Rivers and lakes

The map shows the current drought level based on the average of measured discharge data from monitoring stations over the past 7 days.

The drought level is defined as the deviation from the statistically expected values for the measurement period 1991–2020 (reference or standard period). The current weekly average is compared with the corresponding value of the standard period and then allocated to a drought level.

The reference values are calculated over a period of +/- 15 days. This takes into account the seasonal nature of the variable, and drought is seen as a rare event compared to the usual values for the time of year. Drought levels are set at the 2nd, 5th, 10th and 15th percentiles.  

More information: combined drought index (CDI).

Data basis: Discharge at the stations of the hydrological monitoring network of the Federal Office for the Environment and the Canton of Zurich (Reppisch-Dietikon and Jona-Rüti). For background information see Basic monitoring network: water level and discharge in surface waters. This drought platform shows weekly averages. The temporal development and values of the discharge forecasts on https://www.hydrodaten.admin.ch/ are shown as hourly values and are therefore not comparable.

Note on uncertainties: Measuring low discharges to assess drought is technically challenging and can be prone to errors. Some of the stations are influenced by dams in the upper reaches. At these stations, changes in discharge do not only represent natural processes.

The model projections show possible developments in the future and are therefore subject to uncertainties. In addition to the resolution of the model, this is due to simplifications that have to be taken into account when creating the model. The artificial influence of watercourses by dams can be an additional significant source of uncertainty in the hydrological forecasts. In addition to the hydrological model, uncertainties in the meteorological forecast are relevant. This applies in particular to forecasts over longer periods.