The map shows the Standardized Precipitation Index (SPI), which is derived from precipitation totals. This is available on a regionally aggregated basis for periods of between one month and two years.

Unlike the precipitation total, the SPI standardises precipitation amounts so that comparisons between different regions and time periods can be made. It is thus essential for quantifying the intensity, duration and spatial extent of drought. In meteorology and hydrology, it is recognised as a robust scientific indicator for drought monitoring.

Interpretation: The value usually lies between -3 and 3. A value of zero means a normal level of precipitation. Positive values indicate unusually wet periods and negative values indicate unusually dry periods. The greater the deviation from zero, the rarer the event.

Data basis: Interpolated precipitation amounts from Meteoswiss ground stations (climate analyses).