As is typical with oceanic islands, the climate on Norfolk Island is more moderate than on mainland Australia. The highest summer temperature recorded is 28.4° and the lowest winter temperature 6.2° – frosts are unknown.
Many species of plant and animal are highly sensitive to small variations in temperature, rainfall, day length or other parameters, which trigger stages in their life cycle – germination of seeds, flowering, nesting behaviour, as the case may be. The critical thresholds differ for every species.
The Bureau of Meteorology has tabulated a range of parameters – rainfall, temperature, winds et cetera – and these are publicly accessible on its website; click here: http://www.bom.gov.au/climate/averages/tables/cw_200288.shtml. (After clicking on the link make sure to select “All available” data in the tool bar at the head of the table – otherwise it defaults to “Main statistics”). You can select “Plot” to graph the data. NIFFS thanks the Bureau’s onsite meteorologist Adam Jauczius for assistance in accessing these data.
Note to users of Firefox web browser
If you receive an error message like the following: “The Bureau of Meteorology website does not currently support connections via HTTPS”, change browser to Google Chrome. This is caused by a known bug in Firefox.
Cloud interception and its hydrological contribution to upland forest hydrology
An important paper co-written by Islanders Neil Taverner and Derek Greenwood along with the CSIRO water resource assessment team has reported that Norfolk Island pines and palms can add as much as 25% to measured rainfall by capturing moisture in clouds. A related finding is that the upwardly-angled branches and fronds of both pines and palms funnel water to the stems and then to the ground, contributing as much as 48% of total atmospheric inputs, far surpassing observations from cloud-affected ecosystems elsewhere, which typically record less than 10% contribution from stemflow. The paper was published in 2023 in the open access journal Hydrological Processes. McJannet, D., Marano, J., Petheram, C., Tavener, N., & Greenwood, D. (2023). Quantifying rainfall and cloud water interception in upland forests of Norfolk Island. Hydrological Processes, 37(7), e14945. https://doi.org/10.1002/hyp.14945.
Between 1915 and 2019 Norfolk Island had a mean annual rainfall of 1263 mm. Although rainfall on average has been spread throughout the year, historically the totals have been highest during the cooler months (between April and August).
Reductions in annual rainfall and changes to the seasonal patterns on Norfolk Island are consistent with broader patterns of observed global change. Notably there has been a decline in annual rainfall since about 1970, which manifested in recent decades as long runs of dry years:
There is strong agreement among 21 global climate models (~80%) that mean annual rainfall over Norfolk Island will decrease in future and that potential evaporation will increase (~90%):
CSIRO (2020). Norfolk Island Water Resource Assessment. A summary report. CSIRO, Australia.