Climatological and Anthropogenic Impacts on Contributions to Urban Groundwater in Los Angeles, California

The urban environment greatly alters the paths through which water travels to and from the groundwater system, including increases in imperviousness, groundwater pumping, artificial recharge, leaking infrastructure, and urban irrigation. Many of these pathways are poorly understood, especially in the context of the urban semi-arid environment. Moreover, seasonality, climatic phenomena, and climate change may have notable effects on the characteristics of these urban groundwater fluxes. To analyze the interplay between climate signals and anthropogenic effects, four major groundwater basins in the city of Los Angeles (Central, San Fernando Valley, West Coast, and Santa Monica Basins) are used as a case study. We create a spatially and temporally discretized dataset of the groundwater budget for the years 1990 through 2010 at a monthly time step utilizing observed groundwater level data from wells maintained by the Los Angeles County Department of Public Works (LADPW), precipitation measurements from PRISM, runoff from USGS and LADPW stream gauges in Ballona Creek and the Los Angeles River, evapotranspiration estimates using the Penman Monteith method, and artificial recharge values obtained for the relevant spreading grounds. The effects of various drought restrictions, El Niño/La Niña Southern Oscillation phenomena, and seasonality on the groundwater budget are assessed using correlation coefficients, a principal component analysis, and the Mann-Kendall trend test. Further, projections of the state of the urban semi-arid groundwater system are made with respect to future climate and urban water management scenarios. This study will create a more complete understanding of anthropogenic fluxes and climatic signal effects on urban groundwater and create an important dataset for future work.