CH
Member Since 2006
Ciaran J. Harman
Associate Professor, Johns Hopkins University
Honors and Awards

James B. Macelwane Medal
Received December 2021
Citation
Dr. Ciaran Harman is the preeminent theoretical hydrologist of his generation. He has made fundamental contributions to hydrological theory and model development at hillslope and catchment scales. Ciaran is best known for his work to understand heterogeneity in hillslopes and catchments by inferring transit time distributions from measurements of flow and transport in research catchments. Specifically, Ciaran has advanced a framework for modeling solute transport that can be applied at the catchment scale. This framework is based on StorAge Selection (SAS) functions, which generalize the concept of a transit time distribution to account for unsteady flow and variable storage. This is a substantial breakthrough in hillslope hydrology, literally transforming the way to interpret tracer data and thus conceptualize runoff generation processes. SAS functions express how the outflow of a system is “selected” from the storage. The framework is entirely general and is capable of capturing the nonlinear, time-variable complexities of transport through catchments. After validating the SAS model using field data and experiments, Ciaran embarked on new research to connect the SAS functions to climatic and landscape characteristics. Ciaran has shown that concepts of storage-discharge relationships and transit time distributions can be unified into an age-ranked storage-discharge relationship, which is a major breakthrough in this line of research. In more recent work, instead of asking how the effects of heterogeneity may be inferred from field observations (i.e., his work on SAS) or how they can be captured in upscaled descriptions of hillslope and catchment scales (i.e., closure models), Ciaran has sought to understand deeper questions such as how these heterogeneities arose and how they might have “coevolved,” thus pushing the boundaries of what hydrology might seek to accomplish as a discipline. Ciaran developed a quantitative, physically grounded theory of how hydraulics and chemical weathering coevolve in hillslopes to simultaneously control the subsurface architecture of weathering fronts and shallow subsurface flow systems at geomorphic steady state. His work drew upon fundamental principles of hillslope hydrology, geochemistry and geomorphology to predict the location of weathering zones in hillslopes as a function of overall rates of landscape denudation. In this way he has not only extended the boundaries of hydraulic groundwater theory but has unified two of the main hypotheses driving research in the critical zone science community about the relationships between topography and weathering in hillslopes. This result has had a major impact on the critical zone science community. 
— Martyn Clark Centre for Hydrology, University of Saskatchewan Saskatoon, Saskatchewan, Canada
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Union Fellow
Received December 2021
Hydrologic Sciences Early Career Award
Received December 2016
Ciaran Harman will receive the 2016 Early Career Hydrologic Science Award at the 2016 American Geophysical Union Fall Meeting, to be held 12–16 December in San Francisco, Calif. The award is for significant early-career contributions to hydrologic sc...
Ciaran Harman will receive the 2016 Early Career Hydrologic Science Award at the 2016 American Geophysical Union Fall Meeting, to be held 12–16 December in San Francisco, Calif. The award is for significant early-career contributions to hydrologic science.  
Citation

Ciaran Harman grew up in Western Australia, where he received undergraduate degrees in Arts and Engineering with first class honors. In 2005 he began graduate studies with Murugesu Sivapalan at the University of Illinois, where he earned a Ph.D. in Civil Engineering in 2011.
I met Ciaran for the first time in 2007 at the Joint Assembly in Acapulco, Mexico. I didn’t know who he was, and he introduced himself as a student of Siva’s working on hillslope processes. He asked me details about my papers that I didn’t even remember, and for the next 3 days he basically stalked me. It was the first sign of his persistence and his desire to understand every little detail of the problem he is working on.

By the time he finished his Ph.D., Ciaran had published 22 papers. This productivity is in part due to his ability to make substantive contributions in collaborative enterprises, including the NSF-funded Hydrological Synthesis Summer Institute of 2008, and the early design meetings for the Landscape Evolution Observatory of Biosphere 2. In 2011, Ciaran joined my research group as a CZO postdoc, exploring catchment co-evolution, and the combination of Newtonian and Darwinian approaches to hydrology. His paper on Darwinian hydrology quickly became a classic on the topic.

Since starting at Johns Hopkins University he has focused on nonstationary flow and transport processes, and his work has helped establish the theory of storage selection functions for lumped transport modeling. Together, we continue to work on transport and co-evolution through two NSF-funded collaborative research projects at Biosphere2.

Ciaran is a wonderful friend and colleague, and is an outstanding mentor to his students. It has been a pleasure to see Ciaran develop from a young Ph.D. student into this year’s Early Career Award recipient.

—Peter Troch, University of Arizona, Tucson

Response
I am grateful to AGU; to the Hydrology section and its chair, Efi Foufoula-Georgiou; to those who nominated me; and most especially to Peter Troch for his unwavering support, and generous citation. I never found Newton’s suggestion of standing on the shoulders of giants to be terribly useful. Following them around at conferences, asking lots of questions, and generally being a pest seemed a more effective strategy. I didn’t go to grad school with the intent of being a hydrologist. One fateful day I walked into Siva Sivapalan’s office to talk about a little hillslope model I had been playing with. Siva’s response was enthusiastic. Soon we were talking about heterogeneity, scaling, and closure relations—issues that I have returned to ever since. His fascination with these issues became my own. I have been fortunate to have the mentoring and support of some wonderful people. First among them is Siva—as I work with students of my own I understand more and more the how deft his guidance and support was. But I am indebted to so many—Kitty Lohse, for showing me what tenacity looks like, particularly in the field; Praveen Kumar, for raising my mathematical consciousness; Suresh Rao, for introducing me to transport issues; Peter Wilcock, for his faith; and many more—giants all! I am most grateful for the opportunity to play—to play with data, to play with technology, to play with theory, and, most especially, to play side by side with others—while searching for insights into real societal and environmental issues. Play is the opportunity to wander beyond our limits, and perhaps find something worth cutting a path back to. It is the best opportunity I can hope to share with the talented students I am privileged to work with. —Ciaran Harman, Johns Hopkins University, Baltimore, Md.
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Outstanding Reviewer Award - Geophysical Research Letters
Received December 2015
Horton Research Grant
Received January 2010
Current Roles
Member
Hydrology Langbein Lecture Committee