The blue water footprint of urban green spaces: An example for Adelaide, Australia

The development of ‘greening’ cities introduces an uneasy tension between more green spaces and the increased use of scarce blue water resources to maintain this greenness, particularly in dry regions. This paper presents the first estimate of the blue water footprint (WF) of urban greenery. We estimated total water consumption of a 10-hectare parkland in Adelaide, South Australia. Evapotranspiration of the urban vegetation was estimated by monitoring soil water inflows, outflows, and storage changes at an experimental site representing different species, microclimates, and plant densities, the most critical parameters affecting water use. The total WF was estimated at 11,140 m3/ha per year, 59% from blue water (irrigation), and 41% from green water (rainwater), with the highest water consumption in summer. The dependency on blue water resources for maintaining the greenery varied from 49% in October to 67% in March. Even in the wet period of the year, there was a significant blue WF. Given the lack of blue water resources to allocate for further greening the city in an arid environment, we suggest an integrated adaptive management strategy to maintain available greenery and expand green spaces with a minimum of extra pressure on blue water resources.