Water requirements of urban landscape plants: A comparison of three factor-based approaches

The majority of urban water supplies for irrigation are used to maintain vegetation health, aesthetic appearance and municipal amenity. It is common to estimate the water requirements of agricultural crops but not those of urban vegetation. Unlike agricultural crops, landscape plantings are usually composed of a mixture of trees, shrubs and turf grasses with different species and water demands. This research was conducted in Veale Gardens within the Adelaide Parklands in South Australia. In situ climatic and vegetation data were collected and irrigation monitoring data were provided by the local water authority. Three adjustment factors for reference evapotranspiration were estimated and used to compare predicted and actual irrigation rates. The adjustment factors used were a landscape plant coefficient for the Water Use Classifications of Landscape Species (WUCOLS) method, a plant factor for the plant factor (PF) method and a crop stress factor for the Irrigated Public Open Space (IPOS) method. Considering an irrigation efficiency of 70% resulted in close estimation of gross irrigation rates using the WUCOLS method. The results showed that the IPOS method led to the lowest gross irrigation estimate in contrast to the WUCOLS method which produced the highest estimation. Since the acceptable aesthetic levels were achieved by an annual application of 770 mm of irrigation water, the results confirm that the WUCOLS method produced the best estimation of urban vegetation water requirements for the study area.