Illustration of the upwelling event recorded over the long weekend with a more than 8°C difference of surface temperature between the opposite ends of the lake. The upwelled cold water in the “petit lac” near the city of Geneva is particularly clear when looking at the temperature evolution over a lake transect. Visualisation www.alplakes.eawag.ch.

The response to the strong wind event over the weekend was not limited to Lake Geneva: Upwellings with cold water reaching the surface were also observed in Vierwaldstättersee near Luzern and in lake Thun with a significant drop in the Aare temperature.

Exciting insights into our lakes

The Alplakes platform, operated by Eawag, not only documents the historical upwelling events, but also predicted it several days in advance. So anyone who had taken a look at the platform was not surprised when they jumped into the cold water. Alplakes combines three-dimensional model calculations with satellite data to provide predictions of water temperatures at various depths – in 30-minute steps for the next five days. Alplakes has also been significantly expanded and made more user-friendly recently. The platform thus offers not only exciting insights for researchers, but also valuable information for water experts and citizens alike.

In addition to temperature trends, Alplakes also shows other dynamic processes for 116 lakes in and around the Alps, such as how blue-green algae are currently spreading in our waters. You can also conduct your own experiments: for example, substances can be introduced at any point in a lake – Alplakes then calculates where the substances will be transported by the current circulation. The consequences of climate change for Swiss lakes are also impressively demonstrated, for example how water temperatures have risen in the past and what developments can be expected in the coming decades. Or the effects of warming on lake stratification.

Climate change is altering the mixing of lakes

Depth profiles on Alplakes show, for example, how the upper layers of water heat up in summer and cool down in winter. In comparison, the deep water in deep lakes remains cool throughout the year at around 5 to 6 degrees. This stratification leads to low vertical circulation in summer. In winter, however, when the entire lake cools to a uniform temperature, an important exchange takes place between nutrient-rich deep water and oxygen-rich surface water. “This exchange is essential for the ecosystem of our lakes,” emphasises Bouffard. “But with global warming, the surface water in some places no longer cools sufficiently in winter. The necessary circulation process is disrupted – with drastic consequences for life in the depths.”

Alplakes: knowledge for the sustainable management of our lakes

Last year, the platform recorded around 150,000 hits – a huge success. However, there are still challenges to be overcome. “Our models are currently less accurate in the shore areas,” admits Bouffard. “But that's where most people go swimming. We are currently investing specifically in improving these predictions.”

The aim of Alplakes is to improve the understanding and management of lakes. The platform is aimed not only at researchers, but also at water management experts and interested members of the public. “In times of climate change, we want to help make informed decisions about lake management,” says Bouffard, “And raise awareness of the value and vulnerability of our lakes.”
 

Cover picture: Lake Geneva (Photo: Michael Heck/Pixabay).