Floods in Nepal: Major Disasters from 1993 to 2024

Nepal's flood problem is built into its geography. Around 80 percent of the country's annual precipitation falls during the summer monsoon between June and September, and that water must descend from Himalayan peaks above 8,000 metres to the Terai plains below 200 metres within a horizontal distance of barely 150-200 kilometres. The result is some of the steepest, fastest and most sediment-laden rivers on Earth. Nepal's four great snow-fed river systems - the Koshi (Saptakoshi) in the east, the Gandaki (Narayani) in the centre, and the Karnali and Mahakali in the west - all generate large monsoon floods, as do medium rivers that rise in the Mahabharat hills such as the Bagmati, Kamala, West Rapti, Babai and Kankai.

The worst-hit zone is the Terai, Nepal's southern lowland belt, where rivers slow down, drop their sediment loads and spill across densely settled farmland. Rivers that rise in the fragile Chure (Siwalik) hills are especially dangerous: they can rise from a trickle to a destructive torrent within hours of a cloudburst, and their beds aggrade rapidly as deforestation and quarrying in the Chure send gravel and sand downstream. Districts such as Saptari, Sunsari, Rautahat, Sarlahi, Mahottari, Banke, Bardiya and Kailali appear again and again in flood damage records.

Floods and the landslides that accompany them kill hundreds of Nepalis in a bad year and cause economic losses running into tens of billions of rupees. Climate scientists, including researchers at the Kathmandu-based International Centre for Integrated Mountain Development (ICIMOD), warn that a warming atmosphere is making extreme cloudbursts more frequent and is destabilising glaciers and mountain slopes, so large flood disasters are expected to become more, not less, common.

Not all floods in Nepal behave the same way, and understanding the type matters for warning and preparedness. Slow-onset river floods on the big snow-fed rivers can be forecast hours or days ahead, whereas flash floods and outburst floods in mountain valleys may allow only minutes of warning. Many of Nepal's worst disasters, such as the 2021 Melamchi flood, were cascading events in which several hazard types combined.

Nepal's disaster authorities and researchers generally distinguish the following flood types:

The events below are the benchmark flood disasters of Nepal's recent history, each documented by the National Disaster Risk Reduction and Management Authority (NDRRMA), the United Nations Office for the Coordination of Humanitarian Affairs (UN OCHA)/ReliefWeb situation reports, or government post-disaster assessments. Detailed accounts of the five most searched events follow in the sections below.

Key documented flood disasters include:

From 26 to 28 September 2024 (Ashoj 2081 BS), an exceptionally intense late-monsoon system parked over central and eastern Nepal. Kathmandu Valley stations recorded between roughly 240 mm and 322 mm of rain in 24 hours over 28-29 September, the capital's heaviest rainfall since systematic records from 1970. The Bagmati River rose about two metres above its danger level, and its tributaries - especially the Nakkhu in Lalitpur - tore through riverside settlements. Roads into the Kathmandu Valley were cut, and at least 35 people died on the Prithvi Highway corridor, including passengers in two buses buried by a debris flow at Jhyaple Khola in Dhading.

According to the UN and NDRRMA situation report of 16 October 2024, the disaster killed 250 people, left 18 missing and injured 178, making it one of Nepal's deadliest flood events in three decades. The worst-affected districts included Kavrepalanchok - where the Roshi Khola devastated settlements along the BP Highway - along with Lalitpur, Kathmandu, Dhading, Sindhuli and Makwanpur. Kathmandu district alone recorded at least 37 deaths.

NDRRMA's preliminary loss and damage assessment, released in late October 2024, put direct losses at about NPR 46.68 billion. Physical infrastructure took the largest share, with 41 highway sections damaged, 16 bridges destroyed, around 1,639 drinking-water schemes affected, and roughly NPR 2.45 billion in losses in the hydropower sector; about 65,380 hectares of farmland were damaged just before the paddy harvest. Analysts noted that unplanned settlement on river floodplains in the Kathmandu Valley greatly amplified the death toll.

On 15 June 2021 (2078 BS), at the very start of that year's monsoon, a massive sediment-laden flood surged down the Melamchi River in Sindhupalchok district, burying Melamchi Bazaar under metres of debris. ICIMOD's investigation concluded it was a textbook cascading hazard: intense rainfall high in the Melamchi headwaters combined with the collapse of glacial and moraine material around the Bremthang area, landslides that temporarily dammed the river, and the sudden release of that impounded water and sediment. Informal warnings telephoned downstream by upstream villagers gave people minutes to flee and almost certainly prevented far greater loss of life.

The flood killed five people with around 20 missing, displaced roughly 525 families, fully destroyed 337 houses, and swept away 13 suspension bridges and 7 motorable bridges between Helambu and Melamchi Bazaar. Around 3,500 ropani (approximately 178 hectares) of fertile riverside farmland was converted to bouldery riverbed. Critically for Kathmandu, the flood buried the headworks of the Melamchi Water Supply Project at Ambathan - the national project built to pipe Melamchi water to the capital - only months after it had begun delivering water, forcing years of costly repairs and seasonal shutdowns.

A second large debris flood on 31 July-1 August 2021 re-damaged the valley and confirmed that enormous volumes of loose sediment remain stored in the upper watershed. In places, debris deposits in the river corridor exceeded 10 metres, with about 16 metres measured at Melamchi Bazaar. Researchers treat Melamchi 2021 as the warning case for multihazard risk in a warming Himalaya, where earthquake-weakened slopes (from the 2015 Gorkha earthquake), degrading permafrost and extreme rain can chain together into one disaster.

On 18 August 2008 (2065 BS), the eastern embankment of the Koshi River gave way at Kusaha in Sunsari district, a few kilometres upstream of the Koshi Barrage built in the late 1950s and early 1960s under the 1954 Koshi Agreement between Nepal and India. The river was not carrying an exceptional flood at the time - the breach is widely attributed to poor embankment maintenance and decades of sediment accumulation that had raised the riverbed above the surrounding land. Through the widening gap, the Saptakoshi avulsed eastward into a channel it had abandoned generations earlier, sending an estimated 3,675 cubic metres per second across villages that had not flooded in living memory.

In Nepal, the disaster struck Sunsari and, to a lesser extent, Saptari district. Government and UN figures put the affected population at roughly 42,000-54,000 people (over 7,500-11,500 households), most of whom were displaced into camps for months; because warnings spread quickly, direct deaths on the Nepali side were few. Downstream in Bihar, India, the same avulsion became one of South Asia's great flood catastrophes, affecting more than three million people and killing several hundred.

The breach was finally closed and the river returned to its engineered channel in early 2009, but 'Koshi flood 2008' remains the defining example in Nepal of embankment-failure risk. The event reshaped debate over the Koshi Agreement, cross-border flood management and the wisdom of confining one of the world's most sediment-charged rivers - the Koshi carries one of the highest sediment loads per unit of water of any major river - between earthen walls.

From 11 to 14 August 2017 (2074 BS), sustained torrential rain across the southern plains flooded 35 of Nepal's 77 districts, 18 of them severely - the worst Terai-wide inundation in decades. UN OCHA reported about 1.68 million people affected, with roughly 460,000 displaced; official assessments recorded 134 deaths in the 18 most-affected districts, with Saptari, Rautahat, Mahottari, Bardiya and Banke hit hardest. The National Planning Commission's Post Flood Recovery Needs Assessment estimated total damage and loss at about NPR 60.7 billion (about US$585 million), concentrated in housing, agriculture and roads. The disaster exposed how embankments and road causeways along the Nepal-India border can back water up onto Nepali farmland, an issue that resurfaces every monsoon.

The July 1993 (2050 BS) floods remain the deadliest water-induced disaster in Nepal's modern records. On 19-21 July 1993, an extraordinary cloudburst - about 540 mm of rain in 24 hours in the Kulekhani watershed, among the highest daily totals ever measured in Nepal - unleashed debris flows and floods across central Nepal, from Makwanpur, Sindhuli and Sarlahi to the Kathmandu Valley fringe. Assessments compiled after the disaster put the toll at more than 1,300 people dead or missing, with over half a million affected.

The 1993 disaster crippled national infrastructure: sediment choked the reservoir of the Kulekhani hydropower plant, then the backbone of Nepal's electricity supply, causing prolonged power cuts; the Bagmati barrage and irrigation works in Sarlahi were severely damaged; and bridges on the Tribhuvan and Prithvi highways were washed away, cutting Kathmandu off by road. Nepalis still refer to it simply as the '2050 Sal flood', and it remains the benchmark against which later disasters such as September 2024 are measured.

Flood forecasting in Nepal is the responsibility of the Department of Hydrology and Meteorology (DHM), which runs a national network of rainfall and river-level stations and issues flood bulletins, special weather advisories and SMS alerts when major rivers approach warning and danger levels. Community-based early warning systems on rivers such as the Karnali, Babai and West Rapti - where upstream gauge readers alert downstream villages by phone and siren - have measurably cut deaths in the western Terai. Disaster response is coordinated by the National Disaster Risk Reduction and Management Authority (NDRRMA), established in 2019 under the Disaster Risk Reduction and Management Act 2074 (2017), which publishes official incident data and situation reports through its BIPAD portal.

Structural defences - embankments, river training on the Koshi and Bagmati, and lowering of dangerous glacial lakes such as Tsho Rolpa (partially drained in 2000) - reduce some risks but, as the 2008 Koshi breach showed, can create new ones when they fail. Experts therefore emphasise floodplain zoning, resisting settlement on riverbanks (a key lesson of Kathmandu's 2024 disaster), protecting the Chure hills, and expanding forecast-based early action, in which relief cash and supplies are pre-positioned when DHM forecasts cross agreed danger thresholds.

For households, the practical basics are consistent across flood types: know whether your home sits in a floodplain, keep documents and essentials in a go-bag during the monsoon, follow DHM bulletins and local radio when heavy rain is forecast, move to pre-identified higher ground when warnings are issued, and never attempt to cross flooded rivers or causeways on foot or by motorcycle - a leading cause of monsoon deaths in Nepal.