Abstract
Long time-series of weather grids are fundamental to understanding how weather affects environmental or ecological patterns and processes such as plant distributions, plant and animal phenology, wildfires, and hydrology. Ideally such weather grids should be openly available and be associated with uncertainties so that users can understand any data quality issues. We present a History of Open Weather in New Zealand (HOWNZ) that uses climatological aided natural neighbour interpolation to provide monthly 1-km resolution grids of total rainfall, mean air temperature, mean daily maximum air temperature, and mean daily minimum air temperature across New Zealand from 1910 to 2019. HOWNZ matches the best available temporal extent and spatial resolution of any open weather grids that include New Zealand, and is unique in providing associated spatial uncertainty in appropriate units of measurement. The HOWNZ weather and uncertainty grids capture the dynamic spatial and temporal nature of the monthly weather variables and the uncertainty associated with the interpolation. We also demonstrate how to quantify and visualise temporal trends across New Zealand that recognise the temporal and spatial variation of uncertainties in the HOWNZ data. The HOWNZ data is openly available at https://doi.org/10.7931/zmvz-xf30 (Etherington et al., 2021).
Highlights
Climatologies such as WorldClim2 (Fick and Hijmans, 2017) and Chelsa (Karger et al, 2017) provide spatial grids of climatic variables such as temperature and rainfall that have underpinned thousands of environmental and ecological studies
30 Meteorologists and climatologists are recognising the importance of implementing open access methodologies, as openly sharing data, source code, and knowledge provides exciting opportunities for scientific discovery
35 in remote areas and for earlier time periods. This challenge should not preclude the creation of historical weather data, if we accept that we cannot be consistently successful for all locations and dates and we prioritise providing weather data with associated uncertainty data
Summary
Climatologies such as WorldClim (Fick and Hijmans, 2017) and Chelsa (Karger et al, 2017) provide spatial grids of climatic variables such as temperature and rainfall that have underpinned thousands of environmental and ecological studies. In New Zealand there are limited open access options for national-scale weather grids (Table 1), and none of these meet all the currently optimal criteria amongst these open access options of spatial (≤ 1 km2) and temporal (monthly) resolution over the last century. Producing such historical weather data is challenging because weather station data are often sparse, especially. 55 HOWNZ is a new openly available history of temperature and rainfall weather in New Zealand that matches the best available spatial and temporal extent and resolution of any currently available open data and is unique in providing associated spatial uncertainty grids in appropriate units of measurement (Table 1). Available New Zealand climatology grids for each weather variable giving the average weather in each month for the period 1950-1980 at 100 m grid cell resolution (McCarthy et al, 2021;Leathwick et al, 2002) were reprojected and aggregated to 1-km grid cell resolution. 70
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