Appendix A: Additional technical information
- Greenhouse gas emissions for Aotearoa New Zealand are presented from New Zealand’s Greenhouse Gas Inventory 1990–2021, published April 2023 (MfE, 2023a). The inventory estimates have been compiled by applying the 100-year global warming potential (GWP100) values from the IPCC Fourth Assessment Report (IPCC, 2007) to the non-carbon-dioxide gases when aggregating them together. Subsequent greenhouse gas inventories will apply the GWP100 values from the IPCC Fifth Assessment Report (IPCC, 2013), as required under the Paris Agreement. All projection estimates of greenhouse gases in this report apply the Fifth Assessment Report GWP100 values.
- Greenhouse gas emissions for Aotearoa presented in this report are not directly comparable with values presented in the previous Atmosphere and Climate report. In Our Atmosphere and Climate 2020, we used New Zealand’s greenhouse gas emissions as reported in the 2020 submission of the Greenhouse Gas Inventory but, in this report, we use the 2023 submission of the Greenhouse Gas Inventory because it contains the most up-to-date information. Inventory estimates are continuously improved. The whole inventory time series, from the base year (1990) to the latest year, is recalculated when the methodology or underlying data change. This means the emissions estimates are only up to date in the latest inventory, and previous inventories are not useful for comparisons. Changes made to the inventory are often related to improvements in activity data collection, emission factors and methodology, or the identification of additional emission sources.
- Stats NZ environmental indicator information in this report is based on data from 30 sites that use NIWA’s climate stations for the following indicators: Drought, El Niño Southern Oscillation, Extreme rainfall, Extreme wind, Frost and growing degree days, Rainfall, Temperature, and Wildfire risk. These sites are spread across Aotearoa, in locations designed to capture data in the areas where most people live, while also reflecting monitoring practicalities. As such, lower elevation coastal areas have a high representation and inland higher elevation locations have a low representation.
- For sites where trends could be determined, trends are classified as determinate when the probability of an increasing or decreasing trend is above 66 percent. The term ‘indeterminate’ is used when there is either no trend direction determined or not enough statistical certainty to determine trend direction (less than 66 percent certainty).
- Extreme rainfall: Rainfall due to very wet days (R95pTOT) measures the percentage of annual rainfall from very wet days, where very wet days are defined as those where the daily rainfall exceeds the 95th percentile of daily rainfall totals. For this release, the latest climate normal (1991 to 2020 average) was used to determine the 95th percentile range, where daily rainfall total is greater than or equal to 1mm (Klein Tank et al, 2009). Climate normals serve as a benchmark against which recent or current observations can be compared (WMO, 2017). They can be used for determining how ‘abnormal’ the climate of a particular month, season or year is when compared against the 30-year climate normal. Like air temperature, rainfall can change over time; the latest climate normal period (1991 to 2020) helps us to understand the typical characteristics of our contemporary climate. R95pTOT provides information about extreme rainfall events relative to total rainfall over a period of time. For comparison, we also provide data based on the previously applied 1961 to 1990 climate normal period in the dataset. Maximum one-day rainfall total (Rx1day) measures the maximum amount of rainfall that fell in a single day over a period of time (Klein Tank et al, 2009). This provides information on the magnitude of extreme rainfall events (see Indicator: Extreme rainfall).
- Wildfire: Comparison of fire risk between sites is complicated due to differences in fuel type at each station used for analysis. A fuel type may be one of ‘forest’, ‘grass’ or ‘scrub’, and was derived for each station based on Land Information New Zealand geographic databases. Comparing between sites is therefore not appropriate, because the calculated wildfire risk is dependent on fuel type. Nevertheless, the data support the assessment of trends over time for each site (see Indicator: Wildfire risk).
- Extreme wind: Here, extreme wind measures the annual average of the daily maximum wind gust (a measure of windiness) and annual maximum wind gust (a measure of wind strength) (see Indicator: Extreme wind).
- Drought: One method used to detect and monitor drought is the Standardised Precipitation Evapotranspiration Index (SPEI) (WMO and Global Water Partnership, 2016). Because SPEI accounts for the influence of temperature and precipitation on drought, it is a useful index for studying drought given our changing climate (Our atmosphere and climate 2020). SPEI can also be applied for different periods (like the past 3, 6 or 12 months) to provide information about the frequency and intensity (drought severity divided by its duration) of meteorological, hydrological and agricultural droughts. Extreme dryness refers to SPEI values below –2.
- Trends in frequency of short-term drought events (meteorological drought; across 3 months) are tending to increase, while trends in long-term drought events (hydrological drought; across 12 months) are mostly indeterminate. Short-term drought frequency increased at 18 sites and decreased at 7, while 5 sites had indeterminate trends. Long-term drought frequency increased at 6 sites and decreased at 6, while 18 sites had indeterminate trends.
- Trends in drought intensity are indeterminate at some sites, though more sites showed decreasing rather than increasing trends across short-, medium- and long-term events. Short-term drought intensity increased at 6 sites and decreased at 12, while 12 sites had indeterminate trends. Long-term drought intensity increased at 6 sites and decreased at 10, while 14 sites had indeterminate trends.
- For short-term drought, 21 of 30 sites had extreme dryness, and 13 sites had at least six unique drought events each from 1972 to 2022. Dunedin had the most drought events, at 10 events. Seventeen sites spent at least 25 percent of the time in short-term drought, with Dannevirke and Dunedin spending the most time in short-term drought (47 percent).
- For long-term drought, 14 of 30 sites had extreme dryness from 1972 to 2022. Twenty-three sites spent at least 25 percent of the time in a long-term drought event, with 10 sites in drought at least 50 percent of the time.
Appendix A: Additional technical information
November 2023
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