The deadliest landslides in Nepal’s recent history were triggered by extraordinary rainfall in late September 2024, when 25 weather stations across central Nepal recorded their highest-ever 24-hour rainfall totals. But the rain alone doesn’t explain the scale of destruction. Decades of road construction on unstable slopes, deforestation, river erosion, and lingering damage from the 2015 earthquake all primed the landscape to collapse. The official death toll reached 217 people, with 28 still missing and 142 injured.
Record Rainfall Over Three Days
Between September 26 and 28, 2024, a sustained rainfall event hit central Nepal with an intensity the region had never measured. The weather station at Godavari in Lalitpur District recorded 311.6 mm in a single 24-hour period and 366 mm over the full three days. To put that in perspective, that’s roughly a third of a meter of water dumped on steep hillsides in just 72 hours.
Peak hourly intensity was also unusually high. Godavari logged 26.8 mm of rain in a single hour on the evening of September 28, a figure well outside normal ranges for Nepal. When rain falls this fast, water can’t soak into the ground gradually. Instead, it saturates the upper layers of soil quickly, adds enormous weight to slopes, and reduces the friction holding soil and rock in place. The result is widespread, simultaneous slope failures across entire districts.
Provisional data identified at least 143 individual landslides causing fatalities during and immediately after the event. Many of these happened in areas where people had no time to evacuate.
Road Construction on Unstable Slopes
Nepal has rapidly expanded its rural road network over the past few decades, often cutting into mountainsides without proper engineering. Researchers analyzing landslide records between 1978 and 2005 found that road building could partly explain the rising number of fatal landslides over that period. The pattern has only accelerated since then, with urbanization pushing construction into steeper, more hazard-prone terrain.
When a road is carved into a hillside, it removes material from the base of the slope, which is the part that acts as a natural buttress. The cut face exposes fresh rock and soil to rainfall. Drainage from the road surface concentrates water in new channels. All of these changes make the slope above and below the road more likely to fail, especially during heavy monsoon rains. Many of Nepal’s worst landslide corridors follow major highways and newly built rural roads for exactly this reason.
Deforestation and Changing Land Use
Tree roots act like a mesh that holds soil together on hillsides. When forests are cleared for agriculture, firewood, or development, that binding disappears. Rain hits bare soil directly, increasing surface runoff and erosion. Nepal’s mid-hills, where most landslide fatalities occur, have seen significant forest loss over several decades.
The Food and Agriculture Organization has documented how improper land use patterns and deforestation in Nepal lead to vegetation loss and expose soil to runoff, accelerating erosion and making slopes more vulnerable to collapse. In practical terms, a forested hillside can absorb and slow rainfall that would otherwise saturate and destabilize a cleared slope.
River Erosion Undercuts Slopes
Many of Nepal’s most destructive landslides happen not on isolated hillsides but along river valleys. During heavy rain, swollen rivers carve into the base of adjacent slopes through a process called toe erosion. This removes the natural support at the bottom of a hillside, leaving the material above unsupported and prone to collapse.
Rivers in the Kathmandu Basin, like the Kodku and Bagmati, are frequently subject to this cycle. Bank erosion during floods destabilizes slopes, which then fail as landslides, dumping debris into the river. That debris can temporarily dam the river, creating a secondary flood risk when the dam breaks. This cascading sequence of flood, erosion, landslide, and damming repeats along river corridors throughout central Nepal during every major monsoon event.
Lingering Damage From the 2015 Earthquake
The magnitude 7.8 Gorkha earthquake in April 2015 shattered rock and loosened soil across a vast area of central Nepal. The U.S. Geological Survey assessed that earthquake-triggered landslides continue to pose both immediate and long-term hazards to villages and infrastructure in the affected region. Slopes that were cracked but didn’t collapse during the earthquake remain weakened, and each monsoon season brings new failures from those same fractured hillsides.
This “seismic legacy” effect means that even moderate rainfall can trigger slides on slopes that would have been stable before 2015. Nearly a decade later, the landscape still hasn’t fully recovered, and researchers expect earthquake-loosened material to continue failing for years to come.
Glacial Lake Floods Amplify the Damage
At higher elevations, warming temperatures are melting glaciers and filling lakes behind unstable natural dams made of loose rock and debris (called moraines). When these dams breach, the resulting floods, known as glacial lake outburst floods, tear down narrow valleys with devastating force.
A well-documented case in the Bhotekoshi valley showed how a relatively small glacial lake burst amplified into a massive transborder flood and debris flow. As the floodwater traveled downstream, it picked up sediment from previous landslide deposits and eroded valley walls, growing in volume by orders of magnitude. The event triggered secondary landslides along its path, destroyed hydropower facilities and highways, and caused economic losses exceeding $70 million. This cascading pattern, where a single glacial flood reactivates old landslide sites and collapses riverbanks for kilometers downstream, is becoming more frequent as glacial lakes grow.
Why Early Warnings Often Fail
Nepal’s Department of Hydrology and Meteorology began sending mobile phone alerts in 2018 when upstream rainfall crosses a certain threshold. In theory, these warnings give people in downstream areas time to move to higher ground. In practice, the system has significant gaps.
Warning messages often don’t account for the language spoken locally, the format people can quickly understand, or whether vulnerable groups (elderly residents, people with disabilities) can access them at all. As a result, alerts frequently fail to prompt the actions needed to save lives. An earlier glacial lake warning system installed near Tsho Rolpa Lake in 1998, which used solar-powered sirens, became non-functional after equipment was damaged and solar panels were stolen. The failure was partly attributed to a lack of local community ownership of the system.
For landslides specifically, the challenge is even harder than for floods. A flood moves downstream in a somewhat predictable path. A landslide can happen on any of thousands of vulnerable slopes, with very little lead time between the rain that saturates the ground and the moment the slope gives way. In many of the September 2024 disasters, there was simply no time between the trigger and the collapse.
Multiple Triggers Acting Together
No single factor explains Nepal’s landslide crisis. The September 2024 disaster was driven by record rainfall, but that rain fell on a landscape that had been progressively weakened by road construction, forest loss, river erosion, and earthquake damage over decades. Climate change is intensifying monsoon rainfall and melting glaciers, adding new pressure to an already fragile system. Each of these factors makes every other one worse: a road cut destabilizes a slope, deforestation removes the roots that might have held it, river erosion removes the base, and extreme rain delivers the final push.