PNNL

Abstract

The interactions between population growth, change in urban morphology, and water demand have important implications for the evolution of water demand in urban regions. This is increasingly relevant as growing urban populations contribute to growing regional water demand and multisectoral competition for limited water resources. Outdoor water use for irrigation comprises a significant fraction of urban water demand but it is not well understood how long-term changes in urban morphology could influence outdoor water demand. To investigate this, we use spatially explicit projections of urban land development intensity (fraction impervious area) generated at 30-m resolution from a urban growth model for the Los Angeles region. Recent historical data on water use and high resolution landcover data are used to establish relationships between green area, urban development intensity, and outdoor water demand. These relationships are then used to project outdoor and total water demand in 2100 using the urban growth model outputs. We consider two different population scenarios that are informed by shared socioeconomic pathway (SSP) projections for the region (SSP3 and SSP5), and three scenarios of urban development intensification, a parameter in the urban growth model that controls the sensitivity of urban development to population growth. We find that water demand growth in land constrained regions like Los Angeles significantly deviates from population growth even with the conservative assumption that indoor per capita demands remain unchanged from present amounts. Our analysis is resolved for over 80 water providers in the region and highlights diverse demand responses influenced by initial urban form and water demand attributes. Compared to previous studies, our work is unique in coherently linking high resolution SSP population scenarios, urban land cover evolution, and urban water demand projections, demonstrating the approach for the Los Angeles region – the largest population center in the western United States.