The Metropolitan areas of Kathmandu and Lalitpur are highly exposed to flooding due to their geographic location along a valley with few natural drainage points. Rapid urbanisation (386% increase in built up areas between 1990-2020) and deforestation (28% reduction in forest cover from 1989-2019) in the Kathmandu Valley has disrupted natural water processes, increasing surface runoff and overwhelming drainage systems, while building on flood plains and near rivers has increased the exposure of people and assets to floods.

Nepal has seen many heavy rainfall events followed by severe flooding in the past. Analysing different observation-based datasets, the relative magnitude of the observed event compared to previous years varies between datasets, making it difficult to estimate how rare the event is in today’s climate. According to the Department of Hydrology and Meteorology (DHM), Government of Nepal, the rainfall recorded in several stations during the event was the highest in 54 years of measurements (DHM, 08 October 2024); therefore we use a rounded estimate of 1-in-50 years to define the event for the rest of the analysis.

To assess if human-induced climate change influenced the heavy rainfall, we first determine if there is a trend in the observations. Our best estimate is that heavy 3-day rainfall events have become about 18% more intense and just over twice more likely, but there are substantial differences between the datasets, which limit our confidence in the accuracy of these figures. The trends are stronger in the satellite era, from 1980 onwards.

To quantify the role of human-induced climate change we analyse climate models with high resolution that are in principle able to simulate the influence of the mountains on rainfall in the study region. Overall, the available climate models indicate a 10% increase in intensity compared to a 1.3C cooler climate, and an increase in likelihood of about 70%. Under a future warming scenario where the global temperature is 2°C higher than pre-industrial levels, climate models predict even heavier 3-day rainfall events, with a further expected increase of about 3% in rainfall intensity. As only the subset of models showing the smallest change in rainfall with global warming have future simulations available, this is a conservative estimate.

Given the small mountainous region with complex rainfall-climate dynamics, there is a high level of uncertainty in the results. However, the increase in heavy 3-day rainfall events is in line with a large and growing body of scientific evidence on large-scale extreme rainfall in a warming world, including in Nepal, and the physical understanding that a warmer atmosphere can hold more moisture, leading to heavier downpours.

The floods were well forecasted by the Department of Hydrology and Meteorology (DHM), but warning messages did not focus on the impacts to the Kathmandu Valley specifically, and it’s unclear to what extent the warnings led to early action. The Kathmandu Valley is also not the focus of flood risk management efforts in Nepal, as other regions (notably Terai) generally have been classified as high risk and have historically seen highly impactful floods. This presents an opportunity to further scale anticipatory action systems that have been shown to be cost effective in other parts of Nepal to cover highly exposed urban centres like the Kathmandu Valley.

The 2015 Gorkha earthquake destabilised hillsides and weakened drainage infrastructure, while the COVID-19 pandemic affected the incomes of low and middle class individuals representing long-term compounding factors that increased vulnerability to floods and landslides. Deforestation and rapid urbanisation expansion, especially into river floodplains, increased the number of people in the path of the flood waters. Comprehensive spatial planning, combined with disaster risk reduction and adaptation, effective policy enforcement, and increased public awareness, are crucial to mitigate flood risks across central and eastern Nepal, including the Kathmandu Valley.

Solar geoengineering: a note to inform discussions on physical climate impacts, risks and governance issues

With international efforts on climate action still not on track to limit warming to 1.5°C, technological fixes that aim to intentionally alter the Earth’s climate, such as solar geoengineering, might seem like appealing options for tackling global warming. But they come with questions in terms of feasibility, impacts and risks, governance and geopolitics, and who may or may not benefit.

Achieving net zero greenhouse gas emissions critical to limit climate tipping risks

Current climate policies are putting Earth on a path to a high risk of triggering climatic tipping points – even if temperatures return to below 1.5°C of global warming after a period of overshoot. A new study finds that the risk of crossing these thresholds increases with every additional 0.1 °C of overshoot above 1.5 °C and strongly accelerates above 2.0 °C. These risks can be minimised if stringent emissions reductions are taken in the next decade, and net zero greenhouse gas emissions are met and maintained.

Evaluating the near and long-term role of carbon dioxide removal in meeting global climate objectives

For 1.5°C pathways with limited overshoot, most of the mitigation between now and 2030 should come from emissions reductions (70%), with reductions from cutting non-CO2 emissions (20%) and land-based carbon dioxide removals such as afforestation and preventing deforestation (10%) making up the remainder.

A review of loss and damage in the Caribbean (1994 to 2024)

Loss and damage from climate change has been the lived reality of Caribbean small island developing states (SIDS) for decades. Despite efforts to adapt, it is reversing development gains, leaving lasting financial stress, and causing irreparable damage, including the loss of cultural heritage. This report is the first to provide a systematic overview of how Caribbean countries are framing and reporting on loss and damage.

Heavy precipitation hitting vulnerable communities in the UAE and Oman becoming an increasing threat as the climate warms

Researchers have assessed the extent human-induced climate change altered the likelihood and intensity of the weather conditions that caused the flooding in the United Arab Emirates and the northern parts of Oman in April 14–15 2024. The region was hit by exceptionally heavy rainfall causing massive disruption in infrastructure and public life in the area and leading to at least 20 fatalities in Oman and four in the UAE.

About us

Decarbonisation targets and 1.5℃ pathways

Comment

Rapid urbanisation and climate change key drivers of dramatic flood impacts in Nepal

Publications

The role of northern forests in limiting warming to 1.5°C

Seasonal forecast of two-metre temperature and precipitation in Tanzania: A hybrid cluster and point-by-point machine learning approach

Overconfidence in climate overshoot

Solar geoengineering: a note to inform discussions on physical climate impacts, risks and governance issues

How can event attribution science underpin financial decisions on Loss and Damage?

Achieving net zero greenhouse gas emissions critical to limit climate tipping risks

Evaluating the near and long-term role of carbon dioxide removal in meeting global climate objectives

Increasing April-May rainfall, El Niño and high vulnerability behind deadly flooding in Afghanistan, Pakistan and Iran

A review of loss and damage in the Caribbean (1994 to 2024)

Earth Virtualisation Engines (EVE)

Heavy precipitation hitting vulnerable communities in the UAE and Oman becoming an increasing threat as the climate warms

The impacts of multiple tropical cyclone events and associated precipitation on household income and expenditures