Ticino opens the Ceresio taps towards Italy

More water will flow out of the Ceresio towards Italy. The bilateral Italian-Swiss committee met urgently on 10 August and decided to increase the outflow at the Ponte Tresa barrage: from 3 to 8 cubic metres per second. The measure applies for ten days from 11 August, after which it will be reassessed according to hydrological conditions.

The effect on Lake Lugano is estimated at around ten centimetres of level lost. In absolute terms the drop is modest, but it comes on top of a summer already marked by scarce rainfall.

The request comes from the Italian side. The water crisis affects the Lake Maggiore basin and, downstream, the rice-growing areas of Novara, the Lomellina and the Milan hinterland. There, rice cultivation depends on flooding the paddies, a method that requires steady flows in the canals during precisely the weeks when the rivers are at their lowest. Five extra cubic metres per second do not resolve the situation, but they ease the pressure for a few days.

The limit set on Alpine reservoirs

The Swiss delegation nonetheless rejected the more substantial part of the Italian request, the one concerning additional releases from hydroelectric reservoirs. The reasoning is twofold: the ongoing drought and the security of energy supply.

According to the statement, the water reserves held in Ticino's hydroelectric basins sit at the lower limit of the values recorded over the past ten years. That figure concerns next winter more than the current summer. Water stored at altitude is the form of energy storage Switzerland relies on during the cold months, when photovoltaic output falls and consumption rises. Emptying it in August for agricultural needs downstream means shifting a problem by a few months.

The distinction between the two types of release is therefore substantial. The increase at Ponte Tresa affects a regulated natural lake and has effects that reverse within a few weeks of rain. Drawing on Alpine reservoirs would touch a reserve that only rebuilds with the following year's snowmelt.

The bilateral mechanism governing these flows has existed for decades and, in normal summers, works without making the news. Emergency sessions multiply instead when availability falls below the usual thresholds, as happened in the summers of 2022 and 2023.

It remains to be seen what happens when the ten days expire. If the rain does not come, the same request will return with narrower room for manoeuvre, and the question of how much water Ticino can give up without eating into its own reserves will be back on the table.