Jaime Gómez-Hernández
J. Jaime Gómez-Hernández (born in Requena, Spain, 1960) is a Spanish Civil Engineer specialized in Geostatistics and Hydrogeology. He is a full professor of Hydraulic Engineering at the School of Civil Engineering of the Technical University of Valencia. He was conferred the William Christian Krumbein Medal in 2020 from the International Association for Mathematical Geosciences. He also received the 2020 Prince Sultan bin Abdulaziz International Prize for Water, in the field of Groundwater. Biography. Born on October 28th, 1960 in Requena (Spain), he got his Civil Engineering degree from the Technical University of Valencia in 1983 . After a year working for the Valencian delegation of the Spanish company EPTISA, where he implemented the first aquifer numerical models using his ZX Spectrum connected to a portable TV of his own, he moved to Stanford University in 1984 to conduct an M.Sc. in Applied Hydrogeology under the supervision of Irwin Remson of the Applied Earth Sciences Department, followed by a Ph.D. in Geostatistics for Natural Resources Characterization under the supervision of Andre Journel. Upon his return to Spain in 1990, he worked for the Spanish company EVREN as a civil engineer until his joining the School of Civil  Engineering at the Technical University of Valencia as an associate professor in 1994. He became full professor in the year 2000, position at which he remains active. Research. His MS thesis dealt with the application of the Kalman filter for network design in aquifers. Little he knew that 30 years later, he would supervise several PhD theses and publish an important number of papers on the use of the ensemble Kalman filter for inverse modeling in aquifers. His PhD thesis dealt with the use of geostatistics for the upscaling of hydraulic conductivity in heterogeneous aquifers. Heterogeneity, aquifer characterization, uncertainty  quantification have been the main topics around which his research has revolved. His research can be grouped in four main subjects: Algorithm and Code Development. He developed for his Ph.D. a stochastic simulation technique for random functions that is much more precise and versatile than those existing until then and, more importantly, without limitation on the size of the realizations to be generated. This technique is included in the public domain codes ISIM3D and GCOSIM3D. These codes have been incorporated into commercial programs and have been used routinely by institutions such as the University of Arizona, the British Nuclear Waste  Management Agency (NIREX) or the Polytechnic University of Catalonia. Upscaling. The need to establish a link between laboratory measurements of parameters such as permeability and the value that have to be used in mathematical models for large scale predictions is a central topic of his Ph.D. dissertation, out of which a new methodology for the characterization of the spatial variability of permeability at various scales was developed. In this field, he was the first to demonstrate the difference between block values and effective values and that block values depend on the block size and are generally non-local. The Need  of Non-Gaussian Models. He proposed a paradigm shift in describing how the parameters that control groundwater flow and solute transport are spatially distributed in the subsurface. The publication of the paper "To be or not to be multiGaussian" in 1998 supposed a radical change in the way of understanding and modeling the subsurface. For two decades, a Gaussian model had been used to describe the heterogeneity of aquifers, and a large body of research had been built on this hypothesis. He demonstrated the (harmful) implications of adopting a Gaussian model and proposed a new one. Stochastic Inverse Modeling. He  also proposed a paradigm shift in modeling the transport of dissolved solutes in groundwater. In 1992, as a member of the INTRAVAL project —financed by a pool of nuclear waste management agencies— whose objective was the validation of codes for flow and transport in the subsurface, he detected a serious error in the simulation of scenarios of failure. Predictions of waste residual movement should not be made using “mean permeabilities”, predictions should be made using realistic distributions of permeabilities and then mean values calculated. That shift in focus is critical today for making predictions of solute transport in any context  and for evaluating the uncertainty of those predictions. He demonstrated the need for this change of paradigm in his article on "Probabilistic Assessment of Travel Times" that appeared in 1994, and then developed a new inverse modeling technique, which appeared in a series of three articles on "Stochastic Simulation of Transmissivity Fields". The proposed method, coined as the self-calibrating method, was the most efficient method in aquifer inverse modeling during the code intercomparison exercise promoted by the US Sandia National Laboratories. The results of this benchmarking exercise are collected in the 1998 article "A Comparison of Seven Geostatistically-based  Inverse Approaches". As a result of this paradigm shift and the need to go from inverse modeling to stochastic inverse modeling, he has focused on the development of new techniques that would improve the results of the self-calibrating method. With a number of papers demonstrating the applicability of the ensemble Kalman filter, of which the seminal one is "An approach to handling non-Gaussianity on parameters" of 2011.