A new Global Environmental Change study warns that in the coming decades, climate change-driven reductions in precipitation and river discharge will diminish the Amazon’s hydropower capacity.

The study’s authors examined 351 proposed hydropower projects in the Amazon basin. Their findings suggest that hydrologic shifts by mid-century will reduce hydropower generation at many locations. As river discharge becomes increasingly variable and hydropower output declines, alternative energy sources like solar and wind are expected to become ever more important.

“Hydropower projects in the Amazon basin are designed to operate under flow regimes based on historic river levels,” co-author Stephen Hamilton, an ecosystem ecologist at Cary Institute of Ecosystem Studies, explained. “Climate change is disrupting these patterns, meaning that many existing and proposed projects are unlikely to be as effective under future conditions.”

Using several climate change scenarios defined by the IPCC, the team modelled continent-scale changes in precipitation and runoff, which influence river discharge, using general circulation models that use climate data to project future precipitation trends. Inputs include information on air temperature, humidity, wind speed, solar radiation, pressure, and precipitation. Power output at proposed dam sites was estimated using information on the maximum and minimum river flows at each site under both current and future climate conditions. They also estimated changes in energy costs, comparing costs of hydropower to solar and wind energy in the Amazon region

‘Levelised cost of energy’ (LCOE) – the per-unit price of energy needed for an energy production project to break even – was used to determine how climate change would alter energy cost and project feasibility. LCOE takes into account the costs of building, operating, and maintaining proposed energy plants. The team ran projections under current, intermediate, and worst-case climate change scenarios. They also compared projected costs of hydropower to costs of implementing wind or solar power projects.

They found that by mid-century, river flows at proposed dam sites across the Amazon basin are projected to decline by 13-20% overall, with significant regional variability. Declines in the east (the Brazilian Amazon) range from 18-23%. In the west (Andean Amazon countries), where rainfall is likely to increase, flows could rise by 1.5-2.5%. Energy output is projected to reflect these changes in river discharge. Increasingly variable flows in the Brazilian Amazon tributaries mean this region is likely to be most severely affected.

Climate change-driven reductions in precipitation and river discharge may affect future hydropower capacity in certain regions.

Lead author Rafael Almeida, a postdoctoral researcher at Cornell University who was formerly a visiting graduate student at Cary, explained.

“Run-of-river hydropower dams are designed to operate within a particular range of flows. Flows that are too low won’t generate power and flows that are too high must be ‘spilled’, causing problems, and not generating extra power. As the Brazilian Amazon experiences more variability in precipitation, with higher ‘highs’, lower ‘lows’, and fewer periods of optimal flow, it will mean proposed hydropower plants will operate at full capacity less often,” she said.

In regions where hydropower energy production is projected to diminish, energy costs will increase – in some areas, drastically. In Brazil, the levelized cost of energy for proposed dams could jump by 52-105%.

Almeida says: “We expected to see reduced competitiveness of Amazon hydropower due to climate change, but the projected magnitude is staggering. Looking at dams proposed for Brazil, the cost at which electricity would need to be sold to fully return capital investments could more than double for a quarter of the sites proposed.”

“Hydropower plants take a long time to plan and build,” Hamilton adds. “Many of the proposed projects, if completed, would be coming online close to mid-century. By the time these dams are built, many will not be as reliable or cost-effective as expected due to climate change.

“Hydropower needs to be designed to operate in concert with alternative energy sources like solar and wind so periods of low river flows do not disrupt electrical grids that supply vital power to cities and industries. New hydropower facilities should be carefully sited in locations of more reliable flows and designed to operate over a broader range of flows than historical experience would indicate.”

Almeida concludes that energy planners need to focus on climate resilience. She gives the example of Brazil which has over 200 million people and hydropower is the dominant energy source. This year, Brazilian hydropower reservoirs are at record lows due to extreme drought; as a result, Brazil might need to start rationing power.

“Ensuring energy security into the future will require diversifying energy sources to include solar and wind and adapting hydropower plans to suit future – not historic – river flows,” she said.

This article first appeared in International Water Power magazine.