New Zealand climate: patterns of drought 1941/42 – 2012/13
Drought is important for agriculture and water resources in New Zealand, despite New Zealand’s maritime location, drought does occur. New Zealand’s complex orography gives distinctive regional climatic responses to variations in atmospheric circulation. Thus drought tends to be regional in extent. By utilising an index of agricultural drought (accumulated potential evapotranspiration or PED), rotated principal components (RPC) are used to define five spatially coherent regions, The RPC scores are used for describing variability in drought for the period 1941-2013. The regions are large: northern areas of the North Island, the east of the South Island, southern New Zealand, and the west of the North Island and the north of the South Island. Drought seasons in the five regions were all associated with the persistence of distinct patterns of atmospheric circulation, typically when anticyclones were more frequent. Conversely wetter seasons occurred generally when there were more troughs than usual. Four of the five regions show a distinct trend towards higher values of drought indices over the 72 year period, associated with higher austral summer pressures in the New Zealand region linked to Southern Hemisphere stratospheric ozone depletion.