Recent news has highlighted the impact of strong winds this summer on drinking water in the Stockholm area; SVT Stockholm on 20 Aug: Så har blåsiga sommaren tvingat stockholmare att snåla med vatten (translation: This is how the windy summer has forced Stockholmers to be frugal with water) and SLU News on 18 Aug: Vattenbrist i Stockholm: Starka vindar bakom problemen (Translation: Water shortage in Stockholm: Strong winds behind the problems).As a drinking water source, Lake Mälaren, is not short of water, rather warmer water temperatures have caused the drinking water purification process to become slower. Drinking water is usually collected deeper in Lake Mälaren, where it is generally cooler, but this year, strong winds have mixed the water, so that the temperature at depths are warmer than usual.
Similarly, SITES Lake Erken and Lake Bolmen, which represent critical drinking water supplies, showed similar warmer lake temperature at depths compared to previous years. As part of the SITES Water Thematic Program, lake temperature profiles are collected manually and with high resolution sensors, providing a data set that shows the thermal structure of the lake over time. So far preliminary data suggests that thermal patterns during summer 2025 were different compared to previous years, with a weaker stratification, major mixing events and warmer bottom waters.
Waves in the lake Bolmen (photo: Clemens Klante)