Temperature and Rainfall Changes Observed at Weather Stations Over New Zealand

Abstract

While Global Climate Change has been increasingly accepted in recent decades, the complex interplay of processes in the atmosphere makes changes in temperature and rainfall regionally variable. The degree of reliability from daily observations has been the subject of much debate. Due to these reason, only a limited amount of stations or short time periods have been analyzed over New Zealand. This study have undertaken to homogenize and validate 2450 (600) climate stations for rainfall (temperature) for the period 1911-2019 from New Zealand’s national climate database. We aim to extensively characterize regional changes in the mean temperature and rainfall events over New Zealand, in addition to the frequency, duration and intensity of extreme climate phenomena. Our analysis from the long time period show significant evidence of increasing mean temperature and rainfall (up to 2.5 °Ccentury⁻¹ for at-least 90% of the stations and up to 26%century⁻¹ for at-least 25% of the stations respectively, spread evenly throughout NZ). Similarly, extreme hot temperature and extreme wet rainfall demonstrate increasing trends and consistently with global warming, extreme cold temperature exhibit decreasing trends. NZ temperature experiences decadal variabilities, however, warming trends are consistently observed. In contrast, NZ rainfall exhibits much larger degree of variability, with fluctuating trend directions, although, enhanced orographic rainfall are consistently observed. The relationship that the ‘wet getting wetter and dry getting drier’ were observed from the mean and extreme intensity of rainfall. The equivalent, ‘hot getting hotter’ for daily maximum temperature was also observed. We find that certain Large Scale Modes of Circulations have discernible contributions towards New Zealand’s climate. Particularly, the Southern Annular Mode can contribute up to 50-80%, but only for certain locations. Whereas the El- Niño Southern Oscillation contributes 10%. The homogenized data provides reliable results in understanding temperature and rainfall over New Zealand, but ultimately on observational climate change.