Plans to earmark more than $136m (£109m) of UN money for large dam projects in Nepal, Tajikistan and the Solomon Islands have been angrily condemned by activists, who have warned the projects could have serious environmental consequences.

The UN’s green climate fund was set up during the Paris climate agreement to mobilise $100bn a year by 2020 for poor countries looking for innovative and transformational projects.

These were supposed to promote “paradigm shifts” to clean and climate-resilient energy, in the context of the UN’s sustainable development goals. However, to use the green climate fund to build mega dams ignores the risk they pose to ecology as well as climate.

An alliance of green groups claims that the Tajik funding would merely patch up a decrepit Soviet-era dam, while the Solomon Islands project would flood forests and vegetation, threatening biodiversity and releasing large volumes of methane, a more potent greenhouse gas than CO2.

Andrea Rodriguez, a senior attorney for the Inter-American Association for Environmental Defence, said the projects would have “tremendous negative impacts” on ecosystems and indigenous people.

“Large dams are not suited to adapt to climate risks because they alter seasonal patterns, by storing floods and increasing dry period flows,” she told the Guardian. “Large infrastructure does not guarantee development or climate solutions.”

A protest letter to the board, seen by the Guardian, says that 19m fish are currently being killed each year by turbines at the 126MW Soviet-built Qairokkum plant in Tajikistan. The country’s electricity network is already 98% reliant on hydropower, powered by shrinking glacier melt volumes.

In Nepal, the 216MW Upper Trishuli-1 project “would have no transformational impact,” the letter says. “It faces severe climate and disaster risks, and it would have significant impacts on indigenous communities – and the environment – that have not been adequately studied, nor mitigation plans prepared.”

The letter was signed by nine groups including Friends of the Earth, the Heinrich Böll Stiftung Foundation and the Centre for International Environmental Law.

Hydropower is considered a renewable energy source by international agencies, finance institutions and governments, because of the lack of CO2 emissions created when water is run down elevated reservoirs to power turbines.

But critics say this fails to take into account up to a billion tonnes of greenhouse gases created by dams each year, as well as the damage often inflicted on carbon sinks, and hydropower’s vulnerability to shifts in rainfall patterns likely to accelerate because of climate change.

In all, nine projects worth $854m will be discussed by the green climate fund’s 24-person board in a meeting in Songdo, South Korea, on Tuesday.

Fund board members declined requests for interview, but officials confirmed that the informal meeting would try to reach consensus on the projects.

One source said: “There’s an expectation that the board will consider these funding proposals – and the three [hydro projects] are part of them, so most likely they will address them. It is the usual approach.”

Other projects up for consideration include a $100m programme to help Ethiopian women threatened by drought, and $55m for water irrigation and conservation projects in Morocco.

If all projects are approved, they will take the fund’s disbursements to far to $2.4bn, 62% of which have gone to Africa and 23% to Asia-Pacific region.

Half of the money has been spent on climate mitigation – renewable energy and power efficiency investments – with the remainder split between adaptation to climate change, and “cross-cutting” programmes that contain elements of both.

The UN’s green climate fund declined to comment for this article.