Rodríguez-Iturbe, the James S. McDonnell Distinguished University Professor of Civil and Environmental Engineering and the Princeton Environmental Institute, Emeritus, was among the premiere hydrologists of his generation. A recipient of the Stockholm Water Prize and the American Geophysical Union’s Bowie Medal, Rodríguez-Iturbe conducted pioneering research in several areas of hydrology during his career.

“Ignacio was generally considered to be the best hydrologist in the world, and we were incredibly fortunate to have him with us here at Princeton for 17 years,” said Michael Celia, the Theodora Shelton Pitney Professor of Environmental Studies and Professor of Civil and Environmental Engineering at Princeton.

Celia said Rodríguez-Iturbe possessed an unerring eye for the most critical aspect of scientific questions. The ability to perceive the heart of the problem led him to guide research teams to breakthroughs in widely varying areas.

“One of his most distinguishing characteristics was his ability to cross over into different disciplines,” Celia said. “He had a depth of intellect that allowed him to do it and a deep, innate curiosity that motivated him to do it.”

Rodríguez-Iturbe’s early work focused on the processes by which water moves through Earth’s connected systems, often focusing on extremes. Early findings included a paper describing how landscapes collect water to produce flooding and another creating an optimal way to measure rainfall in a given area. Both problems were critical for a greater understanding of water’s role in the environment, and both were notoriously difficult to solve.

In his early work, and throughout his career, colleagues said Rodríguez-Iturbe demonstrated the ability to see the essence of a problem and reflect it elegantly in mathematics.

“He had the ability to hit the sweet spot between simplicity and complexity,” Celia said.

He followed early papers with research that grabbed the attention of the wider world. Working with Andrea Rinaldo, a professor at EPFL in Switzerland, Rodríguez-Iturbe published “Fractal River Basins: Chance and Self-organization.” The 1997 book described the mathematics behind the branching forms taken by river basins and showed it could be applied universally. The work was taken up beyond hydrology, with applications in physics and other areas of science.

“The river network in Princeton, the Millstone, the Stony Brook, is very similar, statistically, to the Amazon or the Congo,” said Amilcare Porporato, the Thomas J. Wu ’94 Professor of Civil and Environmental Engineering and the High Meadows Environmental Institute (HMEI). “It’s a matter of changing scales, but it’s the same story. This was a very big discovery. They were able to come up with universal laws.”

The next major breakthrough improved science’s understanding of the relationship between water systems and their surrounding environments. Written with Porporato, Rodríguez-Iturbe’s 2004 book, “Ecohydrology of Water-controlled Ecosystems,” became one of the foundational texts of the new discipline of ecohydrology. The field treated the interplay among plants, soil and water in a quantitative fashion and described how each element affected the others and eventually shaped the ecosystem.

“Without water, there is no life,” Porporato said. “But without plants, without the microbiology in soils, there is no hydrology as we know it.”

Rodríguez-Iturbe’s research also extended to the economics of water use. Carole Dalin, who earned a Ph.D. from Princeton in 2014, worked with Rodríguez-Iturbe and his longtime collaborator Rinaldo on a network analysis of the global “virtual water trade.”

“Similar to the carbon footprint, we were looking at the water footprint of agricultural crops. The innovation was to apply network theory techniques to study the virtual water trade between countries — expressing the flows of food commodities in volumes of water consumed instead of dollars or tons of product,” said Dalin, now an associate professor in sustainable food systems at University College London and a researcher at the Ecole Normale Supérieure in Paris.

The study showed that the volume of water associated with global food trade had more than doubled from 1986 to 2007, and revealed shifts leading to water savings, but in some cases accompanied by environmental tradeoffs such as deforestation. The work led her to a broader exploration of the food trade’s environmental impacts, and launched her research career, said Dalin.

After transferring to emeritus status at Princeton in 2016 and moving to Texas A&M University, Rodríguez-Iturbe continued to collaborate with Princeton colleagues. In 2019, he co-wrote a paper with Simon Levin, Princeton’s James S. McDonnell Distinguished University Professor in Ecology and Evolutionary Biology, that analyzed tree cluster patterns on the African savannah. The patterns, challenging to explain mathematically, are related to soil moisture and can be used for conservation efforts.

With his booming voice and cheerful personality, Rodríguez-Iturbe’s presence was felt well beyond the world of research. Elie Bou-Zeid, a professor of civil and environmental engineering, said that although Rodríguez-Iturbe was a giant in his field, he remained a very modest person.

“Despite being very busy, he always found time to talk to people,” Bou-Zeid said. “He was someone who was passionate about science and also extremely passionate about life.”

Celia, a colleague in civil and environmental engineering and former director of HMEI, said Rodríguez-Iturbe “made the quality of life at Princeton much better by his presence.”

“When I was department chair, he was unbelievably helpful in many different ways,” he said. “He never wanted credit, he just wanted to know what he could do to help.”

Porporato said that although Rodríguez-Iturbe loved science, he always put his family first. He was also a very spiritual man and proud to have been invited to serve in the Catholic Church’s Pontifical Academy of Sciences.

“He was very proud of that,” Porporato said. “It was a way to put together his deep spiritual inclination with his mind, which was focused toward science.”

Porporato said that a meeting as a young professor with Rodríguez-Iturbe set the course of his future career.

“His enthusiasm and passion for science was contagious,” he said. “I am still working to follow his example, trying to find the deepest questions in the environmental sciences and hydrology, and trying to solve them in the most elegant way.”

Rodríguez-Iturbe was born in Caracas, Venezuela, and spent most of his youth in Maracaibo. He received his bachelor’s degree in civil engineering from the University of Zulia in 1963. He earned a Master of Science from the California Institute of Technology and a doctorate in civil engineering from Colorado State University in 1967.

He returned to Venezuela to accept a teaching position at the University of Zulia and became an associate professor in civil engineering at the Massachusetts Institute of Technology in 1971. In 1975, he was appointed professor of engineering at the Simón Bolivar University in Caracas, a position he held until 1995. He also served as dean of research and dean of graduate studies at Simón Bolivar, as a professor at the International Institute of Advanced Studies in Caracas, and as a visiting professor and senior lecturer at MIT. Before joining the Princeton faculty in 1999, he held chairs at the University of Iowa and Texas A&M University. He served as a member of the Princeton faculty until 2016.

Rodríguez-Iturbe was elected to the National Academy of Engineering in 1998 and the National Academy of Sciences in 2010. He was a member of the Pontifical Academy of Sciences and the Latin American Academy of Sciences. He was a fellow of the American Geophysical Union, the American Meteorological Society and the American Academy of Arts and Sciences. He was the recipient of the premiere recognition in hydrology, the Stockholm Water Prize, and the Bowie Medal of the American Geophysical Union. Among his other awards were the James B. Macelwane Medal for significant geosciences contributions by early career scientists, Hydrologic Sciences Award, Walter Langbein Lecture Award for lifetime contributions to hydrology, and Robert E. Horton Medal for outstanding contributions to hydrology, all from the American Geophysical Union; the Robert E. Horton Lecturer in Hydrology award from the American Meteorological Society; the Walter Huber Civil Engineering Research Prize and Ven Te Chow Award for lifetime achievement from the American Society of Civil Engineers; and the Prince Sultan Bin Abdulaziz International Prize for Water.

He is survived by his wife Mercedes, daughter Olimpia and sons Oscar, Ignacio, Juan and Luis Rodriguez.

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