Summer 2015 Heatwave – a true test of


The drought information platform, which was developed in NRP 61, was put to the test this summer for the first time.

The heatwave that lasted from the end of June until the beginning of September was an excellent opportunity to verify the drought information and forecasts that were generated each day, as well as to see how the platform was used. The conclusions are positive, although further improvements to the platform will be sought. In mid-June barely anyone expected this summer to prove such a true test of the information platform. At that point of the year, the country’s groundwater storage and lakes were full to the brim, especially in Eastern Switzerland. But within a matter of just days, the monthly forecasts from ECMWF and Meteoschweiz were pointing to a stable period of intense heat. The indicators that a major drought event was occurring also started to accumulate on the information platform. The situation was accordingly observed closely and updated frequently, at least once each day. The number of visitors to the service increased significantly in July, as the platform was accessed up to 700 times a day. Moreover, many new users signed up to use the service throughout July and August.

An interesting yet difficult-to-communicate aspect was the contrast between the meteorological drought (including the very dry surface conditions) and the sustained good availability of underground water sources. For example, it could be observed long into August that trees in forests had a relatively good supply of water, while at the same time there was a major hazard of forest fires.

The intriguing regional differences in the nature of the drought were also clearly visible on the information platform. For example, during the first half of July there was a high precipitation deficit, especially in Western Switzerland. In contrast, in the Engadin Valley the drought came to a relatively early end compared with other regions.

Equally interesting was the contrasting information that was supplied by the flow-measurement stations. As in summer 2003, many rivers that are affected by glaciers showed unusually high flow levels, while the small and medium-sized river waters of the Central Plateau suffered low water levels over a period of several weeks. Such contrasts also point to the unusual nature of the situation that arose in July and August 2015.

Overall, the operators of have drawn positive conclusions from the event. The provision of drought information worked without problems throughout the entire summer heatwave, and feedback has been generally positive. At the same time, the need for some improvements to be made to specific visualisations and content has been revealed. For example, it is not currently possible to show measurements of soil moisture across Switzerland.

One innovation are the monthly forecasts of outflow, soil moisture and groundwater, albeit not available in real time, which are based on ECMWF meteorological forecasts and reveal how the drought may continue to develop over several weeks. This summer was the first occasion on which the product could really be put to the test. The forecasts issued on 25 June clearly pointed to an exceptional drought (see illustration).


Further information on this content


Manfred Stähli Eidg. Forschungsanstalt WSL, Gebirgshydrologie und Massenbewegungen

Luzi Bernhard Eidg. Forschungsanstalt WSL, Gebirgshydrologie und Massenbewegungen

Massimiliano Zappa Eidg. Forschungsanstalt WSL, Gebirgshydrologie und Massenbewegungen