Climate trends in the south-west Pacific

Temperature and precipitation trends are described for newly homogenized historical climate data sets for the South-west Pacific. Regions that exhibit similar temperature and precipitation trends and variability are defined, and the temperature and precipitation time series aggregated according to these regions. Four temperature regions show distinctive trends: two regions south-west of the South Pacific Convergence Zone (SPCZ), which display steady climate warming; two regions north-east of the SPCZ, which cooled during the 1970s, and warmed in the 1980s. Annual anomalies differ in response to the El Niño-Southern Oscillation (ENSO) phenomena, depending on the region's position with respect to a pivotal line along the SPCZ. The climate warming apparent throughout much of the south-west Pacific comes from sites where there can be no question of any urban influence. Five main South-west Pacific precipitation regions show distinctive trends that are connected to the main climatological features. Four New Zealand precipitation subregions relate to the interaction of the main climatological features with local orography. Annual precipitation anomalies show marked variability and are also affected by ENSO in most regions. The pivotal line for the response of precipitation regions lies just to the north-east of the SPCZ. The ENSO relationships with precipitation appear consistent on both annual and interdecadal time-scales. From these climatic trends four climatic response regions are recognized in the South-west Pacific.