Abstract
Abstract. Hydrology has undergone almost transformative changes over the past 50 years. Huge strides have been made in the transition from early empirical approaches to rigorous approaches based on the fluid mechanics of water movement on and below the land surface. However, progress has been hampered by problems posed by the presence of heterogeneity, including subsurface heterogeneity present at all scales. The inability to measure or map the heterogeneity everywhere prevented the development of balance equations and associated closure relations at the scales of interest, and has led to the virtual impasse we are presently in, in terms of development of physically based models needed for hydrologic predictions. An alternative to the mapping of heterogeneity everywhere is a new Earth system science view, which sees the heterogeneity as the end result of co-evolutionary hydrological, geomorphological, ecological, and pedological processes, each operating at a different rate, which help to shape the landscapes that we find in nature, including the heterogeneity that we do not readily see. The expectation is that instead of specifying exact details of the heterogeneity in our models, we can replace it (without loss of information) with the ecosystem function that they perform. Guided by this new Earth system science perspective, development of hydrologic science is now addressing new questions using novel holistic co-evolutionary approaches as opposed to the physical, fluid mechanics based reductionist approaches that we inherited from the recent past. In the emergent Anthropocene, the co-evolutionary view has expanded further to involve interactions and feedbacks with human-social processes as well. In this paper, I present my own perspective of key milestones in the transformation of hydrologic science from engineering hydrology to Earth system science, drawn from the work of several students and colleagues of mine, and discuss their implication for hydrologic observations, theory development, and predictions.
Highlights
Hydrology has undergone an almost complete transformation over the past century, from its empirical origins in the early 20th century, to become a fully fledged and key component of Earth system science by the early 21st century (Chow, 1964; Sivapalan and Blöschl, 2017)
Due to data limitations and limits on computing power, early modeling efforts were restricted to small catchments, and their goal was limited to generating process understanding, and not so much to making predictions in real catchments (Stephenson and Freeze, 1974; Freeze, 1974)
The biggest strength of the top–down approach is the biggest drawback of the bottom–up approach, and vice versa (Sivapalan et al, 2003). These two perspectives will remain irreconcilable until major breakthroughs are made in our understanding of multi-scale spatial heterogeneity and temporal variability, no doubt governed by Newtonian mechanics at small scales, the resulting cross-scale interactions and adaptations at long timescales governed by ecological laws, and the understanding of how these contribute to whole ecosystem function and manifest themselves in more holistic and simplified parameterizations of catchment responses (Sivapalan, 2005; McDonnell et al, 2007)
Summary
Hydrology has undergone an almost complete transformation over the past century, from its empirical origins in the early 20th century, to become a fully fledged and key component of Earth system science by the early 21st century (Chow, 1964; Sivapalan and Blöschl, 2017). Sivapalan: Milestones in the transformation of hydrologic science view of the vast landscape that hydrologists have collectively traversed, so perspectives abound This is not the first commentary of its kind: my thinking during my formative years was guided by the writings of Vit Klemeš and James Dooge, including their classic papers (Klemeš, 1983, 1986; Dooge, 1986). Their writings have provided unique perspectives on the field of hydrological science and its evolution over the past several decades. I hope that by re-telling this story through the admittedly narrow prism of my own observations and experience as a catchment hydrologist, I might be able to provide fresh impetus to early career hydrologists and new entrants to the field, and encourage them to reflect on and chart the course of their own future education and research
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
