TY - JOUR A1 - Baroni, Gabriele A1 - Schalge, Bernd A1 - Rakovec, Oldrich A1 - Kumar, Rohini A1 - Schüler, Lennart A1 - Samaniego, Luis A1 - Simmer, Clemens A1 - Attinger, Sabine T1 - A Comprehensive Distributed Hydrological Modeling Intercomparison to Support Process Representation and Data Collection Strategies JF - Water resources research N2 - The improvement of process representations in hydrological models is often only driven by the modelers' knowledge and data availability. We present a comprehensive comparison between two hydrological models of different complexity that is developed to support (1) the understanding of the differences between model structures and (2) the identification of the observations needed for model assessment and improvement. The comparison is conducted on both space and time and by aggregating the outputs at different spatiotemporal scales. In the present study, mHM, a process‐based hydrological model, and ParFlow‐CLM, an integrated subsurface‐surface hydrological model, are used. The models are applied in a mesoscale catchment in Germany. Both models agree in the simulated river discharge at the outlet and the surface soil moisture dynamics, lending their supports for some model applications (drought monitoring). Different model sensitivities are, however, found when comparing evapotranspiration and soil moisture at different soil depths. The analysis supports the need of observations within the catchment for model assessment, but it indicates that different strategies should be considered for the different variables. Evapotranspiration measurements are needed at daily resolution across several locations, while highly resolved spatially distributed observations with lower temporal frequency are required for soil moisture. Finally, the results show the impact of the shallow groundwater system simulated by ParFlow‐CLM and the need to account for the related soil moisture redistribution. Our comparison strategy can be applied to other models types and environmental conditions to strengthen the dialog between modelers and experimentalists for improving process representations in Earth system models. KW - hydrological models KW - assessments KW - monitoring strategies KW - improvements Y1 - 2019 U6 - https://doi.org/10.1029/2018WR023941 SN - 0043-1397 SN - 1944-7973 VL - 55 IS - 2 SP - 990 EP - 1010 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Erdal, Daniel A1 - Baroni, Gabriele A1 - Sánchez León, Eduardo Emilio A1 - Cirpka, Olaf A. T1 - The value of simplified models for spin up of complex models with an application to subsurface hydrology JF - Computers & geosciences : an international journal devoted to the publication of papers on all aspects of geocomputation and to the distribution of computer programs and test data sets ; an official journal of the International Association for Mathematical Geology N2 - Spinning up large-scale coupled surface-subsurface numerical models can be a time and resource consuming task. If an uninformed initial condition is chosen, the spin-up can easily require 20 years of repeated simulations on high-performance computing machines. In this paper we compare the classical approach of starting from a fixed shallow depth to groundwater (here 3 m) with three more informed approaches for the definition of initial conditions in the spin up. In the first of these three approaches, we start from a known-steady state groundwater table, calculated with a 2-D groundwater model and the yearly net recharge, and combine it with an unsaturated zone that assumes hydrostatic conditions. In the second approach, we start from the same groundwater table combined with vertical profiles in the unsaturated zone with uniform vertical flow identical to the groundwater recharge. In the third approach we calculate a dynamic steady state from a simplified subsurface model combining a transient 2-D groundwater model with a limited number of 1-D transient unsaturated zone columns on top. Results for spinning-up a 3-D Parflow-CLM model using the different initial conditions show that large gains can be made by considering states in groundwater and the vadose zone that are consistent, i.e. where groundwater recharge and the vertical flux in the vadose zone agree. By this, the spin-up time was reduced from about 10 years to about 3 years of simulated time. In the light of seasonal fluctuations of net recharge, using the transient approach showed more stable results. KW - Model spin-up KW - Groundwater-model KW - Unsaturated zone KW - 2.5-D model KW - Computation time Y1 - 2019 U6 - https://doi.org/10.1016/j.cageo.2019.01.014 SN - 0098-3004 SN - 1873-7803 VL - 126 SP - 62 EP - 72 PB - Elsevier CY - Oxford ER -