Optimizing urban irrigation schemes for the trade-off between energy and water consumption

Irrigation of green spaces in cities helps to reduce thermal stress and building energy consumption in hot seasons, but requires an intricate balance between energy and water resource usage. While the objective for agricultural irrigation is focused on the yield of produces, urban irrigation needs a new paradigm. In this study, a cutting-edge urban canopy model is applied to assess the impact of a variety of controlled irrigation schemes for Phoenix. Results show that by increasing surface moisture availability for evapotranspiration, urban irrigation has a cooling effect on the built environment throughout the year. Maximum reduction in canyon air temperature can be more than 3°C in summer as compared to the condition without irrigation. Among all investigated schemes, the soil-temperature-controlled irrigation is the most efficient in reducing the annual building energy consumption and the total cost. The total annual saving depends on the controlling soil temperature for irrigation activation, and can be up to about $1.19 m^-2 wall area as compared to the current irrigation practice. In addition, the scheme can substantially enhance outdoor thermal comfort of pedestrians in summers.