!!Rainer Helmig - Selected Publications \\ Rainer has published important papers on some of the most complex and difficult problems in subsurface hydrology, often involving multi-component, multi-phase, nonisothermal flow systems. For these very difficult problems, Rainer has developed robust and elegant solution methodologies and applied them to some of the most important problems of our times, including groundwater contamination, CO2 sequestration, broad alternative energy problems including detailed simulations for fuel cells, and his recent seminal work on coupling free-flow and porous-media-flow systems with important applications to mass and energy exchange at the land surface. In all of this work, innovative advanced numerical methods and specialized algorithm development have been a hallmark, with a major focus on multi-scale and hybrid approaches tailored for hydrologic applications.\\ \\ A book that is standard textbook for modeling multiphase flow and transport in porous media: \\ Helmig, R. (1997): Multiphase flow and transport processes in the subsurface: a contribution to the modeling of hydrosystems: Springer-Verlag. Cited more than 1350 times\\ This book is translated into Japanese.\\ \\ The following paper is an example of the overall modeling philosophy that Rainer has followed, including representation of important processes across different length and time scales, use of rigorously derived equations to describe the system, and solution methods based on advanced numerical methods:\\ \\ Class, H.; Helmig, R.; Bastian, P. (2002): Numerical simulation of non-isothermal multiphase multicomponent processes in porous media.: 1. An efficient solution technique. In Advances in Water Resources 25 (5), pp. 533–550. DOI: 10.1016/S0309-1708(02)00014-3.P, 260 Citations\\ \\ An important aspect of Rainer's work is the change of the evaporation behavior especially in relation to climate change. In the following papers, completely new approaches were developed that allow a coupling of the atmosphere with the unsaturated zone:\\ \\ Mosthaf, K.; Baber, K.; Flemisch, B.; Helmig, R.; Leijnse, A.; Rybak, I.; Wohlmuth, B. (2011): A coupling concept for two-phase compositional porous-medium and single-phase compositional free flow. In Water Resources Research 47 (10). DOI: 10.1029/2011WR010685, Citations 174\\ \\ Vanderborght, J.; Fetzer, T.; Mosthaf, K.; Smits, K. M.; Helmig, R. (2017): Heat and water transport in soils and across the soil-atmosphere interface: 1. Theory and different model concepts. In Water Resources Research 53 (2), pp. 1057–1079. DOI: 10.1002/2016WR019982. Citations 57\\ \\ Weishaupt, K., Joekar-Niasar, V., Helmig, R.: (2019) An efficient coupling of free flow and porous media flow using the pore-network modeling approach. Journal of Computational Physics: X. https://doi.org/10.1016/j.jcpx.2019.100011.\\ 36 Citations\\ \\ Schneider, M., Weishaupt, K., Gläser, D., Boon, W.M., Helmig, R.: Coupling staggered-grid and MPFA finite volume methods for free flow/porous-medium flow problems. Journal of Computational Physics 401, 109012 (2020), 15 Citations\\ \\ Another important issue in land-atmosphere interaction is the salt spreading and the associated decoupling of precipitation and the water cycle, addressed in the following paper: \\ \\ Jambhekar, V. A.; Helmig, R.; Schröder, N.; Shokri, N. (2015): Free-flow‐porous-media coupling for evaporation-driven transport and precipitation of salt in soil. In Transport in Porous Media 110 (2), pp. 251–280. DOI: 10.1007/s11242-015-0516-7, 72 Citations\\ \\ Rainer has a number of important contributions, including novel numerical approaches for multi-phase flows in fractured rocks:\\ \\ Gläser, D., Helmig, R., Flemisch, B., Class, H.: A discrete fracture model for two-phase flow in fractured porous media. Advances in Water Resources 110, 335-348 (2017), 69 Citations\\ \\ Praditia, T., Helmig, R., Hajibeygi, H.: Multiscale formulation for coupled flow-heat equations arising from single-phase flow in fractured geothermal reservoirs. Computational Geosciences 22 (5), 1305-1322 (2018), 33 Citations\\ \\ A very important, highly respected international contribution has been made by Rainer's group in the development of numerical models for the analysis of e.g. storage of CO2 in the subsurface:\\ \\ Class, H.; Ebigbo, A.; Helmig, R.; Dahle, H. K.; Nordbotten, J. M.; Celia, M. A.; Audigane, P.; Darcis, M.; Ennis-King, J.; Fan, Y. et al. (2009): A benchmark study on problems related to CO2 storage in geologic formations. In Computational Geosciences 13 (4), p. 409. DOI: 10.1007/s10596-009-9146-x. 434 Citations