Ignacio Rodríguez-Iturbe (1942–2022): A review of a pathbreaking academic career combining chance and self-organization

On October 27, 2022, the inspirational and highly influential hydrologist Ignacio Rodríguez-Iturbe suddenly passed away. He was Distinguished University Professor and Wofford Cain I Chair Professor Emeritus at Texas A&M University, and James S. McDonnell Distinguished University Professor Emeritus of Civil and Environmental Engineering, Princeton University. Ignacio, a master of contemporary thought and a pathbreaking scientist, was at the center of the cultural process that transformed the field of hydrology from an empirical branch of applied engineering to a mainstream environmental science. He showed creatively and rigorously that the analysis, synthesis, and sampling of hydrological processes could pave the way for a new and deeper understanding of floods, droughts, and a "fair" distribution of water, including water controls on living communities—in a nutshell, how nature works through the inner workings of the water cycle. Rodríguez-Iturbe’s pioneering work has influenced generations of researchers across many fields and around the world and left a long-lasting legacy through many disciples and in a large number of young people, students of all types, whose lives he changed for the good by his intellectual mark and empathic maieutics. Ignacio made each student and collaborator alike feel special wherever he went, and mobilized entire communities to shift their foci to modern hydrologic research. Within hydrology, his work was wide-ranging and highly mathematical, blending theory from spatial point processes and fractal mathematics to the dynamics of river basins and other hydrological patterns. However, his contributions went well beyo`d hydrology to include ecophysiology and plant community ecology, and his efforts basically created a new discipline at the interface between ecology and hydrology. According to Google Scholar, he has an h-index above 100, and he remained active until his death (Fig. 1).

Ignacio Rodriguez-Iturbe. Image credit: Denise Applewhite.

Ignacio Rodríguez-Iturbe was born in Maracaibo, Venezuela on March 8, 1942, in a large family blessed with deep intellectual gifts. He was educated in the Universidad del Zulia in Maracaibo, where he received a C.E. with maximum honors in 1963. He received a MS at the California Institute of Technology in 1965 and a Ph.D. from Colorado State University in 1967. In 1964, he married Mercedes Maiz, who gave him Oscar, Ignacio, Olimpia, Juan, and Luis. Ignacio only recently retired from Texas A&M, so that he and Mercedes could return home to their native Venezuela, where much of their family lived.

Ignacio served as faculty in various universities: the Universidad del Zulia in Maracaibo (from where he graduated and where his father had long been Dean of the Faculty of Engineering), the Massachusetts Institute of Technology in Cambridge, the Universidad Simon Bolivar in Caracas, the University of Iowa in Iowa City, Texas A&M at College Station, and for twenty years Princeton University, where he was the James S. McDonnell Distinguished University Professor of Civil and Environmental Engineering. He held various appointments as visiting Professor in several countries, where his role in fostering the establishment of thriving research communities in various domains of hydrology was remarkable. This was largely because of his ease in communicating and sharing ideas and knowledge with others, the empathy he emanated, and the enthusiasm he was capable of injecting especially in the young: these gifts proved instrumental, in particular, in the transformative development of the Italian hydrologic community as a spinoff of his regular visits. Several of his former students and postdocs now hold academic positions in major institutions worldwide, and his countless collaborations spread his influence even further.

Ignacio was a towering scientific and academic figure in the field of hydrology. His early research focused on the analysis, synthesis, and sampling of hydrological processes, focusing in particular on the stochastic characters of rainfall events and those of their measurement networks (1–3). His contributions immediately made waves for the extraordinary mathematical and statistical insights they provided; in particular, the theory of stochastic processes was a lifelong love affair for him, one that allowed him to publish a series of fundamental papers jointly with leading hydrologists and statisticians (4–9).

In the late 1970s, Ignacio turned his interests toward the connection of geomorphology and hydrology, and in particular on the role of form and function of river networks. In those years, he pioneered the so-called geomorphological theory of the hydrological response (10, 11), which radically changed the empirical approaches used by engineers for more than a century to predict floods. The theory remains to date a display of insight, usefulness, and elegance that we are only left to admire. Later, he concentrated on the origins, the dynamics, and the stationary states of the geomorphology of natural hydraulic waterways and in particular of river networks in runoff-producing areas (12–14). In the early 90s, he was the leading force behind the development of the theory of optimal channel networks (15, 16), a significant step forward in our understanding of how nature works within the larger debate on the dynamic origins of scale-invariant natural forms (or, the dynamic origins of the fractal geometry of nature) (17). In parallel, Ignacio contributed essentially to the gathering of key field evidence on the form of river networks, using the then cutting-edge technology of remotely acquired and objectively manipulated information of digital terrain maps and the extraction of properly channelized landforms (18). The proof of the scale-invariance of the master variables of river network hydrology over up to six orders of magnitude, from the scale of 1 meter to thousands of kilometers, placed hydrology and geomorphology firmly within a larger stage, that of the physics of fractals (17–29). Overall, the development and the validation of the theory of optimal channel networks represented a major step forward that revolutionized our understanding of the form and function of river networks and of the dynamic origins of fractal geometries in nature.

Toward the turn of the century, Ignacio jump-started the study of the probabilistic structure of the interactions among climate, soil, and vegetation (21). In the process, he became the main architect of the birth and the subsequent establishment of a new discipline, Ecohydrology (22–25), born from his writings with gifted collaborators. A crasis of hydrology and ecology, ecohydrology is now established as the science that has revolutionized the study and the management of ecosystems through the probabilistic characterization (truly realistic) of natural forcings linked to the waters of the hydrological cycle. Ecohydrology now universally means hydrologic controls on the biota. The last decade has been devoted mainly to studies in water controls of the distribution of species, populations, and pathogens in natural ecosystems, and in particular to river networks seen as ecological corridors (26–32). Ignacio used to recall that the fundamental unity of the seemingly disparate problems of water-controlled population ecology, waterborne disease spread, and biological invasions in fluvial systems was cast in a final form during a walk around the pond of the Institute for Advanced Studies in Princeton, in the best tradition of the peripatetic philosophers (32). Although he could work on them only on and off, very dear to him also were other research fields, in particular studies on large-scale soil moisture dynamics (33–35) and theoretical work on evapotranspiration patterns due to spatial heterogeneity of plant species (36). Indeed, patterns in nature were a lifelong passion of his. Finally, across the years he also contributed important work on the virtual water trade networks, whose understanding is crucial toward a rigorous definition of a fair distribution of water (37).

Ignacio Rodríguez-Iturbe coauthored with close friends four research monographs: each book shines separately in its reasoned collection of years of reflections. They dealt with random functions and hydrology (3), fractal river basins (17), ecohydrology of water-controlled ecosystems (25), and river networks as ecological corridors (32), each concluding a phase of his research interests. His books have been instrumental in advertising beyond specialty journals the establishment of hydrology as an earth science, as opposed to the empirical and practice-oriented branch of civil engineering that it was when he began his academic career.

Perhaps the most distinctive character of his scientific production lies in the pathbreaking originality of his contributions, which often gave rise to the establishment of new fields of research or even new disciplines, together with the methodological depth and insatiable curiosity that fueled his research. This led him to explore the limits of the current knowledge in many fields, and to contaminate them with methods and models borrowed from other contexts and other disciplines, in particular, mathematics and especially the theories of probability and stochastic processes. His contributions have transformed hydrology from a minor branch of civil engineering into a field now considered central to the environmental sciences.

It would be improper, however, not to mention here a distinctive trait of his legacy: his boundless generosity and enthusiasm in disseminating ideas and fostering collaborations, his ability to enchant audiences especially made up of young students, his fierce dedication to his research right up to the end: in the messages he sent to his collaborators from the hospital bed during what turned out to be his last weekend, he never failed to refer to the things that needed to be done as soon as possible, always indicating new objectives, and the “where is the gold medal?” question he so often asked to rally his troops. Ignacio was an exceptional mentor, to students from undergraduate studies through the postdoctoral, and indeed including his collaborators.

Ignacio was a Member or Fellow of multiple international honorary societies, including the U.S. National Academy of Sciences and National Academy of Engineering; the American Academy of Arts and Sciences; the Istituto Veneto di Scienze, Lettere ed Arti; the Pontifical Academy of Sciences and the Third World Academy of Sciences. He received honorary degrees, among which those that were dearest to him included one from the University of Zulia in Maracaibo, where he had obtained his CE; the degree in Environmental Engineering from the University of Genoa on the occasion of the Colombian celebrations; and an honorary Ph.D. from the University of Cantabria.

Ignacio Rodríguez-Iturbe was the recipient of an extraordinary number of awards and prizes for his research work, a testament to his exceptional academic standards. Among these, the 2002 Stockholm Water Prize stands out, as it is universally recognized as the Nobel Prize for water studies. Among others, it seems worth mentioning the Prince Sultan Bin Abdulaziz International Water Prize (for creativity) in 2010, and the awards bestowed on him by the American Geophysical Union, including the Macelwane, the Horton, and the Bowie Medals, covering the whole spectrum of geophysics and recognition of unselfish cooperation in science. Significantly, there exist already two Ignacio Rodriguez-Iturbe Awards: one for outstanding scientific achievements in any field of science given by his Alma Mater, Universidad del Zulia; and the other for the best article published each year in the international journal Ecohydrology. A highly cited scientist in the vast field of Environmental Sciences, Ignacio authored and coauthored several monographs that inevitably became the standard references in their field.

Ignacio Rodríguez-Iturbe was a visionary and demanding academician, who believed in the hierarchy of knowledge, the primacy of merit and reason, the value of speculation, and the specificities of the laboratories of modern knowledge. He believed, in particular, in the Universities and Academies as free factories of culture and knowledge, and in the veritable mission of professors, centered on the production and the dissemination of knowledge for the betterment of society. He took this mission to heart, and often quoted the page by Ernst Kantorowicz about the only professions worthy of wearing the gown: the judge, the priest, and the academician—the gown is the epitome of the maturity of the mind, of the independence of judgment, and of one’s direct responsibility only to his conscience.

Brilliant, generous of his time and insight issuing from the cornucopia of research ideas that his mind produced relentlessly, he always and immediately revealed a special empathy with others and a world of sensitivity and attention without distinctions. Legions of collaborators over the years have experienced his generosity without sparing in advising, suggesting new and relevant research directions, and in pointing out relevant documents and studies in the most disparate fields. An example of vast interdisciplinarity, Ignacio Rodriguez-Iturbe showed unlimited intellectual freedom and creativity that originated from his profound theoretical background combined with an insatiable curiosity in study and research, which today many, all over the world, remember fondly with deep affection and admiration. We mourn his passing but celebrate a most fulfilling life, rich in intellectual rewards and recognition, jointly with treasures of personal relations and family ties, and consider it a privilege to have known and worked with him.