Drought Indicator Maps

There are several ways of defining drought and several methods for identifying whether a drought has started.  None of these methods are "the best" indicator of drought, because it very much depends upon the application of the information (i.e. for water supply calculations, for irrigation potential, for pasture production estimates, etc.)

Here we present a range of drought indicators.  These are maps of the soil moisture deficit (SMD) and the standardised precipitation index (SPI) - both updated daily, as well as maps of rainfall deciles (RD) - updated monthly.  In the future, we will also produce maps based on the potential evapotranspiration deficit (PED), which was used as an indicator in the NIWA 2012-2013 drought report.

For each drought indicator, we have identified the threshold values which can be used to indicate whether drought conditions are "imminent" and/or "likely evident". However, we stress here that this information should be used for guidance only and is not the sole source of information used in the official declaration of droughts.

Example soil moisture deficit anomaly map showing, for the particular time of year, drier than normal soils over much of the North Island and wetter than normal soils around Christchurch.