Urban Landscape Irrigation and the Future of Sustainable Cities

Abstract The magnitude and fate of irrigation water are important variables in both urban hydrology and sustainability science. Studies of urban irrigation are relatively few compared to agricultural irrigation. Yet, a growing number of ecohydrologic measurements in cities are revealing general trends in drivers of irrigation practices and their impacts on urban water budgets. Urban irrigation rates are strongly influenced by social factors and highly variable due to intra‐ and inter‐urban land use heterogeneity, climate conditions, water pricing, landscaping norms and behaviors, and water management policies. Irrigation is lost from landscapes through evapotranspiration (ET), surface runoff, or groundwater recharge. Of these fluxes, ET has been the most well‐studied. ET is more strongly driven by climatic variables than irrigation rates, particularly vapor pressure deficit for rough, open canopies and incoming radiation for smooth canopies such as turfgrass lawns, which tend to have much higher ET rates than urban trees. Recent measurements have shown a saturating relationship between ET and irrigation, with many land owners irrigating their yards well in excess of maximum rates of ET. Although urban landscapes can mitigate stormwater runoff, excess irrigation contributes to urban runoff and groundwater, which may exacerbate water quality problems when contaminated with fertilizers or pesticides. Overall, many opportunities still exist to improve the efficiency of urban irrigation while maintaining ecosystem services of irrigated landscapes. By filling critical data and mechanistic gaps, socioecohydrologic studies of irrigated cities can greatly support urban water sustainability.