How will future climate extremes impact the hydropower sector in Nepal?

Rosie Oakes is a Senior Scientist in the International Applied Science and Services Team at the Met Office. Rosie works with partners around the world to ensure that climate information is useful and usable, helping people make climate informed decisions and increase their resilience to climate change. Rosie is also the co-host of the Mostly Climate podcast. 

Nepal is a landlocked country in South Asia, nestled in the magnificent Himalayan Mountain range, which includes Mount Everest. Home to 30 million people, the population are looking to the mountains for their energy source. Nepal currently generates 90% of its electricity from hydropower. Further expansion is planned for the future, with goals of becoming a net power exporter by 2030. 94% of the population currently has access to electricity but the demand is increasing as living standards across the country improve. The expansion and reliability of energy generated from hydropower are therefore a priority for the Nepalese government.  

The hydropower sector is intricately linked with climate, particularly rainfall. Nepal experiences an annual monsoon from July to October when river flows are high. The amount of power a hydropower plant can generate is linked to river flow, with more power generated at high flow, and less power at low flow. But what happens when river flow is exceptionally high? 

The Hindu Kush Himalayas are a geologically-young mountain range, formed 55 million years ago when the Eurasian Plate collided with the Indian subcontinent, and they are still growing today. The fresh rocks exposed during mountain building, combined with constant tectonic activities from the colliding plates which cause landslides, mean there is a lot of sediment in the river basins. When the river is at high flow, it has more energy meaning it can carry more sediment as load. This sediment can damage dam structures and key turbine components limiting energy generation (Figure 1).   

Figure 1: high sediment load can cause damage to dam structures such as the gates at the intake sight (left) and the turbines (repaired turbine, right). Photo credit: Rosie Oakes

At even higher levels of river flow, entire hydropower plants can be destroyed by high rainfall events. An example of this was seen in Jure in 2014 where heavy rains triggered a landslide, damming the Sunkoshi River. The water that built up behind the temporary dam submerged the powerhouse of the Sanima Hydropower project and washed away two gates at the Sunkoshi Hydroelectric project. Overall, five hydropower stations and several transmission lines were damaged which reduced Nepal’s power generation capacity.  

The Met Office has been working with partners in Nepal for the past four years under the Asia Regional Resilience to a Changing Climate (ARRCC) programme funded by the UK’s Foreign Commonwealth and Development Office (FCDO). The aim of the project was to understand the current risk of extreme climate events to the hydropower sector, and how these may change in the future as human-induced emissions continue to increase, changing the climate. After a couple of years of virtual meetings, a team from the Met Office visited Nepal in July 2022 to bring people working in the hydropower sector together to talk about how they can increase the climate resilience of this vital sector. 

In a meeting room at the International Centre for Integrated Mountain Development (ICIMOD), private hydropower owners, government policy makers, electricity buyers and suppliers, engineers and climate scientists gathered together to share knowledge (Figure 2).  

Figure 2: hydropower owners, engineers, policy makers, and climate scientists got together to share knowledge and work towards increasing the resilience of the hydropower sector to climate change.
Photo credit: Utsav Maden, ICIMOD

We have found the current risk of extreme rainfall is higher than would be expected by looking at the relatively short observational record. As the climate continues to change driven by increases in human emissions, the magnitude of extreme rainfall events are projected to increase by 0 to 40 % by 2050 and 0 to 110% by 2080. The ranges are based on which emissions scenario we use including how many fossil fuels are burnt, with lower changes correlated with lower emission scenarios.  

From a hydropower design and operation perspective, there is a lot of interest in preparing plants for future climate change. However, climate science is only part of the information these business owners and engineers need to consider when planning for the future. They also need to ensure that their businesses are profitable, that loans are repaid, and their designs don’t exceed budget and are resilient to other hazards such as earthquakes and droughts.  The uncertainty surrounding future climate projections means they need to calculate how much risk they can take, considering aspects such as whether they will be financially rewarded for having more climate-resilient power supply.  

A changing climate also represents a significant challenge for established hydropower facilities such as the Marsyangdi plant that Met Office scientists visited during our trip. This plant had been commissioned 33 years ago, designed based on historical observations from 1989 and earlier. These data represent a different climate than that of Nepal today, and potentially a very different climate than the country will face by the middle or end of the century. 

Increasing the resilience of the hydropower sector in Nepal can’t happen overnight, but the conversations that were started during the project and continued during the visit have laid the foundations for next steps. These could involve training different users in using climate data, making relevant climate data accessible to users, and starting conversations about whether electricity generated from a more climate resilient plant could fetch a higher cost at market. Regardless of the next steps, this project has highlighted the value of tackling big problems with a diverse group of thinkers, all bringing their individual expertise and working together to find a solution.  

Further reading:  

To learn more about the Asia Regional Resilience to a Changing Climate programme, visit this website: Asia Regional Resilience to a Changing Climate 

To hear more about the project and visit to Nepal, listen to Rosie Oakes and Hamish Steptoe talk to Doug McNeall on the Mostly Climate podcast: https://youtu.be/cNwVOWDz8tM 

To learn more about the work that FCDO fund internationally, visit the development tracker. Climate projects can be found by filtering for ‘disaster relief’ and ‘education’: FCDO Development Tracker 

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