A Case Study: Urban Heat Islands in Las Vegas, Nevada
Understanding Urbanization Impacts on Urban Warming
Motivation
The constant advancement of urbanization comes with many challenges, among which the emergence of the urban heat island (UHI) effect is significant. This phenomenon is characterized by the temperature in city centers being noticeably higher than in the surrounding rural areas. As the city expands, the increasing prevalence of concrete and asphalt replaces the natural landscape, thereby altering the region's thermal dynamics. The motivation for this study stems from an urgent need to understand the complex relationship between urbanization and the severity of UHI. Against the backdrop of urban growth, comprehending the driving factors of UHI is crucial for alleviating its effects and bolstering the resilience of urban ecosystems.
Objectives
- Exploring the urbanization in study area: the city of Las Vegas, Navada.
2. Examine the Human Factors Impacts on UHI under the context of urbanization.
Methods
Urbanization
The City of Las Vegas
The City of Las Vegas is a subtropical desert city located within the Greater Mojave Desert. As the most populous city in Nevada, Las Vegas has undergone rapid urban expansion, evolving from a small railway town at the beginning of the 20th century into a globally recognized center for entertainment and gambling.
Population growth is a primary driver of urban expansion. With the rapid increase in population comes an increased demand for housing, commercial facilities, and infrastructure, leading to the expansion of the city into undeveloped surrounding areas. Over the past two decades, there has been a significant population increase, continuing an upward trend, making population growth as one of the inevitable consequences of urban expansion. This might mean that an increasing number of people will directly affect the worsening of the heat island effect.
The population of Las Vegas has grown significantly since the 1960s, increasing from 273,000 people in 1972 to 2,904,079 in 2023. Since the launch of the first Landsat satellite, this number has increased by over 700%.
This study focuses on the period from 2001 to 2021, a span of 20 years during which Las Vegas experienced substantial urbanization and rapid change. The urban area expanded by an average of 55 square kilometers per year, with a population growth rate as high as 101.6%. During this time, the urban population surged, city boundaries rapidly expanded, and new residential and commercial areas continually emerged.
Urban Sprawl from 2001 to 2021
Las Vegas urban expansion is closely linked to changes in land cover, with alterations in land use during urbanization directly affecting the city's ecosystems and the living environment of its residents. therefore, land information will be extracted from satellite imagery data, and land cover classifications will be obtained through supervised classification methods to examine land use changes from 2001 to 2021.
In this section, we will identify the process of urban expansion in Las Vegas through qualitative observation of land classification. The pink areas in the map represent developed land; from 2001 to 2021, we can see a significant increase in pink areas, indicating notable urban expansion. This expansion may include new residential areas, commercial centers, industrial parks, and the construction of infrastructure such as roads and public facilities. The green areas represent vegetation cover, which, as observed from these images, has decreased overall with the expansion of urban land, reflecting a shift from natural ecosystems to artificial environments that may disrupt ecological balance.
To more clearly see which land type is transformed, we can observe the specific process of land change. The orange areas represent land that has been converted to developed urban land, which has significantly increased from 2001 to 2021, indicating rapid expansion of urban construction land. In the images from 2001 to 2011, we can see that the orange areas are mainly concentrated on the existing urban fringe, indicating that urban expansion is developing outward from the city center. In the images from 2011 to 2021, the orange areas are more widespread, indicating an acceleration in the pace of urban expansion, with new development areas appearing farther beyond the original city boundaries. It can be seen that the reduction of green vegetation areas and the increase in developed land, shows that with the progress of urbanization, natural land cover is being transformed into urban land. The spatial characteristics of Las Vegas's urban expansion show patchy and scattered development, which may be related to specific residential developments, commercial projects, or industrial parks.
Impervious Surface Change
Urban expansion brings an increase in impervious surfaces such as building roofs, roads, and sidewalks. These surfaces reduce the infiltration of rainwater and the evaporation of soil moisture, diminishing the natural cooling effect of the ground.
Land Surface Temperature
By examining areas with severe land surface temperatures in 2001 and 2021 and cross-referencing these with urban remote sensing imagery and land classification maps is an effective method to identify specific area types contributing to the UHI effect.
Land Surface Temperature Comparison between 2001 and 2021
Roof warehouses in Las Vegas
The imagery provides a clear and detailed picture of the thermal landscape across Las Vegas. It's evident that the vast industrial zones, especially those featuring buildings with roofing materials, are major accumulators of heat. In the areas around the industrial zones, you can see the heat increase. It just goes to show how much our buildings and roads can turn up the surface temperature.
Green Space in Las Vegas
In above map, the urban layout reveals distinct thermal patterns. Densely built-up neighborhoods and industrial sectors appear in warmer shades, indicating higher surface temperatures in these areas. Conversely, green areas such as parks or undeveloped land exhibit cooler temperatures, a testament to vegetation's natural cooling effect through transpiration.
Bodies of water, marked by blue patches, are evident thermal regulators, often imparting a cooling influence on their immediate surroundings.
The reasons for these surface temperature variations are multifaceted:
- Roofing materials in darker hues attract more solar energy, raising the temperatures of the buildings and the surrounding air.
- Land use plays a role, where artificial surfaces like parking lots and roads retain heat more effectively than natural landscapes.
- Vegetation acts as a natural coolant, with trees and plants providing shade and releasing moisture, mitigating the urban heat island effect.
- Water bodies, through conductive and evaporative cooling, function as local coolants.
Limitations and Challenges
Performing land surface temperature (LST) analysis without quantitative data poses limitations such as subjective interpretation, lack of precision in assessing temperature changes, inability to evaluate the interactions between contributing factors, and insufficient support for evidence-based policymaking. Quantitative analyses are crucial for addressing these issues, especially regarding the impact of population volume increase, building density, and the decrease in street tree density. By statistically correlating population density with LST variations, the specific effects of increased building footprints and heights can be measured, and the significance of tree cover in mitigating urban heat islands can be precisely evaluated. Such data-driven insights are essential for informed urban planning and effective environmental management strategies.
References
Acknowledgement
I want to express my sincere gratitude to Vicky Tam, my instructor, and my classmates for the invaluable guidance and support provided throughout this journey. Your assistance, insights, and dedication have been deeply appreciated.
