Meteorological drought in Northland, NZ: A regional and local analysis using copulas

Meteorological drought is a significant and recurring hazard in Northland, where eight droughts have been recorded since 1900. An analysis characterised by severity, duration, and frequency (return period) was undertaken for 1893–2018. Severity is measured by the Standardized Precipitation Index (SPI) and severity-duration-frequency relationships are described for 298 Northland rain gauge sites using copulas.

Based on severity the three worst drought years were (in order) 1987, 1913 and 1990. Based on duration the three worst drought years were (in order) 1993, 1913 and 1986. Statistical tests of SPI values showed no consistent and significant temporal trend in drought occurrence in the 125-year period.

Attempts at contouring and clustering demonstrated that SPI relationships are not spatially dependent, implying there are no specific drought-prone areas and drought may occur at any locality and time in Northland.

Further work is needed to improve climatological understanding of drought occurrence, along with continued monitoring of drought conditions. Use of multivariate copulas, including extra variables such as minimum SPI values and spatial extent, should provide a more comprehensive description of drought in Northland.