"I just want to make a difference for the city I live in," mayoral candidate Claudia Sheinbaum Pardo says.

Hazel Cárdenas

Can this environmental engineer—poised to become mayor—fix Mexico City?

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MEXICO CITY—"Clau-dia! Clau-dia! Clau-dia!" The crowd swarms around the smiling woman, chanting her name as she makes her way from her car to the stage at a recent campaign rally in a ramshackle neighborhood of cinder block buildings. Voters jostle to clasp her hands, look in her eyes, and tell her about their troubles.

The enthusiasm still astonishes Claudia Sheinbaum Pardo. "It's like I'm an actress, or someone actually famous!" she says. Until 3 years ago, she worked quietly as an environmental engineer at the National Autonomous University of Mexico (UNAM) here. Now, with a 20-point lead in the polls ahead of the 1 July elections, she seems set to become mayor of this city of nearly 9 million people.

Sheinbaum Pardo considers herself a researcher first and foremost. Her work on energy science and engineering—with a focus on vehicle emissions and climate change mitigation—is respected both in Mexico and abroad, and she's a member of the Mexican Academy of Sciences and a former member of the United Nations Intergovernmental Panel on Climate Change (IPCC). Many say she's uniquely positioned to understand and tackle the myriad problems afflicting this megacity, especially its stuffed-to-the-gills public transportation, epic traffic snarls, and worsening water crisis. "I think she's one of the few people who are aware of the major challenges of the city," says David Bonilla, an economist who studies transportation at UNAM and the University of Oxford in the United Kingdom and has never collaborated with Sheinbaum Pardo. "I can't think of somebody as knowledgeable as her in public policy [in Mexico]."

Critics worry about Sheinbaum Pardo's close ties with Andrés Manuel López Obrador, a leftist populist and the leading candidate in Mexico's presidential election, also taking place on 1 July. She first entered government in 2000, when López Obrador was mayor of Mexico City and appointed her environmental minister. (They met through a family friend, and she shared his progressive politics.) When he founded the National Regeneration Movement in 2014, she followed him to the new party.

Critics liken López Obrador to the late Venezuelan President Hugo Chávez and warn he will weaken Mexico's economy by scaring away investment, but he remains wildly popular here. Sheinbaum Pardo speaks highly of his administrative experience and progressive policies. She acknowledges that voters here "see me as a reflection of him," which partially explains her own popularity.

Yet she has even deeper ties to science. Her mother is a chemist, now emerita at UNAM; her brother, a physicist, helped convince her to study physics as an undergraduate student at UNAM in the 1980s. She completed master's and doctorate degrees in energy engineering, also at UNAM. The combination prepared her well for policymaking, she says. "Training in physics makes you always look for the root causes. Why is something happening? That's fundamental for politics," she says. "And then engineering is much more focused on the ‘how.’ How can I solve it?"

Sheinbaum Pardo spent 4 years as a Ph.D. student at the Lawrence Berkeley National Laboratory in Berkeley, California, comparing energy consumption in Mexico and other industrialized countries. She "has always approached her academic research work with keen curiosity, intense motivation … and a commitment to use information and analysis to inform evidence-based public policy," says Berkeley Lab energy scientist Lynn Price, with whom she has collaborated. In 1995, Sheinbaum Pardo joined the faculty at UNAM's Institute of Engineering.

After she became Mexico City's environment minister 5 years later, she oversaw two major transportation projects: the introduction of the Metrobus, a rapid transit bus with dedicated lanes; and the construction of the second story of the Periférico, Mexico City's ring road. When López Obrador narrowly lost the 2006 presidential election, Sheinbaum Pardo returned to UNAM. She published in top journals, co-authored sections of IPCC's fourth and fifth assessment reports, and doubled down on researching what Adalberto Noyola Robles, a fellow UNAM environmental engineer, calls the "truly unimaginable" number of problems in Mexico City, which has a metropolitan population of more than 20 million people. She saw the city's water crisis up close when she re-entered city politics in 2015 as the president of Tlalpan, a southern city district where taps routinely run dry.

Now, Sheinbaum Pardo is making water and mobility centerpieces of her campaign. Mexico City occupies a former lake, drained by the Spanish during the colonial period. Today, urban sprawl has covered almost the entire former lakebed, and most of the city's water is pumped from beneath it. "We've overexploited the aquifer, and as a result, the city is sinking," Sheinbaum Pardo says.

The unstable ground makes earthquakes more dangerous; during the destructive temblor on 19 September 2017, an elementary school collapsed in Tlalpan. Previous administrations have postponed tackling the problem, says Noyola Robles, a water expert. "Claudia understands the issue. I think her proposals will be solid and feasible." She has proposed overhauling the distribution network to fix a plague of leaks, building treatment plants to recycle water, investigating sources of water outside the city, and subsidizing rainwater collection systems.

Mexico City also lags in public transportation. Those who can afford it buy cars; 70% of the city's greenhouse gas emissions come from vehicles, Sheinbaum Pardo says. She proposes investing in bus lines, light-rail trains, and even cable cars, while reducing use of overcrowded informal systems, such as collective vans; she also wants stricter emission standards for cars. Both her transportation and water plans, she says, aim to reduce inequality in access and services.

Sheinbaum Pardo's academic background comes through in her detail-heavy presentations and stump speeches. Competing candidates have called her "arrogant." Besides assailing her close ties to López Obrador, they point to the school collapse and increasingly visible drug crime in southern Mexico City as failings of her administration in Tlalpan. Still, a recent poll found that 40% of those surveyed planned to vote for her; the second and third place candidates didn't crack 20%.

Will Sheinbaum Pardo parlay her likely stint as mayor into a national political career? She won't say, but insists that she would be happy to return to her research at UNAM. She continues to advise a handful of graduate students, squeezing in the work on Sunday afternoons. "I'm not particularly attracted to a political career," she says. "I just want to make a difference for the city I live in."