Soroosh Sorooshian

2013 Robert E. Horton Medal Winner

Soroosh Sorooshian was awarded the 2013 Robert E. Horton Medal at the AGU Fall Meeting Honors Ceremony, held on 11 December 2013 in San Francisco, Calif. The medal is for “outstanding contributions to hydrology.”


I am proud to introduce Soroosh Soroosh­ian, distinguished professor of civil and environmental engineering and Earth system science at the University of California, Irvine, as the 2013 Horton medalist. Soroosh is an exemplary scholar, who through collaborations with Hoshin Gupta and numerous other talented students and researchers, has made many landmark contributions to hydrology. I will highlight what I consider to be his principal contributions. In the early 1980s, Soroosh was among the first to provide a better statistical underpinning of the rainfall-runoff model calibration problem. This work is still a main reference for hydrologic parameter estimation. Later that decade, Soroosh was the first to explain why local search methods were unable to locate the “best” hydrologic parameter values. This led to the SCE-UA algorithm. The profession suddenly had a consistent way to calibrate watershed models.

In the 1990s, Soroosh and his students introduced artificial neural networks to model the rainfall-runoff transformation. This work reenergized interest in black box models. Later, Soroosh’s group presented a multicriteria approach to model calibration that opened up new frontiers and inspired many of us to better recognize the role of model error. Soroosh then embarked upon a journey to use remote sensing data for precipitation estimation. This led to PERSIANN, used worldwide to predict rainfall amounts at different spatial and temporal scales.

In the 2000s, Soroosh and his students introduced particle-filtering and model-averaging approaches to better characterize modeling errors. This work is at the center of the current debate on uncertainty quantification and has revived the use of data assimilation approaches.

At the same time, Soroosh engaged in sustainability studies to improve water resources management by initiating the Sustainability of Semi-arid Hydrology and Riparian Areas (SAHRA), a National Science Foundation Science and Technology Center. Especially noteworthy are his contributions to understanding the role of climate and soils in regional- and global-scale hydrology, inferring snowpack depths and riparian vegetation from remote sensing data, and understanding the relationship between seasonal streamflow variations and snowpack in the western United States.

Most recently, Soroosh started working on the effects of irrigation on local/regional weather and climate. Further, he has worked tirelessly in the service of the community, as chair of the Science Steering Group of the Global Energy and Water Cycle Experiment (GEWEX), a member of the National Oceanic and Atmospheric Administration Science Advisory Board, and a member of several National Research Council committees. He has also testified to both the U.S. House and Senate committees on water resources issues and has served AGU in numerous roles: editor of Water Resources Research, Hydrology section president, and chair of the Public Affairs Committee.

Soroosh is also an outstanding educator. Many of his former students occupy leading positions in academia, industry, and government. In summary, Soroosh is a skilled diplomat who has propelled hydrology to new synergies and discoveries. His wisdom and vision have inspired many to succeed in their careers. Please join me in congratulating Soroosh Sorooshian as this year’s Horton Medal winner.

—JASPER A. VRUGT, University of California, Irvine


It is a true honor to be named the 2013 Robert E. Horton medalist by AGU. To be considered for such an honor, one must be nominated for consideration. I am grateful to Jasper Vrugt for having led my nomination and to colleagues who wrote supporting letters on my behalf.

My journey to present started in 1967 when I arrived in California from Iran to pursue college education. Cal Poly–San Luis Obispo, where I earned my B.S. degree in mechanical engineering, provided the finest possible hands-on engineer education one could wish for.

My graduate studies at the University of California, Los Angeles (UCLA) in systems and water resources engineering provided me the most unique opportunity to think outside the traditional disciplinary framework and led to my research interests in the parameter estimation of hydrologic models using my optimization knowledge.

I owe much to the three academic institutions (Case Western Reserve University (CWRU), the University of Arizona (UAZ), and the University of California, Irvine (UCI)) that have given me the opportunity to teach and pursue my research interests with access to some of the finest doctoral students one can wish for.

AGU was the first professional society I joined as a member. By far, among all my professional activities AGU has played a key role in my success, with the Horton Medal being the capstone. Serving as the editor of Water Resources Research provided me the opportunity to appreciate the wide range of facets of the hydrologic cycle, leading to some of my research pursuits in hydroclimatology. The presidency of the Hydrology section also provided the most valuable experience with respect to leadership in the functioning of a large professional organization such as AGU.

While the honor has come to me, it is a shared prize with many people who, over the past 40 years, have played a major role in my career. First and foremost is John Dracup, my Ph.D. advisor at UCLA who introduced me to surface hydrology and rainfall runoff modeling; William “Bill” Yeh and Moshe Rubinstein of UCLA also played a major role in my career development. A special thanks goes to Yacov Haimes, who recruited me for my first academic job at CWRU.

During my 20 years at UAZ I benefited from the friendship and wisdom of many colleagues, particularly Ernest Smerdon, Shlomo Neuman, Lucien Duckstein, Tom Maddock, Jim Shuttleworth, Juan Valdes, Roger Bales, and my deceased colleagues Nathan Buras, Don Davis, and Stan Davis.

The contributions of my former graduate students to my success have been indispensable. To name a few, I am indebted to my first doctoral student, Hoshin Gupta. Also, I wish to acknowledge Qingyun Duan, Kuolin Hsu, Xiaogang Gao, David Goodrich, Bisher Imam, and Karen Humes for encouraging me to pursue hydrologic remote sensing.

I would be remiss if I did not acknowledge a few special colleagues, such as Steve Burges, David Dawdy, and John Schaake.

Finally, no success in one’s career can be achieved without the unconditional support of family. My wife of 38 years, Shirin, has done so much that words cannot express my gratitude. Our two sons, Jamshid and Armin, successful in their own respective careers, have been a source of joy and pride for us.

—SOROOSH SOROOSHIAN, University of California, Irvine