Montanari Bahr Blöschl Cai for the Science of Hydrology ... · Legacy and Perspectives ... a...

Legacy and Perspectives for the Science of Hydrology

Water Resources Research 50th Anniversary Special Collection

1965–2015

EditorsA. Montanari, J. Bahr, G. Blöschl, X. Cai, D. S. Mackay, A. M. Michalak, H. Rajaram, G. Sander

We are pleased to present the contributions collected to celebrate the 50th anniversary of Water Resources Research. These include critical discussions of the leg-

acy and perspectives for the science of hydrology in the 21st century. The papers in this collection also highlight exciting pathways to the future of water sciences. New monitoring and modeling techniques and increasing opportunities for data and knowledge sharing from hydrological research will provide in-novative means to improve water management and to ensure a sustainable development to society. We hope that this set of papers will provide valuable inspiration for future hydrologists, and will support the intensification of international coopera-tion among scientists.

EditorsA. Montanari, J. Bahr, G. Blöschl,

X. Cai, D. S. Mackay, A. M. Michalak, H. Rajaram, G. Sander

Legacy and Perspectives for the Science of H

ydrologyW

ater Resources Research 50th Anniversary Special Collection

MontanariBahr

BlöschlCai

MackayMichalakRajaramSander

WRR50_mechanical.indd 1 10/8/15 3:05 PM


Water Resources Research 50th Anniversary Special Collection

1965–2015

EditorsA. Montanari, J. Bahr, G. Blöschl, X. Cai, D. S. Mackay, A. M. Michalak, H. Rajaram, G. Sander

We are pleased to present the contributions collectedto celebrate the 50th anniversary of Water Resources Research. These include critical discussions of the leg-

acy and perspectives for the science of hydrology in the 21st century. The papers in this collection also highlight excitingpathways to the future of water sciences. New monitoring and modeling techniques and increasing opportunities for data and knowledge sharing from hydrological research will provide in-novative means to improve water management and to ensure a sustainable development to society. We hope that this set of papers will provide valuable inspiration for future hydrologists, and will support the intensification of international coopera-tion among scientists.

EditorsA. Montanari, J. Bahr, G. Blöschl,

X. Cai, D. S. Mackay, A. M. Michalak, H. Rajaram, G. Sander

Legacy and Perspectives for the Science of H

ydrologyW

ater Resources Research 50th Anniversary Special Collection

MontanariBahr

BlöschlCai

MackayMichalakRajaramSander


Cover image: Danita Delimont/Alamy Stock Photo

Aims and Scope. Water Resources Research is an interdis-ciplinary journal that publishes original research in the natural and social sciences of water. This includes the role of water in the physical, chemical, biological, and ecolog-ical sciences; public health; and related social and policy sciences. It encompasses methodological development of observational, experimental, theoretical, analytical, numerical, and data driven approaches that advance the science of water and its management. Submissions are evaluated for their novelty, accuracy, significance, and broader implications of the findings.

Copyright and Copying. Copyright © 2015. American Geophysical Union. All rights reserved. No part of this publication may be reproduced, stored or transmitted in any form or by any means without the prior permission in writing from the copyright holder. Authorization to copy items for internal and personal use is granted by the copyright holder for libraries and other users regis-tered with their local Reproduction Rights Organisation (RRO), e.g. Copyright Clearance Center (CCC), 222 Rose-wood Drive, Danvers, MA 01923, USA (www.copyright.com), provided the appropriate fee is paid directly to

the RRO. This consent does not extend to other kinds of copying such as copying for general distribution, for advertising or promotional purposes, for creating new collective works or for resale. Special requests should be addressed to: [email protected].

Disclaimer. The Publisher, American Geophysical Union, and Editors cannot be held responsible for errors or any consequences arising from the use of information con-tained in this journal; the views and opinions expressed do not necessarily reflect those of the Publisher, Amer-ican Geophysical Union, and Editors, neither does the publication of advertisements constitute any endorse-ment by the Publisher, American Geophysical Union, and Editors of the products advertised.

Publisher. Water Resources Research is published on be-half of the American Geophysical Union by Wiley Period-icals, Inc., 111 River St., Hoboken, NJ, 07030-5774, +1 201 748 6000.

View this journal online at http://wrr.agu.org.


©1963, 1964 by Warner Bros. Inc.; renewed 1991, 1992 by Special Rider Music.

50 years of Water Resources Research: The times are changing and so is WRR

Come gather ’round people Wherever you roam And admit that the waters Around you have grown And accept that soon You’ll be drenched to the bone. If your time to you Is worth savin’ Then you better start swimmin’ Or you’ll sink like a stone For the times they are a-changin’ The Times They Are A-Changin’©

Bob Dylan (1964) In the year 1965, more environmental acts were enacted by Congress than in any other year, such as the Land and Water Conservation Fund Act, the Water Quality Act, the Federal Water Project Recreation Act, and the Water Resources Planning Act, following the Water Resources Research Act of 1964. 1965 also marked a key moment in climate change history that few remember: the first presidential mention in a special message to Congress on the environmental risk of carbon dioxide pollution from fossil fuels (Lyndon B. Johnson, 1965, Public Papers of the Presidents of the United States, Volume I, entry 54, pp. 155–165). Rachel Carson’s Silent Spring (1962) and Udall’s The Quiet Crisis (1963) did the spadework for the environmental movement in the mid-60s leading to the Earth Day in 1970. 1965 was a special year for water and the environment, as well as for Water Resources Research (WRR), born in March 1965. In the mid-60s, water scientists took a broad view of water science, and WRR embraced this view by being innovative, interdisciplinary, rigorous, and proactive. The breadth of topics published in its first few issues is stunning, e.g., by Arrow (1965), future Nobel Laureate in Economics, on water-related social investments; by Fox (1965) on the need to improve water management institutions, laws, and policies to solve our pressing water problems; by Yevjevich (1967) criticizing the concepts of Probable Maximum Flood used for design; by Smart (1967) developing subtle mathematics on Horton’s laws; by Lee (1967) on the hydrologic importance of leaf stomata, to mention only a very few. The rigor, the breadth, the depth, the breaking-new-ground mentality of WRR continued throughout its 50 years of history, making it the go-to journal for pioneering ideas, new mathematical theories and models, and state-of-the-art applications to real-world problems, as well as a place to review, criticize, and debate.

Since 1965, the world population has more than doubled, from 3.3 to 7.3 billion, and water challenges have become ever daunting compounded by climate change, the need for sustainable water, food, and energy, environmental consciousness on human rights and equity, and even exploration of life beyond our planet. As this anniversary issue attests, WRR has stood tall to face those emerging problems and has provided the bedrock of science advances and science-based solutions. Who knows what the next 50 years will bring? But it is refreshing to think that the next generation of water scientists and engineers who will define the next 50 years of WRR will be passionate about their science and the world, rigorous, well educated in breadth and depth, and inspirational leaders who will bring about a collective growth and solutions hardly imaginable today. This issue is dedicated to you next generation with our firm commitment to listen, mentor, and pave ways so you can achieve by 2065 what we cannot even imagine today. Efi Foufoula-Georgiou President, Hydrology section of the American Geophysical Union University of Minnesota, September 7, 2015

The 50th Anniversary of Water Resources Research


Alberto Montanari, Jean Bahr, Günter Blöschl, Ximing Cai, D. Scott Mackay, Anna M. Michalak, Harihar Rajaram, and Graham Sander Fifty years of Water Resources Research: Legacy and perspectives for the science of hydrology doi:10.1002/2015WR017998

The legacy of hydrological sciences

Harihar Rajaram, Jean Bahr, Günter Blöschl, Ximing Cai, D. Scott Mackay, Anna M. Michalak, Alberto Montanari, Xavier Sanchez-Villa, and Graham Sander A reflection on the first 50 years of Water Resources Research doi:10.1002/2015WR018089

Matthew Sturm White water: Fifty years of snow research in WRR and the outlook for the future doi:10.1002/2015WR017242

Claudio Paniconi and Mario Putti Physically based modeling in catchment hydrology at 50: Survey and outlook doi:10.1002/2015WR017780

Rafael L. Bras Complexity and organization in hydrology: A personal view doi:10.1002/2015WR016958

T. P. Burt and J. J. McDonnell Whither field hydrology? The need for discovery science and outrageous hydrological hypotheses doi:10.1002/2014WR016839

Martyn P. Clark, Ying Fan, David M. Lawrence, Jennifer C. Adam, Diogo Bolster, David J. Gochis, Richard P. Hooper, Mukesh Kumar, L. Ruby Leung, D. Scott Mackay, Reed M. Maxwell, Chaopeng Shen, Sean C. Swenson, and Xubin Zeng Improving the representation of hydrologic processes in Earth System Models doi:10.1002/2015WR017096

Andrew Binley, Susan S. Hubbard, Johan A. Huisman, André Revil, David A. Robinson, Kamini Singha, and Lee D. Slater The emergence of hydrogeophysics for improved understanding of subsurface processes over multiple scales doi:10.1002/2015WR017016

Hedeff I. Essaid, Barbara A. Bekins, and Isabelle M. Cozzarelli Organic contaminant transport and fate in the subsurface: Evolution of knowledge and understanding doi:10.1002/2015WR017121

Ian L. Molnar, William P. Johnson, Jason I. Gerhard, Clinton S. Willson, and Denis M. O'Carroll Predicting colloid transport through saturated porous media: A critical review doi:10.1002/2015WR017318

Peter K. Kitanidis Persistent questions of heterogeneity, uncertainty, and scale in subsurface flow and transport doi:10.1002/2015WR017639

M. Bayani Cardenas Hyporheic zone hydrologic science: A historical account of its emergence and a prospectus doi:10.1002/2015WR017028

Paul D. Brooks, Jon Chorover, Ying Fan, Sarah E. Godsey, Reed M. Maxwell, James P. McNamara, and Christina Tague Hydrological partitioning in the critical zone: Recent advances and opportunities for developing transferable understanding of water cycle dynamics doi:10.1002/2015WR017039

Water processes monitoring, modeling and interpretation

Jessica D. Lundquist, Nicholas E. Wayand, Adam Massmann, Martyn P. Clark, Fred Lott, and Nicoleta C. Cristea Diagnosis of insidious data disasters doi:10.1002/2014WR016585

Dennis P. Lettenmaier, Doug Alsdorf, Jeff Dozier, George J. Huffman, Ming Pan, and Eric F. Wood Inroads of remote sensing into hydrologic science during the WRR era doi:10.1002/2015WR017616

Peter A. Troch, Tim Lahmers, Antonio Meira, Rajarshi Mukherjee, Jonas W. Pedersen, Tirthankar Roy, and Rodrigo Valdés-Pineda Catchment coevolution: A useful framework for improving predictions of hydrological change? doi:10.1002/2015WR017032

Amilcare Porporato and Salvatore Calabrese On the probabilistic structure of water age doi:10.1002/2015WR017027

H. Vereecken, J. A. Huisman, H. J. Hendricks Franssen, N. Brüggemann, H. R. Bogena, S. Kollet, M. Javaux, J. van der Kruk, and J. Vanderborght Soil hydrology: Recent methodological advances, challenges, and perspectives doi:10.1002/2014WR016852

Laura E. Condon and Reed M. Maxwell Evaluating the relationship between topography and groundwater using outputs from a continental-scale integrated hydrology model doi:10.1002/2014WR016774

A. Fiori, A. Bellin, V. Cvetkovic, F. P. J. de Barros, and G. Dagan Stochastic modeling of solute transport in aquifers: From heterogeneity characterization to risk analysis doi:10.1002/2015WR017388

Valentina Ciriello, Yaniv Edery, Alberto Guadagnini, and Brian Berkowitz Multimodel framework for characterization of transport in porous media doi:10.1002/2015WR017047

Michael L. Roderick , Peter Greve, and Graham D. Farquhar On the assessment of aridity with changes in atmospheric CO2 doi:10.1002/2015WR017031

Marc F. P. Bierkens Global hydrology 2015: State, trends, and directions doi:10.1002/2015WR017173

Matthew R. Hipsey, David P. Hamilton, Paul C. Hanson, Cayelan C. Carey, Janaine Z. Coletti, Jordan S. Read, Bas W. Ibelings, Fiona J. Valesini, and Justin D. Brookes Predicting the resilience and recovery of aquatic systems: A framework for model evolution within environmental observatories doi:10.1002/2015WR017175

Robert L. Runkel On the use of rhodamine WT for the characterization of stream hydrodynamics and transient storage doi:10.1002/2015WR017201

M. Church and R. I. Ferguson Morphodynamics: Rivers beyond steady state doi:10.1002/2014WR016862

Hubert H. G. Savenije Prediction in ungauged estuaries: An integrated theory doi:10.1002/2015WR016936

Enrico Bertuzzo, Ignacio Rodriguez-Iturbe, and Andrea Rinaldo Metapopulation capacity of evolving fluvial landscapes doi:10.1002/2015WR016946

Christopher J. Keylock Flow resistance in natural, turbulent channel flows: The need for a fluvial fluid mechanics doi:10.1002/2015WR016989

Jud Harvey and Michael Gooseff River corridor science: Hydrologic exchange and ecological consequences from bedforms to basins doi:10.1002/2015WR017617

Ying Fan Groundwater in the Earth's critical zone: Relevance to large-scale patterns and processes doi:10.1002/2015WR017037

Diane M. McKnight, Karen Cozzetto, James D. S. Cullis, Michael N. Gooseff, Christopher Jaros, Joshua C. Koch, W. Berry Lyons, Roseanna Neupauer, and Adam Wlostowski Potential for real-time understanding of coupled hydrologic and biogeochemical processes in stream ecosystems: Future integration of telemetered data with process models for glacial meltwater streams doi:10.1002/2015WR017618

Manuel del Jesus, Andrea Rinaldo, and Ignacio Rodríguez-Iturbe Point rainfall statistics for ecohydrological analyses derived from satellite integrated rainfall measurements doi:10.1002/2015WR016935

Water resources, society and water threats

Richard M. Vogel, Upmanu Lall, Ximing Cai, Balaji Rajagopalan, Peter K. Weiskel, Richard P. Hooper, and Nicholas C. Matalas Hydrology: The interdisciplinary science of water doi:10.1002/2015WR017049

Murugesu Sivapalan and Günter Blöschl Time scale interactions and the coevolution of humans and water doi:10.1002/2015WR017896

B. Merz, S. Vorogushyn, U. Lall, A. Viglione, and G. Blöschl Charting unknown waters—On the role of surprise in flood risk assessment and management doi:10.1002/2015WR017464

George M. Hornberger, David J. Hess, and Jonathan Gilligan Water conservation and hydrological transitions in cities in the United States doi:10.1002/2015WR016943

William J. Cosgrove and Daniel P. Loucks Water management: Current and future challenges and research directions doi:10.1002/2014WR016869

Howard S. Wheater and Patricia Gober Water security and the science agenda doi:10.1002/2015WR016892

Dennis McLaughlin and Wolfgang Kinzelbach Food security and sustainable resource management doi:10.1002/2015WR017053

Casey M. Brown, Jay R. Lund, Ximing Cai, Patrick M. Reed, Edith A. Zagona, Avi Ostfeld, Jim Hall, Gregory W. Characklis, Winston Yu, and Levi Brekke The future of water resources systems analysis: Toward a scientific framework for sustainable water management doi:10.1002/2015WR017114

Praveen Kumar Hydrocomplexity: Addressing water security and emergent environmental risks doi:10.1002/2015WR017342

Jay R. Lund Integrating social and physical sciences in water management doi:10.1002/2015WR017125

Giuseppe Gambolati and Pietro Teatini Geomechanics of subsurface water withdrawal and injection doi:10.1002/2014WR016841

Daniel T. Birdsell, Harihar Rajaram, David Dempsey, and Hari S. Viswanathan Hydraulic fracturing fluid migration in the subsurface: A review and expanded modeling results doi:10.1002/2015WR017810

Steven M. Gorelick and Chunmiao Zheng Global change and the groundwater management challenge doi:10.1002/2014WR016825

Alexandra S. Richey, Brian F. Thomas, Min-Hui Lo, John T. Reager, James S. Famiglietti, Katalyn Voss, Sean Swenson, and Matthew Rodell Quantifying renewable groundwater stress with GRACE doi:10.1002/2015WR017349

M. A. Celia, S. Bachu, J. M. Nordbotten, and K. W. Bandilla Status of CO2 storage in deep saline aquifers with emphasis on modeling approaches and practical simulations doi:10.1002/2015WR017609

Shmuel Assouline, David Russo, Avner Silber, and Dani Or Balancing water scarcity and quality for sustainable irrigated agriculture doi:10.1002/2015WR017071

Serena Ceola, Francesco Laio, and Alberto Montanari Human-impacted waters: New perspectives from global high-resolution monitoring doi:10.1002/2015WR017482

Theophile Mande, Natalie C. Ceperley, Gabriel G. Katul, Scott W. Tyler, Hamma Yacouba, and Marc B. Parlange Suppressed convective rainfall by agricultural expansion in southeastern Burkina Faso doi:10.1002/2015WR017144

Chin-Fu Tsang, Ivars Neretnieks, and Yvonne Tsang Hydrologic issues associated with nuclear waste repositories doi:10.1002/2015WR017641

Ellen Wohl, Stuart N. Lane, and Andrew C. Wilcox The science and practice of river restoration doi:10.1002/2014WR016874

Martin W. Doyle, Jai Singh, Rebecca Lave, and Morgan M. Robertson The morphology of streams restored for market and nonmarket purposes: Insights from a mixed natural-social science approach doi:10.1002/2015WR017030

A. Porporato, X. Feng, S. Manzoni, Y. Mau, A. J. Parolari, and G. Vico Ecohydrological modeling in agroecosystems: Examples and challenges doi:10.1002/2015WR017289

Efi Foufoula-Georgiou, Zeinab Takbiri, Jonathan A. Czuba, and Jon Schwenk The change of nature and the nature of change in agricultural landscapes: Hydrologic regime shifts modulate ecological transitions doi:10.1002/2015WR017637

INTRODUCTIONTO A SPECIALCOLLECTION10.1002/2015WR017998

Fifty years of Water Resources Research: Legacy andperspectives for the science of hydrology

Alberto Montanari1, Jean Bahr2, G€unter Bl€oschl3, Ximing Cai4, D. Scott Mackay5, Anna M. Michalak6,Harihar Rajaram7, and Graham Sander8

1Department of Civil, Chemical, Environmental and Materials Engineering, University of Bologna, Bologna, Italy,2Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin, USA, 3Institute for Hydraulic andWater Resources Engineering, Vienna University of Technology, Vienna, Austria, 4Ven Te Chow Hydrosystems Laboratory,Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA,5Department of Geography, State University of New York at Buffalo, Buffalo, New York, USA, 6Department of GlobalEcology, Carnegie Institution for Science, Stanford, California, USA, 7Department of Civil, Environmental and ArchitecturalEngineering, University of Colorado, Boulder, Colorado, USA, 8School of Civil and Building Engineering, LoughboroughUniversity, Loughborough, UK

Abstract We present an overview of the contributions collected to celebrate the fiftieth anniversary ofWater Resources Research along with a critical discussion of the legacy and perspectives for the science ofhydrology in the 21st century. This collection of papers highlights exciting pathways to the future of water sci-ences. New monitoring and modeling techniques and increasing opportunities for data and knowledge shar-ing from hydrological research will provide innovative means to improve water management and to ensure asustainable development to society. We believe that this set of papers will provide valuable inspiration forfuture hydrologists, and will support the intensification of international cooperation among scientists.

1. Premise

Water science will play an increasingly important role for the benefit of humanity during the next decades,as water will be the key to ensuring adequate food and energy resources for future generations. It is wellknown that the interrelation between water and humans is as old as humans themselves. The ancientGreeks recognized water as one of the four essential elements (see Figure 1), and water is an essential partof Hinduism and Buddhism. Challenges associated with water have marked human history and will be moreand more prominent at the global level in the coming years. The intensive environmental changes that areoccurring over the planet are one reason for increasing concerns related to sustainability of the currentdevelopment. Climate dynamics, ecological systems, biological diversity, and diseases of humans and otherspecies are intimately related to water: alterations of the water cycle impact people and society by affectingtheir links with the overall Earth system.

The increasing pace of environmental changes calls for a better understanding of hydrology. It is well knownthat the total amount of freshwater on the Earth could potentially satisfy the actual and future human demand.However, the uneven spatial and temporal distribution of water resources results in insufficient water availabil-ity over large portions of the planet during several months of the year. The uneven distribution of water isresponsible for insufficient food resources, conflicts, and eventually inequitable development that can stimu-late widespread migration. Although the virtual water trade is offering the opportunity to more easily distributewater in space and time, through increasing connections between hydrology, economics, and politics, theabove water problems are still unresolved.

With such a premise, it is not surprising that the discipline of hydrology, which is rooted in engineering tosolve real water problems, emerged in the last 50 years as a primary field of geosciences. It is now calledupon to integrate across an enlarged interdisciplinary water science with fields such as geography, socialsciences, public health, engineering, and advanced monitoring technologies to solve an increasing numberof water sustainability problems.

Special Section:The 50th Anniversary of WaterResources Research

Key Points:! Legacy of hydrological sciences! Future perspectives for hydrology! A reference for young and future

generations of researchers

Correspondence to:A. Montanari,[email protected]

Citation:Montanari, A., J. Bahr, G. Bl€oschl, X. Cai,D. S. Mackay, A. M. Michalak,H. Rajaram, and G. Sander (2015), Fiftyyears of Water Resources Research:Legacy and perspectives for thescience of hydrology, Water Resour.Res., 51, 6797–6803, doi:10.1002/2015WR017998.

Received 16 AUG 2015Accepted 20 AUG 2015Accepted article online 24 AUG 2015Published online 18 SEP 2015

VC 2015. American Geophysical Union.All Rights Reserved.

MONTANARI ET AL. FIFTY YEARS OF WATER RESOURCES RESEARCH 6797

Water Resources Research

PUBLICATIONS

To address such scientific challenges, water science needs to develop a new vision in order to take bestadvantage of increasing computational power, new monitoring techniques, new opportunities for sharinginformation, and the exciting perspectives given by the tremendously enhanced international and interdis-ciplinary cooperation. Looking back in the past, one immediately realizes that most of today’s routineresearch methods could not have been developed 20 years ago, when current monitoring facilities werenot available and the opportunities for cooperation and information exchange were much fewer thannowadays.

Realizing this new vision is an exciting challenge, requiring new theories, new methods, and, above all, newthinking, as well as the capability to proactively look at the future. The science of hydrology will lead suchan endeavor, by capitalizing on its legacy and providing the means to look at water’s future with renewedmotivation and excitement.

2. The Fiftieth Anniversary of Water Resources Research

The awareness of the above scientific challenges inspired the editors of Water Resources Research (WRR)to take the exciting opportunity given by the fiftieth anniversary of the journal to promote an internationalendeavor for shaping innovative perspectives on the future of water science for people. The first issueof WRR was published in March 1965. During the past 50 years, WRR has promoted the growth of hydro-logic science by defining new cutting-edge research, contributing to the solution of important open prob-lems, and acting as a catalyst for interdisciplinary research. In the past five decades, hydrology has

Figure 1. A diagram from Robert Fludd (1574–1637) showing the segment of the macrocosm with the elemental spheres of terra (earth),aqua (water), aer (air), and ignis (fire) (from Wikimedia Commons).

Water Resources Research 10.1002/2015WR017998


emerged as a central discipline of Earth science. The amount of knowledge that has been gained is enor-mous; many new avenues of research have opened to address water problems and to develop the neces-sary knowledge. The milestone of the fiftieth anniversary of WRR is an occasion to reflect on 50 years ofresearch activity and anticipate the exciting future where hydrologists will play a fundamental role toimprove our knowledge of the Earth system, the climate, and water resources as vital elements for the ben-efit of humanity.

An open call for contributions was issued to generate a brainstorming activity and the synthesis of forwardlooking ideas. The resulting collection of papers is an ideal follow up of the special issue Trends and Direc-tions in Hydrology, that was edited by Steven Burges in 1986 to celebrate the twentieth anniversary of WRR[Burges, 1986]. Trends and Directions in Hydrology is still a milestone, providing useful references for bothyoung and senior hydrologists. The ambition of the current editors of WRR is to offer a similar inspiration forthe current and future generations of hydrologic scientists by presenting an outstanding collection ofpapers to celebrate the fiftieth anniversary of WRR. These papers provide an overview of the most advancedresearch in water science.

3. Structure of the Special Section and Overview of the Contributions

The collection of contributions dedicated to the fiftieth Anniversary of Water Resources Research is organ-ized in three chapters:

1. The legacy of hydrological sciences, which includes 12 papers.2. Water processes interpretation and modeling, including 21 contributions.3. Water resources, society, and water threats, including 23 papers.

Contributions are also indexed according to a classification of their main subject. The following subjectareas were identified:

1. Critical zone and ecohydrology (6 papers).2. Fluvial systems and hyporheic zone (10 papers).3. Global hydrology, change and human impact (7 papers).4. Groundwater flow and contaminant transport (5 papers).5. Groundwater resources (6 papers).6. Overarching principles, theories, and methods (12 papers).7. Vadose zone hydrology (2 papers).8. Water resources and risk management (8 papers).

From the above list of chapters and subject areas, readers will recognize the emerging issues in modernhydrology. We offer below a short review of each contribution, which makes clear that the framework ofthe science of hydrology is quickly evolving through a change of scales. The attention of researchers israrely dedicated to the single process or the single site; the focus is shifting from local to global spatialscales, from short to longer time scales, from individual hydrologic processes to an integrated analysis ofthe water cycle, with increasing interdisciplinary connections and international cooperation amongresearchers.

The first chapter, ‘‘The legacy of hydrological sciences,’’ presents a collection of review papers on key sub-jects synthesizing past achievements and establishing the basis for future research. Rajaram et al. [2015]provides an overview of the history of WRR and its development along its 50 year life. Cardenas [2015]presents an historical view of hyporheic zone hydrology while Binley et al. [2015] document how geophysi-cal methods have emerged over the past two decades to elucidate shallow subsurface processes. They alsooffer a vision for future developments in hydrogeophysics. Brooks et al. [2015] review recent work in catch-ment hydrology linked to hydrochemistry, hydrogeology, and ecohydrology. They highlight the significantknowledge gap in quantifying portioning of precipitation in the critical zone. Reviews of advances in snowhydrology, physically based hydrological modeling, organic contaminant transport and fate in the subsur-face, and colloid transport through saturated porous media are offered in papers by Sturm [2015], Paniconiand Putti [2015], Clark et al. [2015], Essaid et al. [2015], and Molnar et al. [2015]. Kitanidis [2015] reviews keyideas related to heterogeneity, uncertainty, and scale in subsurface flow and transport, and Bras [2015]



presents a commentary reflection on the research carried out by the author’s group in the last decades.Finally, Burt and McDonnell [2015] highlight and review a selection of field-based papers and show how fieldscientists have sometimes posed strong hypotheses and approaches.

The chapter ‘‘Water processes monitoring, modeling and interpretation’’ presents a collection of contribu-tions focusing on innovative ideas, principles, and methods. These contributions offer new perspectives forimproving our knowledge of hydrological systems and processes. Fan [2015] discusses the role played bygroundwater in the critical zone to shape large-scale patterns and processes. McKnight et al. [2015] presentideas about future directions for integrating real-time data with real-time modeling of biogeochemical proc-esses in stream ecosystems. del Jesus et al. [2015] discuss point rainfall statistics derived from satellite rainfallmeasurements. Church and Ferguson [2015], Savenije [2015], Bertuzzo et al. [2015], and Keylock [2015] focuson river morphology, river estuaries, and fluvial fluid mechanics, while Runkel [2015] and Hipsey et al. [2015]direct their attention to stream hydrodynamics and aquatic ecosystems, respectively. Harvey and Gooseff[2015] concentrate on rivers, looking at how small-scale physical drivers link to larger-scale fluvial and geo-morphic processes and ecological consequences. Lettenmaier et al. [2015] provide an overview of the inno-vative opportunities offered by remote sensing in hydrology, while Lundquist et al. [2015] comment on dataerrors and their detection. Troch et al. [2015] discuss catchment coevolution, while a global perspective isprovided by Bierkens [2015] and Roderick et al. [2015]; the former focuses on the state, trends, and directionsof global hydrology, while the latter discusses interpretation of climate model projections related to futurearidity and consistency with geological observations. Porporato and Calabrese [2015] present a novel theoryto include the probabilistic effects of random rainfall inputs to the age distributions of water in hydrologicsystems, while Condon and Maxwell [2015] examine the role of topography as a driver of groundwater fluxand water table depth. Vadose zone hydrology is the subject of the contributions by Vereecken et al. [2015]and Or et al. [2015]; the former paper presents the potential of novel technologies in advancing our under-standing of soil hydrologic processes; the latter discusses the applicability of the Richards equation for capil-lary flows. Modeling of solute transport in heterogeneous aquifers and porous media is the subject of thecontributions by Fiori et al. [2015] and Ciriello et al. [2015].

The final chapter, ‘‘Water resources, society, and water threats,’’ deals with the water-humans nexus, whichis becoming more and more important in view of the impacts on the water cycle from human-induced envi-ronmental changes. Ceola et al. [2015] present an analysis of the human pressure on water resources at theglobal level, while Cosgrove and Loucks [2015] offer new perspectives on water resources planning andmanagement under a changing environment. Water security is the subject of the study by Wheater andGober [2015], who propose that the human dimensions of water systems must be integrated into tradition-ally physical-based water science research. McLaughlin and Kinzelbach [2015] consider options for achievingfood security in a sustainable way and estimate associated demands for water and land. Kumar [2015]focuses on hydrocomplexity, proposing a conceptual framework to integrate discovery science and engi-neering, observational and information systems, computational and communication systems, and socialand institutional approaches to support novel and holistic solutions for water security. Lund [2015] offers areview of the scholarly and practical successes in integrating social and physical sciences for water manage-ment in contemporary times, while Sivapalan and Bl€oschl [2015] present a coevolutionary view of hydrologicsystems, revolving around feedbacks between environmental and social processes operating across differ-ent time scales. Vogel et al. [2015] document that water, climate, energy, food, industry, society, economy,and environment are inexorably intertwined, arguing that understanding of human footprint in physi-cal processes and the long-term coevolution of their states is needed for sustainable development andresilience. Brown et al. [2015] present a review of the history of water resource systems analysis fromthe Harvard Water Program developed in the 1960s, through its continuing evolution toward a generalfield of water resources systems science. Hornberger et al. [2015] assemble and analyze a large data-base for U.S. cities to gain a better understanding of the characteristics that lead to a transition tohigher levels of water conservation. Water, agroecosystems, and agricultural landscapes are the subjectof the contributions by Porporato et al. [2015], Foufoula-Georgiou et al. [2015], Assouline et al. [2015],and Mande et al. [2015]. Richey et al. [2015] focus on the estimation of groundwater stress at bothregional and global levels. Gambolati and Teatini [2015] provide an overview of geomechanics linkedto hydrologic processes as it has been developed and applied to predict major effects includinganthropogenic land subsidence and ground uplift over the last 100 years. A review the current state



of geologic carbon storage in deep saline aquifers is offered by Celia et al. [2015], while Tsang et al.[2015] analyze the key hydrologic issues involved in underground nuclear waste repositories. Gorelickand Zheng [2015] present an overview of the impact of global change on groundwater management,while Birdsell et al. [2015] offer a review of modeling results on the contemporary issue of hydraulicfracturing. Wohl et al. [2015] present a comprehensive review of river restoration and elaborate afuture perspective, while Doyle et al. [2015] propose to combine the influences of science, regulations,economic constraints, market demands, and intangible social expectations from other practitioners forstream restoration. Finally, Merz et al. [2015] discuss the role of surprise in flood risk assessment andmanagement.

4. Future Perspectives

The contributions presented herein clearly point out emerging ideas and ways forward for the progress ofhydrology. In particular, the following messages clearly emerge.

1. New monitoring techniques, and in particular, remotely sensed data, are offering exciting opportunitiesfor observing hydrological processes across a wide range of spatial and temporal scales. New ideas andmodels are needed to profit from ever increasing information.

2. Global-scale modeling is offering exciting opportunities for gaining a comprehensive understanding andmapping of water resources availability and water threats. Although uncertainties in global-scale model-ing are still a challenge, they are reduced by growing global data sets; therefore, working on larger spa-tial scales offers new ways forward to resolve global water problems.

3. The study of coevolution of hydrologic processes may provide new basis to gain a better understandingof system behavior and possible future scenarios.

4. Characterizing heterogeneity and quantifying its effects are an emerging challenge to gain a betterunderstanding of hydrological processes.

5. The interaction between human and water systems needs to be analyzed from new perspectives todevelop a comprehensive picture of the inherent feedbacks and coevolving processes and scenarios.

By looking at the above messages, one clearly sees that the working framework for hydrologists in2015 is distinct from that depicted by the special section Trends and Directions in Hydrology thatcelebrated the twentieth anniversary of Water Resources Research [Burges, 1986]. The traditionalbranching of the science of hydrology into subdisciplines, each focusing on a narrow portion of thewater cycle, has given way to vibrant interdisciplinary hydrologic research tradition that focuses on awide range of spatial and temporal scales, and interactions between water, earth, and biologicalsystems.

The target for hydrology in the 21st century must be ambitious; there are relevant and global waterproblems to solve, there is a compelling need to ensure sustainable development of the humancommunity. Our desire is that water science may evolve by gaining the necessary knowledge toaddress the scientific challenges posed by our era. Our hope is that water science may evolve atthe global level, to minimize inequalities between genders, across the continents, and across the eth-nic groups. Water is a unifying element, and water science will be vital to ensure that humans andour planet coevolve sustainably.

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REVIEW ARTICLE10.1002/2015WR018089

A reflection on the first 50 years of Water Resources Research

Harihar Rajaram1, Jean M. Bahr2, G€unter Bl€oschl3, Ximing Cai4, D. Scott Mackay5, Anna M. Michalak6,Alberto Montanari7, Xavier Sanchez-Villa8, and Graham Sander9

1Department of Civil, Environmental, and Architectural Engineering, University of Colorado, Boulder, Colorado, USA,2Department of Geoscience, University of Wisconsin—Madison, Madison, Wisconsin, USA, 3Institute for Hydraulic andWater Resources Engineering, Vienna University of Technology, Vienna, Austria, 4Ven Te Chow Hydrosystems Laboratory,Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA,5Department of Geography, State University of New York at Buffalo, Buffalo, New York, USA, 6Department of GlobalEcology, Carnegie Institution for Science, Stanford, California, USA, 7Department of Civil, Chemical, Environmental, andMaterials Engineering, University of Bologna, Bologna, Italy, 8Department of Geotechnical Engineering and Geosciences,Hydrogeology Group, Universitat Politecnica de Catalunya Barcelona Tech, Barcelona, Spain, 9Department of Civil andBuilding Engineering, Loughborough University, Loughborough, UK

Abstract The year 2015 marks the 50th anniversary of Water Resources Research (WRR), which wasfounded in 1965. More than 15,000 papers have been published in WRR since its inception, and thesepapers have been cited more than 430,000 times. The history of hydrology and the water sciences are alsoreflected in WRR, which has served as a premier publication outlet and instigator of scientific growth overthe last 50 years. The legacy of WRR provides a strong scientific foundation for the hydrology community torise to the challenges of sustainable water resources management in a future where dramatic environmen-tal change and increasing human population are expected to stress the world’s water resources from localto global scales.

1. Introduction

On this occasion of the 50th anniversary of Water Resources Research (WRR), as members of the current edi-torial team, we present some reflections on the history of the journal and its contributions to hydrology andwater science. We perused the collection of articles and editorials published in WRR over the last 50 years,consulted the American Geophysical Union (AGU) newsletter EOS to better understand the context for theestablishment of WRR; and examined various bibliometric indices. We also reached out to several formereditors of WRR for their recollections. WRR was fortunate to be served by 29 dedicated editors in previouseditorial teams. We found that their editorials provided an accurate window into the challenges and trendsin research during various periods, and we have drawn from them to trace the history of the journal.

As an additional approach to tracing the evolution of research trends in WRR, we considered the mosthighly cited papers in each decade in the first 50 years. Our analysis was based on the web of science. Table1 summarizes the topics covered by the 10 most highly cited papers of each decade and is referred to atseveral points below. The titles of the 10 most highly cited papers from each decade and their citation sta-tistics are included as supporting information. Additionally, we examined the 50 most highly cited papers ineach decade for a larger sample of prominent papers. Figure 1 shows word clouds (which give greaterprominence to words that appear more frequently) generated by wordle (www.wordle.net) from the titlesof these papers. We acknowledge that citations alone do not provide a complete picture of research activityor impact. Nevertheless they provide a useful window into the evolution of the discipline as reflected inWRR.

2. A Brief History of WRR

At the time when WRR was established, there were only two other scientific journals devoted to hydrol-ogy—the Hydrological Sciences Journal (established in 1956) and the Journal of Hydrology (established in1963). The first issue of WRR was published in March 1965, with Walter Langbein and Allen Kneese as

Special Section:The 50th Anniversary of WaterResources Research

Key Points:! History of Water Resources Research! Research trends in hydrology over

the last 50 years! Some bibliometrics of Water

Resources Research

Supporting Information:! Supporting Information S1

Correspondence to:H. Rajaram,[email protected]

Citation:Rajaram, H., J. M. Bahr, G. Bl€oschl,X. Cai, D. Scott Mackay, A. M. Michalak,A. Montanari, X. Sanchez-Villa, andG. Sander (2015), A reflection on thefirst 50 years of Water ResourcesResearch, Water Resour. Res., 51, 7829–7837, doi:10.1002/2015WR018089.

Received 9 SEP 2015Accepted 23 SEP 2015Accepted article online 29 SEP 2015Published online 19 OCT 2015

VC 2015. American Geophysical Union.All Rights Reserved.

RAJARAM ET AL. HISTORY OF WATER RESOURCES RESEARCH 7829

Water Resources Research

PUBLICATIONS

co-editors. The minutes of the American Geophysical Union council meeting in December 1964, as reportedin the Transactions of the American Geophysical Union from March 1965, state: ‘‘It was reported that stepswere being taken to implement the approved plan to establish a new quarterly entitled Water ResourcesResearch. Many fliers have been sent to members and to prospective subscribers. Prior to Christmas, 1680orders for the new journal had been received.’’

Under ‘‘special announcements’’ in the same issue of the transactions, the launching of the WRR is high-lighted: ‘‘The journal also covers the activities of the International Hydrological Decade. Papers in the physi-cal, chemical, or biological sciences should be sent to Walter B. Langbein, U. S. Geological Survey,Washington, D.C. 20241. Papers on the social sciences, including economies and law, should be sent toAllen V. Kneese, Resources for the Future, 1755 Massachusetts Avenue, N. W., Washington, D.C. 20036.’’Asreflected in the call for papers, the early editorial teams for WRR (1965–1985) typically involved two editors:one handling papers on physical, chemical, and biological sciences; and the other handling social sciences.Results of research from major initiatives on water resources systems analysis, such as the InternationalHydrological Decade (1965–1975) and the Harvard Water Program (initiated in 1955), were published inWRR. Walter Langbein played an instrumental role in steering the International Hydrological Decade, whichlaid the foundations for standardizing water-related data collection and long-term studies of experimentalbasins internationally. His contributions as founding editor of WRR from 1965to 1969 are recognized in atribute from Helmut Landsberg (then president of AGU) in the first issue of 1970.

George H. Davis, editor of WRR for the physical sciences from 1970 to 1976 elaborates further on the back-ground for the establishment of WRR in his 25th anniversary reflection [Davis, 1990]. He notes that Langbeinand Kneese needed to ‘‘beat the bushes’’ and vigorously solicit papers for the first issue. The very first paperin the first issue of WRR was authored by Kenneth J. Arrow, on criteria for social investments, which isrelated to the welfare theory for which he won the Nobel Prize in economics seven years later. The broadmultidisciplinary focus of WRR was already evident in the topics addressed by papers published in the1960s—economics, social issues, public policy, water resources law and regulations; many aspects of surfaceand groundwater hydrology; stream, lake and groundwater quality; pollution and contaminant transport;hydrogeochemistry; geomorphology and sediment transport; atmospheric radiation and evaporation; snowand snowmelt. The journal was already living up to the vision behind its establishment, as stated in theinside cover of the early issues:

The development of water resources is linked to many sciences. The Section of Hydrology of theAmerican Geophysical Union has long considered that its role as a forum for research in the sciencesof water transcended ‘‘hydrology’’ and included other natural sciences such as fluid mechanics, geo-chemistry, and geomorphology. This readiness to serve is now enlarged to include the sciences thatpertain to the practical reason for water research in all fields. These are the social sciences that pro-vide sound principles as guides to the public decisions about the development of water.

As evident from the mission of the journal stated above, WRR was inspired by a specific desire to integratethe social and natural sciences in the context of water resources development. Charles W. Howe (editor ofWRR for economics and social sciences, 1968–1975) in a personal communication remarked: ‘‘It tooksome urging to get the social science people to publish in WRR since their traditional outlets were else-where. Nonetheless, WRR can proudly exhibit path-breaking articles in the social science areas, including

Table 1. Topics Covered by the 10 Most Highly Cited Papers in Water Resources Research in Each Decade Since Its Inception

Decade Topics Covered by the Top 10 Most Highly Cited Papers of the Decade

1965–1974 Evapotranspiration, runoff generation mechanisms, stochastic hydrology/hydrologic time series (especially in the context of streamflow), fractional stochasticprocesses, infiltration, analytical solutions to subsurface flow and transport.

1975–1984 Subsurface transport processes, unsaturated hydraulic conductivity functions, macropores, soil moisture measurement; atmospheric radiation and surface energybalance; stochastic subsurface hydrology and macrodispersion; statistical hydrology and stochastic simulation.

1985–1994 Rainfall-runoff models (lumped and distributed), unsaturated flow modeling and soil properties, field-scale transport in groundwater and natural-gradient tracertests, inverse problems in groundwater, acid deposition and streamwater chemistry, reservoir management, lansdslides.

1995–2004 Hydrologic and hydroclimatic models, distributed and terrain-based models, ecohydrology and vegetation, calibration and uncertainty assessment of rainfall-runoffmodels, landslides, turbulence-vegetation interactions, arsenic in groundwater.

2005–2014 Uncertainties in hydrologic modeling, Bayesian data assimilation, climate change impacts, and geological CO2 storage.



historically key contributions in the study ofwater demand, the economics of water qualitymanagement and flood control.’’ Since the earlydays, environmental and natural resourceeconomists have published papers in WRR,especially on water resources development andmanagement.

In addition to the various subfields noted above,WRR was also becoming a forum for dissemina-tion of a wide range of innovative mathematicalapproaches for modeling and analysis of hydro-logic and water resources systems—analyticaland numerical methods for partial differentialequations, systems theory, stochastic and statis-tical methods, and optimization. In fact the firstspecial section in WRR was a collection of papersfrom a Symposium on Analytical Methods inHydrology in 1967, which contained overviewpapers on optimization, time series analysis,spectral analysis, nonlinear systems analysis, lin-ear hydrograph theory, finite-difference meth-ods, and electrical analogs for groundwatermodeling. A good balance of papers on engi-neering applications and scientific aspects wasalso evident in the first 5 years. By the end ofthe 1970s, WRR had developed a strong reputa-tion as an outlet for fundamental scientificinquiry into hydrologic processes and thedeeper mathematical underpinnings of model-ing approaches. Freeze [1981] notes that by thistime, WRR was widely perceived as the leadingjournal in the field. At the same time, he notesthe perception that WRR was a ‘‘theoretical jour-nal’’ that favored theoretical papers at theexpense of applied papers. He emphasized thatalthough routine applications/case studies wereunlikely to be accepted, WRR was always inter-ested in seeing more papers that reported care-ful field measurements leading to original orcreative hydrologic insights. This is a standardthat continues to be exercised in the WRRreview process to this day.

In the first decade (1965–1974), the topics thatstand out from Table 1 reflect advances in fun-damental understanding of various componentsof the hydrologic cycle—streamflow and runoffgeneration in particular, evaporation, and infil-tration. It is noteworthy that many of thesepapers indeed developed mathematical modelsand novel insights into hydrologic processes

based on field measurements, as noted by Freeze [1981]. Additional areas of focus were stochastic hydrol-ogy and the properties of hydrologic time series, and analytical solutions to groundwater flow and transportproblems, including well hydraulics. In our view, many significant theoretical developments from this period

Figure 1. Word clouds based on the titles of the 50 most highly citedpapers from each decade of Water Resources Research. The cloudsgive greater prominence to words that appear more frequently in thetitles, providing a visual representation of the themes emphasized ineach decade.



are indeed incorporated into the practice of surface and subsurface hydrology today. Concepts considered‘‘theoretical’’ at one stage in the development of a field, sometimes transition into ‘‘practical’’ tools at a laterstage.

For the second decade (1975–1984), the topics in Table 1 reflect the growing emphasis on subsurface trans-port processes and porous media, especially on unsaturated flow and soil property measurements. Therewas also a tremendous growth of stochastic modeling concepts, both in surface and subsurface hydrology,encompassing physical-stochastic models, stochastic continuum approaches, and synthetic generation ofhydrologic time series and random fields. Other topics that figure prominently in the 50 most highly citedpapers are atmospheric radiation and surface energy balance, hydrochemistry, stochastic simulation, andfundamental studies of hydrologic response.

In editorials at the end of the second decade, Cohon [1984] and Burges [1984] again reflect on the percep-tion that WRR was a ‘‘mathematical’’ or ‘‘theoretical’’ journal. Cohon [1984] writes: ‘‘A perennial problem istheory versus practice. Is WRR too theoretical? Does it really serve the needs of the readership? Is it read atall by practitioners? . . . . Someone has suggested that a new, additional water journal, focusing on applica-tions, be published by AGU.’’ In reflections from former editors of WRR on the occasion of the 25th anniver-sary, Burges [1990] comments further on the dichotomy of ‘‘scientific’’ and ‘‘engineering’’ approaches toresearch: ‘‘Engineers tend to wait and write as completely about a particular problem as is possible becausethey have needed to develop and implement a solution to that problem. The pure scientist is less problemdriven and can explore a major field of inquiry in varying levels of detail.’’ He emphasizes the importance ofWRR as an outlet for both types of work. Indeed, practical engineering applications/needs have inspired fun-damental scientific inquiry in hydrology and the water sciences, and have in turn benefitted from suchinquiry. Freeze [1990] offers the reconciliation of ‘‘process-oriented’’ and ‘‘prediction-oriented’’ schools ofstreamflow forecasting, the hydrologic cycle, and surface water research, as an example of the positiveimpact of interactions between theory and practice that WRR facilitated. The synergy between science andengineering is also apparent in the large body of papers in WRR devoted to groundwater contaminationand remediation, which encompass small-scale chemical and microbial processes controlling contaminanttransformations, field-scale computational models, and numerous controlled and natural field-scale tracertests, all of which have contributed to the science and engineering behind remediation efforts such asSuperfund in the U.S.A. and related efforts in other countries.

From the late 1980s into the mid-1990s, there was a push to establish hydrology as a distinct Earth science,or alternatively to strengthen its status as an Earth science, in parallel with efforts at the National ResearchCouncil of the United States. [National Research Council, 1991] and other initiatives aimed at strengtheninghydrological educational programs [e.g., Nash et al., 1990]. A special issue of WRR titled, ‘‘Trends and Direc-tions in Hydrology,’’ edited by Burges [1986], was published in 1986. In the editorial to that volume, Burges[1986] suggests the need for a greater coherence to the study of hydrology. Hornberger [1993], who servedas editor of WRR from 1993 to 1996, also emphasized the need to overcome fragmentation as a prerequisitefor hydrology to develop as a distinct and unified science. Beginning in this period, significant develop-ments in technology led to a vast expansion in the range of observations that hydrologists could utilize toimprove understanding of hydrologic processes (e.g., advanced weather radar systems, remote sensing, dig-ital terrain models, multi-level samplers, shallow subsurface geophysics). It is noteworthy that many of theearly papers that incorporated these technological developments in hydrologic research were reported inWRR.

Two other classes of developments occurred at the same time, providing a boost to the enterprise of hydro-logic science. First, vastly enhanced computational capabilities made it possible to bridge long-standingscale gaps in surface and subsurface hydrology: high-resolution distributed simulations of large watershedscould be performed by combining digital terrain models and smaller-scale hydrologic models; pore-scaleprocesses could be upscaled to the continuum scale; and subsurface flow and transport models couldemploy submeter-scale grids for simulating behavior at 100 m 21 km field scales. Second, theoretical para-digms for understanding the behavior of complex and heterogeneous systems evolved in many disciplines.WRR, by virtue of its reputation as a ‘‘theoretical’’ journal, led the charge in promoting novel theoreticalapproaches in hydrology and the adaptation of approaches developed in other fields. Indeed, one couldargue that researchers pursuing novel theoretical approaches to hydrologic problems could always counton WRR as a forum for disseminating their ideas. Advances in hydrologic applications of stochastic theories



and stochastic processes, geostatistical methods, Bayesian formalisms for inference and assimilation, sto-chastic optimization, scaling laws and nonlinear dynamics, all reported in WRR papers of this era, bear wit-ness to the expansion of rich analytical tools available to hydrologic science. As noted previously, asubstantial body of research on stochastic models is evident in WRR since the early days. In the period1988–1992, WRR in fact specifically designated an editor to handle papers on stochastic hydrology andrelated areas (Soroosh Sorooshian), while a different editor (Roger Smith) handled papers on physical stud-ies of hydrologic processes.

The third decade 1985–1994 emphasized hydrological modeling. Large-scale natural gradient tracer tests ingroundwater, modeling field-scale dispersion processes, and rainfall-runoff modeling were prominenttopics (Table 1). The breadth of topics covered for 1985–1994 in Table 1 is quite impressive, including aciddeposition and hydrochemical response of watersheds, reservoir management, and landslides. A moredetailed examination of the 50 most highly cited papers reveals a vast expansion of modeling capabilitiesin unsaturated zone hydrology, rainfall runoff processes, and reactive contaminant transport. This periodalso witnessed the integration of mature stochastic streamflow models and stochastic optimization theoryto greatly advance the framework for reservoir operations and water resources management, in what maybe viewed as a culmination of the original vision behind the Harvard Water Program.

In the later half of the 1990s, efforts to strengthen hydrologic science intensified further. The challenges inmaintaining the interdisciplinary flavor of WRR during this time of rapid development and emergence ofother journals in hydrology are summarized in an editorial by Gray and Bencala [2003]. In Table 1, summariz-ing the topics of the 10 most highly cited papers for this period, we find the emergence of hydroclimaticmodels, ecohydrology and vegetation, turbulence-vegetation interactions, and interest in global water crisessuch as arsenic in groundwater. Additionally, research at the interface between hydrology and geomorphol-ogy expanded significantly, while traditional areas such as groundwater continued to receive attention. Closerexamination of the detailed titles of the 50 most highly cited papers suggests an emerging focus on hydro-logic processes and models at scales beyond the ‘‘traditional’’ watershed scale, to regional and continentalscales, and the relevance of soil moisture measurements and dynamics in this context. Analyses of regionaland continental hydrologic data sets also expanded significantly during this period. These developments andtheir influence on hydrology and WRR are recognized in an editorial by Parlange et al. [2005]: ‘‘We envisionWRR continuing as a leader in defining processes that enable upscaling to regional and continental scalesand downscaling to subgrid-scale processes such that the full dynamics of eco-chemo-hydrological systemscan be appreciated and quantified.’’ The emphasis on an integrated hydrologic science comes across clearlyin this vision. It would be fair to say that the hydrology community was making progress towards achieving asense of coherence and overcoming the fragmentation alluded to by Hornberger [1993]. However, there isroom for further progress to this day. Continued efforts must be pursued to build a coherent science by moretightly relating different studies and making published research outcomes generalizable, as noted in themore recent editorial of Bl€oschl et al. [2014]. Hydrologic processes set up a template for a host of other proc-esses influenced by water—including geomorphology, aqueous geochemistry, and ecology. One could addthat advances in all these fields benefitted indirectly from developments in hydrology; this is very much inevidence from the broad interdisciplinary flavor that comes across in WRR during the 1990s and 2000s, andthe fact that researchers from other disciplines regarded WRR as an attractive publication outlet.

The coupling of atmospheric, ecological, and hydrologic models in the context of global environmentalchange led to significant interactions between hydrologists and other geoscientists, with mutual benefits.Efforts to predict global environmental change have benefitted from the incorporation of hydrologic feed-backs in land-atmosphere coupled models. As a result, new opportunities for research in hydrologic scienceemerged, while also expanding the scope of hydrologic practice. The influence of climate change and low-frequency climate variability indices such as El Ni~no on regional streamflows, drought indices, snowpack,and snow hydrology, were also recognized as a result of greater communication across disciplines, andhave contributed significantly to hydrologic forecasting in the context of water management. This is yetanother example of the synergy between theory and practice alluded to by Freeze [1990].

For the period 2005–2014, Table 1 reflects an emphasis on uncertainty assessment. A detailed examinationof the 50 most highly cited papers reveals developments in Bayesian data assimilation techniques appliedto hydrologic models across a range of scales. A new paradigm of global hydrology began to expandgreatly during this period, and several prominent papers addressing global water issues appeared in WRR.



At the same time, the emphasis on ecohydrology and soil moisture continued, while the fields of hydrogeo-physics and subsurface carbon sequestration expanded significantly.

For a period of 16 years (1993–2008) that marked the emphasis on hydrologic science, the editors of WRRwere selected exclusively from the natural sciences. This is not to say that the social science and policyissues were no longer of interest to WRR. In fact, a deputy editor was explicitly assigned to this areabetween 1993 and 2004. Yet, there was a decline in submissions in these areas during the 1990s, and edito-rial teams made efforts to address this. Despite this trend, it is interesting that notable economists contin-ued to publish papers in WRR during this period (including Elinor Ostrom, the only woman to win the NobelPrize in economics to date). Four special sections were devoted to economics and policy in 2004 (the mostrecent previous special sections on these themes had been published in 1993). In the later half of the2000s, the broad themes of water and resource sustainability under climate change came to the fore. Theterm ‘‘anthropocene’’ had already been coined in 2000 to recognize the impact of humans on Earth’s eco-systems. The emergence of global water sustainability and water security as important themes are allclosely related to the notion of change, of considering the long-term dynamics of the water cycle, and ofincluding pervasive human influence during the anthropocene, which is inherently shaped by social andeconomic factors. Quite appropriately, the editorial teams of WRR since 2008 have again included an editorrepresenting the social sciences, economics, and policy. A search in web of science indeed reveals a sharpincrease in the number of papers published in these fields (not just in WRR, but in all journals), in the laterhalf of the 2000s.

In their editorial, Kumar et al. [2009] highlight the changes in the hydrologic cycle at several scales in rela-tion to climate change. They present a renewed charge to the hydrology community: ‘‘The interaction ofthe water cycle and its components across interfaces, disciplines, and scales continues to pose challenges.We welcome articles addressing this coupling and complexity of the hydrologic cycle, the mass and energytransport it facilitates, and the interactions of both natural and anthropogenic processes.’’ It is interestingthat this renewed interest in social sciences and water science for society (one of the themes of this specialissue) is reminiscent of the early years of WRR. WRR may be going back to its roots. The close link of WRRwith early international initiatives such as the International Hydrological Decade and Harvard Water Pro-gram of the 1960s and 1970s, parallels the link between the water science for society theme and currentinternational initiatives such as the Panta Rhei scientific decade promoted by the International Associationof Hydrological Sciences [Montanari et al., 2013].

Much of the early work on human-water interactions revolved around the impact of water on people(including many economic studies); later research centered around the impact of people on water (includ-ing contamination and environmental impact studies); the more recent thrust on sociohydrology may be areflection of the greater recognition of the importance of feedbacks between people and water, which occuracross a range of spatial and temporal scales. The interdisciplinary view that WRR has so effectively fosteredover the last 50 years will then be moved forward to a new coevolutionary view that accounts for the rapidand widespread changes brought about by humans, where the human influence is considered an integralpart of the hydrologic cycle. In approaching these renewed challenges, the 50 year legacy of WRR—the richbody of papers collectively representing tremendous developments in theoretical and computational tools,modern observational and remote sensing technologies, undoubtedly provides a valuable foundation forfuture research.

3. Vignettes on the Financial Aspects of WRR

The financial backdrop for WRR’s establishment is discussed in the appendices of the March 1965 issue ofthe Transactions of the American Geophysical Union—funds were being borrowed from the general reserveof AGU under security of the Horton will, and the council was attempting to secure a grant of $25,000 to aidin the establishment of the journal. The subscription rates were set at $3.00 per calendar year for AGU mem-bers and $6.00 for nonmembers. The expectation was that WRR would be financially self-sufficient within afew years.

The success of WRR as a leading outlet for papers in the water sciences was already evident in the growthfrom a quarterly to a bimonthly publication, starting in 1968 (WRR transitioned to a monthly publicationmuch later, in 1984). By this time, hydrology had already become the largest division within AGU. Davis



[1990] notes that the growth of WRR during this period posed a bit of a challenge for financial reasons.Despite significant growth, the journal was incurring losses, to some extent because of the large number ofpapers on which page charges were not paid. An unusual practice of deferring publications at the end ofthe year (which led to ‘‘thin’’ December and ‘‘fat’’ February issues) was sometimes resorted to, in an attemptto balance budgets. Davis [1990] further notes: ‘‘To AGU’s everlasting credit, however, AGU never rejectedor deferred papers on the basis of whether or not page charges were honored. In my experience, the onlycriterion for publication was technical merit.’’ Freeze [1981] also recalls a misconception among manyauthors that they would not be able to publish their papers in WRR because of an inability to pay pagecharges. In this context, the hydrology community owes a debt to AGU for its sustained support of WRRthrough difficult financial periods. To this day, WRR continues to offer reasonable subscription rates ($138per year online subscription for individuals), thus maintaining its tradition as an accessible publication out-let. Publication costs in WRR today are free of charge up to 25 publication units, with a cost of $125 per pub-lication unit thereafter (a publication unit refers to 500 words of text or a figure or table). In step withtechnological developments that impacted research, the review process in WRR began to transition to elec-tronic submission and review in 2001. Today WRR is mostly an electronic publication, although a few indi-vidual paper subscriptions continue to be honored. WRR is now accessible to researchers worldwide, andthe current policy enables free electronic access to papers between 1997 and 24 months prior to the accessdate.

In 2012, the Board of Directors of AGU decided to outsource the production, sales, distribution, and sub-scription of AGU journals to Wiley-Blackwell starting from January 2013; while retaining ownership and con-trol of the scientific aspects of publications, including editorial control and oversight by AGU governance.This decision was motivated by a need to stay up-to-date in a rapidly evolving publishing marketplace, byadopting a business model for journal production that is widely used by scientific associations. Specifically,with this publication model, the volunteer leadership and staff resources can be focused exclusively onadvancing scientific content, improving quality, and sustaining editorial excellence, rather than on theoperational functions of publishing. Although this may be viewed as a very significant change, the accessi-bility of WRR for authors, the efficiency of the review and publication process, and the scientific reputationof the journal are largely unaffected by it.

4. Some Bibliometrics

The number of papers published in WRR in each year since 1965 is shown in Figure 2. After a period of rapidgrowth between 1965 and 1972, there was a slight decline until 1980 ("200 papers/year in 1979–1980).Subsequently, there was another period of rapid growth until 1995 ("340 papers/year in 1994–1995), fol-lowed by a leveling off until 2005. After 2005, the number of papers has increased substantially in this eraof digital and electronic publication. The number of papers published in 2013 and 2014 were 628 and 591,respectively. Overall, more than 15,000 papers have been published in WRR since its inception. As WRR hasgrown, the magnitude of the number of papers that requires handling has also increased. For instance,there were 1461 submissions in 2013. Correspondingly, the number of associate editors (AEs) also grewfrom about 25 in 1980 (at its inception in 1965, there were 12), to 40 in 1990 (the 25th year) to about 100today. On average, AEs handled about 15 manuscripts per year in 2013. Between 1993 and 2004, the

Figure 2. Papers published in Water Resources Research each year since its inception in 1965.



composition of the editorial board waschanged from the original model of twoeditors with one focused on physical,chemical, and biological sciences, andanother on social sciences, economics,and policy. From 1993 to 2000, therewas a single editor, followed by two edi-tors (2001–2004), with several deputyeditors (DEs) handling different disci-plines between 1993 and 2004. Duringthis period, almost all volumes of WRRappeared with separate sections—sub-surface hydrology; surface water and

climate; hydrogeochemistry and water chemistry; water policy, and economics; and erosion, sedimentation, andgeomorphology. However, it should be emphasized that this division of papers was not intended to separatethe sub-disciplines. It was motivated by a request from the geomorphology community to provide themwith a clearly identified home within the AGU family of publications. Deputy editors were initially assignedto each of the sections mentioned above, but subsequently, the number of DEs ranged from 4 to 10, andthe disciplines covered by the DEs also varied in response to submission trends. Due to the significantgrowth of WRR, the number of editors was increased to five in 2005, eliminating DEs, and grew to eight in2013. Starting in 2005 (coincidentally Journal of Geophysical Research—Earth Surface Processes, incorporat-ing geomorphology, was initiated in 2003), the separation into disciplinary sections was discontinued, toencourage broad submissions and interdisciplinarity that transcended such separation.

In terms of citations, papers published in WRR have been cited over 430,000 times as of 1 September 2015.A total of 31 papers have been cited more than 500 times; most of these papers are reflected in the topicslisted in Table 1. The number of papers cited more than 400, 300, 200, and 100 times, respectively exceed50, 100, 270, and 900. Table 2 shows the total number of citations of WRR papers published in each decade,along with the corresponding cumulative average citations per paper, h-index, and average number of cita-tions during the years 2012–2014. The highest cumulative citations are associated with the papers from1985 to 1994, with an average of 47 citations per paper and an h-index of 159. The lower citations of thepapers from 1995 to 2004 and 2005 to 2014 are in large part due to the time it takes to build up citations.The citations of these papers in 2012–2014 are significantly higher than those of the 1985–1994 papers,and the average citations per paper from 1995 to 2004 may well exceed 50 by the end of this decade. Thesemetrics are clearly indicative of an active and vibrant journal. It is noteworthy that the impact factors ofWRR in 2013 and 2014 were 3.709 and 3.549, respectively, which are the highest among journals inhydrology.

5. Concluding Remarks

During its first 50 years, WRR has witnessed the growth of the discipline of hydrology not just as a publica-tion outlet, but as an instigator of scientific growth by defining new cutting-edge research, contributing tothe solution of important open problems, and acting as a catalyst for interdisciplinary research by produc-ing collections of papers and special volumes. The history of WRR is intertwined with the history of hydrol-ogy and provides a unique perspective on the evolution of the field and the increasing human pressure onwater resources. WRR clearly exemplifies the vital role that journals and scientific publishing play for science,to catalyze scientific discovery and futuristic ideas.

The legacy of WRR provides everlasting inspiration and sets the stage for the hydrology community to riseto the monumental challenges of sustainable water supply and security in a period of dramatic environ-mental change and increasing human population. Challenges related to the water-food-energy nexus, car-bon capture and sequestration, and global environmental sustainability also loom large. Research inhydrology and water resources management will be increasingly affected by (and increasingly importantfor) social development and conflict resolution at the international level. WRR remains committed to servingas a forum for dissemination of novel research that will address these themes. We look forward to the

Table 2. Citation Statistics for Water Resources Research Papers from EachDecade as of 1 September 2015a

Period

Number ofPapers

PublishedTotal

Citations

AverageCitationsper Paper h-Index

CitationsDuring

2012–2014

1965–1974 1,629 40,277 25 93 1,1641975–84 1,976 80,342 41 126 3,0701985–94 2,981 140,716 47 159 5,7761995–2004 3,365 127,257 38 131 9,1912005–2014 4,873 58,488 15 79 12,590

aThe number of papers published in each period varied significantly (seeFigure 1). Note that older papers have received citations over a longer periodthan more recent papers.



second 50 years of WRR, where continued research into physical, chemical, and biological processes andinteractions between them, interactions between natural and anthropogenic systems, innovative measure-ment and sensing technologies, advanced modeling frameworks, and increasing collaborations betweenhydrology and other disciplines, will establish the foundations for an integrated understanding of waterfrom local to global scales.

ReferencesBl€oschl, G., A. B"ardossy, D. Koutsoyiannis, Z. W. Kundzewicz, I. Littlewood, A. Montanari, and H. Savenije (2014), Joint Editorial: On the future

of journal publications in hydrology, Water Resour. Res., 50, 2795–2797, doi:10.1002/2014WR015613.Burges, S. J. (1984), Water Resources Research: The Twentieth Year, Water Resour. Res., 20(3), 321–322.Burges, S. J. (1986), Trends and directions in hydrology, Water Resour. Res., 22(9), 1S–5S.Burges, S. J. (1990), Water resources research: Past, present and future, Water Resour. Res., 26(7), 1321–1322.Cohon, J. L. (1984), Taking stock and saying thank you, Water Resour. Res., 20(1), 1.Davis, G. H. (1990), A quarter century of Water Resources Research, Water Resour. Res., 26(1) 2–4.Freeze, R. A. (1981), A former editor views the editorial process, EOS Trans. AGU, 62(38), 673–675.Freeze, R. A. (1990), Water resources research and interdisciplinary hydrology, Water Resour. Res., 26(9), 1865–1867.Gray, W. G., and K. E. Bencala (2003), Editorial, Water Resour. Res., 39(11), 1325, doi:10.1029/2003WR002829.Hornberger, G. M. (1993), Editorial, Water Resour. Res., 29(5) 1351–1352.Kumar, P., T. Illangasekare, G. Sander, J. Selker, and T. Torgersen (2009), Editorial: Building on the legacy of Water Resources Research, Water

Resour. Res., 45, W06101, doi:10.1029/2009WR008174.Montanari, A., et al. (2013), ‘‘Panta Rhei—Everything Flows’’: Change in hydrology and society—The IAHS Scientific Decade 2013–2022,

Hydrol. Sci. J., 58(6), 1256–1275.Nash, J. E., P. S. Eagleson, J. R. Philip, W. H. Van der Molen, and V. Kleme#s (1990), The education of hydrologists (Report of an IAHS/UNESCO

Panel on hydrological education), Hydrol. Sci. J., 35(6), 597–607.National Research Council (1991), Opportunities in the Hydrologic Sciences, Washington, D. C.Parlange, M. B., B. Berkowitz, A. Porporato, T. Torgersen, and S. W. Tyler (2005), Editorial: Future of Water Resources Research, Water Resour.

Res., 41, W01001, doi:10.1029/2004WR003899.

AcknowledgmentsWe dedicate this paper to all theformer editors and deputy editors,current and former associate editors,conscientious reviewers, editorialassistants, and other AGU staffaffiliated with WRR, who havecontributed to WRR over the last 50years. We also gratefully acknowledgethe American Geophysical Union’ssupport of WRR over the last 50 years.We contacted several former editors ofWRR for clarifications on variousaspects of its history. We thank themsincerely for sharing their insights andexperience. Last but not least, wethank the entire hydrology communityfor their support—a journal succeedsonly if it consistently receives excellentsubmissions from a community ofauthors.



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