scholarly journals EFFECTS OF SOIL MOISTURE HETEROGENEITY ON SPATIALLY AVERAGED EVAPORATION

2000 ◽  
Vol 44 ◽  
pp. 169-174
Author(s):  
Nozomu HIROSE ◽  
Toshio KOIKE ◽  
Hiroshi ISHIDAIRA
Keyword(s):  
Soil Moisture ◽  
Soil Moisture Heterogeneity

A general approach for analytically upscaling the exact root water uptake equations despite heterogeneous soil moisture at the soil-root interface

2021 ◽  
Author(s):  
Martin Bouda ◽  
Jan Vanderborght ◽  
Mathieu Javaux
Keyword(s):  
Soil Moisture ◽  
Exact Solutions ◽  
Root System ◽  
Water Uptake ◽  
Grid Cell ◽  
Earth System ◽  
Water Flows ◽  
Heterogeneous Soil ◽  
Soil Moisture Heterogeneity ◽  
Earth System Models

<p>Recent advances in scaling up water flows on root system networks hold promise for improving predictions of water uptake at large scales. These developments are particularly timely, as persistent difficulties in getting Earth system models to accurately represent soil-root water flows, especially under drying or heterogeneous soil moisture conditions, are now a major obstacle describing the water limitation of terrestrial fluxes.</p><p>One recently developed upscaling formalism has been shown to be both free of discretisation error in flow predictions regardless of scale and with computational cost linearly diminishing with the number of soil subdomains considered. What has been missing from this approach, however, is a proven method to apply it generally – i.e. to an arbitrary root system architecture discretised on an arbitrary grid.</p><p>The work presented here demonstrates a general algorithm that can be applied to a wide range of root system architectures (the only assumption being that only one lateral root originates at one point along a parent root) discretised on a grid consisting of a series of soil layers of variable thickness, as is common in Earth system models. It is further shown theoretically that both of these restrictions can in principle be relaxed and that this approach can in principle be extended to conditions of soil moisture heterogeneity – i.e. situations where each root segment in a soil grid cell faces a different water potential at the soil-root interface.</p><p>This work represents both a practical advance bringing broad applicability to this upscaling approach and a major theoretical advance as exact solutions for water uptake under conditions of soil moisture heterogeneity within grid cells were previously unknown. While obtaining exact solutions despite heterogeneity within the grid cell requires a way of finding the overall mean soil water potential faced by the plant, this advance nevertheless points to possible directions of future research for overcoming the major hurdle of soil moisture heterogeneity.</p>

scholarly journals Soil moisture heterogeneity regulates water use in Populus nigra L. by altering root and xylem sap phytohormone concentrations

2020 ◽  
Vol 40 (6) ◽  
pp. 762-773 ◽  
Author(s):  
Jaime Puértolas ◽  
Marta Pardos ◽  
Carlos de Ollas ◽  
Alfonso Albacete ◽  
Ian C Dodd
Keyword(s):  
Soil Moisture ◽  
Water Use ◽  
Deficit Irrigation ◽  
Xylem Sap ◽  
Irrigation Scheduling ◽  
Populus Nigra ◽  
Soil Drying ◽  
Plant Water ◽  
Plant Water Use ◽  
Soil Moisture Heterogeneity

Abstract Soil moisture heterogeneity in the root zone is common both during the establishment of tree seedlings and in experiments aiming to impose semi-constant soil moisture deficits, but its effects on regulating plant water use compared with homogenous soil drying are not well known in trees. Pronounced vertical soil moisture heterogeneity was imposed on black poplar (Populus nigra L.) grown in soil columns by altering irrigation frequency, to test whether plant water use, hydraulic responses, root phytohormone concentrations and root xylem sap chemical composition differed between wet (well-watered, WW), and homogeneously (infrequent deficit irrigation, IDI) and heterogeneously dry soil (frequent deficit irrigation, FDI). At the same bulk soil water content, FDI plants had greater water use than IDI plants, probably because root abscisic acid (ABA) concentration was low in the upper wetter layer of FDI plants, which maintained root xylem sap ABA concentration at basal levels in contrast with IDI. Soil drying did not increase root xylem concentration of any other hormone. Nevertheless, plant-to-plant variation in xylem jasmonic acid (JA) concentration was negatively related to leaf stomatal conductance within WW and FDI plants. However, feeding detached leaves with high (1200 nM) JA concentrations via the transpiration stream decreased transpiration only marginally. Xylem pH and sulphate concentration decreased in FDI plants compared with well-watered plants. Frequent deficit irrigation increased root accumulation of the cytokinin trans-zeatin (tZ), especially in the dry lower layer, and of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), in the wet upper soil layer. Root hormone accumulation might explain the maintenance of high root hydraulic conductance and water use in FDI plants (similar to well-watered plants) compared with IDI plants. In irrigated tree crops, growers could vary irrigation scheduling to control water use by altering the hormone balance.

scholarly journals An assessment of the effect of horizontal soil moisture heterogeneity on the area-average measurement of cosmic-ray neutrons

2013 ◽  
Vol 49 (10) ◽  
pp. 6450-6458 ◽  
Author(s):  
Trenton E. Franz ◽  
M. Zreda ◽  
T. P. A. Ferre ◽  
R. Rosolem
Keyword(s):  
Soil Moisture ◽  
Cosmic Ray ◽  
Soil Moisture Heterogeneity

scholarly journals Observed Soil Moisture Impact on Strong Convection over Mountainous Tibetan Plateau

2020 ◽  
Author(s):  
E. J. BARTON ◽  
C. M. TAYLOR ◽  
C. KLEIN ◽  
P. P. HARRIS ◽  
X. MENG
Keyword(s):  
Soil Moisture ◽  
Tibetan Plateau ◽  
Surface Temperature ◽  
Land Surface Temperature ◽  
Land Surface ◽  
Strong Wind ◽  
Complex Topography ◽  
Wind Speeds ◽  
Strong Convection ◽  
Soil Moisture Heterogeneity

AbstractConvection over the Tibetan Plateau (TP) has been linked to heavy rain and flooding in downstream parts of China. Understanding processes which influence the development of convection on the TP could contribute to better forecasting of these extreme events. TP scale (~1000 km) soil moisture gradients have been shown to influence formation of convective systems over the eastern TP. The importance of smaller scale (~10 km) variability has been identified in other regions (including the Sahel and Mongolia) but has yet to be investigated for the TP. In addition, compared to studies over flat terrain, much less is known about soil moisture-convection feedbacks above complex topography. In this study we use satellite observations of cold cloud, land surface temperature and soil moisture to analyze the effect of mesoscale soil moisture heterogeneity on the initiation of strong convection in the complex TP environment. We find that strong convection is favored over negative (positive) land surface temperature (soil moisture) gradients. The signal is strongest for less vegetation and low topographic complexity, though still significant up to a local standard deviation of 300 m in elevation, accounting for 65% of cases. In addition, the signal is dependent on background wind. Strong convective initiation is only sensitive to local (10s of km) soil moisture heterogeneity for light wind speeds, though large scale (100s of km) gradients may still be important for strong wind speeds. Our results demonstrate that, even in the presence of complex topography, local soil moisture variability plays an important role in storm development.

scholarly journals Characterizing coarse-resolution watershed soil moisture heterogeneity using fine-scale simulations

2014 ◽  
Vol 18 (7) ◽  
pp. 2463-2483 ◽  
Author(s):  
W. J. Riley ◽  
C. Shen
Keyword(s):  
Soil Moisture ◽  
Hydrological Model ◽  
Surface Soil ◽  
Reduced Order Models ◽  
Watershed Scale ◽  
Surface Soil Moisture ◽  
Near Surface ◽  
Reduced Order ◽  
Coarse Resolution ◽  
Soil Moisture Heterogeneity

Abstract. Watershed-scale hydrological and biogeochemical models are usually discretized at resolutions coarser than where significant heterogeneities in topography, abiotic factors (e.g., soil properties), and biotic (e.g., vegetation) factors exist. Here we report on a method to use fine-scale (220 m grid cells) hydrological model predictions to build reduced-order models of the statistical properties of near-surface soil moisture at coarse resolution (25 times coarser, ~7 km). We applied a watershed-scale hydrological model (PAWS-CLM4) that has been previously tested in several watersheds. Using these simulations, we developed simple, relatively accurate (R2 ~0.7–0.8), reduced-order models for the relationship between mean and higher-order moments of near-surface soil moisture during the nonfrozen periods over five years. When applied to transient predictions, soil moisture variance and skewness were relatively accurately predicted (R2 0.7–0.8), while the kurtosis was less accurately predicted (R2 ~0.5). We also tested 16 system attributes hypothesized to explain the negative relationship between soil moisture mean and variance toward the wetter end of the distribution and found that, in the model, 59% of the variance of this relationship can be explained by the elevation gradient convolved with mean evapotranspiration. We did not find significant relationships between the time rate of change of soil moisture variance and covariances between mean moisture and evapotranspiration, drainage, or soil properties, as has been reported in other modeling studies. As seen in previous observational studies, the predicted soil moisture skewness was predominantly positive and negative in drier and wetter regions, respectively. In individual coarse-resolution grid cells, the transition between positive and negative skewness occurred at a mean soil moisture of ~0.25–0.3. The type of numerical modeling experiments presented here can improve understanding of the causes of soil moisture heterogeneity across scales, and inform the types of observations required to more accurately represent what is often unresolved spatial heterogeneity in regional and global hydrological models.

scholarly journals Characterizing coarse-resolution watershed soil moisture heterogeneity using fine-scale simulations

2014 ◽  
Vol 11 (2) ◽  
pp. 1967-2009 ◽  
Author(s):  
W. J. Riley ◽  
C. Shen
Keyword(s):  
Soil Moisture ◽  
Hydrological Model ◽  
Surface Soil ◽  
Reduced Order Models ◽  
Watershed Scale ◽  
Surface Soil Moisture ◽  
Near Surface ◽  
Reduced Order ◽  
Coarse Resolution ◽  
Soil Moisture Heterogeneity

Abstract. Watershed-scale hydrological and biogeochemical models are usually discretized at resolutions coarser than where significant heterogeneities in topographic, subsurface abiotic and biotic, and surface vegetation exist. Here we report on a method to use fine-resolution (220 m gridcells) hydrological model predictions to build reduced order models of the statistical properties of near-surface soil moisture at coarse-resolution (25 times coarser; ~7 km). We applied a watershed-scale hydrological model (PAWS+CLM) that has been previously tested in several watersheds and developed simple, relatively accurate (R2 ~ 0.7–0.8) reduced order models for the relationship between mean and higher-order moments of near-surface soil moisture during the non-frozen periods over five years. When applied to transient predictions, soil moisture variance and skewness were relatively accurately predicted (R2 ~ 0.7–0.8), while the kurtosis was less accurately predicted (R2 ~ 0.5). We tested sixteen system attributes hypothesized to explain the negative relationship between soil moisture mean and variance toward the wetter end of the distribution and found that, in the model, 59% of the variance of this relationship can be explained by the elevation gradient convolved with mean evapotranspiration. We did not find significant relationships between the time rate of change of soil moisture variance and covariances between mean moisture and evapotranspiration, drainage, or soil properties, as has been reported in other modeling studies. As seen in previous observational studies, the predicted soil moisture skewness was predominantly positive and negative in drier and wetter regions, respectively. In individual coarse-resolution gridcells, the transition between positive and negative skewness occurred at a mean soil moisture of ~0.25–0.3. The type of numerical modeling experiments presented here can improve understanding of the causes of soil moisture heterogeneity across scales, and inform the types of observations required to more accurately represent unresolved spatial heterogeneity in regional and global hydrological models.

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