As for other natural hazards, official warnings are issued so that affected authorities and sectors can prepare for an impending drought in good time. These warnings, issued per region, are based on the weekly expert assessment of the current situation and the combined drought index forecast. They differ from the automatically calculated CDI in that they interpret trends and take into account forecast uncertainty.
The drought hazard levels issued for each region are explained below. They are based on the hazard levels specified in the Civil Protection Ordinance (Art. 24) (german).
Normal situation. There is little or no risk of a prolonged drought developing over the next four weeks.
No (significant) impact.
No special measures are required to prevent drought occurring.
Annually recurring or locally ordered water-saving measures may still be imposed.
Short version: No recommendation for action.
The combined drought index for the coming weeks does not deviate significantly from the long-term average for several variables (precipitation, discharge and soil moisture).
There are signs of a prolonged drought. The situation may get worse. (Initial) impacts and restrictions are to be expected.
Local soils are dry, which may lead to crop failure.
Water demand may exceed the available resources in the local area.
No (significant) impact.
An increased risk of forest fires is to be expected.
It may be necessary to reduce the maximum payload for vessels on the Rhine.
There may be a slight reduction in output at run-of-river power plants.
The combined drought index for the coming weeks deviates significantly from the long-term average for several variables (precipitation, discharge and soil moisture).
Drought warnings are only issued at hazard levels 2 and 4.
Hazard level 2 has already been reached and forecasts indicate that the situation is likely to deteriorate significantly. There are considerable impacts and restrictions at this drought level.
Local soils are very dry, which is likely to lead to crop failure.
An increased risk of forest fires is to be expected.
There may be a reduction in output at run-of-river power plants.
Observe any instructions issued by the local authorities.
The combined drought index for the coming weeks deviates considerably from the long-term average for several variables (precipitation, discharge and soil moisture). An event of this magnitude happens only a few times in 50 years in this regionat this time of year.
Drought warnings are only issued at hazard levels 2 and 4.
Hazard level 2 is primarily intended to alert the authorities and affected sectors. These should then observe the situation and put any necessary measures in place. The general public is informed that the cantons and/or communes may introduce restrictions.
Hazard level 4 is intended to warn the general public that there is a drought situation with considerable impact. At this level and above, the public can expect to be directly affected by restrictions (e.g. on water use) imposed by the cantons and/or communes.
Hazard levels 3 (considerable risk) and 5 (very high risk) are not used for drought, as they do not impact the public additionally to levels 2 and 4.