the 1980 Nangama glacial lake bursts are further proof that such disasters can happen again without warning because of climate breakdown.

Besides droughts and floods, landslides are also the reason many people from eastern Nepal have migrated to the relative safety of the plains. A huge landslide in 1946 in Hangdeva in Taplejung is still displacing many people. East of Hangdeva, another landslide in 1977 killed 25 people and the rest of the village just moved out.

It is clear that with the climate crisis, extreme weather events and glacial lake bursts will be more serious and frequent, affecting lives and livelihoods, contributing to outmigration. 

This is the final of a three-part series supported by the Barbara Foundation.