Theodore C. Hsiao

Theodore C. Hsiao, Emeritus Professor of Land, Air and Water Resources at the University of California, Davis, passed away peacefully at home on October 16, 2023 at the age of 91.

Theodore (Ted) Hsiao was born and grew up in China, where he developed his interest in agriculture while observing peasants in the fields around Kunming. His father became a member of China’s United Nations delegation and relocated the family to the U.S. while Ted was in high school. As his father’s death and the communist revolution prevented the family’s return to China, he finished high school in New York City. After receiving his B.S. in Soil Science at Cornell University in 1955, he was drafted into the U.S. Army. While serving in Germany from 1956 to 1958, he met and married his German wife, Edith Dürr. He subsequently returned to the U.S. to pursue a M.S. degree in Soil Chemistry and Fertility at the University of Connecticut from 1958 to 1960. His interest in international agriculture led him to pursue a Ph.D. in Crop Physiology and Biochemistry from the University of Illinois, which he received in 1964. He then worked for two years as an Assistant Research Plant Physiologist at UCLA before being hired as an Assistant Professor at UC Davis in 1965, initially into the Water Science and Engineering Department, which later merged into the Land, Air and Water Resources Department. He was promoted to full Professor in 1975 and served with distinction until his retirement in 2004. He remained active as emeritus faculty, submitting his final paper for publication just three months before passing away.

Hsiao’s research focused on plant-water-soil interactions and crop productivity in relation to water and climate. His early studies were more biochemical, identifying the physiological responses of plants to water deficits. This included pioneering studies of how stomata (pores in the leaves allowing entry of carbon dioxide but also evaporation of water) are regulated to optimize photosynthesis and, particularly, the importance of plant cell turgor pressure for growth. His review of “Plant Responses to Water Stress” in the Annual Review of Plant Physiology in 1973 became one of its most highly cited articles ever, having now been cited nearly 6000 times. His interests then moved first towards field studies of crop performance and water use, and then to various agricultural applications of plant water relations aimed at the efficient and productive use of water in agriculture. In the last decade of his career and during retirement, he embodied that knowledge in work focused on crop yield response to water and a computer simulation of crop water use and productivity as a lead member of the core group supported by the Food and Agriculture Organization of the United Nations (FAO) that developed the AquaCrop model. This model has a water-driven engine that simulates water-limited crop yields. Hsiao taught trainings on its use in many countries around the world to assist water managers in optimizing both crop water-use efficiency and yield. His commitment to AquaCrop, from 2003 until the last meeting he attended in Tunisia in 2o19 and beyond, was exceptional and led to its global adoption.

Hsiao’s leadership in all these areas resulted in his receipt of the Alexander von Humboldt Prize for Senior U.S. Scientists from Germany in 1985, and he was recognized for outstanding contributions to drought studies at the Interdrought II conference in Rome in 2005. He was awarded a Doctor Honoris Causa by the University of Lleida, Spain in 2005 and Honorary Membership by the American Society of Agronomy in 2007. He has been listed among most-cited researchers in agriculture for more than a decade, with more than 100 published works and over 13,000 citations.

At UC Davis, Hsiao taught a number of undergraduate and graduate courses on water science, hydrology, evapotranspiration and water management. He was also invited to offer lectures or courses on these topics in Chile, China, India, Italy, Morocco, Spain, Taiwan, Turkey and other countries. He supervised 6 M.S. students, 20 Ph.D. students and mentored 27 international postdoctoral researchers and visiting scholars, many of whom went on to distinguished and honored careers around the world.

Hsiao also contributed to numerous and diverse service activities. He served on the editorial boards of a number of key refereed journals in his field and as a reviewer for many journals and granting agencies. He was a member of scientific advisory committees and exchange panels for diverse governmental agencies and organizations. He spent sabbatical leaves in Australia (Australian National University), Philippines (International Rice Research Institute) and Germany (University of Bayreuth), and presented dozens of invited speeches at conferences around the world, which continued for a decade after his official retirement. He also served on numerous academic committees at UC Davis, including chairing the Personnel Committee of the College of Agricultural and Environmental Sciences in 1991-92.

In addition to these more readily documented impacts, Hsiao exerted an inspirational influence on his students and colleagues. He was unique in his exceptional analytical and critical thinking, being able to retain a comprehensive view of the biological system under investigation, from cell to field scale, from plant physiology to agronomy. He always required excellence in the performance of research and was uncompromising in assuring the integrity of his own and his students’ research. Similarly, he was an informed critic of any research or publications that did not meet his standards. An important lesson to his mentees was that just because something was published did not prove it was correct. He lamented the valuing of citation volume over publication quality, as well as the pressure on graduate students to immediately focus on research with an eye to publication, at the expense of taking coursework that would give them a broad foundation of knowledge for their career. At the same time, he was quick to praise and support high-quality efforts and to be a collegial contributor in collaborations. When asked, Hsiao was always responsive and available to provide guidance and mentoring to his peers and junior colleagues for their success and the greater good of scientific advancement. His devotion to plant science, his work ethic, and his family loyalty were inspiring to his younger colleagues and made him a terrific mentor. As noted by one of his former postdoctoral researchers, “I experienced first-hand Ted’s amazing command of the field of water stress physiology and his creative and detailed approach to research, and that experience has endured as a source of inspiration and stimulation.” Hsiao, in turn, felt fortunate to receive what he described as “a lifelong education” from his graduate students and postdocs.

Not only was Hsiao an outstanding scientist and dedicated teacher, but he was also committed to outreach. As an expert in plant stress physiology, he promoted improvements in irrigation management for the public good. He was a strong supporter of the University of California Cooperative Extension (UCCE) efforts to enhance water use efficiency within the State. In particular, he was actively involved in multimillion-dollar state-funded projects to improve water management, including the California Irrigation Management Information System (CIMIS) and the California Crop Coefficient (3-C) Science Collaborative. Hsiao was a valuable resource and mentor for UCCE specialists and farm advisors, which greatly impacted the quality and quantity of information disseminated to all people involved in enhancing the performance and sustainability of irrigated agriculture and urban plant water use within and beyond California.

Hsiao’s cherished wife Edith predeceased him in 2019, and he is survived by his sons Terence and Gregor and his grandchildren, Melina, Leilani, Karsten and Melani.

Kent Bradford
Elias Fereres
Kyaw Tha Paw U
Wendy Silk
Ken Shackel
Bob Sharp
Rick Snyder
Pasquale Steduto
Daniele Zaccaria