In South and Southeast Asia, hydropower accounts for 14.5% of total electricity generation with a total hydropower installed capacity of 117 GW. In some countries, such as Bhutan and Nepal, hydropower accounts for over 90% of total electricity generation. The installed hydropower capacity is expected to grow further in order to meet the region’s growing electricity demand and electricity export opportunities, and to maximise the merits of a cost-effective and flexible low-carbon power source.

However, the rising temperatures, extreme rainfall patterns, melting glaciers and increasing occurrence of extreme weather events associated with climate change pose serious challenges to South and Southeast Asian hydropower. They can affect hydropower generation by increasing variability in streamflow, shifting seasonal flows and augmenting evaporation losses from reservoirs. Extreme weather events such as heavy rainfall and associated landslides can hinder development of hydropower projects as seen in the cases of Viet Nam’s Thua Thien Hue hydropower project in 2020 and Lao People's Democratic Republic (Lao PDR)’s Xe-Pian Xe-Namnoy Dam in 2018. Glacier melt due to rising temperatures and the consequent glacial lake outburst floods caused severe damage to the Dhauliganga Hydropower Plant in India in 2021 and to the Golen Goal Hydropower Plant in Pakistan in 2019. Given that climate change could significantly affect the operation of hydropower plants, which usually operate for multiple decades, a comprehensive assessment of climate impacts is vital.

This report assesses potential climate impacts on about 86% of the total hydropower installed capacity in South and Southeast Asia, focusing on 13 countries with the largest hydropower installed capacity. It is based on three different scenarios: Below 2°C, Around 3°C and Above 4°C. Each represents a different level of greenhouse gas (GHG) concentration and its global average temperature outcome by 2100. The assessment shows changes in annual and monthly capacity factors from each country between 2020 and 2099, and compares the projected results against the values of the baseline period spanning 1970 to 2000.

From now until the end of the century, the regional mean hydropower capacity factor is projected to decrease due to changing climate conditions. The regional mean capacity factor from 2020 to 2059 is likely to decrease by around 4.6% on average (from 3.9% in the Below 2°C Scenario to 5.2% in the Above 4°C Scenario), compared with the baseline level of 1970 to 2000. Between 2060 and 2099, the regional mean hydropower capacity factor is projected to be lower than the baseline by 5.1% on average (from 4.7% in the Below 2°C Scenario to 5.4% in the Above 4°C Scenario).

Comparison of the results from three different GHG concentration scenarios demonstrates that a higher GHG concentration will have stronger negative impacts on hydropower generation in South and Southeast Asia. Relative to the other scenarios, in the Above 4°C Scenario, which assumes a continuous increase in GHG emissions, there could be a stark decrease in the regional mean hydropower capacity factor over the remainder of 21^st century. 

Although all three scenarios estimate a decline in the regional mean hydropower capacity factor by 2100, this does not mean that climate change will have an equal impact on every hydropower plant. Rather, the impacts of climate change are likely to be spread unevenly across South and Southeast Asia, leaving some plants more exposed to climate change than others.

All three scenarios indicate that two sub-regions, the Indian Subcontinent (India, Pakistan, and Sri Lanka) and Mainland Southeast Asia (Cambodia, Lao PDR, Myanmar, Thailand, and Viet Nam) will see a continuous decline in hydropower capacity factor until the end of the century. Relative to the baseline, the hydropower plants in the Indian Subcontinent are projected to decrease by 5.1% in the Below 2°C Scenario and by 6.8% in the Above 4°C Scenario until the end of the century. Similarly, the hydropower capacity factor of Mainland Southeast Asia is expected to decrease by 5.9% in the Below 2°C Scenario and by 8.2% in the Above 4°C Scenario.

In contrast, the other two sub-regions, the Maritime Continent (Indonesia, Malaysia and the Philippines) and the Himalayan region (Bhutan and Nepal) show more complicated trends in hydropower capacity factors: a drop in 2020-2059 and a recovery in 2060-2099. In both sub-regions, a higher GHG concentration will lead to a more dramatic bounce in the hydropower capacity factor in the latter 40 years of the century. 

Anticipating, absorbing, accommodating and recovering from adverse climate impacts, climate-resilient hydropower systems can bring multiple benefits: it can support the shift to low-carbon electricity technologies and provide power system flexibility for the rapid deployment of variable renewable energy sources such as wind and solar. It can also contribute to achieving universal access to affordable and reliable electricity services in countries such as Pakistan and Myanmar, where the rates of electricity access in 2019 were 73.9% and 68.4%, respectively.

To minimise the adverse impacts of climate change on South and Southeast Asian hydropower systems, governments and utilities need to scale up their efforts to address potential climate risks and impacts and identify effective measures to enhance resilience to climate change. The following policy recommendations can contribute to enhancing the climate resilience of South and Southeast Asian hydropower:

• Build robust climate databases and strengthen climate impact assessments.

Although various climate-related changes have critical implications for hydropower generation in the region, the climate data and projections for specific locations or events are still limited due to a lack of reliable data and the complexity of meteorological systems. In addition, the further development of frameworks, guidelines and tools could support and guide climate risk and impact assessments.

• Integrate climate resilience as a key element in hydropower planning and construction.

As the region seeks to expand hydropower generation to meet its growing economy and energy needs, integrating climate resilience in new project planning and construction will be crucial. Recent damage to India’s Tapovan Vishnugad Hydropower Project and Lao PDR’s Xe-Pian Xe-Namnoy Hydropower Project demonstrate the importance of factoring in climate resilience in the initial stages of hydropower projects. Governments can encourage developers and operators to integrate climate resilience in early stages of hydropower projects by adopting relevant regulations for climate resilience, such as climate-resilient construction codes and mandatory climate risk assessments and emergency response plans.

• Build climate resilience into hydropower operation and maintenance strategies.

As hydropower plants age, they tend to become more vulnerable to climate change. Given that extreme weather events are likely to occur more frequently and with greater intensity, the design of old hydropower plants may not suit the changed climate conditions. Governments can set guidelines or standards for project operators to integrate climate resilience monitoring and adaptation processes into operation and maintenance plans. These could include the regular collection of climate and hydrological information, the implementation of risk assessment updates, the effectiveness evaluation of adopted measures, and the clarification of responsibilities, thresholds and action plans for further adaptations. Leveraging public and private investment will be key to financing the modernisation of ageing hydropower plants.

• Enhance regional cooperation to coordinate sustainable resource development and achieve mutual benefits.

South and Southeast Asia have many transboundary rivers such as the Mekong River which runs through the People’s Republic of China (hereafter “China”), Myanmar, Lao PDR, Thailand, Cambodia and Viet Nam, and the Ganges-Brahmaputra-Meghna river basin that spreads across China, Bangladesh, Bhutan, Nepal and India. Regional cooperation is vital among countries with major shared water resources, in order to form mutually-beneficial strategies and to coordinate actions on water source development. The further institutionalisation of cooperation frameworks and strengthened implementation mechanisms would support better coordination and build the region’s adaptive capacity against the adverse impacts of climate change.