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Colorado School of Mines (2019)

Anthropogenic Impacts on the Water and Energy Balance of an Urban Semi-Arid Environment

Reyes, Bryant

Titre : Anthropogenic Impacts on the Water and Energy Balance of an Urban Semi-Arid Environment

Auteur : Reyes, Bryant

Université de soutenance : Colorado School of Mines,

Grade : Doctor of Philosophy (PhD) 2019

As the world rapidly urbanizes, a grasp of water resources within an urban context becomes crucial to both the policy and scientific communities. Yet many of the operational and management models used to inform these policies lack vital parameterizations needed to simulate the hydrologic system holistically. Anthropogenic processes and changes to the hydrologic cycle caused by urbanization (land use change, denser building patterns, increases in imported water and water use, increased surface imperviousness, increased subsurface infrastructure, etc.) are known to have significant and interacting impacts on the hydrologic system as a whole ; only recently has the hydrologic community been able to quantify these effects and understand their behavior. The work presented here assesses the processes simulated by an integrated, coupled land surface and hydrologic model at various spatial scales in the urban domain. Throughout this work data pertaining to Ballona Creek watershed in Los Angeles, California is used in both model building and analysis. The watershed contains highly urbanized and diverse portions of the cities of Santa Monica and Los Angeles, along with more natural land surfaces in the northern portions of the watershed, with a wide range of urban land cover and land use scenarios in a semi-arid environment. We begin this work by utilizing two land cover datasets for the City of Los Angeles : (1) the National Land Cover Database (NLCD) dataset at a 30-m resolution ; and (2) an ultra-high-resolution dataset at a 0.6-m resolution. Various permutations and resolutions of the model are simulated for a spin-up and two-year study period. The impact of the highly organized, yet heterogeneous, land cover typical of the urban domain is shown to impact the runoff/runon process characteristics of these domains, creating variations in overland flow and evapotranspiration (ET). Spatial scaling land surface and hydrologic parameters creates systematic diurnal biases in the surface energy budget in contrast to the seasonal biases causes by lateral flow processes. In addition to creating land surface parameters for the widely used NLCD urban land covers, this work illustrates nonlinear issues of scale and resolution and improves understanding of how these processes affect the surface energy and hydrologic budgets. Next, remotely sensed observations of land surface temperature and land cover are paired with domestic water use data to assess the direct impact of outdoor water use. We find a decrease of up to 3.2 ± 0.02 Kelvin between low and high irrigation areas of similar land cover ; simulations are able to capture this difference but underestimate absolute values throughout. Model simulations show that irrigation timing has a small impact on ET and runoff and that relatively low irrigation volumes push the semi-arid urban environment of Ballona Creek into a sub-humid regime. Finally, we utilize a range of land surface and hydrologic models applied at a high spatial resolution (1-km) to quantify some of the deficiencies seen in the simulation of semi-arid urban environments and to provide a framework for future work in the field.

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Page publiée le 14 janvier 2020