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  • Author or Editor: J. Noilhan x
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B. Decharme
,
H. Douville
,
A. Boone
,
F. Habets
, and
J. Noilhan

Abstract

This study focuses on the influence of an exponential profile of saturated hydraulic conductivity, k sat, with soil depth on the water budget simulated by the Interaction Soil Biosphere Atmosphere (ISBA) land surface model over the French Rhône River basin. With this exponential profile, the saturated hydraulic conductivity at the surface increases by approximately a factor of 10, and its mean value increases in the root zone and decreases in the deeper region of the soil in comparison with the values given by Clapp and Hornberger. This new version of ISBA is compared to the original version in offline simulations using the Rhône-Aggregation high-resolution database. Low-resolution simulations, where all atmospheric data and surface parameters have been aggregated, are also performed to test the impact of the modified k sat profile at the typical scale of a climate model. The simulated discharges are compared to observations from a dense network consisting of 88 gauging stations.

Results of the high-resolution experiments show that the exponential profile of k sat globally improves the simulated discharges and that the assumption of an increase in saturated hydraulic conductivity from the soil surface to a depth close to the rooting depth in comparison with values given by Clapp and Hornberger is reasonable. Results of the scaling experiments indicate that this parameterization is also suitable for large-scale hydrological applications. Nevertheless, low-resolution simulations with both model versions overestimate evapotranspiration (especially from the plant transpiration and the wet fraction of the canopy) to the detriment of total runoff, which emphasizes the need for implementing subgrid distribution of precipitation and land surface properties in large-scale hydrological applications.

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A. G. Slater
,
C. A. Schlosser
,
C. E. Desborough
,
A. J. Pitman
,
A. Henderson-Sellers
,
A. Robock
,
K. Ya Vinnikov
,
J. Entin
,
K. Mitchell
,
F. Chen
,
A. Boone
,
P. Etchevers
,
F. Habets
,
J. Noilhan
,
H. Braden
,
P. M. Cox
,
P. de Rosnay
,
R. E. Dickinson
,
Z-L. Yang
,
Y-J. Dai
,
Q. Zeng
,
Q. Duan
,
V. Koren
,
S. Schaake
,
N. Gedney
,
Ye M. Gusev
,
O. N. Nasonova
,
J. Kim
,
E. A. Kowalczyk
,
A. B. Shmakin
,
T. G. Smirnova
,
D. Verseghy
,
P. Wetzel
, and
Y. Xue

Abstract

Twenty-one land surface schemes (LSSs) performed simulations forced by 18 yr of observed meteorological data from a grassland catchment at Valdai, Russia, as part of the Project for the Intercomparison of Land-Surface Parameterization Schemes (PILPS) Phase 2(d). In this paper the authors examine the simulation of snow. In comparison with observations, the models are able to capture the broad features of the snow regime on both an intra- and interannual basis. However, weaknesses in the simulations exist, and early season ablation events are a significant source of model scatter. Over the 18-yr simulation, systematic differences between the models’ snow simulations are evident and reveal specific aspects of snow model parameterization and design as being responsible. Vapor exchange at the snow surface varies widely among the models, ranging from a large net loss to a small net source for the snow season. Snow albedo, fractional snow cover, and their interplay have a large effect on energy available for ablation, with differences among models most evident at low snow depths. The incorporation of the snowpack within an LSS structure affects the method by which snow accesses, as well as utilizes, available energy for ablation. The sensitivity of some models to longwave radiation, the dominant winter radiative flux, is partly due to a stability-induced feedback and the differing abilities of models to exchange turbulent energy with the atmosphere. Results presented in this paper suggest where weaknesses in macroscale snow modeling lie and where both theoretical and observational work should be focused to address these weaknesses.

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Lifeng Luo
,
Alan Robock
,
Konstantin Y. Vinnikov
,
C. Adam Schlosser
,
Andrew G. Slater
,
Aaron Boone
,
Pierre Etchevers
,
Florence Habets
,
Joel Noilhan
,
Harald Braden
,
Peter Cox
,
Patricia de Rosnay
,
Robert E. Dickinson
,
Yongjiu Dai
,
Qing-Cun Zeng
,
Qingyun Duan
,
John Schaake
,
Ann Henderson-Sellers
,
Nicola Gedney
,
Yevgeniy M. Gusev
,
Olga N. Nasonova
,
Jinwon Kim
,
Eva Kowalczyk
,
Kenneth Mitchell
,
Andrew J. Pitman
,
Andrey B. Shmakin
,
Tatiana G. Smirnova
,
Peter Wetzel
,
Yongkang Xue
, and
Zong-Liang Yang

Abstract

The Project for Intercomparison of Land-Surface Parameterization Schemes phase 2(d) experiment at Valdai, Russia, offers a unique opportunity to evaluate land surface schemes, especially snow and frozen soil parameterizations. Here, the ability of the 21 schemes that participated in the experiment to correctly simulate the thermal and hydrological properties of the soil on several different timescales was examined. Using observed vertical profiles of soil temperature and soil moisture, the impact of frozen soil schemes in the land surface models on the soil temperature and soil moisture simulations was evaluated.

It was found that when soil-water freezing is explicitly included in a model, it improves the simulation of soil temperature and its variability at seasonal and interannual scales. Although change of thermal conductivity of the soil also affects soil temperature simulation, this effect is rather weak. The impact of frozen soil on soil moisture is inconclusive in this experiment due to the particular climate at Valdai, where the top 1 m of soil is very close to saturation during winter and the range for soil moisture changes at the time of snowmelt is very limited. The results also imply that inclusion of explicit snow processes in the models would contribute to substantially improved simulations. More sophisticated snow models based on snow physics tend to produce better snow simulations, especially of snow ablation. Hysteresis of snow-cover fraction as a function of snow depth is observed at the catchment but not in any of the models.

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