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 . Climate scientists predict that relative to 1986-2005, New Zealand will continue to warm by 0.7°C and 1.0°C by the year 2040 and 0.7°C and 3.0°C by the year 2090. Northern and eastern New Zealand will have the strongest warming trend .
Figure 1: Mean annual temperature anomaly in New Zealand, 1909-2018
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 .
Data from 2019 show hot days were more common in the north and east of both islands. Regions particularly affected by warm temperatures were the Hawke’s Bay as well as the Waikato and Coromandel region. Cold days were most frequent in parts of the South Island, such as Otago and Canterbury.
Movie 1 and movie 2 show how these temperature extremes have changed year-by-year over the past 40 years (1981-2019) 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)
More hot days and less cold days in 2019 compared to 1981
The average number of hot days in New Zealand increased from 25.4 (16.8-33.9) in 1981 to 47.1 (39.7-54.4) in 2019 (Figure 2). In the 30-year climate normal period from 1981-2010, New Zealand experienced on average 23.8 hot days per year. From 2014 onwards, the number of hot days per year was consistently higher than the baseline average. In 2019, the number of hot days was almost twice as high as during the climate normal period.
Figure 2: Number of days above 25°C in New Zealand and comparison to the 1981-2010 baseline average, 1981-2019
Note: The baseline average period refers to the most recent Climate Normal Period, 1981-2010 (WMO 2017). 30 years of data were averaged to act as a benchmark against which current or recent observations can be compared to.
Source: National Climate Database (CliFlo), NIWA
The average number of cold days in New Zealand decreased from 26.9 (9.7-44.1) in 1981 to 17.2 (11.3-23.1) in 2019 (Figure 3). In the 30-year climate normal period from 1981-2010, New Zealand experienced on average 23.6 cold days per year.
Figure 3: Number of days below 0°C in New Zealand and comparison to the 1981-2010 baseline average, 1981-2019
Note: The baseline average period refers to the most recent Climate Normal Period, 1981-2010 (WMO 2017). 30 years of data are averaged to act as a benchmark against which current or recent observations can be compared to.
Source: National Climate Database (CliFlo), NIWA
A warmer climate will affect our health
Fewer cold days will result in fewer cold-related deaths and hospitalisations from cardiorespiratory (heart and lung) conditions .
Increased temperatures can affect health in several ways.
- Gastrointestinal infections: The rate of gastrointestinal infections is affected by temperature. Research suggests that periods of higher temperatures are linked to an increase in salmonellosis notifications .
- Infectious diseases: Increasing temperatures can change the geographical distribution of some mosquitoes, carrying infectious diseases.
- Respiratory problems: Increasing temperatures bring a longer pollen season and increased fire risk, associated with increases in respiratory problems.
- Cardiac (heart) problems: Heat is linked to worsening of heart problems and to an increase in overall death rates , , and .
- Heat stroke: Extreme temperatures can cause heat stroke. Young children, older adults, those with a chronic disease, and people working outdoors are especially at risk.
Effects on vulnerable populations
Populations that are more vulnerable to temperature-related health effects are:
Combining temperature (Movie 1) and population data (see Population Vulnerability for more information) shows that Northland, the east coast of the North Island, and parts of the Bay of Plenty are likely to be regions where people will be particularly affected by the health effects of temperature increases. For example, many Māori live in the north and east of New Zealand, where hot days are projected to increase . There are also high numbers of older people over 85 years living in northern and eastern areas such as Christchurch city, Auckland city, Whangarei and Hastings.
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.
- 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).
- Ministry for the Environment. 2018. Climate change projections for New Zealand: Atmospheric projections based on simulations undertaken for the IPCC 5th Assessment. 2nd Edition. Wellington: Ministry for the Environment.
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