scholarly journals Stem-root flow effect on soil–atmosphere interactions and uncertainty assessments

2015 ◽  
Vol 12 (11) ◽  
pp. 11783-11816
Author(s):  
T.-H. Kuo ◽  
J.-P. Chen ◽  
Y. Xue
Keyword(s):  
Heat Flux ◽  
Soil Moisture ◽  
Moisture Content ◽  
Soil Water ◽  
Sensible Heat Flux ◽  
Soil Layer ◽  
Soil Evaporation ◽  
Soil Layers ◽  
Flow Effect ◽  
Top Soil

Abstract. Soil water can rapidly enter deeper layers via vertical redistribution of soil water through the stem–root flow mechanism. This study develops the stem–root flow parameterization scheme and coupled this scheme with the Simplified Simple Biosphere model (SSiB) to analyze its effects on land–atmospheric interactions. The SSiB model was tested in a single column mode using the Lien Hua Chih (LHC) measurements conducted in Taiwan and HAPEX-Mobilhy (HAPEX) measurements in France. The results show that stem–root flow generally caused a decrease in the moisture content at the top soil layer and moistened the deeper soil layers. Such soil moisture redistribution results in significant changes in heat flux exchange between land and atmosphere. In the humid environment at LHC, the stem–root flow effect on transpiration was minimal, and the main influence on energy flux was through reduced soil evaporation that led to higher soil temperature and greater sensible heat flux. In the Mediterranean environment of HAPEX, the stem–root flow significantly affected plant transpiration and soil evaporation, as well as associated changes in canopy and soil temperatures. However, the effect on transpiration could either be positive or negative depending on the relative changes in the moisture content of the top soil vs. deeper soil layers due to stem–root flow and soil moisture diffusion processes.

scholarly journals Stem–root flow effect on soil–atmosphere interactions and uncertainty assessments

2016 ◽  
Vol 20 (4) ◽  
pp. 1509-1522
Author(s):  
Tzu-Hsien Kuo ◽  
Jen-Ping Chen ◽  
Yongkang Xue
Keyword(s):  
Heat Flux ◽  
Soil Moisture ◽  
Diffusion Processes ◽  
Sensible Heat Flux ◽  
Soil Layer ◽  
Soil Surface ◽  
Soil Evaporation ◽  
Soil Layers ◽  
Flow Effect ◽  
Top Soil

Abstract. Rainfall that reaches the soil surface can rapidly move into deeper layers in the form of bulk flow through the stem–root flow mechanism. This study developed the stem–root flow parameterization scheme and coupled this scheme with the Simplified Simple Biosphere model (SSiB) to analyze its effects on land–atmospheric interactions. The SSiB model was tested in a single-column mode using the Lien Hua Chih (LHC) measurements conducted in Taiwan and HAPEX–Mobilhy (HAPEX) measurements in France. The results show that stem–root flow generally caused a decrease in soil moisture in the top soil layer and moistened the deeper soil layers. Such soil moisture redistribution results in substantial changes in heat flux exchange between land and atmosphere. In the humid environment at LHC, the stem–root flow effect on transpiration was minimal, and the main influence on energy flux was through reduced soil evaporation that led to higher soil temperature and greater sensible heat flux. In the Mediterranean environment of HAPEX, the stem–root flow substantially affected plant transpiration and soil evaporation, as well as associated changes in canopy and soil temperatures. However, the effect on transpiration could be either positive or negative depending on the relative changes in the soil moisture of the top soil vs. deeper soil layers due to stem–root flow and soil moisture diffusion processes.

Modelling the seasonal dynamics of the soil water balance of vineyards

2003 ◽  
Vol 30 (6) ◽  
pp. 699 ◽  
Author(s):  
Eric Lebon ◽  
Vincent Dumas ◽  
Philippe Pieri ◽  
Hans R. Schultz
Keyword(s):  
Water Balance ◽  
Soil Water ◽  
Soil Layer ◽  
Water Storage ◽  
Soil Evaporation ◽  
Water Dynamics ◽  
Soil Water Balance ◽  
Sensitivity Analyses ◽  
Rooting Depth ◽  
Top Soil

A geometrical canopy model describing radiation absorption (Riou et al. 1989, Agronomie 9, 441–450) and partitioning between grapevines (Vitis vinifera L.) and soil was coupled to a soil water balance routine describing a bilinear change in relative transpiration rate as a function of the fraction of soil transpirable water (FTSW). The model was amended to account for changes in soil evaporation after precipitation events and subsequent dry-down of the top soil layer. It was tested on two experimental vineyards in the Alsace region, France, varying in soil type, water-holding capacity and rooting depth. Simulations were run over four seasons (1992–1993, 1995–1996) and compared with measurements of FTSW conducted with a neutron probe. For three out of four years, the model simulated the dynamics in seasonal soil water balance adequately. For the 1996 season soil water content was overestimated for one vineyard and underestimated for the other. Sensitivity analyses revealed that the model responded strongly to changes in canopy parameters, and that soil evaporation was particularly sensitive to water storage of the top soil layer after rainfall. We found a close relationship between field-average soil water storage and pre-dawn water potential, a relationship which could be used to couple physiological models of growth and / or photosynthesis to the soil water dynamics.

scholarly journals An Analytical Model of Evaporation Efficiency for Unsaturated Soil Surfaces with an Arbitrary Thickness

2011 ◽  
Vol 50 (2) ◽  
pp. 457-471 ◽  
Author(s):  
Olivier Merlin ◽  
Ahmad Al Bitar ◽  
Vincent Rivalland ◽  
Pierre Béziat ◽  
Eric Ceschia ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Analytical Model ◽  
Land Surface ◽  
Soil Layer ◽  
Soil Evaporation ◽  
Atmospheric Conditions ◽  
Potential Evaporation ◽  
Evaporative Demand ◽  
Soil Layers ◽  
Arbitrary Thickness

Abstract Analytical expressions of evaporative efficiency over bare soil (defined as the ratio of actual to potential soil evaporation) have been limited to soil layers with a fixed depth and/or to specific atmospheric conditions. To fill the gap, a new analytical model is developed for arbitrary soil thicknesses and varying boundary layer conditions. The soil evaporative efficiency is written [0.5 − 0.5 cos(πθL/θmax)]P with θL being the water content in the soil layer of thickness L, θmax being the soil moisture at saturation, and P being a function of L and potential soil evaporation. This formulation predicts soil evaporative efficiency in both energy-driven and moisture-driven conditions, which correspond to P < 0.5 and P > 0.5, respectively. For P = 0.5, an equilibrium state is identified when retention forces in the soil compensate the evaporative demand above the soil surface. The approach is applied to in situ measurements of actual evaporation, potential evaporation, and soil moisture at five different depths (5, 10, 30, 60, and 100 cm) collected in summer at two sites in southwestern France. It is found that (i) soil evaporative efficiency cannot be considered as a function of soil moisture only because it also depends on potential evaporation, (ii) retention forces in the soil increase in reaction to an increase of potential evaporation, and (iii) the model is able to accurately predict the soil evaporation process for soil layers with an arbitrary thickness up to 100 cm. This new model representation is expected to facilitate the coupling of land surface models with multisensor (multisensing depth) remote sensing data.

scholarly journals The role of improved soil moisture for the characteristics of surface energy fluxes in the ECMWF reanalyses

2017 ◽  
Author(s):  
Wilhelm May
Keyword(s):  
Heat Flux ◽  
Soil Moisture ◽  
Surface Energy ◽  
Moisture Content ◽  
Regional Differences ◽  
Soil Moisture Content ◽  
Sensible Heat Flux ◽  
Sensible Heat ◽  
Energy Fluxes ◽  
Surface Energy Fluxes

Abstract. In this study, the role that more realistic soil moisture has for the characteristics of surface energy fluxes in two sets of reanalyses performed at ECMWF is investigated. These are the standard set of reanalyses ERA-Interim (ERAInt) and the ERA-Interim/Land reanalyses of the land surface conditions (ERAInt/Land). In the latter, the ECMWF's land surface model has been forced with the meteorological fields from ERAInt, including an adjustment of precipitation based on the monthly mean values from the Global Precipitation Climatology Project data set. Adjusting precipitation has a distinct impact on the soil moisture content in the two sets of reanalyses. ERAInt is characterized by a general tendency to underestimate (overestimate) soil moisture in regions with a relatively high (low) soil moisture content. The differences in soil moisture between ERAInt and ERAInt/Land vary only slightly in the course of the year. This is not the case for precipitation, where the differences between the two sets of reanalyses vary markedly between different seasons. The direct impact of the regional differences in precipitation between ERAInt and ERAInt/Land on the corresponding deviations in soil moisture varies considerably by region. One reason is that the regional differences in precipitation vary by season, while the regional differences in soil moisture typically persist throughout the year. Another reason is that the specific nature of the interaction between precipitation and soil moisture diverges between different regions, depending on the climate conditions and on the degree to which the soil is saturated with moisture. The differences in soil moisture between the two sets of reanalyses have notable effects on the characteristics of surface energy fluxes. The nature of these effects differs by region and also by season, that is the coupling between soil moisture and the latent or the sensible heat flux is positive in one region or season, respectively, and negative in another one. In any case, the differences in the soil moisture content typically affect the latent and the sensible heat flux in opposite ways. Increases (decreases) in latent heat flux typically coincide with decreases (increases) in sensible heat flux. By this, the differences in soil moisture have a substantial impact on the partitioning of latent and sensible heat flux. The effect of the soil moisture differences on the evaporative fraction, for instance, is mainly governed by the impact on the latent heat flux because of the opposite effects on latent and sensible heat fluxes and, hence, only a weak impact on the total surface energy flux. The effect on the Bowen ratio, on the other hand, is for the most part controlled by the impact on the sensible heat flux, with higher (lower) values of the Bowen ratio in regions with increased (decreased) sensible heat flux.

scholarly journals Will the conversion of evergreen and deciduous broad-leaved mixed forests to Chinese fir plantations affect the transportation of soil water?

2021 ◽  
Author(s):  
qi Chen ◽  
Yuanqiu Liu ◽  
Jiahui Huang ◽  
Yunhong Xie ◽  
Tianjun Bai ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Moisture Content ◽  
Soil Water ◽  
Water Movement ◽  
Soil Depth ◽  
Soil Layer ◽  
Chinese Fir ◽  
Jiangxi Province ◽  
Natural Forests ◽  
Mixed Forests

The conversion of natural forests to planted forests has become a global trend, and the practice has wide-ranging effects on soil. This study aimed to explore the differences in soil water movement after the conversion of evergreen and deciduous broad-leaved mixed forests (natural forest, NF) to Chinese fir (Cunninghamia lanceolate (Lamb.) Hook.) plantations (CFP, 20–21 years old). Soil samples from five layers (0–5, 5–10, 10–20, 20–30, and 30–50 cm) were collected from NF and CFP before and after rainfall event in the Peng Chongjian watershed, Jiangxi Province. The physical properties of the soils, including the mean and coefficient of variation (CV) of soil moisture content and the soil particle composition, were determined in both forest types. The δD of soil water and the litter water-holding capacity were also measured. The results showed that the variation ranges of moisture content in each soil layer after the rainfall was 21.13%–49.40% in CFP and 21.33%–43.87% in NF. There were no significant differences in soil bulk density or porosity; the clay and silt contents were significantly increased in topsoil, while the sand was significantly decreased (P < 0.05). After the rainfall, soil water in CFP responded more promptly than NF. In the process of infiltration, the contribution of rainfall to soil moisture gradually decreased with increasing soil depth. Topsoil (0–5 cm) in NF responded promptly to rainfall, but the response showed a lag effect with the increase of soil depth. With the extension of infiltration time, the contribution of precipitation to deep soil gradually increased. The results showed that the soil did not degrade after the conversion of NF to CFP, a significant guiding result for plantation cultivation.

scholarly journals Divergent water sources of three dominant plant species following precipitation events in enclosed and mowing grassland steppes

PeerJ ◽  
2019 ◽  
Vol 7 ◽  
pp. e7737
Author(s):  
Tiejun Bao ◽  
Yunnuan Zheng ◽  
Ze Zhang ◽  
Heyang Sun ◽  
Ran Chao ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Soil Water ◽  
Plant Species ◽  
Water Use ◽  
Soil Layer ◽  
Deep Soil ◽  
Soil Layers ◽  
Typical Steppe ◽  
Dominant Plant Species ◽  
Precipitation Events

Understanding of the dynamic patterns of plant water use in a changing environment is one of foci in plant ecology, and can provide basis for the development of best practice in restoration and protection of ecosystem. We studied the water use sources of three coexisting dominant plant species Leymus chinensis, Stipa grandis and Cleistogenes squarrosa growing in both enclosed and mowing grassland in a typical steppe. The oxygen stable isotope ratios (δ18O) of soil water and stem water of these three species were determined, along with soil moisture, before and after precipitation events. The results showed that (1) mowing had no significant effect on the soil moisture and its δ18O, whereas precipitation significantly changed the soil moisture though no significant effect detected on its δ18O. (2) C. squarrosa took up water majorly from top soil layer due to its shaollow root system; L. chinensis took up relative more water from deep soil layer, and S. grandis took up water from the middle to deep soil layers. (3) L. chinensis and S. grandis in mowing grassland tended to take up more water from the upper soil layers following precipitation events, but showed no sensitive change in water source from soil profile following the precipitation in the enclosed grassland, indicating a more sensitive change of soil water sources for the two species in mowing than enclosed grassland. The differences in root morphology and precipitation distribution may partly explain the differences in their water uptake from different soil layers. Our results have important theoretical values for understanding the water competition among plants in fluctuating environment and under different land use in the typical steppe.

Influence of trees and topography on soil water content in semi-arid region, the case of an agro-silvo-pastoral ecosystem dominated by Faidherbia albida (Senegal)

2021 ◽  
Author(s):  
Djim Diongue ◽  
Didier Orange ◽  
Waly Faye ◽  
Olivier Roupsard ◽  
Frederic Do ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Moisture Content ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Soil Layer ◽  
Rainfall Infiltration ◽  
Faidherbia Albida ◽  
Lower Slope ◽  
Upper Slope

&lt;p&gt;Vegetation strongly affects the water cycle, and the interactions between vegetation and soil moisture are fundamental for ecological processes in semiarid regions. Therefore, characterizing the variation in soil moisture is important to understand the ecological sustainability of cropping systems towards food security. The present study aims at exploring factors and mechanisms influencing soil moisture variability in the Faidherbia albida (FA) parkland at Sob basin located in the center of Senegal [1]. Volumetric soil moisture content at multiple depths was monitored at 15 locations distributed along a transect (upper slope, mid-slope and lower slope) and different FA tree position (under, at the limit and outside canopy) from August to October 2020. A portable TRIME Time Domain Reflectometry (TDR) Tube Probe (IMKO, Germany) was used to determine soil volumetric moisture content while being placed at specific depth intervals inside a PVC access tube set up at each location. Soil moisture was monitored at 10 cm interval from 20 to 420 cm during the rainy season from July to October 2020. Results of soil moisture profiles along the transects exhibit two main zones based on the standard deviation (SD) and the inflection of the coefficient of variation (CV): shallow soil moisture (SSM) and deep soil moisture (DSM). For SSM observed at 20-60 cm of the soil layer, both mean soil moisture and SD increase with depth, the lowest mean value (8%) being observed at the top surface. This soil layer is influenced by rainfall infiltration and daily evaporation. For DSM observed at 70-420 cm, the moisture pattern can be further divided into 4 soil sublayers taking the mean soil moisture vertical distribution as reference: (i) a rainfall infiltration layer (70-160 cm) which appears mainly influenced by cumulative rainfall infiltration in addition to transpiration of grassland and crops (shallow root system); (ii) a rainfall-transpiration layer (170-250 cm) which is still an infiltration layer but more influenced by crops transpiration; (iii) a transpiration layer (260-350 cm) which can be recharged by rainfall infiltration during heavy rainfall and supply deep root system; and (iv) deep transpiration layer (360-400 cm) which has DSM that can be influenced by extremely deep root vegetation such as FA. The factors influencing the soil water content varied with the topography. The soil water content SWC (mean and median value of 27.2 and 29.6% respectively) in the lower slope was significantly higher than that at middle (mean and median value of 14.4 and 13.2 % respectively) and upper slope (mean and median value of 16.8 and 18.4 % respectively). At last, soil water content was positively correlated with the distance from the FA, regardless the slope. The higher water content for both SSM and DSM was observed outside the FA canopy. This result refutes the initial hypothesis of higher SWC under trees and support a more detailed analysis of the infiltration capacity in relationship with the FA position.&lt;/p&gt;&lt;div&gt; &lt;div&gt; &lt;p&gt;[1] Faidherbia-Flux : https://lped.info/wikiObsSN/?Faidherbia-Flux&lt;/p&gt; &lt;/div&gt; &lt;/div&gt;

Assessment of similarity theory under 2m in a semi-arid environment over moderately complex terrain

2021 ◽  
Author(s):  
Belén Martí ◽  
Daniel Martínez-Villagrasa ◽  
Joan Cuxart
Keyword(s):  
Heat Flux ◽  
Soil Moisture ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Relative Error ◽  
Similarity Theory ◽  
Sensible Heat Flux ◽  
Soil Layer ◽  
Sensible Heat ◽  
Stable Regime

&lt;p&gt;The similarity theory equations relate the vertical turbulent flux of a variable with its vertical gradient in the surface layer. They were derived from 16-m towers (or higher) with the first measurement typically at 1 or 2 m above the surface, using pairs of values or adjusting functions to the profiles. The resulting expressions are of widespread use for multiple applications although they are supposed to be only valid over flat homogeneous terrain.&lt;/p&gt;&lt;p&gt;The current work applies the standard functions to a site in the centre of an east-west oriented valley, locally flat and at approximately 2 km from the mountain slopes at both sides. The area is surrounded by rain-fed agricultural fields with the upper soil layer getting dry during Summer. Momentum and sensible heat fluxes are derived with the standard similarity functions considering the Obukhov length as the stability parameter, taking measurements of wind and temperature at 2 m and a supplementary temperature observation at 0.3 m, just above the roughness sub-layer. These results are compared against the turbulent fluxes observed with an eddy-covariance system located at the same site during 8 consecutive months in 2018.&lt;/p&gt;&lt;p&gt;The estimated friction velocity differs less than a 20% respect to the observation for the 74% of cases under unstable conditions (61% for the stable regime). For the sensible heat flux, its goodness depends on the soil moisture. Again, a 74% of cases have a relative error below 20% for dry soils, when the observed latent heat flux is&lt;strong&gt; &lt;/strong&gt;small. When soil moisture is significant, only a 24% of cases provide a sensible heat flux that differs less than a 20% from the observation. In addition, this error is positive and grows with the observed latent heat flux. For the stable regime, the number of cases with a relative error below 20% decreases to 31% and 19% for dry and moist soils, respectively.&lt;/p&gt;&lt;p&gt;These results show that similarity theory provides a good performance for the momentum flux over a moderately heterogeneous terrain with sloping surfaces relatively close and with observations below 2 m above the surface. For the sensible heat flux, estimations are similarly good under unstable conditions over a dry soil, while it gets over-estimated when soil moisture and, consequently, the latent heat flux are important. At night, the sensible heat flux is much smaller and thus ill estimated under the aforementioned conditions.&lt;/p&gt;

scholarly journals Root Response to Soil Water Status via Interaction of Crop Genotype and Environment

Agronomy ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 708
Author(s):  
Phanthasin Khanthavong ◽  
Shin Yabuta ◽  
Hidetoshi Asai ◽  
Md. Amzad Hossain ◽  
Isao Akagi ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Soil Water ◽  
Root Distribution ◽  
Water Status ◽  
Soil Layer ◽  
Shoot Biomass ◽  
Soil Conditions ◽  
Crop Adaptation ◽  
Soil Moisture Status ◽  
Root Distributions

Flooding and drought are major causes of reductions in crop productivity. Root distribution indicates crop adaptation to water stress. Therefore, we aimed to identify crop roots response based on root distribution under various soil conditions. The root distribution of four crops—maize, millet, sorghum, and rice—was evaluated under continuous soil waterlogging (CSW), moderate soil moisture (MSM), and gradual soil drying (GSD) conditions. Roots extended largely to the shallow soil layer in CSW and grew longer to the deeper soil layer in GSD in maize and sorghum. GSD tended to promote the root and shoot biomass across soil moisture status regardless of the crop species. The change of specific root density in rice and millet was small compared with maize and sorghum between different soil moisture statuses. Crop response in shoot and root biomass to various soil moisture status was highest in maize and lowest in rice among the tested crops as per the regression coefficient. Thus, we describe different root distributions associated with crop plasticity, which signify root spread changes, depending on soil water conditions in different crop genotypes as well as root distributions that vary depending on crop adaptation from anaerobic to aerobic conditions.

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