OBSERVATIONS AND MODELING OF SOIL MOISTURE IN URBAN PARKS: IMPLICATIONS FOR GROUNDWATER RECHARGE IN PHOENIX, ARIZONA

Outdoor water use in urban parks consists of a considerable portion of the water demands in the City of Phoenix. As a result, irrigated urban parks are artificial sources and pathways of incidental groundwater recharge and should be considered carefully in groundwater models to improve aquifer management practices in arid cities such as Phoenix, Arizona. Most urban parks consist of a mosaic of turf grass and trees which receive scheduled maintenance, fertilization and water application through either sprinkler or flood irrigation. Recent sustainability efforts in the City of Phoenix have focused on replacing traditional fertilization methods with the use of compost derived from residential green waste. In this study, we evaluate the effects that the application of compost has had on soil moisture profile observations in three urban parks with different irrigation systems. Each of the study parks has a control plot and two treatment sites with either a once per year or a twice per year compost applications in the fall or spring seasons. Additional observations are provided through a local network of rainfall gauges and weather stations, as well as the installation of an eddy covariance system. This preliminary assessment covers approximately a one-year study period, including the active period of turf grass growth and irrigation in the summer. We then utilize the observations to setup and test a soil water balance model (SWB) to simulate changes in relative soil moisture in response to irrigation, precipitation and evapotranspiration. The model includes a deep percolation term from the soil layer which is evaluated as a proxy for groundwater recharge in irrigated urban parks. By combining modeling and observations of climate-soil-vegetation processes, we provide guidance on incidental recharge rates that can be useful for sustainable aquifer management in Phoenix.