This paper reports some of the first measurements of energy exchanges over an urban area in New Zealand. Christchurch has a population of about 350,000 and is located on the Canterbury Plains with a maritime climate, which is mild and moist, and is strongly influenced by the presence of the Southern Alps to the west and the Pacific Ocean to the east.
The eddy correlation method was used to measure the surface energy balance over the suburban neighbourhood of St. Albans for short periods during both summer and winter. As expected, the energy partitioning shows considerable variation between summer and winter. In summer, on a daily basis the sensible heat flux is the dominant heat sink followed by latent heat and storage. However, during daytime the storage flux can be considerable and may approach, or even exceed, the magnitude of the sensible heat flux. Evaporation is more variable on a day to day basis compared to sensible heat, and is influenced in part by residential water use, particularly irrigation.
In winter the small daily surplus of net radiation is partitioned mainly into storage, with some evaporation and a small sensible heat flux that may be directed either away from, or towards the surface depending largely on the synoptic conditions. Under strong inversion conditions which occur frequently in Christchurch during winter, the sensible heat flux may be directed towards the surface for many hours each day. Similarly under nor'west foehn events, sensible heat may also be directed towards the surface.
The results highlight the importance of seasonal and synoptic controls in energy partitioning at this location. In winter strong inversions have a significant impact on surface energetics, while in both winter and summer foehn events substantially alter energy partitioning.