LITTLETON, Colorado, June 5 (Reuters) - Europe's power generation mix looks set to get dirtier over the coming summer after an enduring dry spell depleted reservoirs and crimped hydro-electricity output.

Hydro dams are Europe's third-largest electricity source after natural gas and nuclear plants, and historically reach their annual production peak just before summer as snow melt and spring rains recharge dams and river systems.

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That network of reservoirs and run-of-river hydro plants is then typically used as a key source of so-called dispatchable power, which can be discharged on command by grid operators to balance system power needs.

This year, however, a lingering drought has hit hydro generation and cut hydro-powered electricity supplies by 13% over the first five months of 2025 from the year before, to the lowest level for the month of May since 2017, data from Ember shows.

That shortfall of hydro output has in turn forced utilities to rely on other dispatchable power sources - including natural gas and coal plants - which may need to be deployed at even higher levels this summer if hydro output stays stunted.

HIGH & DRY

Below-normal snow cover across Europe's Alps has been a key source of the hydro headache this year.

From January through the end of May, a model of snow-fed hydro generation potential by LSEG estimates that output from across the Alps region is roughly a third below the long-term average so far this year.

Stunted spring rains have also hurt, with output generation potential across the Danube catchment area - one of Europe's main river-fed hydro networks - over 60% below normal, LSEG data shows.

HYDRO HIT

The combination of below-average snow cover and precipitation has led to a roughly 13% drop in cumulative hydro-powered electricity production over the January-to-May period from the same months in 2024, according to Ember.

During May, the 71 terawatt hours (TWh) of electricity generated from Europe's hydro plants was the lowest for the month of May since 2017, and was 11 TWh short of the output total during the same month a year ago.

This year's January-to-May hydro-fed electricity output was 48.5 TWh less than the same period in 2024, which reduced hydro power's share of Europe's electricity generation mix to 16.7% so far this year from over 19% during the same months in 2024.

FOSSIL FIX

To offset the drop in hydro generation, as well as a 36 TWh drop in cumulative output from Europe's wind farms so far this year, European power firms have had to boost fossil fuel power generation.

Output from gas-fired power plants was 31 TWh, or 7%, above the January to May 2024 total, while output from coal-fired plants was 12.5 TWh, or 5%, higher, Ember data shows.

Going forward, European utilities may need to crank coal and gas plant output higher still if hydro production remains constrained while power demand remains at average levels.

Output from Europe's fleet of nuclear reactors can also be potentially increased to offset the decline in hydro plants.

However, regional nuclear power output could also be constrained if the region's river temperatures rise during any potential heatwaves and reduce their ability to act as a source of cooling water in reactors.

That means that Europe's network of gas and coal-fired power plants will likely remain the primary source of dispatchable generation through the coming summer, especially if the dry conditions that have prevailed so far this year drag on.

The opinions expressed here are those of the author, a columnist for Reuters.

https://www.reuters.com/business/energy/europes-dispatchable-power-woes-worsen-fresh-hydro-hit-maguire-2025-06-05/