Bengaluru: The flash floods in Nepal’s Rasuwagadhi – along its border with China – have killed more than 300 people as of Thursday (August 27) evening. At least 1,500 others are missing, Nepali authorities have said.Disturbing visuals of angry brown rivers breaching banks, sweeping over buildings and consuming everything – and everyone – in their way keep overwhelming our social media feeds. India, too, is taking precautions to prepare for downstream impact, if any, from the neighbouring country.What triggered the devastating flash floods? And what is the current status? The Wire breaks it down.What happened?On Wednesday, August 26, water levels in the Bhotekoshi river basin in Nepal began rising rapidly around 9:00 AM local time, according to the Kathmandu-based International Centre for Integrated Mountain Development (ICIMOD). Severe flash floods ensued downstream, in the Bhotekoshi, Trishuli and Narayani rivers. The floods first hit the Rasuwa district on Wednesday morning.Recorded impacts so far have been devastating. The rivers breached their banks. Entire buildings, roads and homes were washed away. Visuals also show huge waves of water washing away people trying to flee and get out of the flood’s path. Three districts in Nepal that are worst-hit include Rasuwa, Nuwakot and Dhading.As of the afternoon of August 27, authorities in Nepal have been able to retrieve 177 dead bodies. They have urged caution in downstream areas, including Devghat where they retrieved around 12 dead bodies on Thursday afternoon. The death toll, however, has risen to 270 this evening, per PTI, and may continue to rise further. The BBC reported that per the Nepal Police, the death toll was 332 as of 15:50 local time.Nearly 1,500 people are still unaccounted for. This included more than 300 missing Indian tourists. As of the evening of August 27, 21 tourists from Tamil Nadu have been rescued; 288 are still missing.Minister for External Affairs S. Jaishankar has said that he met with the foreign secretary, members of the external affairs ministry and the Indian ambassadors in Kathmandu and Beijing to discuss the Nepal flood disaster and take stock of the situation. “Urgent efforts are underway to ascertain the status and well-being of all Indians in the flood-affected areas,” he said in a post on X on August 27. “MEA is coordinating with various Ministries, State Governments, tour operators and project authorities in this regard. We are working closely with the Nepali side, both on this aspect and on the relief efforts.”Why did it happen?What caused the flash floods? Theories are many, and contradicting, as scientists still analyse what went wrong. Some reports such as this one suggest that an earthquake on the morning of August 26 set off an avalanche and landslides that then led to the flash floods. Some of Nepal’s ministers also held to this view initially. Others called it a Glacial Lake Outburst Flood – or GLOF – as less than a year ago, the same area had witnessed this phenomenon.However, the US Geological Survey on Thursday ruled out any possibility of an earthquake causing the avalanche and resulting flash floods. It said, instead, that what was initially reported as a magnitude 4.4 earthquake that struck Tibetan territory (about 47 kilometres north of Gosainkunda) was, in fact, an earthquake caused by the impact of a glacial collapse and followed by an ice-rock avalanche.A glacial collapse occurs when a large piece of an existing glacier detaches and breaks away. Such glacial collapses are not GLOFs, but can trigger them. Reuters reported that according to experts citing satellite imagery from Planet Labs, the flash floods, therefore, may have been triggered when the lower part of a glacier broke off and crashed onto the valley floor hundreds of meters below.India’s National Remote Sensing Centre on August 26 also said that according to a preliminary satellite assessment, a sudden flash flood and heavy surge of debris in the Trishuli (also called the Bhotekoshi) river caused rapid inundation. The preliminary cause sequence suggests that an ice-rock avalanche or landslide may have caused a temporary river blockage. A sudden release of this blocked water and debris could have caused the flash floods downstream. However, the NRSC has said that is a preliminary analysis only, and that it will be undertaking a detailed assessment.Source: NRSOPreliminary assessment based on video footage and information from affected areas suggest that a large volume of ice and rock debris may have entered the Lende Khola, a tributary of the Bhote Koshi River, the ICIMOD said in a press release on August 26. The event could have generated a sudden surge that carried water, sediment and large boulders downstream, it said.“Experts are also assessing whether debris temporarily blocked the river at a narrow section, forming a landslide dam,” ICIMOD said. “Such blockage can create secondary hazard if impounded water is suddenly released. Authorities and scientists are continuing to evaluate the size, location and stability of any potential blockage.”Meanwhile, Chinese media house Global Times reported that according to China’s Ministry of Water Resources, a huge barrier lake had formed near the confluence of the Chhochen Khola and Purepu Tsangpo rivers in Nepal, with its water volume estimated at 2 million cubic meters as of Thursday morning. Another 3 million cubic meters of water is expected to flow into the lake over the next three days, posing a high risk of a breach, the report quoted China Central Television as saying on Thursday.Will it impact India?The flash floods in Nepal could spill over, downstream, into Indian territory. The states of Uttar Pradesh, Bihar and West Bengal have been put on high alert. According to Reuters, around 5,000 people were evacuated in Bihar after flood alerts were issued.Several teams of the National Disaster Response Force (NDRF) have been pressed into action. On Thursday, NDRF officials told PTI that there has been no “adverse” impact of the flash floods in the border areas of Bihar and Uttar Pradesh till now, but the situation is being continuously monitored in coordination with the two states’ governments. NDRF Inspector General Narendra Singh Bundela told reporters that a total of 20 teams (nine in Bihar and 11 in Uttar Pradesh) have been deployed on the ground to launch evacuation, relief and rescue operations in case these areas experience floods and waterlogging.According to Bundela, the Central Water Commission is also monitoring the water level and providing updates on the discharge from the Valmikinagar barrage, the first barrage on the Gandak River. The Gandak is a part of the Trishuli river system that flows in from Nepal. India, meanwhile, has also sent relief material to Nepal. On Wednesday, it sent 10 tonnes of HADR (Humanitarian Assistance and Disaster Relief), and 37.5 tonnes of HADR, medicines and food on Thursday.Global warming and the larger pictureThough ICIMOD stated that it was too early to determine what role climate change played in the event, others have noted a high possibility of its role in the floods.Manish Mehta, a scientist at the Wadia Institute of Himalayan Geology in Dehradun, Uttarakhand, said that that glacial terrain is “vulnerable and very fragile”. And with global warming and climate change, glaciers are retreating. “As the glacier retreats, it leaves behind loose, unconsolidated material at its front. When a glacier advances, it creates and transports a lot of material, debris, moraines, and other deposits,” he said.With global warming, precipitation patterns are also changing and the areas receiving snowfall and rainfall are shifting and expanding too, he added: “As a result, at high elevations, rainfall patterns are changing, from gradual drizzling to more torrential rainfall. This affects those vulnerable, weak zones and can trigger landslides.”What we saw in Nepal is not a regular seasonal monsoon flood, but a compound climate disaster, said climate activist Harjeet Singh. “Scientists have been warning for a very long time that, as the planet warms, we are going to see more and more compounding and cascading climate impacts, one incident, whether a geological or climate event, leading to another and causing a chain reaction,” he told PTI. “And that is exactly what we have seen. Higher temperatures in the Himalayan region have already destabilised glaciers and amplified extreme precipitation, causing entire river systems to become far more destructive within minutes.”Researchers have also said that the Nepal flash floods are yet another reason for countries to collaborate on such cross-border hazards.“Today’s disaster in the Lhende Khola is another cause for regional collaboration where governments should take some joint, consolidated steps to react to such cross-border hazards,” said Mohd. Farooq Azam, Senior Cryosphere Specialist, ICIMOD, Nepal, in a statement on August 26.This is a developing story, and will be updated as more news and data come in.