Ever since climate change became a prominent international issue, hydroelectric power plants (HPPs) have risen in numbers and scale. They do not generate carbon emissions as opposed to coal, and so are a ‘cleaner’ source of electricity.

HPPs are, however, known to cause deforestation, land use change, and biodiversity loss (Asher & Bhandari, 2021). HPPs also affect the hydrology of the region. The way water collects, flows, and moves is affected as a result of land use changes. These ecological impacts of HPPs have been an acceptable trade-off in the quest to decarbonize.

While the effect of HPPs on land use and hydrology has been extensively studied, not many have studied the reverse impact: how is HPP operation affected by land use and hydrological changes it caused in the first place?

The generation of hydro power assumes that enough water will flow and can be used for electricity. What happens if this assumption breaks?

Itaipu, Belo Monte, and the Cost of Forest Loss in Brazil

Pinto and Arbache, 2025 looks at two HPPs in Brazil to examine this reverse effect. They study the impact of deforestation in the Itaipu HPP and the Bel Monte HPP, located in the north central and southern parts of Brazil. The study compares a hypothetical scenario of no deforestation in the HPP catchment vs. the actual scenario. They compare the amount of rainfall that would have occurred if there was no deforestation with actual rainfall and water flow data. The hypothesis is that the reduced forest cover has affected the microclimate in the catchments, resulting in less rainfall from the moisture laden winds of the Atlantic and reduced water flow in rivers.

Their research finds that between 2002 and 2022, the Itiapu HPP has potentially lost US$ 1.8 billion or US$ 86 million per year because of the reduced modeled rainfall. For the Bel Monte HPP that began operations in 2016, the cumulative loss till 2022 was US$ 2.3 billion, or an average loss of US$ 110 million per year.

Nature’s sense of irony never ceases to amaze me.

What does this mean for the past and upcoming HEPs in the Himalayas?

Several projects were undertaken in the Himalayas since the 1990s. In fact, dam construction in the Himalayas is 62 times more dense than global average (Pandit & Grumbine 2012). Results from Pinto and Arbache, 2025 point to potential losses in the future electricity generation by these projects. It would also be interesting to see if glacial melt is compensating for any reduction in rainfall from microclimatic changes. Answering this question and addressing the land use changes in the region will be critical in India’s decarbonization and climate adaptation story.