Time series of relative humidity, wet-bulb temperature, and dewpoint temperature at Kelburn and Masterton over the last 90 years.

NIWA has recently digitised daily wet- and dry-bulb temperature records for both Kelburn, Wellington and Masterton, Wairarapa sites back to 1929 and undertaken an analysis of these records and comparison with reanalysis products. This article presents key results of the analysis in the context of climate change and also the steps taken to account for site moves, complications around a plethora of daylight savings changes, and observing methods. Overall, there was a 0.7°C increase in dewpoint temperature (Td) averaged over all seasons with the strongest trend being an increase in winter, amounting to +1.7°C over 90 years at Kelburn, and +1.8°C at Masterton for the same period. Autumn also saw increasing trends at both locations whereas summer and spring saw smaller increases. Other points of interest were that January 2018 had the highest average Td values of any month in both the Kelburn and Wairarapa records while February 1998 was ranked third in the Kelburn record. Both 1998 and 2018 are tied for third-warmest years on record for Aotearoa New Zealand (dry-bulb air temperature). Despite the long-term upward trend, average Td values for February 1938 and February 1935 were ranked second- and tenth-highest respectively in the Kelburn record. February 1935 is also ranked eighth-highest in the Wairarapa record. Extreme high summer and autumn values of Td occurred in the 1930s where there was considerable yearto-year variability. Of the ten months with lowest average Td values, seven occurred in the 1930s and 1940s for Wellington. At Masterton, six were in the 1930s and all ten had occurred by 1972. [ABSTRACT FROM AUTHOR]