Temperature

This section describes changes in Aotearoa New Zealand's temperatures over time, and who might be most at risk of health impacts from temperature extremes.

New Zealand’s climate is warming

Over the period 1909-2018 (Figure 1), the mean annual temperature in New Zealand rose at a rate of almost 1°C per 100 years [1]. Climate scientists predict that relative to 1986-2005, New Zealand will continue to warm by 0.7°C to 1.0°C by the year 2040, and between 0.7°C and 3.0°C by 2090. Northern and eastern New Zealand will have the strongest warming trend [2].

Figure 1: Mean annual temperature anomaly in New Zealand, 1909-2021

Hot days are more common in northern and eastern New Zealand

There will very likely be an increase in the number of hot days (maximum temperatures above 25°C), particularly in the north of the North Island. At the same time, there will very likely be a decrease in the number of cold days (minimum temperatures below 0°C), particularly in the South Island [2].

Data from 2022 show hot days were more common in the north and east of both islands. Regions particularly affected by warm temperatures were the Bay of Plenty and Waikato regions. Cold days were most frequent in parts of the South Island, particularly Otago and Canterbury.

Movies 1 and 2 show how these temperature extremes have changed year-by-year between 1981 and 2019 across territorial authorities (TAs) in New Zealand.

Movie 1: Number of days over 25°C, 1981-2019, by Territorial Authority (TA) (click here for a larger version)

Movie 2: Number of days below 0°C, 1981-2019, by Territorial Authority (TA) (click here for a larger version)

Information about the data

Number of hot days and number of cold days

Source: CliFlo. NIWA's National Climate Database

Definition: Climate station data of the daily maximum and minimum temperatures from around New Zealand was sourced from the National Climate Database (CliFlo, a web services provided by the National Institute of Water and Atmospheric Research (NIWA). One climate station was selected per territorial authority, based on their proximity to the population-weighted centroid of each TA (2018 Census data). The number of hot days (days with a maximum air temperature above 25°C) and the number of cold days (days with a minimum temperature below 0°) was counted for each year by TA. Only years with more than 90% of valid data were counted. Data was compared to the most recent Climate Normal Period, 1981-2010, where the 30-year average acts as a benchmark against which more recent observations can be compared to.

References

1. NIWA. nd. ‘Seven-station’ series temperature data. URL: https://www.niwa.co.nz/our-science/climate/information-and-resources/nz-temp-record/seven-station-series-temperature-data (accessed 20 April 2021).
2. Ministry for the Environment. 2018. Climate change projections for New Zealand: Atmospheric projections based on simulations undertaken for the IPCC 5^th Assessment. 2nd Edition. Wellington: Ministry for the Environment.
3. Smith KR, Woodward A, Campbell-Lendrum D, et al. 2014. Human Health: Impacts, Adaptation, and Co-Benefits. In: Barros VR,  Field C, Dokken D, et al (eds). Climate Change 2014: Impacts, Adaptation, and Vulnerability Part B: Regional Aspects Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (pp. 709-754). Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press.
4. Britton E, Hales S, Venugopal K, et al. 2010. Positive association between ambient temperature and salmonellosis notifications in New Zealand. Australian and New Zealand Journal of Public Health 34(2): 126-9. DOI: 10.1111/j.1753-6405.2010.00495.x (accessed 23 October 2018).
5. Hales S, Salmond C, Town GI, et al. 2007. Daily mortality in relation to weather and air pollution in Christchurch, New Zealand. Australian and New Zealand Journal of Public Health 24(1): 89-91. DOI: 10.1111/j.1467-842X.2000.tb00731.x (accessed 23 October 2018).
6. McMichael AJ, Woodruff R, Whetton P, et al. 2003. Human health and climate change in Oceania: A risk assessment. Canberra: Commonwealth of Australia.
7. Lal A, Hales S, Kirk M, et al. 2016. Spatial and temporal variation in the association between temperature and salmonellosis in NZ. Australian and New Zealand Journal of Public Health 40(2): 165-9. DOI: 1111/1753-6405.12413 (accessed 9 February 2021).