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Demetris Koutsoyiannis

Demetris Koutsoyiannis
Demetris Koutsoyiannis

The 2009 Henry Darcy Medal is awarded to Demetris Koutsoyiannis for his outstanding contributions to the study of hydrometeorological variability and to water resources management.

Professor Koutsoyiannis has focused his career on strengthening the foundations of stochastic hydrology, often by courageously tearing down flawed ideas and rebuilding sections of the discipline anew. His work has addressed problems in frequency analysis of extreme events, trend analysis, disaggregation modeling, characterization of rainfall data, evaluation of model reliability and robustness, coupling of hydrologic models, the role of entropy in hydrologic systems, and, most recently and importantly, interpretation of time series corresponding to long-memory processes. All of these are critically important for water management issues.

Long-Memory Processes

Long-memory processes, also known as the “Hurst Phenomenon,” present a special practical problem to hydrologists and water managers alike despite their having staked claim to the field over 50 years ago. The physical basis for Hurstian long memory continues to elude complete explanation. However, in part due to Prof. Koutsoyiannis’s recent work, the existence of the phenomenon has become increasingly recognized in hydrology as well as in countless other disciplines from economics to electrical engineering. In fact, long memory appears to be nearly ubiquitous in large-scale natural and anthropogenic systems, including both global climate and Internet traffic.

As a practical hydrological matter, understanding the physics and statistics associated with long memory, and their implications, is becoming increasingly urgent as water resources managers face concerns at larger spatial and temporal scales. Specifically, climate change occurs at the largest scales – global and multi-decadal scales – and it is at these scales where long memory becomes an essential component of the stochastic description of the system.

Professor Koutsoyiannis’s contributions include providing a rigorous mathematical underpinning for the long memory observed in hydroclimatological systems. He has shown how simple assumptions involving Markov processes can lead to stationary long memory – an important observation with deep implications for science. Koutsoyiannis has also presented “toy” models that capture the essential character of long memory while avoiding mathematical formalism, making the concepts accessible to colleagues, students, and the public.

Correspondence of Model Outputs to Real Physical Processes

Professor Koutsoyiannis has investigated the correspondence between hydrological, and now climatological, models and data, and how to judge such relationships. In particular, he has recently begun work on quantifying the “skill” of GCM climate models. This task presents many challenges because of the need to account for the cumulative impact of the many ways in which GCM outputs differ qualitatively from the observable phenomena. For example, GCMs produce grid-based results corresponding to large land areas and long time intervals; rainfall and temperature data are collected at a sparse array of distinct points. Downscaling, which partly solves problem, introduces issues of comparability. It is reasonable to wonder if there is any rigorous way to test such models. If not, what purpose do such models serve? Professor Koutsoyiannis has demonstrated that the models are in fact testable – those problems can be overcome – but his work has also raised substantial doubts about the skill of GCM forecasts. This finding in itself has significant implications for both science and public policy.

Practical Applications and Historical Writings

As noted above, the scope of Professor Koutsoyiannis’s research and work is enormous. It ranges from the purely theoretical concerns involving fundamental physical processes to developing practical applications such as a hydrologic information system for managing the Athens water supply, in the spirit of Henry Darcy. Many of the methods he has developed extend standard engineering techniques – often developed to perform in the context of “ordinary” hydrologic variability – so that they can deal with the unexpected variability associated with climate change or long-memory noise. Professor Koutsoyiannis has been frequently engaged in resolving practical problems related to lakes and rivers throughout Greece and southeastern Europe.

Professor Koutsoyiannis has also written eloquently on the history of water resource development during antiquity. Who invented the bathroom and when? Addressing this question might not qualify as a direct to water resources management yet it reflects the broader interest that the Darcy Award recognizes and which Professor Koutsoyiannis possesses in abundance.

International Impact and Scientific Recognition

Publication record

Professor Koutsoyiannis has co-authored approximately 70 papers in peer-reviewed international journals, 3 books, and hundreds of additional articles which have appeared in conference proceedings, technical reports and book chapters. His prolific publication record includes more than 20 of his publications have each been cited at least a dozen times.

Leadership and Recognition

Professor Koutsoyiannis has a rapidly growing reputation as a leader in the field of stochastic hydrology. In the past few years he has served on the editorial board of 4 international journals and as guest editor for two special volumes. He has also been actively involved with EGU for most of his career, and currently chairs the Sub-Division on Precipitation & Climate of the Hydrological Sciences Section of the European Geophysical Society (EGS). It is also interesting to note that Professor Koutsoyiannis’s research tends to show up at the top of Google searches – for example, googling “Hurst phenomenon” identifies a Koutsoyiannis paper as the most likely match. In addition, Koutsoyiannis work is frequently cited on climate-related blogs such as RealClimate and Climate Audit.

Finally, Professor Koutsoyiannis is a delightful and brilliant speaker. He is frequently invited to give keynote lectures at conferences across the Globe.


Professor Koutsoyiannis exhibits extraordinary enthusiasm and passion for hydrology in all of its forms, with a particular emphasis on the application of stochastic methods to water resource management. His research has challenged widely held beliefs, yet it has stood up to scrutiny and, so far, none of his work has been discredited. Professor Koutsoyiannis is a true leader in our field whose contribution to hydrological research and water resources management is recognized worldwide. Awarding the Darcy medal to Professor Koutsoyiannis is a fitting way to recognize these substantial contributions.