Understanding the impacts of anthropogenic processes on the Los Angeles Basin with an integrated high-resolution hydrologic model

Abstract:

The increasing importance of sustainable urban water use practices globally has motivated the creation of various conservation and management schemes. However, many of the operational and management models used to inform these policies do not simulate the hydrologic system holistically. Anthropogenic fluxes and changes to the hydrologic cycle are known to have significant and interacting impacts on the hydrologic system as a whole; however, only recently has the hydrologic community been able to quantify the effects and understand their behavior. At regional scales in humid cities, infrastructure leakage has an overwhelming impact on subsurface storage change. In semi-arid cities, both the large amount of water importation and the natural hydrometerological regime are particularly important drivers of land surface processes. This work seeks to understand the relative importance of land cover change, unmanaged infrastructure recharge, and urban irrigation on the hydrologic fluxes of urban semi-arid regions. To assess the impacts of these changes we utilize an integrated hydrologic model (ParFlow) coupled to a land surface model (CLM) to simulate Ballona Creek watershed and the underlying groundwater system in Los Angeles, CA. All simulations are conducted at a very high (30-m) spatial resolution over the watershed, a 388-km² (150 sq. mi.) domain, and modeled over a 2-year period at an hourly timestep. The following model simulations are used to study anthropogenic impacts to the semi-arid urban water cycle: (1) a “naturalized” hydrologic simulation with no anthropogenic inputs and no land-surface feedbacks; (2) a hydrologic simulation with current imperviousness levels; (3) a simulation with the inclusion of urban land use/land cover features to assess their impacts; (4) using the model developed in 3, we evaluate the impact of infrastructure leakage; (5) using the model developed in 3, we assess the effects of the urban irrigation flux; (6) finally, we simulate the full land surface and hydrologic system with both infrastructure leakage and urban irrigation included. This approach assesses the processes individually and provides an understanding of how the anthropogenic effects may interact.