Even as California grapples with the effects of an extremely wet winter, the threat of drought and heat lingers, especially for areas where vegetation is too sparse to blunt the dangers. The impacts are profound across these cityscapes, according to a new study that focuses specifically on Los Angeles, which also found they have a disproportionate effect on disadvantaged communities of color.
Areas now flush with green will again brown, rearing familiar hazards brought about by warming weather. And when urban vegetation – which plays a key part in keeping cities cool – grows parched and shrivels against cooking concrete, residents pay the price. Rising temperatures spike higher without greenery, spurring the cycle of drying and heating that makes landscapes even less hospitable for the remaining plants to thrive.
“This is one year in what’s been long-term slide toward a browning,” said Dr Glen MacDonald, a distinguished professor of geography at the University of California, Los Angeles, and co-author of the study, reflecting on the recent rains. “What happens the year after? If we have a dry winter and we have high temperatures and we begin to deplete those water resources – what are we going to see going forward?”
Across the urban core of the sprawling metropolis, a crisscross of freeway overhangs hug and swirl over swaths of pavement that bake streets and communities on hot days and nights. Vegetation in these already lightly landscaped areas is also faster to brown, researchers found. MacDonald said it has effects on mental and physical health that go beyond the heightened heat index.
Often exposed to higher levels of pollution, areas where people of color have historically called home bear the burden of both infrastructure and industry that continue to wreak havoc on health and environment. The highest temperatures are expected to increase by 5.4F on average across Los Angeles county, according to a 2021 climate vulnerability assessment, which will only accelerate the cycle.
MacDonald said researchers decided to look more deeply at urban vegetation and the role it plays. “We thought, let’s turn our gaze to where the majority of people are living – in the city,” he said. “We wanted to see what was happening to the vegetation that people are experiencing every day in their life and see what is happening with this warming and the droughts that we have experienced in the 21st century.”
Chunyu Dong, who headed the study as a UCLA postdoctoral researcher and is now a researcher at the Sun Yat-sen University School of Civil Engineering in China, said the work highlights an urgent policy question that needs answering as Los Angeles and other areas across the water-stressed west grapple with scarcity in the future.
“In our maps, you can see that neighborhoods in a broad area of south Los Angeles are the most impacted by the drought,” Dong said in a statement released with the study, noting that low-income communities of color were making the greatest sacrifices when water supplies are scarce.
The study zoomed in on areas across Los Angeles, extending into Orange county, and looked at both census-generated socioeconomic data and satellite-based data that reflected patterns of drought and photosynthesis. It found that affluent neighborhoods – the tree-lined cul-de-sacs in Beverly Hills, the beachside west and parklet-filled Pasadena – retained their green even when temperatures rose. Across the interior areas, where there are more pockets of poverty and pavement, desiccation was more apparent.
“If you look at the difference between drought years and non-drought years, it is communities of color in areas of Compton, Inglewood, South Central – they are the ones seeing the greatest loss of vegetation greenness,” MacDonald said, adding that this increases the heat in these areas when conditions are dry.
Trees are most helpful when it comes to cooling ground-level temperatures, according to the study, and keep things roughly 2F cooler with each additional 10% of tree cover. Shrubs have a lesser effect, lowering temperatures by 0.7F with 10% of cover. Grass, which grows and browns quickly, does little, the researchers found.
Los Angeles – and, more broadly, California and the rest of the west – will continue to face water stresses into the future, especially as the climate crisis pushes extremes at both ends of the hydrological spectrum. “We are facing real water stresses,” MacDonald said, emphasizing that important planning and policy decisions will need to take place to protect those most vulnerable to the impacts. “How can we strategize to keep some greenness – some nature – in Los Angeles?” he asked, adding: “What are we willing to give up?”
It’s a crucial question, and one that not only affects health and wellness but also the lifespans of those who dwell in concrete-covered urban areas. In a separate study, UCLA public health researchers have linked life expectancy to vegetation in Los Angeles county, with grave conclusions.
People in disadvantaged areas with less plant-cooling coverage – where about two-thirds of the county’s Latino and Black populations reside – live decades less on average than their more affluent neighbors who live in areas where tree canopies are plentiful. Those in southern Los Angeles communities, for example, have a median life expectancy of 77, while just 15 miles away in Beverly Hills residents’ life expectancy is in the 90s.
The study controlled for outside variables, including smoking and obesity, and found if tree canopy disparities were equalized, areas in need of more green could see boosts in lifespan of between 570,300 and 908,800 years collectively across their populations. Of them, more than 110,000 more years of life could be added for Black and Latino Angelenos alone.
“If policies are implemented where they are needed most, there could be a significant decrease in life expectancy disparities across Los Angeles,” Dr Michael Jerrett, professor of environmental health sciences at the UCLA Fielding School of Public Health and corresponding author of the study, said in a statement.
For his colleague MacDonald, the research indicates how urgent and important it will be to plan for a drier future in order to ensure more equitable access to essential greenery.
“Communities of color, disadvantaged communities – as is typical – are taking the biggest hit,” MacDonald said, noting that the study enabled him to focus more specifically on the environmental justice issues playing out in his own community.
“I hope it does spur us to ask these questions,” he added. “How much is our greenness worth, and what can we do to protect it?”
