Abstract
Indigenous tussock grasslands have been found to have increased water yield compared to other vegetation covers at many sites across Otago, New Zealand. The role of fog deposition in providing hydrological inputs to these ecosystems has been studied at various sites across Otago with varying results. One area that has lacked focus in these studies has been determining the synoptic-scale conditions that results in fog deposition. Therefore, this study aims to establish the hydroclimatology and significance of fog deposition at Swampy Summit, Dunedin. Fog deposition was measured using two passive-harp style fog collectors with differing lid sizes over a 405-day period, as well as rainfall using a standard tipping bucket rain gauge. Fog deposition over the study period totalled 1736.1 mm to the 1.2 m lid fog collector and 1524.8 mm to the 0.7 m lid fog collector, over. Fog deposition was much greater than rainfall of 940.2 mm for the same period. Fog events at Swampy Summit experienced a distinct NE:SW split in prevailing wind direction with 66% of all fog events with a modal wind direction of NE compared to 21% with a modal wind direction of SW. Kidson weather types were used to classify synoptic conditions during fog, rain and fog+rain events. HSE of the blocking regime was the most frequent Kidson weather type for fog events, which was distinctly different to that of rain and fog+rain events which had T and SW of the trough regime as the most frequent weather type during events, respectively. A combined approach of ERA5 Reanalysis IVT data and an automated atmospheric river (AR) detection technique was used to determine if there was AR influence for different event types. It was found that four of the top ten NE fog deposition events, and two of the top ten SW fog deposition events had AR influence; possibly the first study in the world to connect fog deposition to the influence of ARs. Overall, this thesis has provided new information about the local importance of fog as a hydrologic input and the role of ARs for New Zealand’s hydroclimatology, as well as establishing a more holistic understanding of the controls on fog deposition to indigenous tussock grasslands.