Interaction Soil Biosphere Atmosphere Research Articles

High-Resolution SMAP-Derived Root-Zone Soil Moisture Using an Exponential Filter Model Calibrated per Land Cover Type

Root-zone soil moisture (RZSM) plays a key role for most water and energy budgets, as it is particularly relevant in controlling plant transpiration and hydraulic redistribution. RZSM data is needed for a variety of different applications, such as forecasting crop yields, improving flood predictions and monitoring agricultural drought, among others. Remote sensing provides surface soil moisture (SSM) retrievals, whose key advantage is the large spatial coverage on a systematic basis. This study tests a simple method to retrieve RZSM estimates from high-resolution SSM derived from SMAP (Soil Moisture Active Passive). A recursive exponential filter using a time constant τ is calibrated per land cover type, which uses as an intermediate step a long-term ISBA-DIF (Interaction Soil Biosphere Atmosphere—Diffusion scheme) dataset over an area located in Catalonia, NE of Spain. The τ values thus obtained are then used as an input to the same recursive exponential filter, to derive 1 km resolution RZSM estimates from 1 km SMAP SSM, which are obtained from the original data by downscaling to a 1 km resolution, through the DISPATCH (DISaggregation based on a Physical and Theoretical scale CHange) methodology. The results are then validated with scaled in situ observations at different depths, over two different areas, one representative of rainfed crops, and the other of irrigated crops. In general, the estimates agree well with the observations over the rainfed crops, especially at a 10 cm and 25 cm depth. Nash–Sutcliffe (NS) scores ranging between 0.33 and 0.58, and between 0.37 and 0.56 have been found, respectively. Correlation coefficients for these depths are high, between 0.76 and 0.91 (10 cm), and between 0.71 and 0.90 (25 cm). For the irrigated sites, results are poorer (partly due to the extremely high heterogeneity present), with NS scores ranging between −2.57 and 0.16, and correlations ranging between −0.56 and 0.48 at 25 cm. Given the strong correlations and NS scores found in the surface, the sensitivity of the filter to different τ values was investigated. For the rainfed site, it was found, as expected, with increasing τ, increasing NS and correlations with the deeper layers, suggesting a better coupling. Nevertheless, a strong correlation with the surface (5 cm) or shallower depths (10 cm) observed over certain sites indicates a certain lack of skill of the filter to represent processes which occur at lower levels in the SM column. All in all, a calibration accounting for the vegetation was shown to be an adequate methodology in applying the recursive exponential filter to derive the RZSM estimates over large areas. Nevertheless, the relative shallow surface at which the estimates correlate in some cases seem to indicate that an effect of evapotranspiration in the profile is not well captured by the filter.

An urban trees parameterization for modeling microclimatic variables and thermal comfort conditions at street level with the Town Energy Balance model (TEB-SURFEX v8.0)

Abstract. The Town Energy Balance (TEB) urban climate model has recently been improved to more realistically address the radiative effects of trees within the urban canopy. These processes necessarily have an impact on the energy balance that needs to be taken into account. This is why a new method for calculating the turbulent fluxes for sensible and latent heat has been implemented. This method remains consistent with the “bigleaf” approach of the Interaction Soil–Biosphere–Atmosphere (ISBA) model, which deals with energy exchanges between vegetation and atmosphere within TEB. Nonetheless, the turbulent fluxes can now be dissociated between ground-based natural covers and the tree stratum above (knowing the vertical leaf density profile), which can modify the vertical profile in air temperature and humidity in the urban canopy. In addition, the aeraulic effect of trees is added, parameterized as a drag term and an energy dissipation term in the evolution equations of momentum and turbulent kinetic energy, respectively. This set of modifications relating to the explicit representation of the tree stratum in TEB is evaluated on an experimental case study. The model results are compared to micrometeorological and surface temperature measurements collected in a semi-open courtyard with trees and bordered by buildings. The new parameterizations improve the modeling of surface temperatures of walls and pavements, thanks to taking into account radiation absorption by trees, and of air temperature. The effect of wind speed being strongly slowed down by trees is also much more realistic. The universal thermal climate index diagnosed in TEB from inside-canyon environmental variables is highly dependent and sensitive to these variations in wind speed and radiation. This demonstrates the importance of properly modeling interactions between buildings and trees in urban environments, especially for climate-sensitive design issues.

A New Process‐Based Soil Methane Scheme: Evaluation Over Arctic Field Sites With the ISBA Land Surface Model

AbstractPermafrost soils and arctic wetlands methane emissions represent an important challenge for modeling the future climate. Here we present a process‐based model designed to correctly represent the main thermal, hydrological, and biogeochemical processes related to these emissions for general land surface modeling. We propose a new multilayer soil carbon and gas module within the Interaction Soil‐Biosphere‐Atmosphere (ISBA) land‐surface model (LSM). This module represents carbon pools, vertical carbon dynamics, and both oxic and anoxic organic matter decomposition. It also represents the soil gas processes for CH4, CO2, and O2 through the soil column. We base CH4 production and oxydation on an O2 control instead of the classical water table level strata approach used in state‐of‐the‐art soil CH4 models. We propose a new parametrization of CH4 oxydation using recent field experiments and use an explicit O2 limitation for soil carbon decomposition. Soil gas transport is computed explicitly, using a revisited formulation of plant‐mediated transport, a new representation of gas bulk diffusivity in porous media closer to experimental observations, and an innovative advection term for ebullition. We evaluate this advanced model on three climatically distinct sites : two in Greenland (Nuuk and Zackenberg) and one in Siberia (Chokurdakh). The model realistically reproduces methane and carbon dioxide emissions from both permafrosted and nonpermafrosted sites. The evolution and vertical characteristics of the underground processes leading to these fluxes are consistent with current knowledge. Results also show that physics is the main driver of methane fluxes, and the main source of variability appears to be the water table depth.

Providing a non-deterministic representation of spatial variability of precipitation in the Everest region

Abstract. This paper provides a new representation of the effect of altitude on precipitation that represents spatial and temporal variability in precipitation in the Everest region. Exclusive observation data are used to infer a piecewise linear function for the relation between altitude and precipitation and significant seasonal variations are highlighted. An original ensemble approach is applied to provide non-deterministic water budgets for middle and high-mountain catchments. Physical processes at the soil–atmosphere interface are represented through the Interactions Soil–Biosphere–Atmosphere (ISBA) surface scheme. Uncertainties associated with the model parametrization are limited by the integration of in situ measurements of soils and vegetation properties. Uncertainties associated with the representation of the orographic effect are shown to account for up to 16 % of annual total precipitation. Annual evapotranspiration is shown to represent 26 % ± 1 % of annual total precipitation for the mid-altitude catchment and 34% ± 3 % for the high-altitude catchment. Snowfall contribution is shown to be neglectable for the mid-altitude catchment, and it represents up to 44 % ± 8 % of total precipitation for the high-altitude catchment. These simulations on the local scale enhance current knowledge of the spatial variability in hydroclimatic processes in high- and mid-altitude mountain environments.

Impacts of snow and organic soils parameterization on northern Eurasian soil temperature profiles simulated by the ISBA land surface model

Abstract. In this study we analyzed how an improved representation of snowpack processes and soil properties in the multilayer snow and soil schemes of the Interaction Soil-Biosphere-Atmosphere (ISBA) land surface model impacts the simulation of soil temperature profiles over northern Eurasian regions. For this purpose, we refine ISBA's snow layering algorithm and propose a parameterization of snow albedo and snow compaction/densification adapted from the detailed Crocus snowpack model. We also include a dependency on soil organic carbon content for ISBA's hydraulic and thermal soil properties. First, changes in the snowpack parameterization are evaluated against snow depth, snow water equivalent, surface albedo, and soil temperature at a 10 cm depth observed at the Col de Porte field site in the French Alps. Next, the new model version including all of the changes is used over northern Eurasia to evaluate the model's ability to simulate the snow depth, the soil temperature profile, and the permafrost characteristics. The results confirm that an adequate simulation of snow layering and snow compaction/densification significantly impacts the snowpack characteristics and the soil temperature profile during winter, while the impact of the more accurate snow albedo computation is dominant during the spring. In summer, the accounting for the effect of soil organic carbon on hydraulic and thermal soil properties improves the simulation of the soil temperature profile. Finally, the results confirm that this last process strongly influences the simulation of the permafrost active layer thickness and its spatial distribution.

Evaluation of climate anomalies impacts on the Upper Blue Nile Basin in Ethiopia using a distributed and a lumped hydrologic model

Summary Evaluating the climate anomalies impacts on the Upper Blue Nile Basin (UBNB), Ethiopia, a large basin with scarce hydroclimatic data, through hydrologic modeling is a challenge. A fully distributed, physically-based model, a modified version of the Interactions Soil–Biosphere Atmosphere model of Meteo France (MISBA), and a lumped, conceptual rainfall–runoff Sacramento model, SAC-SMA of the US National Weather Service, were used to simulate the streamflow of UBNB. To study the potential hydrologic effect of climate anomalies on the UBNB, rainfall and temperature data observed when climate anomalies were active, were resampled and used to drive MISBA and SAC-SMA. To obtain representative, distributed precipitation data in mountainous basins, it was found that a 3% adjustment factor for every 25 m rise in elevation was needed to orographically correct the rainfall over UBNB. The performance of MISBA applied to UBNB improved after MISBA was modified so that it could simulate evaporation loss from the canopy, providing coefficient of determination (R2) = 0.58, and root mean square error (RMSE) = 0.34 m3/s in comparison with the observed streamflow. In contrast, the performance of SAC-SMA at the calibration run and the validation run is better than that of MISBA, such that R2 is 0.79 for calibration and 0.82 for validation even though it models the hydrology of UBNB in a lumped, conceptual framework as against the physically-based, fully distributed framework of MISBA. El Nino tends to decrease the June–September rainfall but increase the February–May rainfall, while La Nina has opposite effect on the rainfall of UBNB. Based on the simulations of MISBA and SAC-SMA for UBNB, La Nina and Indian Ocean Dipole (IOD) tend to have a wetting effect while El Nino has a drying effect on the streamflow of the UBNB. In addition, El Nino Southern Oscillation (ENSO) and IOD increase the streamflow variability more than changing the magnitude of streamflow. The results provide useful information on the effects of global oceanic anomalies on the hydrology of UBNB.

Improving the ISBA<sub>CC</sub> land surface model simulation of water and carbon fluxes and stocks over the Amazon forest

Abstract. We evaluate the ISBACC (Interaction Soil Biosphere Atmosphere Carbon Cycle) land surface model (LSM) over the Amazon forest, and propose a revised parameterization of photosynthesis, including new soil water stress and autotrophic respiration (RA) functions. The revised version allows the model to better capture the energy, water and carbon fluxes when compared to five Amazonian flux towers. The performance of ISBACC is slightly site dependent although similar to the widely evaluated LSM ORCHIDEE (Organizing Carbon and Hydrology In Dynamic Ecosystems – version 1187), which is based on different assumptions. Changes made to the autotrophic respiration functions, including a vertical profile of leaf respiration, lead to yearly simulated carbon use efficiency (CUE) and carbon stocks which is consistent with an ecophysiological meta-analysis conducted on three Amazonian sites. Despite these major improvements, ISBACC struggles to capture the apparent seasonality of the carbon fluxes derived from the flux tower estimations. However, there is still no consensus on the seasonality of carbon fluxes over the Amazon, stressing a need for more observations as well as a better understanding of the main drivers of autotrophic respiration.

Potential combined hydrologic impacts of climate change and El Niño Southern Oscillation to South Saskatchewan River Basin

A physically based land surface scheme, the Modified Interaction Soil Biosphere Atmosphere (MISBA) of Kerkhoven and Gan (2006) was used to assess the future streamflow of the South Saskatchewan River Basin (SSRB) of Alberta under the combined impacts of climate change and El Niño Southern Oscillation (ENSO). Potential impacts of climate change on the streamflows of 15 sub-basins of the SSRB for the 2010–2039 (2020s), 2040–2069 (2050s) and 2070–2099 (2080s) were simulated by MISBA based on 30 years (1961–1990) of re-analysis data of the European Centre for Mid-range Weather Forecasts (ERA-40) adjusted with climate scenarios projected by four General Circulation Models (GCMs) for three Special Report on Emissions Scenarios (SRES) emissions (A1FI, A21, B21) of Intergovernmental Panel on Climate Change (IPCC). Next, the combined impacts of climate change and ENSO are simulated by driving MISBA with the ERA-40 dataset re-sampled for active El Niño and La Niña episodes adjusted for climate projections of 2050s. Under SRES climate projections alone, MISBA simulated an overall decrease in streamflow for sub-basins of SSRB in 2020s, 2050s, and 2080s. While under a combined impact of climate change and ENSO, a further decrease (increase) in the streamflow of SSRB by 2050s was simulated if the climate anomaly considered was El Niño (La Niña).

Predicting the response of the Amazon rainforest to persistent drought conditions under current and future climates: a major challenge for global land surface models

Abstract. While a majority of global climate models project drier and longer dry seasons over the Amazon under higher CO2 levels, large uncertainties surround the response of vegetation to persistent droughts in both present-day and future climates. We propose a detailed evaluation of the ability of the ISBACC (Interaction Soil–Biosphere–Atmosphere Carbon Cycle) land surface model to capture drought effects on both water and carbon budgets, comparing fluxes and stocks at two recent throughfall exclusion (TFE) experiments performed in the Amazon. We also explore the model sensitivity to different water stress functions (WSFs) and to an idealized increase in CO2 concentration and/or temperature. In spite of a reasonable soil moisture simulation, ISBACC struggles to correctly simulate the vegetation response to TFE whose amplitude and timing is highly sensitive to the WSF. Under higher CO2 concentrations, the increased water-use efficiency (WUE) mitigates the sensitivity of ISBACC to drought. While one of the proposed WSF formulations improves the response of most ISBACC fluxes, except respiration, a parameterization of drought-induced tree mortality is missing for an accurate estimate of the vegetation response. Also, a better mechanistic understanding of the forest responses to drought under a warmer climate and higher CO2 concentration is clearly needed.

Differences in the Potential Hydrologic Impact of Climate Change to the Athabasca and Fraser River Basins of Canada with and without Considering Shifts in Vegetation Patterns Induced by Climate Change

Abstract The research objectives are to estimate differences between the potential impact of climatic change to the Athabasca River basin (ARB) and Fraser River basin (FRB) of Canada with and without considering shifts in vegetation patterns induced by climate change and how much the difference will depend on vegetation types and climate. The hydrologic effects of vegetation shifts on ARB and FRB were estimated by applying the Mapped Atmosphere–Plant–Soil System (MAPSS) simulated results based on the Intergovernmental Panel on Climate Change’s First and Second Assessment Report general circulation model (GCM) scenarios to the modified Interaction Soil–Biosphere–Atmosphere (MISBA) scheme. According to MAPSS, vegetation shifts in mountainous regions of FRB are expected to be dominated by conifer/broadleaf competition, while in ARB, climate projections of MAPSS predicted a southern expansion of the boreal forest. Because of differences in sublimation, there is a tendency for more snow to accumulate in open grassland than forests. Furthermore, changes to simulated mean annual maximum snowpack, runoff, and basin area covered by grassland are positively correlated to each other. Generally, a 4% increase in snow water equivalent (SWE) results in a 1% increase in mean annual runoff. These relationships hold true in both basins over a wide range of GCM-projected climate conditions and vegetation responses, suggesting that most changes in mean annual flow can be attributed to changes in SWE. Because of the different modeling approaches between MAPSS and MISBA, it seems that the treatment of these processes in vegetation and hydrologic models should be similar before conclusions can be drawn from various stand-alone simulations. Ideally, a land surface scheme should be coupled with a vegetation model in future studies.

Inclusion of vegetation in the Town Energy Balance model for modelling urban green areas

Abstract. Cities impact both local climate, through urban heat islands and global climate, because they are an area of heavy greenhouse gas release into the atmosphere due to heating, air conditioning and traffic. Including more vegetation into cities is a planning strategy having possible positive impacts for both concerns. Improving vegetation representation into urban models will allow us to address more accurately these questions. This paper presents an improvement of the Town Energy Balance (TEB) urban canopy model. Vegetation is directly included inside the canyon, allowing shadowing of grass by buildings, better representation of urban canopy form and, a priori, a more accurate simulation of canyon air microclimate. The surface exchanges over vegetation are modelled with the well-known Interaction Soil Biosphere Atmosphere (ISBA) model that is integrated in the TEB's code architecture in order to account for interactions between natural and built-up covers. The design of the code makes possible to plug and use any vegetation scheme. Both versions of TEB are confronted to experimental data issued from a field campaign conducted in Israel in 2007. Two semi-enclosed courtyards arranged with bare soil or watered lawn were instrumented to evaluate the impact of landscaping strategies on microclimatic variables and evapotranspiration. For this case study, the new version of the model with integrated vegetation performs better than if vegetation is treated outside the canyon. Surface temperatures are closer to the observations, especially at night when radiative trapping is important. The integrated vegetation version simulates a more humid air inside the canyon. The microclimatic quantities (i.e., the street-level meteorological variables) are better simulated with this new version. This opens opportunities to study with better accuracy the urban microclimate, down to the micro (or canyon) scale.

Effects of Climate Change on the Surface-Water Management of the South Saskatchewan River Basin

AbstractThe Modified Interaction Soil Biosphere Atmosphere (MISBA) model, the Water Resources Management Model (WRMM) of Alberta Environment, and the Irrigation District Model (IDM) of Alberta Agriculture Food and Rural Development were used to assess the future outlook of water resource management of the South Saskatchewan River Basin (SSRB) of Alberta under the potential impacts of climate change. Using the SSRB hydrometeorological base data from 1928–1995, potential effects of climate change on the SSRB for 2010–2039, 2040–2069, and 2070–2099 were simulated by MISBA, IDM, and WRMM with the climate scenarios projected by four general circulation models forced by emissions reported by the Intergovernmental Panel on Climate Change. Under these climate projections, MISBA simulated a significant decrease in the mean annual average and mean annual maximum streamflows over selected nodes within the SSRB; the irrigation water demand projected by IDM is expected to increase progressively over the 21st century; ...

Regional-scale evaluation of a land surface scheme from atmospheric boundary layer observations

[1] The study describes an evaluation of three configurations of the Interactions Soil-Biosphere-Atmosphere (ISBA) land surface scheme fully coupled with the Meso-NH mesoscale atmospheric model. The ability of the modeling system to correctly reproduce the screen-level variables as well as the boundary layer characteristics is examined for more than 30 clear convective days monitored during the CERES 2005 and 2007 field campaigns. For the horizontal resolution considered (8 km), this study shows that the boundary layer characteristics and the low-level variables are better simulated when the subgrid-scale surface process variability is simulated explicitly using the so-called “tiling method.” An additional improvement is brought when the CO2 diurnal cycle is used interactively because of the physical link between the stomatal conductance used both for CO2 assimilation and plant transpiration. The parameterization of this link between CO2 and evaporation fluxes improves the simulation of the Bowen ratio and therefore of the atmospheric boundary layer. The last part of the paper discusses the realism of the simulated regional field of CO2 when the carbon configuration is activated in the mesoscale model. Large regional variability of CO2 within the atmospheric boundary layer is found in response to the spatial and seasonal variability of CO2 surface fluxes with respect to the three main land covers in the area: pine forest, extensive winter (wheat), and summer (maize) crops.

An Intercomparison of ERS-Scat and AMSR-E Soil Moisture Observations with Model Simulations over France

Abstract This paper presents a study undertaken in preparation of the work leading up to the assimilation of Soil Moisture and Ocean Salinity (SMOS) observations into the land surface model (LSM) Interaction Soil Biosphere Atmosphere (ISBA) at Météo-France. This study consists of an intercomparison experiment of different space-borne platforms providing surface soil moisture information [Advanced Microwave Scanning Radiometer for Earth Observing (AMSR-E) and European Remote Sensing Satellite Scatterometer (ERS-Scat)] with the reanalysis soil moisture predictions over France from the model suite of Système d’analyse fournissant des renseignements atmosphériques à la neige (SAFRAN), ISBA, and coupled model (MODCOU; SIM) of Météo-France for the years of 2003–05. Both modeled and remotely sensed data are initially validated against in situ observations obtained at the experimental soil moisture monitoring site Surface Monitoring of the Soil Reservoir Experiment (SMOSREX) in southwestern France. Two different AMSR-E soil moisture products are compared in the course of this study—the official AMSR-E product from the National Snow and Ice Data Center (NSIDC) and a new product developed at the Vrije Universiteit Amsterdam and NASA (VUA–NASA)—which were obtained using two different retrieval algorithms. This allows for an additional assessment of the different algorithms while using identical brightness temperature datasets. This study shows that a good correlation generally exists between AMSR-E (VUA–NASA), ERS-Scat, and SIM for low altitudes and low-to-moderate vegetation covers (1.5–3 kg m−2 vegetation water content), with a reduction in the correlation in mountainous regions. It also shows that the AMSR-E (NSIDC) soil moisture product has significant differences when compared to the other datasets.

Calibration of the Interaction Soil Biosphere Atmosphere land‐surface scheme on a small tropical high‐mountain basin (Cordillera Real, Bolivia)

In a continuing effort to test the behavior of Meteo France's land‐surface scheme, Interaction Soil Biosphere Atmosphere (ISBA), under a wide range of hydrometeorological conditions, the scheme was applied to a small tropical high‐mountain river basin of the Cordillera Real in Bolivia. The surface scheme simulates the key hydrological processes, such as evaporation, infiltration, surface runoff, and snow and soil ice freeze‐thaw processes, which are essential for accurately simulating the hydrological behavior of the river basin in this type of location. The 12.5 km2 nonglacierized subbasin has been divided into homogeneous surface units with irregular shapes, on the basis of their elevation and soil surface characteristics. The ISBA scheme was applied to each unit and the water fluxes were transferred from one unit to another using a system dynamics modeling approach. The method was applied step by step, improving its efficiency based on several hypotheses. This special application of the ISBA scheme, combining the high‐mountain conditions and the tropical seasonality is discussed.

Improvement of the hydrological component of an urban soil–vegetation–atmosphere–transfer model

AbstractA numerical study was conducted on the Rezé suburban catchment (Nantes, France) to evaluate the hydrological component of the town energy balance (TEB) scheme, which simulates in a coupled way the water and energy balances for the urban covers. The catchment is a residential area where hydrological data were continuously collected from 1993 to 1998 by the Laboratoire Central des Ponts et Chaussées (LCPC), notably the runoff in the stormwater drainage network. A 6‐year simulation with the TEB and interaction soil–biosphere–atmosphere (ISBA) schemes in off‐line mode enabled the comparison of modelled and observed runoff. Some weaknesses of the TEB were uncovered and led to improved parameterization of water exchanges: (1) calibration of the maximum capacity of the rainfall interception reservoir on roads and roofs and (2) inclusion of water infiltration through the roads, according to a simple formulation. The calibration of this water flux gives results that are consistent with direct measurements of water infiltration performed on the Rezé site and from the literature. The new parameterization produces better runoff in terms of timing and magnitude, which are comparable to those obtained by the LCPC with other hydrological models. It shows also the impact of the water infiltration through the roads, corresponding to a water transfer from the TEB to ISBA, on the water balance: the water contents of road, roof and soil reservoirs being modified, the evaporation from artificial surfaces decreases, while the evapotranspiration from natural covers increases. Through the evaporative flux, such a modification of the water balance induces large repercussions on the surface energy balance. Copyright © 2007 John Wiley & Sons, Ltd.

A Global Root-Zone Soil Moisture Analysis Using Simulated L-band Brightness Temperature in Preparation for the Hydros Satellite Mission

Abstract The aim of this study is to test a land data assimilation prototype for the production of a global daily root-zone soil moisture analysis. This system can assimilate microwave L-band satellite observations such as those from the future Hydros NASA mission. The experiments are considered in the framework of the Interaction Soil Biosphere Atmosphere (ISBA) land surface scheme used operationally at the Meteorological Service of Canada for regional and global weather forecasting. A land surface reference state is obtained after a 1-yr global land surface simulation, forced by near-surface atmospheric fields provided by the Global Soil Wetness Project, second initiative (GSWP-2). A radiative transfer model is applied to simulate the microwave L-band passive emission from the surface. The generated brightness temperature observations are distributed in space and time according to the satellite trajectory specified by the Hydros mission. The impact of uncertainties related to the satellite observations, the land surface, and microwave emission models is investigated. A global daily root-zone soil moisture analysis is produced with a simplified variational scheme. The applicability and performance of the system are evaluated in a data assimilation cycle in which the L-band simulated observations, generated from a land surface reference state, are assimilated to correct a prescribed initial root-zone soil moisture error. The analysis convergence is satisfactory in both summer and winter cases. In summer, when considering a 3-K observation error, 90% of land surface converges toward the reference state with a soil moisture accuracy better than 0.04 m3 m−3 after a 4-week assimilation cycle. A 5-K observation error introduces 1-week delay in the convergence. A study of the analysis error statistics is performed for understanding the properties of the system. Special features associated with the interactions between soil water and soil ice, and the presence of soil moisture vertical gradients, are examined.

An intercomparison study of two land surface models using a 1‐D model and fife measurements

AbstractTwo land‐surface parameterization schemes (ISBA (Interactions Soil‐Biosphere‐Atmosphere) and LAPS (Land‐Air‐Parameterization‐Scheme)) of differing complexity were implemented into a 1‐D atmospheric boundary layer model and evaluated utilizing the special observational data collected during the summer of 1987 from the FIFE measurements. Results from two case studies were analyzed during which boundary layer processes dominated the lower atmospheric processes. In the first case study (6 June 1987), we found that differences in the estimation of stomatal resistance in the two land‐surface models (LSMs) triggered many of the differences in results obtained using the two LSMs. In the second case study (11 July 1987), only minor differences existed between respective net radiation and stomatal resistance estimations, leading to similar boundary layer structures. Diagnostic results indicate that in both case studies growth rates of and depths of atmospheric boundary layers and vertical profiles of virtual potential temperatures, water vapor mixing ratio, and horizontal winds are very similar in LAPS and ISBA. Our future studies are directed at evaluating these two schemes using a regional climate version of the WRF model. Copyright © 2006 Royal Meteorological Society.

Impact of an Exponential Profile of Saturated Hydraulic Conductivity within the ISBA LSM: Simulations over the Rhône Basin

Abstract This study focuses on the influence of an exponential profile of saturated hydraulic conductivity, ksat, 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 ksat 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 ksat 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.

Hydrometeorological modeling of the Seine basin using the SAFRAN‐ISBA‐MODCOU system

As the Seine basin is the most urbanized and industrialized French basin, with intensive crop areas, the impact of floods and low flow is very important. The aim of this study is to improve the understanding of the hydrological functioning of the Seine basin and to estimate the influence of the large aquifers that cover a great part of the domain, as well as the impact of the urbanized areas. The simulation is based on the SAFRAN‐ISBA‐MODCOU (SIM) coupled system, which includes the Analysis System for Providing Atmospheric Information Relevant to Snow (SAFRAN) analysis of the atmospheric forcing, two surface schemes that take into account the urban areas (Town Energy Budget (TEB)) and the natural areas (Interactions Soil‐Biosphere‐Atmosphere (ISBA)), and the distributed hydrological model Coupled Model (MODCOU). A 17‐year simulation was performed and validated against the observations of about 100 river gauges and 130 piezometric stations. The simulated streamflows are comparable with the observations, especially for large river stations of the Seine and its main tributaries. The spatial and temporal variations of the aquifer levels simulated by MODCOU are also comparable to the observed piezometric data, although the local comparison can present differences. The impact of urban areas on the streamflows appears to be important at the local scale but not very marked at the basin scale, but their impact on the energy budget is strong. Moreover, it is shown that the aquifers play a very important role. The underground contribution to the discharge reaches more than 80% of the Seine river flow in summertime and ∼40% in winter. Even during the wintertime floods, the aquifers play a crucial role, since the larger part of the drainage is stored in the water tables, which significantly reduces the intensity of the floods and, thus, of their consequences. It is finally shown that the ability of SIM to reproduce the evolution of the aquifers and the partition between surface runoff and drainage leads to a good simulation of the main floods of the Seine.