scholarly journals A New Characterization of the Land Surface Heterogeneity over Africa for Use in Land Surface Models

2011 ◽  
Vol 12 (6) ◽  
pp. 1321-1336 ◽  
Author(s):  
Armel Thibaut Kaptué Tchuenté ◽  
Jean-Louis Roujean ◽  
Agnès Bégué ◽  
Sietse O. Los ◽  
Aaron A. Boone ◽  
...  
Keyword(s):  
Land Cover ◽  
Vegetation Cover ◽  
Land Surface ◽  
Extended Period ◽  
Surface Heterogeneity ◽  
Ecological Communities ◽  
Area Index ◽  
Fractional Vegetation Cover ◽  
Land Surface Heterogeneity

Abstract Information related to land surface is immensely important to global change science. For example, land surface changes can alter regional climate through its effects on fluxes of water, energy, and carbon. In the past decades, data sources and methodologies for characterizing land surface heterogeneity (e.g., land cover, leaf area index, fractional vegetation cover, bare soil, and vegetation albedos) from remote sensing have evolved rapidly. The double ECOCLIMAP database—constituted of a land cover map and land surface variables and derived from Advanced Very High Resolution Radiometer (AVHRR) observations acquired between April 1992 and March 1993—was developed to support investigations that require information related to spatiotemporal dynamics of land surface. Here is the description of ECOCLIMAP-II: a new characterization of the land surface heterogeneity based on the latest generation of sensors, which represents an update of the ECOCLIMAP-I database over Africa. Owing to the many features of the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors (more accurate in spatial resolution and spectral information compared to the AVHRR sensor), a variety of methods have been developed for an extended period of 8 yr (2000–07) to strengthen consistency between land surface variables as required by the meteorological and ecological communities. The relative accuracy (or performance) quality of ECOCLIMAP-II was assessed (i.e., by comparison with other global datasets). Results illustrate a substantial refinement; for instance, the fractional vegetation cover resulting in a root-mean-square error of 34% instead of 64% in comparison with the original version of ECOCLIMAP.

scholarly journals Land Surface Heterogeneity Signature in Tornado Climatology? An Illustrative Analysis over Indiana, 1950–2012*

2014 ◽  
Vol 18 (10) ◽  
pp. 1-32 ◽  
Author(s):  
Olivia Kellner ◽  
Dev Niyogi
Keyword(s):  
Land Use ◽  
Population Density ◽  
Land Cover ◽  
Land Surface ◽  
Strong Relationship ◽  
Surface Heterogeneity ◽  
Temporal Analysis ◽  
Antecedent Rainfall ◽  
Land Surface Heterogeneity ◽  
Tornado Climatology

Abstract Land surface heterogeneity affects mesoscale interactions, including the evolution of severe convection. However, its contribution to tornadogenesis is not well known. Indiana is selected as an example to present an assessment of documented tornadoes and land surface heterogeneity to better understand the spatial distribution of tornadoes. This assessment is developed using a GIS framework taking data from 1950 to 2012 and investigates the following topics: temporal analysis, effect of ENSO, antecedent rainfall linkages, population density, land use/land cover, and topography, placing them in the context of land surface heterogeneity. Spatial analysis of tornado touchdown locations reveals several spatial relationships with regard to cities, population density, land-use classification, and topography. A total of 61% of F0–F5 tornadoes and 43% of F0–F5 tornadoes in Indiana have touched down within 1 km of urban land use and land area classified as forest, respectively, suggesting the possible role of land-use surface roughness on tornado occurrences. The correlation of tornado touchdown points to population density suggests a moderate to strong relationship. A temporal analysis of tornado days shows favored time of day, months, seasons, and active tornado years. Tornado days for 1950–2012 are compared to antecedent rainfall and ENSO phases, which both show no discernible relationship with the average number of annual tornado days. Analysis of tornado touchdowns and topography does not indicate any strong relationship between tornado touchdowns and elevation. Results suggest a possible signature of land surface heterogeneity—particularly that around urban and forested land cover—in tornado climatology.

Sensitivity of the ECMWF Land surface model to vegetation and LU/LC maps

2020 ◽  
Author(s):  
Souhail Boussetta ◽  
Gianpaolo Balsamo ◽  
Emanuel Arduini ◽  
Miguel Nogueira ◽  
Gabriele Arduini ◽  
...  
Keyword(s):  
Land Cover ◽  
Vegetation Cover ◽  
Land Surface ◽  
Land Surface Model ◽  
Global Scale ◽  
Surface Model ◽  
Land Use Land Cover ◽  
Area Index ◽  
Land Cover Map ◽  
Land Cover Maps

<p><span><span>The effects of vegetation and land use/land cover maps on surface energy and carbon fluxes predictions from land surface model are investigated. The model is applied at global scale and a comparison between two configurations using different land cover maps is performed. In the first configuration, the land cover is based on the operational GLCCv1.2 map, in the second the ESA-CCI land cover map is used.</span></span></p><p><span><span>Based on these two configurations, the observation operator that disaggregates the satellite-based leaf area index into high and low vegetation components is also modified to ensure optimal conservation of the observed LAI. The Seasonal variability of the vegetation cover is also investigated by introducing a modified lamber-beer formulation that allows varying the vegetation cover as a function of the LAI. </span></span></p>

Modelling Regional Water and Energy balance in East Africa

2020 ◽  
Author(s):  
Sopan Patil ◽  
John Musau ◽  
Michael Marshall
Keyword(s):  
Surface Water ◽  
Energy Balance ◽  
Land Cover ◽  
Vegetation Structure ◽  
Land Surface ◽  
Surface Heterogeneity ◽  
Time Varying ◽  
Energy Fluxes ◽  
Vegetation Parameters ◽  
Land Surface Heterogeneity

<p>Effective modeling of surface water and energy balance is crucial in planning and management of regional resources. However, the heterogeneous and clumped vegetation structure controls the portioning of land surface water and energy fluxes, which leads to large variations of local radiative and hydrological processes. The aim of this study is to characterize the land surface heterogeneity in East Africa and examine the impact of the spatially and temporally varying vegetation parameters on energy and water balance in the region.  We used MODIS datasets on Leaf Area Index (LAI), Enhanced Vegetation Index (EVI) and albedo to derive time-varying vegetation parameters for the period 2001 – 2011 period at 0.05° resolution. These parameters were integrated with the Variable Infiltration Capacity (VIC) model to characterize the effects of varying vegetation properties on surface water and energy fluxes. A twin simulation was also carried based on seasonally averaged vegetation parameters to isolate the effects of time-varying and spatially heterogeneous parameters on the water and energy fluxes. The simulation results were compared to rigorously validated global datasets on evapotranspiration and sensible heat. Results showed that the time-varying and spatially heterogeneous vegetation parameters provided surface water and energy fluxes which were more consistent with the validation datasets. The simulated evapotranspiration matched reasonably well with the observed values particularly in areas characterized by sparse vegetation and which are more prone to human influence. The improvements were highly noticeable in grassland and savanna land cover types. However, due to intensive human activities in region which affect not only the lad cover but also the vegetation structure, there is need for characterization of the land cover parameters based on high resolution data which can better capture the land surface heterogeneity in the region.</p>

Impact of Land Surface Heterogeneity on Mesoscale Atmospheric Dispersion

2009 ◽  
Vol 133 (3) ◽  
Author(s):  
Yuling Wu ◽  
Udaysankar S. Nair ◽  
Roger A. Pielke ◽  
Richard T. McNider ◽  
Sundar A. Christopher ◽  
...  
Keyword(s):  
Land Surface ◽  
Atmospheric Dispersion ◽  
Surface Heterogeneity ◽  
Land Surface Heterogeneity

scholarly journals Representation of fire, land-use change and vegetation dynamics in the Joint UK Land Environment Simulator vn4.9 (JULES)

2019 ◽  
Vol 12 (1) ◽  
pp. 179-193 ◽  
Author(s):  
Chantelle Burton ◽  
Richard Betts ◽  
Manoel Cardoso ◽  
Ted R. Feldpausch ◽  
Anna Harper ◽  
...  
Keyword(s):  
Land Use ◽  
Land Use Change ◽  
Land Cover ◽  
Vegetation Cover ◽  
Land Surface ◽  
Vegetation Dynamics ◽  
Fire Disturbance ◽  
Substantial Contribution ◽  
Surface Model ◽  
The Impact

Abstract. Disturbance of vegetation is a critical component of land cover, but is generally poorly constrained in land surface and carbon cycle models. In particular, land-use change and fire can be treated as large-scale disturbances without full representation of their underlying complexities and interactions. Here we describe developments to the land surface model JULES (Joint UK Land Environment Simulator) to represent land-use change and fire as distinct processes which interact with simulated vegetation dynamics. We couple the fire model INFERNO (INteractive Fire and Emission algoRithm for Natural envirOnments) to dynamic vegetation within JULES and use the HYDE (History Database of the Global Environment) land cover dataset to analyse the impact of land-use change on the simulation of present day vegetation. We evaluate the inclusion of land use and fire disturbance against standard benchmarks. Using the Manhattan metric, results show improved simulation of vegetation cover across all observed datasets. Overall, disturbance improves the simulation of vegetation cover by 35 % compared to vegetation continuous field (VCF) observations from MODIS and 13 % compared to the Climate Change Initiative (CCI) from the ESA. Biases in grass extent are reduced from −66 % to 13 %. Total woody cover improves by 55 % compared to VCF and 20 % compared to CCI from a reduction in forest extent in the tropics, although simulated tree cover is now too sparse in some areas. Explicitly modelling fire and land use generally decreases tree and shrub cover and increases grasses. The results show that the disturbances provide important contributions to the realistic modelling of vegetation on a global scale, although in some areas fire and land use together result in too much disturbance. This work provides a substantial contribution towards representing the full complexity and interactions between land-use change and fire that could be used in Earth system models.

Using Spatial Eddy Covariance to Investigate Energy Balance Closure over a Heterogeneous Ecosystem

2020 ◽  
Author(s):  
Brian Butterworth ◽  
Ankur Desai ◽  
Sreenath Paleri ◽  
Stefan Metzger ◽  
David Durden ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Energy Balance ◽  
Surface Energy ◽  
Atmospheric Boundary Layer ◽  
Eddy Covariance ◽  
Land Surface ◽  
Surface Heterogeneity ◽  
Energy Fluxes ◽  
Surface Energy Fluxes ◽  
Land Surface Heterogeneity

<p>Land surface heterogeneity influences patterns of sensible and latent heat flux, which in turn affect processes in the atmospheric boundary layer. However, gridded atmospheric models often fail to incorporate the influence of land surface heterogeneity due to differences between the temporal and spatial scales of models compared to the local, sub-grid processes. Improving models requires the scaling of surface flux measurements; a process made difficult by the fact that surface measurements usually find an imbalance in the energy budget.</p><p>The Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors (CHEESEHEAD19) was an observational experiment designed to investigate how the atmospheric boundary layer responds to scales of spatial heterogeneity in surface-atmosphere heat and water exchanges. The campaign was conducted from June – October 2019, measuring surface energy fluxes over a heterogeneous forest ecosystem as fluxes transitioned from latent heat-dominated summer through sensible heat-dominated fall. Observations were made by ground, airborne, and satellite platforms within the 10 x 10 km study region, which was chosen to match the scale of a typical model grid cell. The spatial distribution of energy fluxes was observed by an array of 20 eddy covariance towers and a low-flying aircraft. Mesoscale atmospheric properties were measured by a suite of LiDAR and sounding instruments, measuring winds, water vapor, temperature, and boundary layer development. Plant phenology was measured in-situ and mapped remotely using hyperspectral imaging.</p><p>The dense set of multi-scale observations of land-atmosphere exchange collected during the CHEESEHEAD field campaign permits combining the spatial and temporal distribution of energy fluxes with mesoscale surface and atmospheric properties. This provides an unprecedented data foundation to evaluate theoretical explanations of energy balance non-closure, as well as to evaluate methods for scaling surface energy fluxes for improved model-data comparison. Here we show how fluxes calculated using a spatial eddy covariance technique across the 20-tower network compare to those of standard temporal eddy covariance fluxes in order to characterize of the spatial representativeness of single tower eddy covariance measurements. Additionally, we show how spatial EC fluxes can be used to better understand the energy balance over heterogeneous ecosystems.</p>

Sensitivity of Summertime Heatwaves to Vegetation Cover in the Northern Hemisphere

2020 ◽  
Author(s):  
Jing Li ◽  
Chi-Yung Tam ◽  
Amos P. K. Tai ◽  
Ngar-Cheung Lau
Keyword(s):  
North America ◽  
Latent Heat ◽  
Vegetation Cover ◽  
Land Surface ◽  
Large Scale ◽  
Longwave Radiation ◽  
Surface Friction ◽  
Sensible Heat ◽  
Southeastern Part ◽  
Area Index

<p>Heatwaves are a serious threat to society and can lead to grave consequences. It is well known that persistent large-scale circulation anomalies are the key to generating heatwaves. Vegetation plays a vital role in energy and water exchange between land and atmosphere, through its responses to incoming radiation and emission of longwave radiation, its imposition of surface friction and transpiration. However, its impact on surface energy exchange during heatwaves is largely unknown. In this study, we first analyzed the relationship between summer heatwaves and vegetation cover, based on the Global Heatwave and Warm-spell Record (GHWR) and leaf area index (LAI) products from satellites during 1982-2011. Our results revealed differences in the correlation between heatwave characteristics and summertime LAI in different regions. In particular, lower LAI over Central Europe is associated with more frequent heatwaves locally. Over the south to the southeastern part of North America, a similar negative correlation is found. However, in the northeastern part of the continent, the reverse tends to be true, with higher-than-normal LAI associated with an increase of heatwave occurrence. These findings are in general supported by composite analyses of extreme LAI years in these regions and heatwave characteristics therein.</p><p>We speculate that the difference between surface heat flux responses for different vegetation types during heatwaves may explain the results. Focusing on North America, and using various datasets including those generated by the Global Land Data Assimilation System (GLDAS) with three different land surface models (CLM, MOS, NOAH), three reanalysis datasets (MERRA-2, NOAA-CIRES-DOS, NCEP/NCAR), and also observations from an extensive network of flux towers, it was found that over coniferous forests (both boreal and temperate), the sensible heat anomalies increase significantly during heatwaves in high-LAI years. Also, during high-LAI years, over boreal evergreen forests (BEF), changes of latent heat anomalies are much smaller than positive sensible heat anomalies, so that BEF can prolong and amplify heatwaves significantly. On the other hand, for temperate deciduous forests (TDF) and grassland (GSL), both negative sensible heat anomalies and positive latent heat anomalies during heatwaves are found in all datasets; these response act to weaken the heatwave amplitudes. Model experiments were further carried out, in order to test the sensitivity of heatwaves to LAI forcings. It was found that heatwaves are most sensitive to BEF LAI variations, but the response of heatwaves are opposite between middle and high latitudes when BEF LAI increased. For TDF and GSL, heatwaves shortened slightly when LAI increased.</p>

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