The Serbian government has called on citizens to save electricity. Not as an environmental recommendation, but as a measure for the next ten days, while temperatures run between 36 and 39 degrees. When a state with its own hydro plants and thermal power stations has to publicly ask people not to turn on the air conditioning, that is no longer a heatwave. That is a deficit.

The number that explains everything else comes from Đerdap. According to Minister of Mining and Energy Dubravka Đedović Handanović, Đerdap 1 is running at 20 percent of capacity and Đerdap 2 at 30 percent. Water inflow is 1,500 cubic metres per second, the lowest level since 2003, and before that since 1985. That means the largest hydro plant in the region is producing at one fifth of what it was built for, at the exact moment consumption peaks.

The Danube as a shared bill

The problem is not Serbian. Hungary and Romania are shutting down nuclear reactors because the Danube does not have enough water to cool their systems. So the same river is simultaneously cutting hydropower in Serbia and switching off nuclear power next door. If anyone wondered what climate risk looks like expressed in megawatts, this is the answer.

Prime Minister Đuro Macut convened a crisis staff meeting on the extreme temperatures and low water levels. The hydrological situation on the Drina is somewhat better - the water is below average, but above the biological minimum. That is a phrase worth remembering: "above the biological minimum" means the river has not yet reached the state in which it stops being a river.

What this says about the whole region

The Balkan power system is interconnected. When one state goes into deficit, it does not stop consuming - it buys. And it buys on a market where everyone else is in deficit at the same time, on days of 40 degrees. Serbia's hydrometeorological service forecasts temperatures around 40 degrees mid-week, with lows of 23 to 25.

For years the region has talked about the energy transition as something that will happen at some point, in some document with deadlines running to 2040. This heatwave shows something simpler: the systems were designed for a climate that no longer exists. The hydro plants were built for rivers with a different water regime, and the thermal plants for summers that used to be shorter.

The question for anyone paying a bill from Skopje to Belgrade is whether there is a plan behind the calls to save power, or only a hope that this wave passes faster than the next one.