🇳🇿New Zealand

New Zealand spans 34°–47°S as a South Pacific island nation (approximately 268,021 km²) comprising two main islands — North Island (Te Ika-a-Māui) and South Island (Te Waipounamu) — plus Stewart Island/Rakiura and roughly 600 smaller islands stretching 1,600 km north–south.

Intensely mountainous and volcanic, the landscape features the Southern Alps/Kā Tiritiri o te Moana on the South Island rising to Aoraki/Mount Cook (3,724 m, the highest peak), active volcanic plateau in the central North Island with Mount Ruapehu, Mount Ngauruhoe, and Mount Tongariro, and over 360 glaciers.

This extraordinary topography produces a complete climate spectrum — subtropical (Cfa) in Northland with warm humid summers, temperate maritime (Cfb / Cfc) across most regions with mild wet winters and cool summers, and alpine (ET) above 1,500 m in the Southern Alps and on volcanic peaks.

Auckland averages 15°C in July and 24°C in January with 1,240 mm rainfall distributed year-round plus occasional subtropical cyclones. Wellington registers 10°C in July and 18°C in January with 1,250 mm and famously strong winds (Windy Wellington). Christchurch records 6°C in July and 18°C in January with 650 mm — the driest major city with distinct seasons. Dunedin averages 7°C in July and 15°C in January with 810 mm.

New Zealand experiences significant extreme weather and climate-driven environmental change. Cyclone Gabrielle struck in February 2023, bringing rainfall exceeding 400 mm and causing widespread flooding and landslides across Hawke's Bay and Tairāwhiti, killing 11 people.

The Auckland Anniversary Weekend floods of 27 January 2023 brought 258 mm of rain in one day—the wettest 24-hour period on record—prompting a national emergency declaration and four deaths. Marine heatwaves around the Tasman Sea from 2017 through 2023 recorded temperatures up to 6°C above average, threatening marine ecosystems. Glaciers are retreating rapidly: the Tasman Glacier is 4.5 kilometers shorter than in 1990 and has lost 50% of its ice volume since 1900. These events reflect intensifying climate-driven hazards across hydrometeorological and cryospheric systems.

Our archive covers 9 New Zealand cities with daily ERA5 reanalysis data going back to 1940. The warmest July averages occur in Manukau City, around 14.1°C, while Dunedin records the coldest January nights near 11.4°C. Comparing the last decade against the 1940–1970 baseline, mean temperatures across these cities have risen by about 1.4°C.