When Tianmei Wang, ’17 MS, ’22 PhD, traveled home to China in 2019 to test whether remote sensing technology could detect arsenic levels in rice paddies, she had plenty of willing assistants: Her father and an aunt and uncle volunteered to help as she familiarized herself with the drone she was using to photograph the rice fields; one of her relatives owned the rice paddy that served as the control of her study because of its low levels of arsenic.
“They helped with some of the sampling” before the experiment started in earnest, explains Wang, a recent recipient of a graduate student fellowship at the Stanford King Center on Global Development.
Wang’s relatives own and operate small family farms. But the question Wang is studying—how the coupled effects of climate change and increasing arsenic levels will affect rice yields in the future—has implications for the entire world. Rice is a staple for more than half the global population. Arsenic, which is naturally occurring in some locations and caused by pesticide use in others, is highly toxic; long-term exposure can lead to skin lesions and cancer.
“It is so crucial to look into this problem,” Wang says. “We want to figure out ways to reduce the influence of this coupled impact on rice.”
Earth System Science Professor David Lobell, a King Center faculty affiliate who sits on Wang’s thesis committee, said Wang’s research examines “a really important health problem.”
“Tianmei’s work is aiming to pinpoint where the problems are, so that we can develop solutions that aren’t super expensive to deploy,” Lobell said. “It’s a tough, technical problem. But tough problems with a high societal payoff are exactly the type of projects that Stanford students should be tackling.”
Wang’s interest in agriculture dates back to her childhood; she grew up in part on her grandparents’ small, self-sufficient family farm, which included a rice paddy. In high school and at Shanghai Jiao Tong University, she participated in Model UN, discussing and debating environmental pollution issues. After earning her BSE in environmental science and engineering, Wang came to Stanford, earning a master’s degree in civil and environmental engineering in 2017. As a PhD student, she focuses on sustainable agriculture, with an emphasis on improving crop yields and mitigating toxins under a changing climate.
“I’m interested in food security, the quality of food, and soil science,” Wang says.
Starting in 2016, Wang worked with Marie Muehe, who was an Earth System Science postdoctoral fellow and is now a Helmholtz Young Investigator Group Leader at the Helmholtz Center for Environmental Research (UFZ) in Germany; King Center Faculty Affiliate and Professor of Earth System Science Scott Fendorf, who is Wang’s advisor; and two others on an experiment, published in Nature Communications, that found that rice grain yields decrease by 40 percent with increased arsenic levels and the higher temperatures and carbon dioxide levels associated with climate change. The researchers found that a shift in climatic conditions alone resulted in a yield loss of 16 percent, which is consistent with other studies.
The team notes that their results might be magnified because their rice was grown in pots with restricted roots and flood water rather than fields with more dynamic water flow and root growth, but the implications are clear:
“With more than half the world’s population relying on rice for substance, decreased rice yields and grain quality will have a devastating impact on human health, especially in developing countries,” Wang wrote in a King Center report after her trip to China.
One problem Wang hopes to solve is that most regions do not have reliable maps that show arsenic distribution in soil. Using remote sensing technology, Wang aims to develop a model that will allow farmers to assess arsenic levels and—hopefully—mitigate them through water management or other agricultural practices. With funding from the Stanford King Center on Global Development, she was able to travel to China to test the technology at multiple sampling sites in Hunan Province. She plans to return to China as soon as she can to continue her research.
“Our hypothesis is that since arsenic is a heavy metalloid, it will alter the physiological impact of the rice plants,” she says. “We’re hoping to have a kind of prediction map to identify the most vulnerable regions that are susceptible to the coupled impacts of climate change and soil arsenic.”
Wang’s other research examines how different rice varieties respond to the effects of climate change and increasing arsenic levels. She has found that the effects of arsenic are even more detrimental under extreme heat conditions, which are more common now around the world. At around 40 degrees Celsius, a majority of the panicles—the top part of the rice plant—are empty husks rather than filled grains.
“Above that critical temperature, the rice barely produced any grains,” Wang says. “With climate extremes, we will see that more often.”
In addition to the King Center funding that allowed her to conduct remote sensing experiments in China, Wang says she has benefited from the mentorship and guidance of Fendorf and Lobell.
Wang plans to continue her field research in the future and, eventually, to partner with policymakers and rice farming communities to learn how to mitigate the effects of arsenic and higher temperatures and carbon dioxide levels. Possible solutions include soil amendments; development of a rice breed that is resistant to both arsenic and the effects of high temperatures; and better water management practices.
“We want to bridge science and government to see how best to address this problem,” she says. “And, of course, for people around the globe to see climate change as a pressing issue and to react.”