Hydrol. Earth Syst. Sci., 22, 1665–1693, 2018 https://doi.org/10.5194/hess-22-1665-2018 © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License. From engineering hydrology to Earth system science: milestones in the transformation of hydrologic science Murugesu Sivapalan1,* 1Department of Civil and Environmental Engineering, Department of Geography and Geographic Information Science, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA * Invited contribution by Murugesu Sivapalan, recipient of the EGU Alfred Wegener Medal & Honorary Membership 2017. Correspondence: Murugesu Sivapalan (
[email protected]) Received: 13 November 2017 – Discussion started: 15 November 2017 Revised: 2 February 2018 – Accepted: 5 February 2018 – Published: 7 March 2018 Abstract. Hydrology has undergone almost transformative hydrology to Earth system science, drawn from the work of changes over the past 50 years. Huge strides have been made several students and colleagues of mine, and discuss their im- in the transition from early empirical approaches to rigorous plication for hydrologic observations, theory development, approaches based on the fluid mechanics of water movement and predictions. on and below the land surface. However, progress has been hampered by problems posed by the presence of heterogene- ity, including subsurface heterogeneity present at all scales. எப்ெபாள் யார்யாரவாய் ் க் ேகட்ம் The inability to measure or map the heterogeneity every- அப்ெபாள் ெமய் ப்ெபாள் காண் ப த where prevented the development of balance equations and In whatever matter and from whomever heard, associated closure relations at the scales of interest, and has Wisdom will witness its true meaning.