Estimating potential outdoor water consumption in private urban landscapes by coupling high-resolution image analysis, irrigation water needs and evaporation estimation in Spain

In the past two decades, the Spanish Mediterranean coast has experienced urban and demographic growth through the expansion of low-density residential areas characterized by ornamental gardens, swimming pools, and lawns. To determine the potential outdoor water demand, land cover data were mapped from high-resolution WorldView-2 imagery along a climatic gradient from Mallorca, in the Balearic Islands, to Andalusia in Spain. WorldView-2 imagery was analyzed by adopting object-based feature extraction to generate spatial information layers as additional input features (predictor variables) for supervised per-pixel classification. Swimming pools and gardens planted with turf grass, trees and shrubs were mapped automatically with high levels of overall accuracy, ranging from 88.98% to 96.13%. The resulting GIS (geographic information systems)-ready vector layer was used to calculate net irrigation requirements with the landscape coefficient method and to assess evaporative loss from swimming pools. The method and results can be used by urban planners, water managers, property owners and others to assess the implications of landscaping styles for water demand. Net irrigation requirements (April-September) range from 2335 m3/ha to 6330 m3/ha compared to 5400 m3/ha per year in irrigated agriculture in Spain. Per unit area, the same outdoor landscaping produces a 45.5% higher net irrigation requirement and 21.6% more evaporation from swimming pools along the climatic gradient. The combination of high-resolution image analysis and the landscape coefficient method captures the relevant information for the identification and quantification of outdoor water consumption in private urban landscapes.