Jean-Yves Parlange

2002 Robert E. Horton Medal Winner

Cornell University, Ithaca, N.Y.

Jean-Yves Parlange was awarded the Horton Medal at the AGU Fall Meeting Honors Ceremony, which was held on 10 December 2003, in San Francisco, California. The medal honors “outstanding contributions to hydrology.”


“It was in 1969 that Jean-Yves Parlange had his ‘road to Damascus’ experience on that fateful day in the Yale library, when he happened to come across a recent paper on nonlinear diffusion, as applied to soil water seepage. It immediately struck him that there had to be a better and more efficient way of approaching this problem. He plunged right in, never looking back, for it seems he had found his true calling. Over the next three decades, Jean-Yves Parlange established himself as a pioneer in soil water hydrology, and he is now recognized as an undisputed intellectual leader in our field. He is especially renowned for his penetrating analytical insight into uncovering the physical and mathematical basis for a deeper understanding of soil hydrologic behavior.

“His countless contributions to the literature have covered an incredibly broad range and have consistently been of a quality and thoroughness most of us can only dream of achieving. On an occasion like this, it is impossible to do full justice to the real impact of his work; therefore, I will merely enumerate some of the areas of his more important contributions.

“Even before he entered hydrology, he had already formulated stability criteria for chemical diffusion in laminar flows near flame interfaces. For this work, he received in 1962 the prestigious Minta Martin National Award by the Institute of Aerospace Sciences. Early on, he also showed his mettle in surface tension physics, as related to homogeneous nucleation during phase transition in a gas, and to the movement of deformable drops and bubbles.

“After he entered hydrology, he explored the convective-dispersive equation and the impact of boundary and initial conditions on solute transport in porous materials. Through observations, backed up by theoretical boundary layer considerations, he and his associates elucidated the thermal exchanges between a leaf and the atmosphere. Together with his associates, he was equally successful in clarifying overland flows, by extending the kinematic wave approach, to analyze situations with converging/diverging surfaces, surface curvature, and shocks.

“Building on his earlier work on flame stability, Parlange directed his attention to wetting front instabilities in soils; such instabilities can result in rapid water and solute movement over great distances and can have major implications for the hydrology of waste disposal, fertilizers and pesticides, fingering of water through oil spills, and the effects of surfactants in soil remediation. Jean-Yves Parlange quickly realized that hysteresis is a key mechanism in these instabilities and developed a parameterization that yields all possible scanning curves. I found it to be the most effective formulation among the available approaches. Parlange and his co-workers introduced several refinements to Boussinesq’s hydraulic groundwater theory, allowing the inclusion of a capillary fringe, a seepage surface, leakage through the bottom, and slope.

“Infiltration theory is the area in which Jean-Yves Parlange has probably made the biggest impact. The essence of his approach consisted of replacing Richards’s equation by an integral representation, to obtain parsimonious yet remarkably accurate analytical approximations. Specifically, he represented several facets of partly-saturated flow by concise equations involving only sorptivity, saturated water content, conductivity, and water entry potential. The validity of these approximations was confirmed time and again numerically and with exact idealized solutions. It is no exaggeration that Parlange’s paradigm was one of the major breakthroughs in infiltration theory of the past three decades. The concept was made use of extensively by John Philip and his associates in Australia in their flux-concentration approach. Certainly, from my personal point of view, several of Parlange’s papers in this category have been seminal to my own thinking and have greatly affected my subsequent research in this field.

“Through it all, Jean-Yves Parlange has not only been a source of inspiration on the importance of fundamentals, but also a model of unselfish cooperation to be emulated by the rest of us. Most of his papers are co-authored, yet from personal experience I know that in most of them, with few exceptions, he was the intellectual leader and the main driving force.

“In summary, it is clear that Jean-Yves Parlange’s unwavering commitment in scholarship and teaching, coupled with his outstanding contributions in such a wide range of frontline topics, together with his generosity toward his colleagues, put him at the very top of our scientific enterprise. Unquestionably, there can hardly be a more deserving candidate for recognition through the Horton Medal.”

—WILFRIED H. BRUTSAERT, Cornell University, Ithaca, N.Y.


“President McNutt, Ladies and Gentlemen,

“Thank you very much Wilfried for your kind words and more than generous citation. It is, of course, a great honor to receive the Horton Medal especially considering the 17 previous recipients and I am extremely lucky to add my name to that list. I find it interesting that I know, to different degrees, more than half the scientists on it. I think it shows that hydrologists are a small close-knit community. It is also friendly and open-minded and I always felt welcome, even though I was never formally trained in that field.

“Wilfried gave the accurate account of my switch from aeronautical engineering to hydrology and I very quickly was encouraged by him as well as Don Kirkham and Don Nielsen, all Horton Medalists to pursue my research in hydrology. We always credit luck for our successes and indeed looking at our past it seems to be a random walk through life, but in fact we might be diffusing in response to gradients without even realizing it as individuals. However, and without any doubt, our main source of success is due to friends with whom we collaborate and who guide us without ulterior motives. I am deeply grateful to them. Several of them have been critical in determining the research paths I have explored. Among them are my Ph.D. advisor B. T. Chu whose teaching of mathematics and thermodynamics has had a profound influence and with whom I studied hydrodynamic stability; Calvin Rose and Bill Hogarth who introduced me to erosion and sediment transport, and Matt Romkens on the related topic of surface scaling; Peter Ross with his remarkable numerical skills; Larry Walker and his students who initiated me to biological engineering; Wilfried Brutsaert who is forever providing me with new ideas on all kinds of topics from mathematical derivations to the study of aquifers; Randel Haverkamp and Carlos Fuentes on infiltration and the inverse problem; Tammo Steenhuis with whom I have the closest research relationship at present who has a marvelous physical intuition and carries out illuminating experiments.

“I have also been blessed with outstanding students (and nowadays sometimes their own students) with inquiring minds and boundless energy and with whom I never stopped collaborating; without them, my research efforts would have been greatly reduced: John Selker, Andrew Barry, David Lockington, Frank Stagnitti, Ling Li, Todd Walter, and my own son Marc. There are many others who are too numerous to mention and yet their help has always been crucial and deeply appreciated. This is reflected in joint publications and I am quite proud to have half as many different co-authors as I have publications. All this would not have been possible without my wife’s support and encouragement, I was very lucky there as well. Finally, I am deeply grateful to the American Geophysical Union and specifically to the members of the Horton Medal committee for choosing me as the 2002 recipient of this wonderful medal.”

—JEAN-YVES PARLANGE, Cornell University, Ithaca, N.Y.