Water Balance of a Small Island Experiencing Climate Change

Small islands provide challenges to hydrological investigation, both in terms of the physical environment and available resources for hydrological monitoring. Furthermore, small islands are generally more vulnerable to natural disasters and water shortages for resident populations. Norfolk Island in the South-west Pacific, is typical in these respects, and recent water shortages have highlighted the lack of hydrological knowledge required to make informed decisions regarding water supply. Accordingly, a campaign of field measurements and analysis was conducted on Norfolk Island in the 2019-2020 period and these were compared to data from the 1970's and 1980's along with climate records to provide some insight into the behaviour and changes to the hydrology of the island over the last 50 years. Data indicates that a decline in rainfall across the 50 year water balance period (13%) combined with increased potential evapo-transpiration and changes to land cover have reduced recharge by 27%. Reduced recharge resulted in a significant decline in the groundwater potentiometric surface and runoff (reduced by around 57%). Examination of the water balance indicates that the majority (70-80%) of recharge across the 50 year period discharges to the ocean via cliff or submarine discharge.