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Snow-hydrological forecasting

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The SLF maintains an operational snow-hydrological service (OSHD) which continuously analyses the spatial and temporal distribution of snow water resources in Switzerland and thereby facilitates improved hydrological forecasting and timely regulation of water resources.

 

In Switzerland snow plays a major role in the water cycle. The snow melt influences the seasonal runoff dynamics and can – often in combination with other factors, such as heavy precipitation – give rise to flooding. Since 2009 we have therefore been hosting an operational snow-hydrological service (OSHD) which continuously analyses the spatial and temporal distribution of snow water resources in Switzerland and thus contributes not only to heightening the accuracy of hydrological forecasts, but also to calibrating the timely regulation of water resources.

Operational analyses

The OSHD regularly produces snow-hydrological bulletins containing a variety of products. Maps, for example, illustrate the current distribution of the snow water equivalent (SWE) (Figs. 1a and 1b).

 

SWE climatologies, in turn, reflect the temporal evolution of the current snow water reservoir and allow comparisons to be made with past winters. And the snow-hydrological bulletins also provide spatial information on the condition of the snowpack. Only a snowpack that is capable of generating and releasing melt water is relevant for short-term runoff forecasting. The bulletins are submitted to the Federal Office for the Environment (FOEN), which integrates the content in its Hydrological bulletin.

Methods

The OSHD analyses are primarily based on snow data gathered by a variety of monitoring networks and therefore reflect actual observations and measured data rather than information obtained by modelling precipitation. Some of the data are collected by observers in the field. These sources are supplemented by data captured by climate stations and by precipitation measurements. For more information, refer to OSHD models.

Organisation and collaboration

The OSHD is integrated in the forecasting and warning activities of the responsible national agencies, which are coordinated by the Steering Committee for Intervention against Natural Hazards (LAINAT). In the field of hydrology the Federal Office for the Environment (FOEN), the Federal Office of Meteorology and Climatology (MeteoSwiss), and the WSL Institute for Snow and Avalanche Research SLF work closely together. Flood-related warnings are issued in consultation with these competent bodies. In case of exceptional events, the natural hazards steering committee is convened. It coordinates the competent agencies' response to complex natural events and thus facilitates a concerted evaluation of the hazard situation.