It rains and then? Numerical challenges with the 1D Richards equation in kilometer-resolution land surface modelling

Abstract. Over the last decade kilometer-scale weather predictions and climate projections have become established. Thereby both the representation of atmospheric processes, as well as land-surface processes need adaptions to the higher-resolution. Soil moisture is a critical variable for determining the exchange of water and energy between the atmosphere and the land surface on hourly to seasonal time scales, and a poor representation of soil processes will eventually feed back on the simulation quality of the atmosphere. Especially the partitioning between infiltration and surface runoff will feed back on the hydrological cycle. Several aspects of the coupled system are affected by a shift to kilometer-scale, convection-permitting models. First of all, the precipitation-intensity distribution changes to more intense events. Second, the time-step of the numerical integration becomes smaller. The aim of this study is to investigate the numerical convergence of the one-dimensional Richards Equation with respect to the soil hydraulic model, vertical layer thickness and time-step during the infiltration process. Both regular and non-regular (unequally spaced) grids typical in land surface modelling are considered, using a conventional semi-implicit vertical discretization. For regular grids, results from a highly idealized experiment on the infiltration process show poor numerical convergence for layer thicknesses larger than approximately 5 cm and for time steps greater than 40 s, irrespective of the soil hydraulic model. The velocity of the wetting front decreases systematically with increasing time step and decreasing vertical resolution. For non-regular grids, a new discretization based on a coordinate transform is introduced. In contrast to simpler vertical discretizations, it is able to represent the solution second-order accurate. The results for non-regular grids are qualitatively similar, as a fast increase in layer thickness with depth is equivalent to a lower vertical resolution. It is argued that the sharp gradients in soil moisture around the propagating wetting front must be resolved properly in order to achieve an acceptable numerical convergence of the Richards Equation. Furthermore, it is shown that the observed poor numerical convergence translates directly into a poor convergence of infiltration-runoff partitioning for precipitation time series characteristic of weather and climate models. As a consequence, soil simulations with low resolution in space and time may produce almost twice the amount of surface runoff within 24 hours than their high-resolution counterparts. Our analysis indicates that the problem is particularly pronounced for kilometer-resolution models.

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Large-Eddy Atmosphere–Land-Surface Modelling over Heterogeneous Surfaces: Model Development and Comparison with Measurements

Boundary-Layer Meteorology ◽

10.1007/s10546-013-9823-0 ◽

2013 ◽

Vol 148 (2) ◽

pp. 333-356 ◽

Cited By ~ 35

Author(s):

Yaping Shao ◽

Shaofeng Liu ◽

Jan H. Schween ◽

Susanne Crewell

Keyword(s):

Land Surface ◽

Model Development ◽

Heterogeneous Surfaces ◽

Surface Modelling ◽

Large Eddy ◽

Land Surface Modelling

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Application of an optimality-based model to operate at half-hourly timestep to implement plant acclimation within a land-surface modelling framework

10.5194/egusphere-egu21-2801 ◽

2021 ◽

Author(s):

Giulia Mengoli ◽

Anna Agustí-Panareda ◽

Souhail Boussetta ◽

Sandy P. Harrison ◽

Carlo Trotta ◽

...

Keyword(s):

Time Scales ◽

Land Surface ◽

Multiple Time Scales ◽

Multiple Time ◽

Extended Model ◽

Test Model ◽

Area Index ◽

Surface Modelling ◽

Plant Acclimation ◽

Land Surface Modelling

Vegetation and atmosphere are linked through the perpetual exchange of water, carbon and energy. An accurate representation of the processes involved in these exchanges is crucial in forecasting Earth system states. Although vegetation has become an undisputed key component in land-surface modelling (LSMs), the current generation of models differ in terms of how key processes are formulated. Plant processes react to environmental changes on multiple time scales. Here we differentiate a fast (minutes) and a slower (acclimated &#8211; weeks to months) response. Some current LSMs include plant acclimation, even though they require additional parameters to represent this response, but the majority of them represent only the fast response and assume that this also applies at longer time scales. Ignoring acclimation in this way could be the cause of inconsistent future projections. Our proposition is to include plant acclimation in a LSM schema, without having to include new plant-functional-type-dependent parameters. This is possible by using an alternative model development strategy based on eco-evolutionary theory, which explicitly predicts the acclimation of photosynthetic capacities and stomatal behaviour to environmental variations. So far, this theory has been tested only at weekly to monthly timescales. Here we develop and test an approach to apply an existing optimality-based model of gross primary production (GPP), the P model, at the sub-daily timestep necessary for use in an LSM, making an explicit differentiation between the fast and slow responses of photosynthesis and stomatal conductance. We test model performance in reproducing the diurnal cycle of GPP as recorded by flux tower measurements across different biomes, including boreal and tropical forests. The extended model requires only a few meteorological inputs, and a satellite-derived product for leaf area index or green vegetation cover. It is able to manage both timescales of acclimation without PFT-dependent photosynthetic parameters and has shown to operate with very good performance at all sites so far investigated. The model structure avoids the need to store past climate and vegetation states. These findings therefore suggest a simple way to include both instantaneous and acclimated responses within a LSM framework, and to do so in a robust way that does not require the specification of multiple parameters for different plant functional types.

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ECLand: an ECMWF land surface modelling platform

10.5194/egusphere-egu21-16240 ◽

2021 ◽

Author(s):

Gianpaolo Balsamo ◽

Souhail Boussetta

Keyword(s):

Land Surface ◽

Urban Areas ◽

Land Surface Model ◽

Open Water ◽

Surface Fluxes ◽

Surface Model ◽

New Developments ◽

Surface Modelling ◽

Land Surface Modelling ◽

New Research

The ECMWF operational land surface model, based on the Carbon-Hydrology Tiled ECMWF Scheme for Surface Exchanges over Land (CHTESSEL) is the baseline for global weather, climate and environmental applications at ECMWF. In order to expedite its progress and benefit from international collaboration, an ECLand platform has been designed to host advanced and modular schemes. ECLand is paving the way toward a land model that could support a wider range of modelling applications, facilitating global kilometer scales testing as envisaged in the Copernicus and Destination Earth programmes. This presentation&#160;introduces the CHTESSEL and its recent new developments that aims at hosting new research applications.These new improvements touch upon different components of the model: (i) vegetation, (ii) snow, (iii) soil hydrology, (iv) open water/lakes (v) rivers and (vi) urban areas. The developments are evaluated separately with either offline simulations or coupled experiments, depending on their level of operational readiness, illustrating the benchmarking criteria for assessing process fidelity with regards to land surface fluxes and reservoirs involved in water-energy-carbon exchange, and within the Earth system prediction framework, as foreseen to enter upcoming ECMWF operational cycles.Reference: Souhail Boussetta, Gianpaolo Balsamo*, Anna Agust&#236;-Panareda, Gabriele Arduini, Anton Beljaars, Emanuel Dutra, Glenn Carver, Margarita Choulga, Ioan Hadade, Cinzia Mazzetti, Joaqu&#236;n Mun&#245;z-Sabater, Joe McNorton, Christel Prudhomme, Patricia De Rosnay, Irina Sandu, Nils Wedi, Dai Yamazaki, Ervin Zsoter, 2021: ECLand: an ECMWF land surface modelling platform, MDPI Atmosphere, (in prep).

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Land-surface modelling in hydrological perspective

Biogeosciences Discussions ◽

10.5194/bgd-2-1815-2005 ◽

2005 ◽

Vol 2 (6) ◽

pp. 1815-1848 ◽

Cited By ~ 4

Author(s):

J. Overgaard ◽

D. Rosbjerg ◽

M. B. Butts

Keyword(s):

Remote Sensing ◽

Land Surface ◽

Potential Evapotranspiration ◽

Distributed Data ◽

Atmospheric Models ◽

Dynamic Coupling ◽

Surface Modelling ◽

Evaluation Procedures ◽

Surface Models ◽

Land Surface Modelling

Abstract. A comprehensive review of energy-based land-surface modelling, as seen from a hydrological perspective, is provided. We choose to focus on energy-based approaches, because in comparison to the traditional potential evapotranspiration models, these approaches allow for a stronger link to remote sensing and atmospheric modelling. New opportunities for evaluation of distributed land-surface models through application of remote sensing are discussed in detail, and the difficulties inherent in various evaluation procedures are presented. Remote sensing is the only source of distributed data at scales that correspond to hydrological modelling scales. Finally, the dynamic coupling of hydrological and atmospheric models is explored, and the future perspectives of such efforts are discussed.

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Comparing Assimilation of Synthetic Soil Moisture versus C‐band Backscatter for Hyper‐resolution Land Surface Modelling

Water Resources Research ◽

10.1029/2020wr028921 ◽

2021 ◽

Author(s):

Leqiang Sun ◽

Stephane Belair ◽

Marco L. Carrera ◽

Bernard Bilodeau ◽

Mohammed Dabboor

Keyword(s):

Soil Moisture ◽

Land Surface ◽

Surface Modelling ◽

Land Surface Modelling

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Algorithms for Solving Darcian Flow in Structured Porous Media

Acta Polytechnica ◽

10.14311/1829 ◽

2013 ◽

Vol 53 (4) ◽

Author(s):

Michal Kuráž ◽

Petr Mayer

Keyword(s):

Proper Time ◽

Time Integration ◽

Mass Term ◽

Step Length ◽

Richards Equation ◽

Parabolic Problems ◽

Computational Domain ◽

Wetting Front ◽

Time Step ◽

The Matrix

This paper presents several algorithms that were implemented in DRUtES [1], a new open source project. DRUtES is a finite element solver for coupled nonlinear parabolic problems, namely the Richards equation with the dual porosity approach (modeling the flow of liquids in a porous medium). Mass balance consistency is crucial in any hydrological balance and contaminant transportation evaluations. An incorrect approximation of the mass term greatly depreciates the results that are obtained. An algorithm for automatic time step selection is presented, as the proper time step length is crucial for achieving accuracy of the Euler time integration method. Various problems arise with poor conditioning of the Richards equation: the computational domain is clustered into subregions separated by a wetting front, and the nonlinear constitutive functions cover a high range of values, while a very simple diagonal preconditioning method greatly improves the matrix properties. The results are presented here, together with an analysis.

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Irrigation management under limited water resources : radar retrieved topsoil moisture, disaggregation, crop growth and land surface modelling and data assimilation

10.3990/1.9789036545952 ◽

2018 ◽

Author(s):

Omar Ali Ahmed Mohamed

Keyword(s):

Water Resources ◽

Data Assimilation ◽

Land Surface ◽

Irrigation Management ◽

Crop Growth ◽

Surface Modelling ◽

Land Surface Modelling

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Towards a simple representation of chalk hydrology in land surface modelling

Hydrology and Earth System Sciences ◽

10.5194/hess-21-459-2017 ◽

2017 ◽

Vol 21 (1) ◽

pp. 459-471 ◽

Cited By ~ 9

Author(s):

Mostaquimur Rahman ◽

Rafael Rosolem

Keyword(s):

Land Surface ◽

Unsaturated Zone ◽

Large Scale ◽

Management Practices ◽

Preferential Flow ◽

Water Movement ◽

Model Parameters ◽

Catchment Scale ◽

Surface Modelling ◽

Land Surface Modelling

Abstract. Modelling and monitoring of hydrological processes in the unsaturated zone of chalk, a porous medium with fractures, is important to optimize water resource assessment and management practices in the United Kingdom (UK). However, incorporating the processes governing water movement through a chalk unsaturated zone in a numerical model is complicated mainly due to the fractured nature of chalk that creates high-velocity preferential flow paths in the subsurface. In general, flow through a chalk unsaturated zone is simulated using the dual-porosity concept, which often involves calibration of a relatively large number of model parameters, potentially undermining applications to large regions. In this study, a simplified parameterization, namely the Bulk Conductivity (BC) model, is proposed for simulating hydrology in a chalk unsaturated zone. This new parameterization introduces only two additional parameters (namely the macroporosity factor and the soil wetness threshold parameter for fracture flow activation) and uses the saturated hydraulic conductivity from the chalk matrix. The BC model is implemented in the Joint UK Land Environment Simulator (JULES) and applied to a study area encompassing the Kennet catchment in the southern UK. This parameterization is further calibrated at the point scale using soil moisture profile observations. The performance of the calibrated BC model in JULES is assessed and compared against the performance of both the default JULES parameterization and the uncalibrated version of the BC model implemented in JULES. Finally, the model performance at the catchment scale is evaluated against independent data sets (e.g. runoff and latent heat flux). The results demonstrate that the inclusion of the BC model in JULES improves simulated land surface mass and energy fluxes over the chalk-dominated Kennet catchment. Therefore, the simple approach described in this study may be used to incorporate the flow processes through a chalk unsaturated zone in large-scale land surface modelling applications.

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