From the REA Concept to a High Resolution Digital Twin of the Earth's Water Cycle
Authors: Samaniego Luis 
Published: March 2022

&lt;p&gt;Eric F. Wood will be remembered as a visionary scientist and mentor to many hydrologists. As a master student, I had the good fortune to read one of his thought-provoking questions: &lt;em&gt;What modelling experiments need to be performed to resolve the scale question?&lt;/em&gt; [1]. Further reading of his scientific contributions led me to appreciate the usefulness of the representative elementary area concept (REA) [2] for developing meso- or macro-scale hydrological models that benefit from the subgrid variability of model paramterizations to derive hydrological fluxes at multiple scales. Eric's scientific writings intrigued us so much that they lead to the development of the multiscale parameter regionalization (MPR) [3] technique originally implemented in the mesoscale hydrological model [4] and now applicable to any land surface model to derive seamless parameter fields at continental or global scales [5].&lt;/p&gt;&lt;p&gt;Eric was an early advocate of &lt;em&gt;hyperresolution global land surface modeling&lt;/em&gt; and continental drought monitoring and forecasting initiatives [6,7]. His support and motivation were key to devising a project to demonstrate, for the first time, the feasibility of a high-resolution seasonal forecasting and projection system for Europe using a multi-model approach that use the same hyperresolution physiographic datasets and a common river routing model to reduce the predictive uncertainty of the target variables. We called this project the &lt;em&gt;End to End Demonstrator for Improved Decision Making in Europe &lt;/em&gt;(EDgE) [8]. This proof-of-concept constitutes now a blueprint for several follow-up projects at national or global scales [e.g., 9].&lt;/p&gt;&lt;p&gt;Eric F. Wood's scientific legacy will shape future developments in land surface modeling and his contributions will keep guiding generations of hydrologists. I was one of the fortunate ones who had the opportunity to know him as a mentor, project partner and friend. In this presentation, I will attempt to synthesize some of his key contributions that are the cornerstone for developing a Digital Twin [11] of the Earth's water cycle.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;[&lt;/strong&gt;1] Wood, E. (Ed.): Land Surface, atmosphere interactions for climate&amp;#160;modelling: observations, models, and analysis, Kluwer, 1990.&lt;br&gt;[2] Wood, E. F. et al. https://doi.org/10.1016/0022-1694(88)90090-X&amp;#160;1988.&lt;br&gt;[3] Samaniego, L. et al. https://doi.org/10.1029/2008WR007327, 2010b.&lt;br&gt;[4] mhm-ufz.org&lt;br&gt;[5] Schweppe, R et al. https://doi.org/10.5194/gmd-2021-103. 2021.&lt;br&gt;[6] Wood, E.F. et al. https://doi.org/10.1029/2010WR010090 2010.&lt;br&gt;[7] Sheffield, J., Wood, E. F. et al. https://doi.org/10.1175/BAMS-D-12-00124.1, 2014.&lt;br&gt;[8] Samaniego, L. et al. https://doi.org/10.1175/BAMS-D-17-0274.1 2019&lt;br&gt;[9] https://www.ufz.de/ulysses&lt;br&gt;[10] Bauer, P. et al. https://doi.org/10.1038/s41558-021-00986-y 2021&lt;strong&gt;&lt;br&gt;&lt;/strong&gt;&lt;/p&gt;