Abstract
Flash drought is a relatively new term describing drought events that develop far more rapidly (i.e. within a sub-monthly period) than the slowly evolving phenomenon that drought is usually characterised as. Their rate of onset means they can lead to highly significant impacts for agriculture in particular, yet there is little understanding of the occurrence of these events in a New Zealand context. Thirteen locations were selected to investigate the occurrence of flash droughts across New Zealand for the period 2003 to 2023, with soil moisture data the basis for identifying these events. Flash drought occurrence ranged from zero events at five locations up to 12 events for Lake Tekapo. The median duration of these events was approximately six pentads, with a maximum event duration of 47 pentads. In terms of New Zealand-scale atmospheric drivers of these location-specific flash droughts, anticyclonic conditions (as indicated by the H, HW and HSE Kidson weather types) were prevalent during event initiation, as well as above normal temperatures and below normal precipitation. Analysis of larger-scale atmospheric drivers showed a relatively higher occurrence of the La Niña phase of the El Niño Southern Oscillation and neutral or weak positive phases of the Southern Annular Mode during the initiation of flash drought events, compared to the average for 2003 to 2023. Correspondingly, this preliminary research has uncovered evidence for the occurrence of these potentially damaging flash drought events in New Zealand, with relatively clear links from the point scale to synoptic- and larger-scale atmospheric drivers. However, further research is needed to better understand the controls on their occurrence beyond the locations examined here, and longer-term variation with respect to climate change.