The Surface Monitoring Of the Soil Reservoir Experiment (SMOSREX) site is used in this study to evaluate the performance of the Interaction between Soil Biosphere Atmosphere soil multilayer diffusion ...scheme (ISBA‐DF) in reproducing short‐term and long‐term evolution of soil moisture and temperature profiles, surface energy fluxes, and drainage rate using both the Brooks and Corey and the van Genuchten models describing soil‐water retention and conductivity curves. The site consists of a fallow field in southwestern France where intensive measurements were made during the 2001–2007 period. Two sets of four simulations describing homogeneous and heterogeneous soil properties are performed using four continuous pedotransfer functions. ISBA‐DF is also compared with the ISBA “force‐restore” soil scheme (ISBA‐FR) since this version is currently used in several meteorological, hydrological, and/or climate applications. ISBA‐DF exhibits a good performance in terms of simulating the soil moisture profile and the surface energy fluxes, especially when heterogeneous soil properties are considered. Its soil moisture dynamic does not depend on the field capacity, which is a clear advantage compared with ISBA‐FR. However, it shows some drawbacks in simulating the surface temperature. The Brooks and Corey model exhibits the best skill scores in simulating the soil moisture profile and the surface fluxes compared with the van Genuchten model. Nevertheless, the differences are not significant, and the results on a single site reduce the generality of this intercomparison. Finally, two additional sets of experiments are performed to assess the scheme sensitivity to increasing soil depth and to the soil vertical discretization.
Key Points
Soil diffusion scheme
Pedotransfer function sensitivity
Soil vertical configurations sensitivity
The Plumbing of Land Surface Models Best, M. J.; Abramowitz, G.; Johnson, H. R. ...
Journal of hydrometeorology,
06/2015, Volume:
16, Issue:
3
Journal Article
Peer reviewed
Open access
The Protocol for the Analysis of Land Surface Models (PALS) Land Surface Model Benchmarking Evaluation Project (PLUMBER) was designed to be a land surface model (LSM) benchmarking intercomparison. ...Unlike the traditional methods of LSM evaluation or comparison, benchmarking uses a fundamentally different approach in that it sets expectations of performance in a range of metrics a priori—before model simulations are performed. This can lead to very different conclusions about LSM performance. For this study, both simple physically basedmodels and empirical relationships were used as the benchmarks. Simulations were performed with 13 LSMs using atmospheric forcing for 20 sites, and then model performance relative to these benchmarks was examined. Results show that even for commonly used statistical metrics, the LSMs’ performance varies considerably when compared to the different benchmarks. All models outperform the simple physically based benchmarks, but for sensible heat flux the LSMs are themselves outperformed by an out-of-sample linear regression against downward shortwave radiation. While moisture information is clearly central to latent heat flux prediction, the LSMs are still outperformed by a three-variable nonlinear regression that uses instantaneous atmospheric humidity and temperature in addition to downward shortwave radiation. These results highlight the limitations of the prevailing paradigm of LSM evaluation that simply compares an LSM to observations and to other LSMs without a mechanism to objectively quantify the expectations of performance. The authors conclude that their results challenge the conceptual view of energy partitioning at the land surface.
This study presents an off-line global evaluation of the ISBA-TRIP hydrological model including a two-way flood scheme. The flood dynamics is indeed described through the daily coupling between the ...ISBA land surface model and the TRIP river routing model including a prognostic flood reservoir. This reservoir fills when the river height exceeds the critical river bankfull height and vice versa. The flood interacts with the soil hydrology through infiltration and with the overlying atmosphere through precipitation interception and free water surface evaporation. The model is evaluated over a relatively long period (1986–2006) at 1° resolution using the Princeton University 3-hourly atmospheric forcing. Four simulations are performed in order to assess the model sensitivity to the river bankfull height. The evaluation is made against satellite-derived global inundation estimates as well as in situ river discharge observations at 122 gauging stations. First, the results show a reasonable simulation of the global distribution of simulated floodplains when compared to satellite-derived estimates. At basin scale, the comparison reveals some discrepancies, both in terms of climatology and interannual variability, but the results remain acceptable for a simple large-scale model. In addition, the simulated river discharges are improved in term of efficiency scores for more than 50% of the 122 stations and deteriorated for 4% only. Two mechanisms mainly explain this positive impact: an increase in evapotranspiration that limits the annual discharge overestimation found when flooding is not taking into account and a smoothed river peak flow when the floodplain storage is significant. Finally, the sensitivity experiments suggest that the river bankfull depth is potentially tunable according to the river discharge scores to control the accuracy of the simulated flooded areas and its related increase in land surface evaporation. Such a tuning could be relevant at least for climate studies in which the spatio-temporal variations in precipitation are generally poorly represented.
This paper describes the main characteristics of CNRM‐CM6‐1, the fully coupled atmosphere‐ocean general circulation model of sixth generation jointly developed by Centre National de Recherches ...Météorologiques (CNRM) and Cerfacs for the sixth phase of the Coupled Model Intercomparison Project 6 (CMIP6). The paper provides a description of each component of CNRM‐CM6‐1, including the coupling method and the new online output software. We emphasize where model's components have been updated with respect to the former model version, CNRM‐CM5.1. In particular, we highlight major improvements in the representation of atmospheric and land processes. A particular attention has also been devoted to mass and energy conservation in the simulated climate system to limit long‐term drifts. The climate simulated by CNRM‐CM6‐1 is then evaluated using CMIP6 historical and Diagnostic, Evaluation and Characterization of Klima (DECK) experiments in comparison with CMIP5 CNRM‐CM5.1 equivalent experiments. Overall, the mean surface biases are of similar magnitude but with different spatial patterns. Deep ocean biases are generally reduced, whereas sea ice is too thin in the Arctic. Although the simulated climate variability remains roughly consistent with CNRM‐CM5.1, its sensitivity to rising CO2 has increased: the equilibrium climate sensitivity is 4.9 K, which is now close to the upper bound of the range estimated from CMIP5 models.
Key Points
Description of CNRM‐CM6‐1 model components, their coupling, and tuning procedures are described
Historical simulations and DECK experiments are assessed
Preindustrial simulation is stable and mean climate and variability in historical runs is realistic
Characteristics and radiative forcing of the aerosol and ozone fields of two configurations of the Centre National de Recherches Météoroglogiques (CNRM) and Cerfacs climate model are analyzed over ...the historical period (1850–2014), using several Coupled Model Intercomparison Project 6 (CMIP6) simulations. CNRM‐CM6‐1 is the atmosphere‐ocean general circulation model including prescribed aerosols and a linear stratospheric ozone scheme, while the Earth System Model CNRM‐ESM2‐1 has interactive tropospheric aerosols and chemistry of the midtroposphere aloft. The representations of aerosols and ozone in CNRM‐CM6‐1 are issued from simulations of CNRM‐ESM2‐1, and this ensures some comparability of both representations. In particular, present‐day anthropogenic aerosol optical depths are similar (0.018), and their spatial patterns correspond to those of reference data sets such as MACv2 and MACv2‐SP despite a negative bias. Effective radiative forcings (ERFs) have been estimated using 30‐year fixed sea surface temperature simulations (piClim) and several calls to the radiative scheme. Present‐day anthropogenic aerosol ERF, aerosol‐radiation ERF, and aerosol cloud ERF are fully within CMIP5 estimates and, respectively, equal to
−1.10,
−0.36, and
−0.81 W m
−2 for CNRM‐CM6‐1 and
−0.21,
−0.61, and
−0.74 W m
−2 for CNRM‐ESM2‐1. Additional CMIP6‐type piClim simulations show that these differences are mainly due to the interactivity of the aerosol scheme whose impact is confirmed when assessing the response of both climate model configurations to rising CO
2. Present‐day stratospheric ozone ERF, equal to
−0.04 W m
−2, is in agreement with that of the CMIP6 ozone. No trend appears in the ozone ERF over the historical period although the evolution of the total column ozone is correctly simulated.
Plain Language Summary
The manuscript documents the Météo‐France Centre National de Recherches Météorologiques aerosol‐chemistry modeling contributions to the sixth Coupled Model Intercomparison Project that supports the sixth IPCC Assessment Report of climate change. It establishes that their results are suitable for use by the scientific community in the analysis of the sixth Coupled Model Intercomparison Project experiments. The authors provide an evaluation of the model performance in both present‐day and historical (1850–2014) contexts, as well as a detailed analysis of the model calculated effective radiative forcing due to ozone and aerosols.
Key Points
The representations of aerosol and ozone in the CMIP6 CNRM‐CM6‐1 and CNRM‐ESM2‐1 models is described
Present‐day and historical aerosol and ozone distributions are assessed, as well as their effective radiative forcing (ERF)
The present‐day anthropogenic aerosol ERF (‐1.10 W m
−2 for CNRM‐CM6‐1) is sensitive to the interactivity of aerosols
A new version of the general circulation model CNRM-CM has been developed jointly by CNRM-GAME (Centre National de Recherches Météorologiques—Groupe d’études de l’Atmosphère Météorologique) and ...Cerfacs (Centre Européen de Recherche et de Formation Avancée) in order to contribute to phase 5 of the Coupled Model Intercomparison Project (CMIP5). The purpose of the study is to describe its main features and to provide a preliminary assessment of its mean climatology. CNRM-CM5.1 includes the atmospheric model ARPEGE-Climat (v5.2), the ocean model NEMO (v3.2), the land surface scheme ISBA and the sea ice model GELATO (v5) coupled through the OASIS (v3) system. The main improvements since CMIP3 are the following. Horizontal resolution has been increased both in the atmosphere (from 2.8° to 1.4°) and in the ocean (from 2° to 1°). The dynamical core of the atmospheric component has been revised. A new radiation scheme has been introduced and the treatments of tropospheric and stratospheric aerosols have been improved. Particular care has been devoted to ensure mass/water conservation in the atmospheric component. The land surface scheme ISBA has been externalised from the atmospheric model through the SURFEX platform and includes new developments such as a parameterization of sub-grid hydrology, a new freezing scheme and a new bulk parameterisation for ocean surface fluxes. The ocean model is based on the state-of-the-art version of NEMO, which has greatly progressed since the OPA8.0 version used in the CMIP3 version of CNRM-CM. Finally, the coupling between the different components through OASIS has also received a particular attention to avoid energy loss and spurious drifts. These developments generally lead to a more realistic representation of the mean recent climate and to a reduction of drifts in a preindustrial integration. The large-scale dynamics is generally improved both in the atmosphere and in the ocean, and the bias in mean surface temperature is clearly reduced. However, some flaws remain such as significant precipitation and radiative biases in many regions, or a pronounced drift in three dimensional salinity.
While human influence has been detected in global and regional surface air temperature, detection–attribution studies of direct (i.e., land use and water management) and indirect (i.e., climate ...related) effects of human activities on land surface hydrology remain a crucial and controversial issue. In the present study, a set of global offline hydrological simulations is performed during the 1960–94 period using the Interactions between Soil, Biosphere, and Atmosphere–Total Runoff Integrating Pathways (ISBA-TRIP) modeling system. In contrast to previous numerical sensitivity studies, the model captures the observed trend in river runoff over most continents without including land use changes and/or biophysical CO₂ effects, at least when the comparison is made over 154 large rivers with a minimum amount of missing data. The main exception is northern Asia, where the simulated runoff trend is negative, in line with the prescribed precipitation forcing but in contrast with the observed runoff trend. The authors hypothesize that the observed surface warming and the associated decline of permafrost and glaciers, not yet included in most land surface models, could have contributed to the increased runoff at high latitudes. They also emphasize that the runoff trend is a regional-scale issue, if not basin dependent. In line with recent observational studies, their results suggest that CO₂ stomatal conductance effects and land use changes are not the primary drivers of the multidecadal runoff variability at continental scales. However, the authors do not rule out a human influence on land runoff, at least through the high-latitude surface warming observed over recent decades.
The equilibrium climate sensitivity, that is, the global‐mean surface‐air temperature change in response to a doubling of the carbon dioxide concentration is a widely used metric in climate change ...studies. Its exact value is rarely known because its estimation requires a long integration time of several thousand years. We propose a method to estimate an accurate value of the equilibrium response from fully coupled climate models at a reasonable computational cost. Using this method, our state‐of‐the‐art climate model CNRM‐CM6‐1 reaches a stationary state after only few hundred of years of integration. This “Fast‐Forward” method consists of an optimal two‐step forcing pathway designed using the framework of a two‐layer energy balance model. It can be applied easily to any coupled climate model.
Key Points
A simple method for estimating the equilibrium climate sensitivity is proposed
The method allows to simulate the stationary climate corresponding to any given radiative perturbation with a limited computational cost
The method can be applied to any atmosphere‐ocean coupled climate model
A comprehensive set of hydrological parameterizations without any basin‐scale calibration was recently introduced into the global ISBA land surface model in order to improve the simulation of the ...hydrological impacts of both seasonal climate anomalies and global warming. In this study, the same approach is introduced into the Noah land surface model, in order to improve the representation of surface runoff. The Dunne runoff is computed using topographic information via a TOPMODEL approach and the Horton runoff using an explicit distinction between frozen and unfrozen soils, while land surface heterogeneities are introduced via a tile approach. The validation is conducted at a 1° by 1° horizontal resolution using global off line simulations that were driven by Global Soil Wetness Project atmospheric forcing. The simulated runoff is converted into discharges using the TRIP river routing model and compared to observations from a dense network of gauging stations distributed over the world's largest river basins. Results confirm that the relationships between the Dunne runoff and the topography, as well as between the Horton runoff and the frozen soils, are among the main hydrological processes to simulate realistic global river discharges. The comparison between the old and the new versions of Noah and ISBA reveal that the model disparity, in term of water flux production, is globally reduced due to the use of similar surface hydrology that lead to comparable improvements of discharge scores. This confirms the relevance of these surface hydrological processes for regional and global applications.
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