scholarly journals Plant- and Soil-Parameter-Caused Uncertainty of Predicted Surface Fluxes

2005 ◽  
Vol 133 (12) ◽  
pp. 3498-3516 ◽  
Author(s):  
Nicole Mölders
Keyword(s):  
Heat Flux ◽  
Leaf Area Index ◽  
Leaf Area ◽  
Stomatal Resistance ◽  
Surface Fluxes ◽  
Critical Parameters ◽  
Net Radiation ◽  
Area Index ◽  
Vegetation Fraction ◽  
Ground Heat Flux

Abstract Simulated surface fluxes depend on one or more empirical plant or soil parameters that have a standard deviation (std dev). Thus, simulated fluxes will have a stochastic error (or std dev) resulting from the parameters’ std dev. Gaussian error propagation (GEP) principles are used to calculate the std dev for fluxes predicted by the hydro–thermodynamic soil–vegetation scheme to identify prediction limitations due to stochastic errors, parameterization weaknesses, and critical parameters, and to prioritize which parameters to measure with higher accuracy. Relative errors of net radiation, sensible, latent, and ground heat flux, on average, are 7%, 10%, 6%, and 26%, respectively. The analysis identified the parameterization of thermal conductivity as the dominant influence on the std dev of ground heat flux. For net radiation, critical parameters are vegetation fraction and ground emissivity; for sensible and latent heat fluxes, vegetation fraction. Minimum stomatal resistance and leaf area index dominate the std dev of stomatal resistance for most vegetation and soil types. The empirical parameters with the highest relative error are not necessarily the greatest contributors to the std dev of the predicted flux. Based on the analysis high priority should be given to measurements of vegetation fraction, ground emissivity, minimum stomatal resistance, leaf area index in general, and the permanent wilting point and field capacity for clay and clay loam. Moreover, further specification of clay-type soils and tundra-type vegetation may improve the accuracy of the lower boundary condition in Arctic numerical weather prediction. Since GEP showed itself able to identify critical parameters and (parts of) parameterizations, GEP analysis could form a basis for parameterization intercomparisons and for parameter determination aimed at improving models.

scholarly journals Sensitivity of ground heat flux to vegetation cover fraction and leaf area index

1999 ◽  
Vol 104 (D16) ◽  
pp. 19505-19514 ◽  
Author(s):  
Z-L. Yang ◽  
Y. Dai ◽  
R. E. Dickinson ◽  
W. J. Shuttleworth
Keyword(s):  
Heat Flux ◽  
Leaf Area Index ◽  
Leaf Area ◽  
Vegetation Cover ◽  
Area Index ◽  
Ground Heat Flux

scholarly journals Sensitivity of Surface Fluxes in the ECMWF Land Surface Model to the Remotely Sensed Leaf Area Index and Root Distribution: Evaluation with Tower Flux Data

Atmosphere ◽  
2020 ◽  
Vol 11 (12) ◽  
pp. 1362
Author(s):  
David Stevens ◽  
Pedro M. A. Miranda ◽  
René Orth ◽  
Souhail Boussetta ◽  
Gianpaolo Balsamo ◽  
...  
Keyword(s):  
Leaf Area Index ◽  
Leaf Area ◽  
Land Surface ◽  
Root Distribution ◽  
Land Surface Model ◽  
Moisture Stress ◽  
Stomatal Resistance ◽  
Surface Fluxes ◽  
Surface Model ◽  
Area Index

The surface-atmosphere turbulent exchanges couple the water, energy and carbon budgets in the Earth system. The biosphere plays an important role in the evaporation process, and vegetation related parameters such as the leaf area index (LAI), vertical root distribution and stomatal resistance are poorly constrained due to sparse observations at the spatio-temporal scales at which land surface models (LSMs) operate. In this study, we use the Carbon Hydrology Tiled European Center for Medium-Range Weather Forecasts (ECMWF) Scheme for Surface Exchanges over Land (CHTESSEL) model and investigate the sensitivity of the simulated turbulent fluxes to these vegetation related parameters. Observed data from 17 FLUXNET towers were used to force and evaluate model simulations with different vegetation parameter configurations. The replacement of the current LAI climatology used by CHTESSEL, by a new high-resolution climatology, representative of the station’s location, has a small impact on the simulated fluxes. Instead, a revision of the root profile considering a uniform root distribution reduces the underestimation of evaporation during water stress conditions. Despite the limitations of using only one model and a limited number of stations, our results highlight the relevance of root distribution in controlling soil moisture stress, which is likely to be applicable to other LSMs.

scholarly journals Representing winter wheat in the Community Land Model (version 4.5)

2017 ◽  
Vol 10 (5) ◽  
pp. 1873-1888 ◽  
Author(s):  
Yaqiong Lu ◽  
Ian N. Williams ◽  
Justin E. Bagley ◽  
Margaret S. Torn ◽  
Lara M. Kueppers
Keyword(s):  
Heat Flux ◽  
Winter Wheat ◽  
Leaf Area Index ◽  
Leaf Area ◽  
Latent Heat Flux ◽  
Carbon Allocation ◽  
Net Ecosystem Exchange ◽  
Area Index ◽  
Community Land Model ◽  
The Us

Abstract. Winter wheat is a staple crop for global food security, and is the dominant vegetation cover for a significant fraction of Earth's croplands. As such, it plays an important role in carbon cycling and land–atmosphere interactions in these key regions. Accurate simulation of winter wheat growth is not only crucial for future yield prediction under a changing climate, but also for accurately predicting the energy and water cycles for winter wheat dominated regions. We modified the winter wheat model in the Community Land Model (CLM) to better simulate winter wheat leaf area index, latent heat flux, net ecosystem exchange of CO2, and grain yield. These included schemes to represent vernalization as well as frost tolerance and damage. We calibrated three key parameters (minimum planting temperature, maximum crop growth days, and initial value of leaf carbon allocation coefficient) and modified the grain carbon allocation algorithm for simulations at the US Southern Great Plains ARM site (US-ARM), and validated the model performance at eight additional sites across North America. We found that the new winter wheat model improved the prediction of monthly variation in leaf area index, reduced latent heat flux, and net ecosystem exchange root mean square error (RMSE) by 41 and 35 % during the spring growing season. The model accurately simulated the interannual variation in yield at the US-ARM site, but underestimated yield at sites and in regions (northwestern and southeastern US) with historically greater yields by 35 %.

scholarly journals Examining the link between vegetation leaf area and land-atmosphere exchange of water, energy, and carbon fluxes using FLUXNET data

2020 ◽  
Author(s):  
Anne J. Hoek van Dijke ◽  
Kaniska Mallick ◽  
Martin Schlerf ◽  
Miriam Machwitz ◽  
Martin Herold ◽  
...  
Keyword(s):  
Leaf Area Index ◽  
Leaf Area ◽  
Primary Productivity ◽  
Large Scale ◽  
Vegetation Type ◽  
Carbon Fluxes ◽  
Surface Fluxes ◽  
Energy Fluxes ◽  
Area Index ◽  
Vegetation Control

Abstract. Vegetation regulates the exchange of water, energy, and carbon fluxes between the land and the atmosphere. This regulation of surface fluxes differs with vegetation type and climate, but the effect of vegetation on surface fluxes is not well understood. A better knowledge of how and when vegetation influences surface fluxes could improve climate models and the extrapolation of ground-based water, energy, and carbon fluxes. We aim to study the large-scale link between vegetation and surface fluxes by combining MODIS leaf area index with flux tower measurements of water (latent heat), energy (sensible heat), and carbon (gross primary productivity and net ecosystem exchange). We show that the correlation between leaf area index and water and energy fluxes depends on vegetation and aridity. In water-limited conditions, the link between vegetation and water and energy fluxes is strong, which is in line with a strong stomatal or vegetation control found in earlier studies. In energy-limited forest we found no vegetation control on water and energy fluxes. In contrast to water and energy fluxes, we found a strong correlation between leaf area index and gross primary productivity that was independent of vegetation type and aridity index. This study provides insight in the large-scale link between vegetation and surface fluxes. The study indicates that for modelling or extrapolating large-scale surface fluxes, LAI can be useful in savanna and grassland, but only of limited use in deciduous broadleaf forest and evergreen needleleaf forest.

scholarly journals Changes of surface energy partitioning caused by plastic mulch in a cotton field

2018 ◽  
Vol 32 (3) ◽  
pp. 349-356 ◽  
Author(s):  
Zhipin Ai ◽  
Yonghui Yang ◽  
Qinxue Wang ◽  
Shumin Han ◽  
Yanmin Yang ◽  
...  
Keyword(s):  
Heat Flux ◽  
Surface Energy ◽  
Leaf Area Index ◽  
Surface Soil ◽  
Soil Heat Flux ◽  
Energy Partitioning ◽  
Sensible Heat ◽  
Net Radiation ◽  
Plastic Mulch ◽  
Area Index

Abstract Widely used in croplands, plastic mulch can significantly change land surface properties and energy partitioning. However, the magnitude of these modifications caused by plastic mulch (and its variations) on leaf area index remain largely unclear. Field experiments were, therefore, conducted to analyse the differences in energy partitioning between plastic mulch and non-plastic mulch conditions in cotton fields in arid Tarim Basin. Each component net radiation, surface soil heat flux, sensible heat and latent heat was either measured or estimated at different growth stages of the cotton crop. Results showed that the effects of plastic mulch on field energy partitioning was most evident when leaf area index was less than 1.0. During this period, net radiation decreased mainly due to the increase of surface reflectance. Surface soil heat flux and sensible heat were also increased due to the increase of surface temperature. Finally, latent heat decreased after plastic mulch application. As over 20% of net radiation was allocated to the soil surface under plastic mulch at the seedling stage, this suggests that surface soil heat flux should not be ignored for evaluating surface energy balance at the seedling stage under plastic mulch conditions.

scholarly journals Numerical Study of Heat and Water Vapour Exchanges Inside a Green Roof Building in a High Irradiation Area for Passive Cooling Purpose

2021 ◽  
Vol 1 ◽  
Author(s):  
Hodo-Abalo Samah ◽  
N’Detigma Kata ◽  
Kodjo Kpode ◽  
Magolmèèna Banna ◽  
Belkacem Zeghmati
Keyword(s):  
Heat Flux ◽  
Mixed Convection ◽  
Leaf Area Index ◽  
Leaf Area ◽  
Indoor Air ◽  
Numerical Study ◽  
Green Roof ◽  
Passive Cooling ◽  
Area Index ◽  
Solar Heat Flux

Vegetation cover provides shading and protects the soil beneath them from warming.  Vegetation can be used as passive cooling technique that reduces the thermal load of a building. A numerical study has been carried out on laminar double-diffusive mixed convection in a green roof enclosure. The model is equipped with inlet and outlet openings for air removal while the left vertical wall is heated and partially saturated with water for indoor air humidification. The mathematical model is governed by the two-dimensional continuity, momentum, energy and concentration equations. Transfer equations are solved using a finite difference scheme and Thomas algorithm. The model was applied for the simulation of a building with green roof in Togolese climate conditions. Results showed that, the flow structure is a mixed convection type, but the isotherms et iso-concentration distributions reveal a vertical stratification of the temperatures and the relative humidity.To predict heat transfers inside the cavity, a correlation has been established for the estimation of the average Nusselt number as a function of the Leaf Area Index and Reynolds number under solar heat flux of 350 W.m-2, the average in case of Togo. It was found that a larger Leaf Area Index reduces the solar flux penetration and therefore, reduces significantly heat transfer inside the enclosure and then stabilizes it temperature. For the LAI equal to 3, the indoor air fluctuates around 26°C and the relative humidity range is found to be 50% - 60% under solar heat flux of 350 W.m-2.

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