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UCLA-led study discusses drought impacts on urban vegetation in coastal greater LA

A car drives by vegetation. (Christine Kao/Daily Bruin staff)

By Christine Kao

April 13, 2023 11:50 p.m.

A recent UCLA-led study revealed drought’s disproportionate impacts on urban vegetation in socioeconomically disadvantaged communities in the coastal greater Los Angeles area.

According to the study, lower-income neighborhoods, many of which have disproportionately large Black and Hispanic populations, have lost more greenness than affluent neighborhoods during dry periods. Urban vegetation helps cool a city space in the hot summer months, the study said, aiding in the prevention of heat-related illnesses and death.

The coastal greater LA area is a fitting place to study the impacts extreme heat has on different populations in the region, said geography professor Glen MacDonald, the study’s primary investigator. Alongside its Mediterranean climate, the region is characterized by economic and racial disparities that create conditions necessary for research, MacDonald added.

“We can talk about climate change, and we can talk about how it’s affecting important ecosystems and vegetation,” MacDonald said. “But we also have to ask the question: How is climate change affecting people, and is it an unequal effect?”

[Related: Campus Queries: Recent LA heat wave highlights climate change, thermal inequality]

The case study processed remote-sensing data from 2001 to 2020 across the region, where more than 10 million people reside and where garden species live alongside natural ones, according to the study. The research focuses on urban vegetation, including turfgrass, shrubs and trees. However, the paper excludes plants in the mountain areas of LA because human intervention doesn’t determine their survival to the same extent, said Chunyu Dong, associate professor at Sun Yat-sen University in China and lead author of the study, who was a postdoctoral researcher at UCLA at the time.

Tracing satellite images allowed researchers to see how different neighborhoods’ land surface temperatures and greenness changed throughout a 20-year period, said Thomas Gillespie, co-author of the study and professor of environmental science and engineering.

The research suggests vegetation in wealthier neighborhoods such as UCLA, broader Westwood and Beverly Hills is less vulnerable to drought, Dong said. Those who live in these neighborhoods have higher water use in dry periods, he said.

In contrast, urban plants degrade more severely in lower-income areas, such as in the cities of South LA, Dong said, as residents use less water compared to West LA.

“The correlation is very strong,” he said. “When we increase water use, the vegetation sensitivity also declines.”

[Related: UCLA study links extreme heat waves in Southern California to financial distress]

Vegetation dried out by droughts forfeits the ability to cool down urban landscapes, Dong said. In turn, land temperature increases and threatens the lasting vegetation, creating a vicious cycle that fails to protect the less green neighborhoods from heat, he added.

The study serves as evidence for the public to help understand how climate warming has been inordinately affecting LA’s communities of color and what changes may be necessary to alleviate the issue, Gillespie said.

The issue does not call for a short-term solution – a reason why researchers observe data that spans two decades, Gillespie said. Planting more trees that thrive in the Mediterranean climate is one way for LA to alleviate the consequences of climate change and excessive heat exposure, he added.

“If you had a chance to spend time in drought in an area where there are trees, I think you’d be happy,” Gillespie said. “If you were out in the sculpture garden where there’s grass, you’d be kind of OK. But what if you were in something like a parking lot?”

[Related: UCLA study highlights heat-based health hazards in unsheltered LA Metro bus stops]

Governments could set an example by cooling public streets with tree canopy and shade coverage, which may encourage private landowners who see the benefit to do the same, Gillespie added.

As the city’s temperature continues to rise, it’s important to maintain its green spaces to prevent health concerns associated with heat, MacDonald said.

“The city of Los Angeles, the county, the people of Los Angeles, the state have to see how we can avoid exacerbating environmental injustice,” MacDonald said. “We can’t allow these areas of communities of color, in particular, to suddenly see their vegetation disappearing as we get into a warmer and drier 21st century.”

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Christine Kao | Photographer
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