New Zealand climate: temperature and precipitation variations and their links with atmospheric circulation 1930-1994

New Zealand's complex orography gives distinct regional responses to variations in atmospheric circulation. By using rotated principal components, three spatially coherent temperature, and eight rainfall regions are defined for describing climate variations and trends for the period 1930–1994. Two main circulation changes have occurred in the New Zealand area over the record examined, around 1950 and 1975, making it convenient to analyse the data in three periods: 1930–1950, 1951–1975 and 1976–1994. From 1930 to 1950 more south to southwest anomalous flow occurred, relative to later years. All three temperature regions recorded lower temperatures, and wetter years occurred in the northeast of the South Island, with drier years in the north and west of the South Island. Airflow from the east and northeast increased during the period 1951–1975. This was accompanied by increases in mean temperature in all regions, with wetter conditions in the north of the North Island, and drier conditions in the southeast of the South Island. In the final period analysed (1976–1994) more prevalent west to southwest airflows occurred accompanying the higher incidence of El Niño events. Annual rainfall decreased in the north of the North Island, and increased in the north, west, south and southeast of the South Island. However, in spite of more southerly flow, regional temperatures showed little change from the 1951–1975 period. These results demonstrate that variations and trends in New Zealand regional temperature and rainfall respond significantly to circulation changes in the southwest Pacific. Copyright © 1999 Royal Meteorological Society