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Description
Rapid urbanization and population growth occurring in the cities of South Western

United States have led to significant modifications in its environment at local and

regional scales. Both local and regional climate changes are expected to have massive

impacts on the hydrology of Colorado River Basin (CRB), thereby accentuating the need

of study of

Rapid urbanization and population growth occurring in the cities of South Western

United States have led to significant modifications in its environment at local and

regional scales. Both local and regional climate changes are expected to have massive

impacts on the hydrology of Colorado River Basin (CRB), thereby accentuating the need

of study of hydro-climatic impacts on water resource management in this region. This

thesis is devoted to understanding the impact of land use and land cover (LULC) changes

on the local and regional hydroclimate, with the goal to address urban planning issues

and provide guidance for sustainable development.

In this study, three densely populated urban areas, viz. Phoenix, Las Vegas and

Denver in the CRB are selected to capture the various dimensions of the impacts of land

use changes on the regional hydroclimate in the entire CRB. Weather Research and

Forecast (WRF) model, incorporating the latest urban modeling system, is adopted for

regional climate modeling. Two major types of urban LULC changes are studied in this

Thesis: (1) incorporation of urban trees with their radiative cooling effect, tested in

Phoenix metropolitan, and (2) projected urban expansion in 2100 obtained from

Integrated Climate and Land Use Scenarios (ICLUS) developed by the US

Environmental Protection Agency for all three cities.

The results demonstrated prominent nocturnal cooling effect of due to radiative

shading effect of the urban trees for Phoenix reducing urban surface and air temperature

by about 2~9 °C and 1~5 °C respectively and increasing relative humidity by 10~20%

during an mean diurnal cycle. The simulations of urban growth in CRB demonstratedii

nocturnal warming of about 0.36 °C, 1.07 °C, and 0.94 °C 2m-air temperature and

comparatively insignificant change in daytime temperature, with the thermal environment

of Denver being the most sensitive the urban growth. The urban hydroclimatic study

carried out in the thesis assists in identifying both context specific and generalizable

relationships, patterns among the cities, and is expected to facilitate urban planning and

management in local (cities) and regional scales.
ContributorsUpreti, Ruby (Author) / Wang, Zhihua (Thesis advisor) / Vivoni, Enrique R. (Committee member) / Mascaro, Giuseppe (Committee member) / White, Dave (Committee member) / Arizona State University (Publisher)
Created2017
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Description
The world has been continuously urbanized and is currently accommodating more than half of the human population. Despite that cities cover only less than 3% of the Earth’s land surface area, they emerged as hotspots of anthropogenic activities. The drastic land use changes, complex three-dimensional urban terrain, and anthropogenic heat

The world has been continuously urbanized and is currently accommodating more than half of the human population. Despite that cities cover only less than 3% of the Earth’s land surface area, they emerged as hotspots of anthropogenic activities. The drastic land use changes, complex three-dimensional urban terrain, and anthropogenic heat emissions alter the transport of mass, heat, and momentum, especially within the urban canopy layer. As a result, cities are confronting numerous environmental challenges such as exacerbated heat stress, frequent air pollution episodes, degraded water quality, increased energy consumption and water use, etc. Green infrastructure, in particular, the use of trees, has been proved as an effective means to improve urban environmental quality in existing research. However, quantitative evaluations of the efficacy of urban trees in regulating air quality and thermal environment are impeded by the limited temporal and spatial scales in field measurements and the deficiency in numerical models.

This dissertation aims to advance the simulation of realistic functions of urban trees in both microscale and mesoscale numerical models, and to systematically evaluate the cooling capacity of urban trees under thermal extremes. A coupled large-eddy simulation–Lagrangian stochastic modeling framework is developed for the complex urban environment and is used to evaluate the impact of urban trees on traffic-emitted pollutants. Results show that the model is robust for capturing the dispersion of urban air pollutants and how strategically implemented urban trees can reduce vehicle-emitted pollution. To evaluate the impact of urban trees on the thermal environment, the radiative shading effect of trees are incorporated into the integrated Weather Research and Forecasting model. The mesoscale model is used to simulate shade trees over the contiguous United States, suggesting how the efficacy of urban trees depends on geographical and climatic conditions. The cooling capacity of urban trees and its response to thermal extremes are then quantified for major metropolitans in the United States based on remotely sensed data. It is found the nonlinear temperature dependence of the cooling capacity remarkably resembles the thermodynamic liquid-water–vapor equilibrium. The findings in this dissertation are informative to evaluating and implementing urban trees, and green infrastructure in large, as an important urban planning strategy to cope with emergent global environmental changes.
ContributorsWang, Chenghao (Author) / Wang, Zhihua (Thesis advisor) / Myint, Soe W. (Committee member) / Huang, Huei-Ping (Committee member) / Mascaro, Giuseppe (Committee member) / Arizona State University (Publisher)
Created2019