The floods and mudflows that swept through Nepal’s Bhotekoshi–Trishuli river system last week left an estimated 2.2 million tonnes of debris across the areas analysed, according to a preliminary assessment by the United Nations Development Programme (UNDP).

The UNDP’s Rapid Assessment and Analysis for Immediate Recovery and Development Action (RAPIDA) assessment found that the debris comprises collapsed building materials, household belongings, vegetation, rocks and sediment.

The flash flood, reportedly triggered by a glacial collapse on 26 August, swept water, mud and rocks through communities in the affected districts. Nepal has reported over 1,110 dead, with over 4,000 people reported missing.

Of the estimated total, around 556,200 tonnes is building debris, based on satellite assessments of damage to 2,359 buildings. UNDP said the figure could increase as additional damage is identified.

The debris includes parts of buildings, household belongings, vegetation, rocks and sediment. An estimated 556,200 tonnes comes from building debris, based on satellite assessments of damage covering 2,359 buildings. This figure is expected to rise as more damage is identified.

The flash flood, reportedly triggered by a glacial collapse on August 26, swept large volumes of water, mud and rocks through settlements along the Bhotekoshi–Trishuli corridor.

For families and rescue teams, the debris is more than a measure of the destruction: people remain trapped or missing beneath collapsed buildings and piles of mud and debris, making rescue operations difficult and dangerous, said the UN agency's preliminary report.

The amount of debris shows the scale of the destruction, and the challenge communities face as they clear homes, roads and public spaces and begin to rebuild, reads the report. Damage to hydropower and other energy infrastructure has also disrupted electricity supplies, adding to the difficulties faced by communities and slowing the restoration of essential services.

According to government figures cited by UNDP, 84,270 people across 17 municipalities in six districts have been affected. Around three-fourths of those affected were already living in areas facing greater challenges in terms of livelihoods, access to basic services and living conditions.

The disaster has also caused extensive damage to Nepal’s energy infrastructure. Eleven hydropower stations and one solar plant, with a combined capacity of 431.1 megawatts, had stopped operating, while another 15 hydropower projects under construction, with a planned capacity of 470 MW, were damaged.

UNDP said its assessment combines satellite-based building damage assessments from Copernicus EMS and SERTIT with other available data and locally adapted engineering estimates to map the scale and distribution of the debris.

“The scale of destruction is immense,” UNDP Resident Representative in Nepal Kyoko Yokosuka said, stressing the need to ensure that recovery reaches the communities hit hardest by the disaster and enables them to rebuild more safely and resiliently.

The UNDP assessment is preliminary and will be updated as more information becomes available.

The floods have struck communities that were already among the most vulnerable in Nepal. Around three in four affected people were living in areas where people already faced greater difficulties with their livelihoods, access to basic services and living conditions.

“This is a devastating disaster for communities along the Trishuli corridor. Families have lost loved ones, homes and livelihoods, while entire communities are struggling to reconnect with essential services and one another,” said Kyoko.

“The scale of destruction is immense, and as the immediate response continues, we must make sure that recovery reaches the people who have been hit hardest and helps them rebuild safely and with greater resilience,” she said.

Most of the affected municipalities are rural and in Nepal’s hill regions, where 67.4 percent of people work in agriculture. For households dependent on agriculture, damage to crops, livestock and farmland could have a lasting impact on food security and family incomes. Nepal’s main monsoon planting season runs from June through September, making the timing of the floods particularly difficult for farming communities.