Beyond the Headlines: Heatwaves, Nuclear, and Energy Security.
Extreme heat, drought, and wildfires are causing anxiety across Europe this summer. Headlines about high electricity demand and nuclear reactors forced to reduce output across Europe are adding to this. These disruptions are real. But they make the case for climate-proofing nuclear power and building more solar, not choosing between them.
Pictures of exposed riverbeds and idle turbines make for an unsettling story. This summer, heat and drought have affected reactors across Europe from France to Romania. Historically low water levels in the Danube have forced severe cuts at Hungary’s Paks station and put Romania’s Cernavodă plant under pressure. The immediate question is understandable: if nuclear plants need water, can Europe rely on them in a warming climate?
That is the right question. The common answer, that nuclear power is uniquely unreliable, is wrong.
Heatwaves test the whole energy system at once. They push up demand for cooling, reduce hydropower, constrain some thermal power stations, and often coincide with low wind. Resilience is about recognising the various trade-offs and combining clean energy technologies with different strengths, upgrading vulnerable assets and planning for several problems to arrive together.
A hotter, drier Europe
This summer did not come from nowhere. Copernicus and the World Meteorological Organization report that Europe is warming more than twice as fast as the global average. Heat stress is increasing, and drought is placing more pressure on rivers, ecosystems and infrastructure.
Across western Europe, the average temperature for June and July 2026 reached 21.62°C. That was 2.79°C above the 1991–2020 average and almost 0.9°C above the previous record set in 2022. June was the region’s warmest on record. Copernicus data shows that the heat continued through July across France, Spain, Switzerland, England and parts of Germany and Italy.
But those averages conceal the severity and persistence of individual events. France’s late-June heatwave lasted 14 days with temperatures exceeding 40°C across more than 40 percent of the country at least once, and temperatures at Saintes reached as high as 43.8°C on two consecutive days. Many locations in Spain also rose well above 40°C on consecutive days. France then endured another 16-day heatwave in July.
The heatwave coincided with Drier-than-average conditions conditions across western and central Europe, putting additional pressure on the energy system. The Seine, Rhine and Danube recorded exceptionally low flows. In Austria, the main hydropower operator pointed to very little snow throughout winter, with precipitation falling as rain instead of being stored in the mountains and released later as snowmelt. Copernicus’ latest Europe-wide assessment found that end-of-season snow-cover extent and snow mass were 31 and 45 percent below average, respectively, continuing a two-decade decline. In Switzerland, glaciers had exhausted their winter snow reserves by late June, closely tracking the record melt year of 2022. Glacier melt can temporarily cushion low river levels, but continued retreat reduces the ice available to play that role. For Alpine-fed rivers, less snow and shrinking glaciers make prolonged summer heat and drought harder to absorb.
All of this paints a challenging picture for Europe’s energy system as a result of our warming climate.
Energy constraints are bigger than just nuclear
Media coverage has unjustly focused almost exclusively on nuclear reactor shutdowns and output reductions. While there have been real reductions and shutdowns of nuclear reactors, they are part of a broader story of an energy system under pressure on multiple fronts and how different clean energy technologies can support each other.
In France, environmental limits on the temperature of discharged cooling water reduced available nuclear capacity by as much as 8 GW in late June and 9 GW in mid-July. But a combination of France’s large, robust nuclear fleet, and midday solar delivering around 20 GW meant that France performed better than other European countries during this difficult period.
In Switzerland, the river-cooled Beznau station was shut down. While many think this was for reactor safety, the real reason was to protect the river ecosystem when the Aare became too warm.
The consequences were sharper along the Danube. In Hungary, the Paks nuclear power station which normally provides nearly half of the country’s electricity was forced to shutdown a number of reactors putting pressure on the electricity grid temporarily. Water flows have since increased allowing the plant to begin restarting reactors.
In Romania, one Cernavodă reactor had been offline since 28 July and, as of 11 August, the second was approaching a controlled shutdown. The plant normally supplies about one-fifth of national electricity. The government declared an energy emergency and prepared demand reductions while crews dredged the river and modified the channel near the water intake.
The contrast with France is notable. While France's large nuclear fleet divided across multiple power stations and locations allowed them to absorb temporary cuts, Hungary and Romania depend much more on a single plant drawing from a depleted river basin. This concentration creates a potential risk that can be mitigated with a more geographically diverse nuclear fleet, or combining with a diverse clean energy mix.
This was far from a nuclear only story. Low rivers also reduced hydropower and coal generation, disrupted freight on the Rhine and Danube. Heat raised air-conditioning demand and reduced the efficiency of gas turbines and solar panels. This all contributed to push summer electricity prices to levels more often associated with winter.
What this summer’s generation data shows
The generation data makes the system-wide nature of this summer’s disruption clearer. Across the EU-27, nuclear produced 4.5 percent less electricity than the average for the same period in 2024 and 2025. That’s not insignificant, but it was far smaller than hydropower’s 21 percent fall and sat alongside substantial day-to-day swings in wind. Solar was the clear positive outlier, generating 30 percent more electricity across the EU and 36 percent more in Great Britain.
Raw generation alone does not tell the whole story, because Europe has added a great deal of wind and solar capacity. Capacity factor sounds technical, but the idea is simple: it compares the electricity actually generated with what the installed fleet could have produced if it ran at full power throughout the day.
On this measure, the EU’s nuclear fleet does not look like a technology experiencing an unprecedented collapse. Its average capacity factor this summer is 67 percent, between 69 percent in 2024 and 66 percent in 2025. Wind also sits between the previous two summers, while solar has remained broadly stable. Hydro is the clearest sustained fall, dropping from 29 percent in 2024 to 21 percent this summer. Great Britain’s smaller nuclear fleet has performed notably worse which is the result of a small number of aging reactors of an earlier design. That being Advanced gas-cooled reactors (AGRs) vs the more standard light-water reactor designs found in more modern plants in Great Britain and Europe.
Solar is the standout in total generation. Some of the increase comes from the rapid expansion of installed capacity, but its capacity factor has held up through the heat. Solar panels lose some efficiency as they get hotter, yet long, clear days and dry skies often make solar highly productive at the very times when hydropower and river-cooled plants are most exposed.
That is the central resilience lesson: different clean technologies respond differently to the same climate stress. The engineering challenge is to reduce the vulnerabilities of each and combine them so that one source can be strongest when another is constrained.
What heat and drought actually do to a nuclear plant
A nuclear reactor produces heat, which turns water into steam and drives a turbine. Afterwards, that steam must be cooled back into water so the cycle can begin again. At plants that use rivers for cooling, an extreme summer creates two different engineering problems.
Water temperature: Warmer intake water makes the plant less efficient. Returning heat to an already warm river can also breach environmental limits designed to protect fish and other aquatic life. This was the main constraint in France and Switzerland.
Water level and flow: A low river may leave an intake partly exposed, reduce the volume of water available for pumps, or make it harder to dilute discharged heat. This was the more acute problem on the Danube.
These are availability problems, not reactor-safety failures. A controlled reduction or shutdown removes most of the heat being produced, while safety systems continue to cool the reactor using much smaller volumes of water. That distinction is important but does not make lost generation irrelevant.
The scale also needs perspective. The International Atomic Energy Agency estimates that weather and environmental hazards have historically caused average production losses of around 0.1 to 0.5 percent of annual nuclear generation. Fleet-wide averages, however, can conceal much larger national consequences when a country depends heavily on one plant or river. Climate change makes adaptation more urgent even if the overall loss remains modest.
Engineering solutions already exist
Operators can lower or redesign water intakes; improve pumps, condensers and heat exchangers; dredge vulnerable channels where it is environmentally appropriate; add cooling towers; use recycled water; and improve forecasting so maintenance is scheduled away from the riskiest periods. New plants can be sited and designed for future river flows, temperatures and sea levels rather than historical averages.
There is no universal fix. Cooling towers withdraw less water but can consume more through evaporation. Dry cooling uses very little water but costs more and performs less efficiently in extreme heat. Coastal plants avoid river drought but still face marine heatwaves, rising seas and biological hazards. Good resilience planning is site-specific.
The potential gain is substantial. In a modelled 2050 European power system consistent with 2°C of warming, the European Commission’s Joint Research Centre found that less water-intensive cooling could reduce the projected climate impact on nuclear generation from 2.8 percent to 0.6 percent.
Nuclear and Solar are natural partners for resilience
Upgrading individual plants is only half the answer. The International Energy Agency defines climate resilience as the capacity to anticipate, absorb, accommodate and recover from climate impacts. For electricity, that means building a portfolio whose parts fail at different times and can support one another.
Solar is especially valuable during long, bright summer afternoons, when cooling demand is high and river-cooled generators may be constrained. Nuclear complements it by supplying firm, low-carbon electricity overnight, through cloudy and windless periods, and during the darker months when solar output falls sharply.
The summer-to-date data we explored earlier shows the immediate response to heat and drought. The full-year EU generation profile shows why the partnership matters beyond one season. Solar ranged from about 10 TWh in December 2025 to 46 TWh in June. Nuclear moved in almost the opposite direction, from around 45 TWh in June to 62 TWh in December. In June 2025, solar became the EU’s largest electricity source for the first time, supplying 22 percent of generation, narrowly ahead of nuclear at 21.6 percent.
This is complementarity, not competition. Solar can carry more of the system during bright summer days, including when hydropower and some thermal plants are constrained. Nuclear provides the firm low-carbon foundation for nights and winters. Batteries, stronger interconnectors, demand response and other flexible resources bridge the gaps. The IEA’s work on secure electricity transitions and the new era for nuclear energy points in the same direction: diversity and flexibility are central to a secure, low-emissions power system.
Five priorities for a more resilient European power system
Climate-proof vulnerable plants. Prioritise cooling and intake upgrades at river-cooled stations, especially where a single site is nationally important. Adaptation plans should include triggers, costs and delivery dates, not just risk assessments.
Design for the climate ahead. New reactors, life extensions and grid investments should be tested against projected temperatures, river flows, droughts and sea levels through 2050 and beyond, rather than mainly against the historical average.
Preserve firm, low-carbon capacity while replacements are built. Safely operating reactors should not be closed before equivalent firm, low-carbon capacity is available. Otherwise Europe becomes more dependent on fossil gas, imports and favourable weather at exactly the wrong time.
Plan nuclear and solar as partners. Investment, market rules and grid planning should recognise their complementary daily and seasonal profiles, backed by storage, flexible demand, interconnectors and other dispatchable low-carbon sources.
Future system planning. More work needs to be done to model heat, drought, low wind, generation outages and transmission limits across several countries at once. Governments should distinguish environmental curtailments from safety events and publish comparable data for nuclear, hydro, fossil generation, wind, solar and grids.
The lesson from this summer
Summer 2026 has exposed genuine weaknesses in Europe’s energy infrastructure. Some nuclear plants are too dependent on river conditions that can no longer be treated as stable. Some countries are too reliant on a single large station. Grids and emergency plans are not yet fully prepared for climate stresses that cross borders and hit several technologies together.
Science, not dogma, should guide the response. A hotter Europe should not be forced to choose between climate-proofed nuclear energy and rapidly expanding solar. It needs both, connected by storage, flexible demand and a stronger grid. Europe’s rivers are running low. That is a warning to adapt the energy system, not an argument to discard one of its largest sources of firm, low-carbon electricity.