scholarly journals Mosaic versus dual source approaches for modelling the surface energy balance of a semi-arid land

1999 ◽  
Vol 3 (2) ◽  
pp. 247-258 ◽  
Author(s):  
G. Boulet ◽  
A. Chehbouni ◽  
I. Braud ◽  
M. Vauclin
Keyword(s):  
Surface Energy ◽  
Bare Soil ◽  
Surface Fluxes ◽  
Surface Energy Budget ◽  
Arid Land ◽  
Data Sets ◽  
Sparse Vegetation ◽  
Land Surfaces ◽  
Using Data ◽  
Semi Arid

Abstract. Two-layer parameterisation of the surface energy budget proves to be realistic for sparse but homogeneously distributed vegetation. For semi-arid land surfaces however, sparse vegetation is usually interspersed by large patches of unshaded bare soil which may interact directly with the atmosphere with little interference with the vegetation. Therefore such surfaces might not be realistically represented by a two-layer parameterisation. The objective of this study is to investigate the issue of representing water and energy transfer processes in arid and semi-arid regions. Two different surface schemes, namely the classic two layer (one-compartment) approach and a two adjacent compartment ("mosaic") approach are used. The performance of both schemes is documented using data sets collected over two sparsely vegetated surfaces in the San Pedro river basin: homogeneously distributed grassland and heterogeneously distributed shrubs. In the latter case the mosaic scheme seems to be more realistic given the quality of the temperature estimates. But no clear statement can be made on the efficiency of both schemes for the total fluxes. Over each site, we investigate the possibility of artificially modifying some of the surface parameters in order to get the surface fluxes simulated by the one-compartment scheme to reproduce the two-compartment ones. The "cost" associated with this process in terms of surface temperature estimates is eventually discussed.

scholarly journals Modeling long-term fire impact on ecosystem characteristics and surface energy using a process-based vegetation–fire model SSiB4/TRIFFID-Fire v1.0

2020 ◽  
Vol 13 (12) ◽  
pp. 6029-6050
Author(s):  
Huilin Huang ◽  
Yongkang Xue ◽  
Fang Li ◽  
Ye Liu
Keyword(s):  
Surface Energy ◽  
Surface Fluxes ◽  
Surface Energy Budget ◽  
Biophysical Model ◽  
Burned Area ◽  
Area Index ◽  
Fire Model ◽  
Vegetation Height ◽  
Fire Impact

Abstract. Fire is one of the primary disturbances to the distribution and ecological properties of the world's major biomes and can influence the surface fluxes and climate through vegetation–climate interactions. This study incorporates a fire model of intermediate complexity to a biophysical model with dynamic vegetation, SSiB4/TRIFFID (The Simplified Simple Biosphere Model coupled with the Top-down Representation of Interactive Foliage and Flora Including Dynamics Model). This new model, SSiB4/TRIFFID-Fire, updating fire impact on the terrestrial carbon cycle every 10 d, is then used to simulate the burned area during 1948–2014. The simulated global burned area in 2000–2014 is 471.9 Mha yr−1, close to the estimate of 478.1 Mha yr−1 in Global Fire Emission Database v4s (GFED4s), with a spatial correlation of 0.8. The SSiB4/TRIFFID-Fire reproduces temporal variations of the burned area at monthly to interannual scales. Specifically, it captures the observed decline trend in northern African savanna fire and accurately simulates the fire seasonality in most major fire regions. The simulated fire carbon emission is 2.19 Pg yr−1, slightly higher than the GFED4s (2.07 Pg yr−1). The SSiB4/TRIFFID-Fire is applied to assess the long-term fire impact on ecosystem characteristics and surface energy budget by comparing model runs with and without fire (FIRE-ON minus FIRE-OFF). The FIRE-ON simulation reduces tree cover over 4.5 % of the global land surface, accompanied by a decrease in leaf area index and vegetation height by 0.10 m2 m−2 and 1.24 m, respectively. The surface albedo and sensible heat are reduced throughout the year, while latent heat flux decreases in the fire season but increases in the rainy season. Fire results in an increase in surface temperature over most fire regions.

Observed Impact of Atmospheric Aerosols on the Surface Energy Budget

2013 ◽  
Vol 17 (14) ◽  
pp. 1-22 ◽  
Author(s):  
Allison L. Steiner ◽  
Dori Mermelstein ◽  
Susan J. Cheng ◽  
Tracy E. Twine ◽  
Andrew Oliphant
Keyword(s):  
Heat Flux ◽  
Surface Energy ◽  
Latent Heat ◽  
Atmospheric Aerosols ◽  
Sensible Heat Flux ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Surface Energy Budget ◽  
Environmental Drivers ◽  
Sensible Heat

Abstract Atmospheric aerosols scatter and potentially absorb incoming solar radiation, thereby reducing the total amount of radiation reaching the surface and increasing the fraction that is diffuse. The partitioning of incoming energy at the surface into sensible heat flux and latent heat flux is postulated to change with increasing aerosol concentrations, as an increase in diffuse light can reach greater portions of vegetated canopies. This can increase photosynthesis and transpiration rates in the lower canopy and potentially decrease the ratio of sensible to latent heat for the entire canopy. Here, half-hourly and hourly surface fluxes from six Flux Network (FLUXNET) sites in the coterminous United States are evaluated over the past decade (2000–08) in conjunction with satellite-derived aerosol optical depth (AOD) to determine if atmospheric aerosols systematically influence sensible and latent heat fluxes. Satellite-derived AOD is used to classify days as high or low AOD and establish the relationship between aerosol concentrations and the surface energy fluxes. High AOD reduces midday net radiation by 6%–65% coupled with a 9%–30% decrease in sensible and latent heat fluxes, although not all sites exhibit statistically significant changes. The partitioning between sensible and latent heat varies between ecosystems, with two sites showing a greater decrease in latent heat than sensible heat (Duke Forest and Walker Branch), two sites showing equivalent reductions (Harvard Forest and Bondville), and one site showing a greater decrease in sensible heat than latent heat (Morgan–Monroe). These results suggest that aerosols trigger an ecosystem-dependent response to surface flux partitioning, yet the environmental drivers for this response require further exploration.

scholarly journals Analysis of effective resistance calculation methods and their effect on modelling evapotranspiration in two different patches of vegetation in semi-arid SE Spain

2007 ◽  
Vol 4 (1) ◽  
pp. 243-286 ◽  
Author(s):  
A. Were ◽  
L. Villagarcía ◽  
F. Domingo ◽  
L. Alados-Arboledas ◽  
J. Puigdefábregas
Keyword(s):  
Aerodynamic Resistance ◽  
Surface Fluxes ◽  
Effective Parameters ◽  
Retama Sphaerocarpa ◽  
Sparse Vegetation ◽  
In Series ◽  
Eddy Covariance System ◽  
Patch Scale ◽  
Monteith Equation ◽  
Semi Arid

Abstract. Effective parameters are of major importance in modelling surface fluxes at different scales of spatial heterogeneity. Different ways to obtain these effective parameters for their use in meso-scale and GCM models have been studied. This paper deals with patch-scale heterogeneity, where effective resistances were calculated in two patches with different vegetation (Retama sphaerocarpa (L.) Boiss shrubs, and herbaceous plants) using different methods: aggregating soil and plant resistances in parallel, in series or by an average of both. Effective aerodynamic resistance was also calculated directly from patch fluxes. To assess the validity of the different methods used, the Penman-Monteith equation was used with effective resistances to estimate the total λ E for each patch. The λ E estimates found for each patch were compared to Eddy Covariance system measurements. Results showed that for effective surface resistances, parallel aggregation of soil and plant resistances led to λ E estimates closer to the measured λ E in both patches (differences of around 10%). This may be due to the fact that in semi-arid areas, with very sparse vegetation, soil resistances are much higher than plant resistances, and therefore parallel aggregation attenuates the effect of the high soil resistances on λ E modelling. Results for effective aerodynamic resistances differed depending on the patch considered and the method used to calculate them. The use of effective aerodynamic resistance calculated from fluxes provided less accurate estimates of λ E compared to the measured λ E, than the use of effective aerodynamic resistances aggregated from soil and plant resistances. The results reported in this paper show that the best way of aggregating soil and plant resistances depend on the type of resistance, and the type of vegetation in the patch.

scholarly journals The aggregate description of semi-arid vegetation with precipitation-generated soil moisture heterogeneity

1997 ◽  
Vol 1 (1) ◽  
pp. 205-212 ◽  
Author(s):  
C. B. White ◽  
P. R. Houser ◽  
A. M. Arain ◽  
Z.-L. Yang ◽  
K. Syed ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Surface Energy ◽  
Meteorological Data ◽  
Surface Fluxes ◽  
Convective Precipitation ◽  
Soil Parameters ◽  
Energy Fluxes ◽  
Average Surface ◽  
Surface Energy Fluxes ◽  
Semi Arid

Abstract. Meteorological measurements in the Walnut Gulch catchment in Arizona were used to synthesize a distributed, hourly-average time series of data across a 26.9 by 12.5 km area with a grid resolution of 480 m for a continuous 18-month period which included two seasons of monsoonal rainfall. Coupled surface-atmosphere model runs established the acceptability (for modelling purposes) of assuming uniformity in all meteorological variables other than rainfall. Rainfall was interpolated onto the grid from an array of 82 recording rain gauges. These meteorological data were used as forcing variables for an equivalent array of stand-alone Biosphere-Atmosphere Transfer Scheme (BATS) models to describe the evolution of soil moisture and surface energy fluxes in response to the prevalent, heterogeneous pattern of convective precipitation. The calculated area-average behaviour was compared with that given by a single aggregate BATS simulation forced with area-average meteorological data. Heterogeneous rainfall gives rise to significant but partly compensating differences in the transpiration and the intercepted rainfall components of total evaporation during rain storms. However, the calculated area-average surface energy fluxes given by the two simulations in rain-free conditions with strong heterogeneity in soil moisture were always close to identical, a result which is independent of whether default or site-specific vegetation and soil parameters were used. Because the spatial variability in soil moisture throughout the catchment has the same order of magnitude as the amount of rain falling in a typical convective storm (commonly 10% of the vegetation's root zone saturation) in a semi-arid environment, non-linearity in the relationship between transpiration and the soil moisture available to the vegetation has limited influence on area-average surface fluxes.

scholarly journals Extending the Spatio-Temporal Applicability of DISPATCH Soil Moisture Downscaling Algorithm: A Study Case Using SMAP, MODIS and Sentinel-3 Data

2021 ◽  
Vol 9 ◽  
Author(s):  
Nitu Ojha ◽  
Olivier Merlin ◽  
Christophe Suere ◽  
Maria José Escorihuela
Keyword(s):  
Soil Moisture ◽  
Land Surface ◽  
Arid Regions ◽  
Data Sets ◽  
Sparse Vegetation ◽  
Thermal Data ◽  
Spatio Temporal ◽  
Temporal Coverage ◽  
Semi Arid

DISPATCH is a disaggregation algorithm of the low-resolution soil moisture (SM) estimates derived from passive microwave observations. It provides disaggregated SM data at typically 1 km resolution by using the soil evaporative efficiency (SEE) estimated from optical/thermal data collected around solar noon. DISPATCH is based on the relationship between the evapo-transpiration rate and the surface SM under non-energy-limited conditions and hence is well adapted for semi-arid regions with generally low cloud cover and sparse vegetation. The objective of this paper is to extend the spatio-temporal coverage of DISPATCH data by 1) including more densely vegetated areas and 2) assessing the usefulness of thermal data collected earlier in the morning. Especially, we evaluate the performance of the Temperature Vegetation Dryness Index (TVDI) instead of SEE in the DISPATCH algorithm over vegetated areas (called vegetation-extended DISPATCH) and we quantify the increase in coverage using Sentinel-3 (overpass at around 09:30 am) instead of MODIS (overpass at around 10:30 am and 1:30 pm for Terra and Aqua, respectively) data. In this study, DISPATCH is applied to 36 km resolution Soil Moisture Active and Passive SM data over three 50 km by 50 km areas in Spain and France to assess the effectiveness of the approach over temperate and semi-arid regions. The use of TVDI within DISPATCH increases the coverage of disaggregated images by 9 and 14% over the temperate and semi-arid sites, respectively. Moreover, including the vegetated pixels in the validation areas increases the overall correlation between satellite and in situ SM from 0.36 to 0.43 and from 0.41 to 0.79 for the temperate and semi-arid regions, respectively. The use of Sentinel-3 can increase the spatio-temporal coverage by up to 44% over the considered MODIS tile, while the overlapping disaggregated data sets derived from Sentinel-3 and MODIS land surface temperature data are strongly correlated (around 0.7). Additionally, the correlation between satellite and in situ SM is significantly better for DISPATCH (0.39–0.80) than for the Copernicus Sentinel-1-based (−0.03 to 0.69) and SMAP/S1 (0.37–0.74) product over the three studies (temperate and semi-arid) areas, with an increase in yearly valid retrievals for the vegetation-extended DISPATCH algorithm.

scholarly journals Phenology and nurse plant of Sotoa confusa (Garay) Salazar (Orchidaceae) in the Southern Potosino Zacatecano Highlands

2019 ◽  
pp. 13-17
Author(s):  
Alejandro Muñoz-Urias ◽  
Claudia Aurora Uribe-Mú ◽  
Francisco Martín Huerta Martínez ◽  
Cecilia Neri-Luna
Keyword(s):  
Life History ◽  
Bare Soil ◽  
Negative Association ◽  
Arid Land ◽  
Survival Strategy ◽  
Arid Environments ◽  
Nurse Plant ◽  
Dodonaea Viscosa ◽  
Terrestrial Orchid ◽  
Semi Arid

Sotoa confusa is a little conspicuous terrestrial orchid that is distributed in arid and semi-arid land of Mexico and south of USA, its life history is poorly known, so phenology and interaction of this species with shrubs was studied; its bloom occurs in March and fructifies in April (the driest period of the year), latter, from July to September it develops leaves, which disappear in October, so this orchid remains eight months without leaves. By other hand, S. confusa does not grow in areas with bare soil, so it shows preference to grow under the canopy of plants such as Dodonaea viscosa, Opuntia imbricata, O. robusta, O. leucotricha and Pittocaulon praecox; however, it shows a negative association with Jatropha dioica. The survival strategy of this plant in arid environments is to grow under the canopy of other plants that provide a favorable microclimate and develop leaves only during rainy seasons.

scholarly journals Modeling long-term fire impact on ecosystem characteristics and surface energy using a process-based vegetation-fire model SSiB4/TRIFFID-Fire v1.0

2020 ◽  
Author(s):  
Huilin Huang ◽  
Yongkang Xue ◽  
Fang Li ◽  
Ye Liu
Keyword(s):  
Surface Energy ◽  
Surface Fluxes ◽  
Surface Energy Budget ◽  
Biophysical Model ◽  
Burned Area ◽  
Area Index ◽  
Fire Model ◽  
Vegetation Height ◽  
Fire Impact

Abstract. Fire is one of the primary disturbances to the distribution and ecological properties of the world’s major biomes and can influence the surface fluxes and climate through vegetation-climate interactions. This study incorporates a fire model of intermediate complexity to a biophysical model with dynamic vegetation, SSiB4/TRIFFID (The Simplified Simple Biosphere Model coupled with the Top-down Representation of Interactive Foliage and Flora Including Dynamics Model). This new model, SSiB4/TRIFFID-Fire, updating fire impact on the terrestrial carbon cycle every 10 days, is then used to simulate the burned area during 1948–2014. The simulated global burned area in 2000–2014 is 471.9 Mha yr−1, close to the estimate, 478.1 Mha yr−1, in Global Fire Emission Database v4s (GFED4s) with a spatial correlation of 0.8. The SSiB4/TRIFFID-Fire reproduces temporal variations of the burned area at monthly to interannual scales. Specifically, it captures the observed decline trend in northern African savanna fire and accurately simulates the fire seasonality in most major fire regions. The simulated fire carbon emission is 2.19 Pg yr−1, slightly higher than the GFED4s (2.07 Pg yr−1). The SSiB4/TRIFFID-Fire is applied to assess long-term fire impact on ecosystem characteristics and surface energy budget by comparing model runs with and without fire (FIRE-ON minus FIRE-OFF). The FIRE-ON simulation reduces tree cover over 6.14 % of the global land surface, accompanied by a decrease in leaf area index and vegetation height by 0.13 m2 m−2 and 1.27 m, respectively. The surface albedo and sensible heat are reduced throughout the year, while latent heat flux decreases in the fire season but increases in the rainy season. Fire results in an increase in surface temperature over most fire regions.

Landscape Change in the Steppe of Algeria South-West Using Remote Sensing

2018 ◽  
Vol 18 (1) ◽  
pp. 41-52
Author(s):  
Tayeb Sitayeb ◽  
Ishak Belabbes
Keyword(s):  
Remote Sensing ◽  
Social Systems ◽  
Bare Soil ◽  
Climatic Conditions ◽  
Landscape Dynamics ◽  
Landsat 8 ◽  
Natural Ecosystems ◽  
Stipa Tenacissima ◽  
Steppe Species ◽  
Sparse Vegetation

Abstract Landscape dynamics is the result of interactions between social systems and the environment, these systems evolving significantly over time. climatic conditions and biophysical phenomena are the main factors of landscape dynamics. Also, currently man is responsible for most changes affecting natural ecosystems. The objective of this work is to study the dynamics of a typical landscape of western Algeria in time and space, and to map the distribution of vegetation groups constitute the vegetation cover of this ecosystem. as well as using a method of monitoring the state of a fragile ecosystem by remote sensing to understand the processes of changes in this area. The steppe constitutes a large arid area, with little relief, covered with low and sparse vegetation. it lies between the annual isohyets of 100 to 400 mm, subjected to a very old human exploitation with an activity of extensive breeding of sheep, goats, and camels. Landsat satellite data were used to mapping vegetation groups in the Mecheria Steppe at a scale of 1: 300,000. Then, a comparison was made between the two maps obtained by a classification of Landsat-8 sensor Operational Land Imager (OLI) acquired on March 18, 2014, and Landsat-5 sensor Thematic Mapper (TM) acquired on April 25, 1987. The results obtained show the main changes affecting the natural distribution of steppe species, a strong change in land occupied by the Stipa tenacissima steppe with 65% of change, this steppe is replaced by Thymelaea microphylla, Salsola vermiculata, lygeum spartum and Peganum harmala steppe. an absence from the steppe Artemisia herba-alba that has also been replaced by the same previous steppes species. The groups with Quercus ilex and Juniperus phoenicea are characterized by a strong regression that was lost 60% of its global surface and transformed by steppe to stipa tenacissima and bare soil.

Assessment of Regional Explosion Discriminants Using Data Sets of Unparalleled Spatial Sampling

2012 ◽  
Author(s):  
Kate C. Miller ◽  
Lindsay L. Worthington ◽  
Steven Harder ◽  
Scott Phillips ◽  
Hans Hartse ◽  
...  
Keyword(s):  
Spatial Sampling ◽  
Data Sets ◽  
Using Data
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