Using land cover maps, the increase of urban and built-up land-cover in the Houston Metropolitan Area was measured. It was found that the area of urban and built-up land cover increased by more than 20% in the last two decades. By comparing land cover maps from 2001 and 2019, a substantial increase in urban areas along the southwestern part of the city can be seen.
Andrew Blackford, UAH Earth System Science Center (ESSC).
Trent Cowan, UAH Earth System Science Center (ESSC).
Researchers at The University of Alabama in Huntsville (UAH) have employed a NASA open-source program to reveal that disadvantaged populations may be subject to greater heat stress and poor air quality. For this study, the researchers focused on Houston, Tex. Combining changes in heat and land cover with Houston's socioeconomic data demonstrated that economically disadvantaged populations are subject to greater heat stress. For example, in 2020, areas in Harris County with the lowest poverty levels – less than 5% of the county’s population – were an average of 2°F (1°C) cooler than areas with higher poverty levels. While the researchers focused on the Houston metropolitan area, the findings are applicable to cities across the United States.
Andrew Blackford and Trent Cowan, a Ph.D. candidate and master’s student respectively, are both in the Department of Atmospheric and Earth Science at UAH, a part of The University of Alabama System, where they are advised by Dr. Udaysankar Nair. The researchers’ findings began as a data story on the NASA Visualization, Exploration and Data Analysis (VEDA) dashboard, a scalable, interactive system for science data that is part of the NASA VEDA project.
“This type of research is a very timely topic, as numerous cities around the world are expanding their urban footprints in similar fashion to Houston,” Blackford explains. “Houston is one of the best locations for this study due to the rapid amount of urban growth that has occurred in several directions out from the center of the city. Over the past 20 years, Houston has urbanized the equivalent of two times the land coverage of New York City.”
The study examined data from the first two decades of the 21st century, analyzing the expansion of urban land cover, urban heat island (UHI) and urban pollution island (UPI) data in the Houston metropolitan area (HMA). The project found that urban land cover within the HMA increased by 1,345.09 square kilometers, over the period, accompanied by a 74% expansion of the urban heat island. The findings were obtained from land cover classifications derived from NASA Landsat and land/aerosol products from NASA's Moderate Resolution Imaging Spectroradiometer.
As with temperature, an analysis of 2020 vegetation data showed a significant difference based on levels of poverty. Areas with the lowest poverty levels (again, less than 5%) have approximately 6% more vegetation than areas with the highest poverty levels (greater than 20%). The study also notes that the Clean Air Act’s efficacy is locally diminished by Houston’s urban pollution island. At the same time, poorer populations may face decreased access to green spaces, where even small increases or decreases in vegetation can affect how residents experience heat, the researchers report.
“Further, the UPI showed localized enhancement in particulate pollution caused by increases in vehicular traffic,” the researchers note. “Our analysis found that the social vulnerability of the HMA urban regions increased during the study period. Overall, we found that the urban growth resulted in a synergy of UHI, UPI and social vulnerability, causing an increase in environmental inequalities within the HMA.”
The VEDA program, in alignment with NASA's Transform to Open Science (TOPS) initiative, provides an interactive visual interface for data storytelling. Open source code provided by VEDA allows for collaboration and transparency. The VEDA dashboard supports a number of capabilities, including sharing and interacting with datasets and their respective stories. Through visualizations, trend analyses and comparative analyses of datasets, users can explore the applications and implications of those data. The dashboard facilitates the use of NASA’s Earth science data and enables faster science, while the TOPS initiative seeks to transform agencies, organizations and communities to an inclusive culture of open science.
“Being able to utilize VEDA resources and build data stories to expand into this publication was instrumental in encouraging efficiency with preparing the publication for release and having NASA civil servants mentor me as I took on my first lead author publication,” Blackford says.
The United Nations projects that by 2050, 87% of the American population and 68% of the world population will live in urbanized locations. Looking to the future of this research, Blackford points out that “the same methodology can be applied to any major city. Results may not be as dramatic as Houston's due to several factors, such as the rate and amount of urbanization, geographic location and prior land use-land cover in areas that have since been urbanized, but regardless of the city's background there can still be certain approaches we took in this study that can be utilized elsewhere.”
Kristina Hendrix
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Credit: Courtesy NASA VEDA
Caption: Using land cover maps, the increase of urban and built-up land-cover in the Houston Metropolitan Area was measured. It was found that the area of urban and built-up land cover increased by more than 20% in the last two decades. By comparing land cover maps from 2001 and 2019, a substantial increase in urban areas along the southwestern part of the city can be seen.
Credit: Michael Mercier / UAH
Caption: Andrew Blackford, UAH Earth System Science Center (ESSC).
Credit: Courtesy Trent Cowan
Caption: Trent Cowan, UAH Earth System Science Center (ESSC).
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