EVAPOTRANSPIRATION AND LEAF WATER STATUS OF ALFALFA GROWING UNDER ADVECTIVE CONDITIONS

1981 ◽  
Vol 61 (3) ◽  
pp. 601-607 ◽  
Author(s):  
R. J. WILLIAMS ◽  
DARRYL G. STOUT
Keyword(s):  
Soil Moisture ◽  
Potential Evapotranspiration ◽  
Water Status ◽  
Bowen Ratio ◽  
High Rate ◽  
Leaf Water Status ◽  
Leaf Osmotic Potential ◽  
Physically Based ◽  
Environmental Demand ◽  
Moisture Conditions

Actual evapotranspiration (LE) and leaf osmotic potential (ψs) were measured on a Medicago sativa L. (alfalfa, cv. Thor) field in interior British Columbia that is subject to advection. During periods of advection, LE, measured by the Bowen ratio energy balance method, exceeded both the net radiation (Q*) and the potential evapotranspiration (PE) calculated by the physically based formula of Priestley and Taylor (1972). During advection, Q* was a better approximation of LE than was PE. During nonadvection periods, LE was approximately equal to PE. It was found that the Jury and Tanner (1975) modification of PE for advective conditions gave favorable results during periods immediately following irrigation. Diurnal measurements revealed that leaf ψs reached a minimum by about 1200 h and then remained constant even though LE continued at a high rate. Leaf ψs measured at 0800 h reflected soil moisture conditions, and leaf ψs measured at 1400 h reflected both soil moisture conditions and environmental demand.

Retrieval of an Available Water-Based Soil Moisture Proxy from Thermal Infrared Remote Sensing. Part I: Methodology and Validation

2009 ◽  
Vol 10 (3) ◽  
pp. 665-683 ◽  
Author(s):  
Christopher R. Hain ◽  
John R. Mecikalski ◽  
Martha C. Anderson
Keyword(s):  
Soil Moisture ◽  
Potential Evapotranspiration ◽  
Thermal Infrared ◽  
Surface Energy Budget ◽  
Rooting Depth ◽  
Thermal Infrared Remote Sensing ◽  
Water Fraction ◽  
Available Water ◽  
Oklahoma Mesonet ◽  
Moisture Conditions

Abstract A retrieval of available water fraction ( fAW) is proposed using surface flux estimates from satellite-based thermal infrared (TIR) imagery and the Atmosphere–Land Exchange Inversion (ALEXI) model. Available water serves as a proxy for soil moisture conditions, where fAW can be converted to volumetric soil moisture through two soil texture dependents parameters—field capacity and permanent wilting point. The ability of ALEXI to provide valuable information about the partitioning of the surface energy budget, which can be largely dictated by soil moisture conditions, accommodates the retrieval of an average fAW over the surface to the rooting depth of the active vegetation. For this method, the fraction of actual to potential evapotranspiration ( fPET) is computed from an ALEXI estimate of latent heat flux and potential evapotranspiration (PET). The ALEXI-estimated fPET can be related to fAW in the soil profile. Four unique fPET to fAW relationships are proposed and validated against Oklahoma Mesonet soil moisture observations within a series of composite periods during the warm seasons of 2002–04. Using the validation results, the most representative of the four relationships is chosen and shown to produce reasonable (mean absolute errors values less than 20%) fAW estimates when compared to Oklahoma Mesonet observations. Quantitative comparisons between ALEXI and modeled fAW estimates from the Eta Data Assimilation System (EDAS) are also performed to assess the possible advantages of using ALEXI soil moisture estimates within numerical weather predication (NWP) simulations. This TIR retrieval technique is advantageous over microwave techniques because of the ability to indirectly sense fAW—and hence soil moisture conditions—extending into the root-zone layer. Retrievals are also possible over dense vegetation cover and are available on spatial resolutions on the order of the native TIR imagery. A notable disadvantage is the inability to retrieve fAW conditions through cloud cover.

scholarly journals Trends in evapotranspiration and its drivers in Great Britain: 1961 to 2015

2019 ◽  
Vol 43 (5) ◽  
pp. 666-693 ◽  
Author(s):  
Eleanor M Blyth ◽  
Alberto Martínez-de la Torre ◽  
Emma L Robinson
Keyword(s):  
Soil Moisture ◽  
Great Britain ◽  
Water Budget ◽  
Potential Evapotranspiration ◽  
Evaporative Demand ◽  
East Anglia ◽  
Meteorological Forcing ◽  
Physically Based Model ◽  
Warming Climate ◽  
Physically Based

In a warming climate, the water budget of the land is subject to varying forces such as increasing evaporative demand, mainly through the increased temperature, and changes to the precipitation, which might go up or down. Using a verified, physically based model with 55 years of observation-based meteorological forcing, an analysis of the water budget demonstrates that Great Britain is getting warmer and wetter. Increases in precipitation (2.96.0 ± 2.03 mm yr–1 yr–1) and air temperature (0.20 ± 0.13 K decade–1) are driving increases in runoff (2.18 ± 1.84 mm yr–1 yr–1) and evapotranspiration (0.87 ± 0.55 mm yr–1 yr–1), with no significant trend in the soil moisture. The change in evapotranspiration is roughly constant across the regions, whereas runoff varies greatly between regions: the biggest change is seen in Scotland (4.56 ± 2.82 mm yr–1 yr–1), where precipitation increases were also the greatest (5.4 ± 3.0 mm yr–1 yr–1), and the smallest trend (0.33 ± 1.50 mm yr–1 yr–1, not statistically significant) is seen in the English Lowlands (East Anglia and Midlands), where the increase in rainfall is not statistically significant (1.07 ± 1.76 mm yr–1 yr–1). Relative to its contribution to the evapotranspiration budget, the increase in interception is higher than the other components. This is due to the fact that it correlates strongly with precipitation, which is seeing a greater increase than the potential evapotranspiration. This leads to a higher increase in actual evapotranspiration than the potential evapotranspiration, and a negligible increase in soil moisture or groundwater store.

scholarly journals Modelling of Unsaturated Flow in Heterogeneous Soils

1986 ◽  
Vol 17 (4-5) ◽  
pp. 281-294 ◽  
Author(s):  
K. Høgh Jensen ◽  
M. B. Butts
Keyword(s):  
Soil Moisture ◽  
Hydraulic Conductivity ◽  
Unsaturated Flow ◽  
Soil Surface ◽  
Saturated Hydraulic Conductivity ◽  
Stochastic Methods ◽  
Physical Parameters ◽  
Heterogeneous Soils ◽  
Physically Based ◽  
Moisture Conditions

Modelling of soil moisture conditions in spatially variable fields is treated using stochastic methods. Spatial variability of moisture content in a vegetation covered field is partly caused by field variability in soil physical parameters. In the present study a physically based model is coupled with a statistical description of retention properties and saturated hydraulic conductivity respectively to simulate moisture conditions in heterogeneous soils. Results are compared with measurements obtained from two 0.5 ha field sites. Simulations based on the variation in retention properties are shown to account for much of the observed variation in soil moisture conditions with some deficiencies evident close to the soil surface. Variations in saturated hydraulic conductivity alone give an incomplete description of observed variability in soil moisture conditions.

scholarly journals Leaf Curl and Water Relations of Kousa Dogwoods Showing Resistance to Summer Stress

2002 ◽  
Vol 20 (3) ◽  
pp. 143-147 ◽  
Author(s):  
Robert M. Augé ◽  
Mark T. Windham ◽  
Jennifer L. Moore ◽  
Will T. Witte ◽  
Elena Kubikova ◽  
...  
Keyword(s):  
Water Status ◽  
Control Groups ◽  
Leaf Water Status ◽  
Visual Appearance ◽  
Cornus Kousa ◽  
Leaf Osmotic Potential ◽  
Summer Stress ◽  
June July ◽  
And Control ◽  
Leaf Curl

Abstract Kousa dogwood (Cornus kousa Hans.) trees often develop unattractive leaf curling throughout canopies during hot and/or dry weather. Aesthetically superior trees were compared to control trees for their ability to tolerate summer stress, in an established kousa dogwood plantation in 2000 and 2001. An index of leaf curl revealed that superior trees showed less curling than controls during June, July and August of 2000 and 2001. Superior trees often had higher stomatal conductance than trees in both control groups during both years, with seasonal averages 16 to 40% higher in superior than in control trees. Leaf water status, characterized by leaf osmotic potential, remained similar in superior trees and control trees throughout the 2000 summer season. Leaf temperatures were similar between groups during each summer. We confirmed that trees initially selected as having superior visual appearance had measurable differences in foliar characteristics compared to control trees, and that these trees better tolerated summer stress.

scholarly journals Estimating evapotranspiration over vegetated surfaces based on wet patch patterns

2019 ◽  
Vol 50 (4) ◽  
pp. 1037-1046 ◽  
Author(s):  
Peiyuan Li ◽  
Zhi-Hua Wang
Keyword(s):  
Soil Moisture ◽  
Soil Water ◽  
Energy Exchange ◽  
Hydrological Cycle ◽  
Turbulent Transfer ◽  
Near Surface ◽  
Local Climate ◽  
Water Energy Nexus ◽  
Physically Based ◽  
Moisture Conditions

Abstract Evapotranspiration (ET) is a critical component of the hydrological cycle and natural water-energy nexus. The dynamics of soil water content (θ) in the top surface layer, regulated by local climate, predominates the surface energy exchange and ET behavior. In this study, we proposed a novel ET-θ relation using a physically based wet patch radius coupling the near surface turbulent transfer and soil water availability. The model is tested against the dataset from eddy covariance (EC) sites in the AmeriFlux network. The results show that ET rate is supply-driven under low soil moisture conditions since the plant controls the transpiration rate to conserve water due to water stress. While in energy-limited condition, increasing soil moisture will not promote ET rate as it is bounded by the lower atmospheric demand. The proposed method is practically designed to calculate ET using variables readily measured by standard EC towers such as soil moisture and meteorological measurements. The method can also potentially be extended to predict the spatial and physical patterns of ecosystem services under different hydroclimatic conditions.

scholarly journals A comment on inter-field spatial extrapolation of vine (Vitis vinifera L.) water status

OENO One ◽  
2011 ◽  
Vol 45 (2) ◽  
pp. 121
Author(s):  
James A. Taylor ◽  
César Acevedo-Opazo ◽  
Serge Guillaume ◽  
Hernán Ojeda ◽  
Bruno Tisseyre
Keyword(s):  
Soil Moisture ◽  
Water Status ◽  
Soil Types ◽  
Moisture Regime ◽  
Production Region ◽  
Growing Seasons ◽  
Soil Moisture Regime ◽  
Growing Conditions ◽  
Moisture Conditions ◽  
Similar Soil

<p style="text-align: justify;"><strong>Aim</strong>: Recent work has identified strong intra-field relationships of predawn leaf water potential (<strong>Ψ</strong><sub>PD</sub>) between paired sites. This study investigates if these relationships exist at the inter-field level when soil types between fields are constant or different in a vineyard in Southern France.</p><p style="text-align: justify;"><strong>Method and result</strong>: Nine fields were sampled for <strong>Ψ</strong><sub>PD</sub> on 6 dates over two growing seasons. When general assumptions of uniformity in climate, growing conditions and soil moisture were able to be met, a linear relationship between the mean <strong>Ψ</strong><sub>PD</sub> responses of different fields was observed. The relationship was no longer linear when the soil moisture regime between fields differed.</p><p style="text-align: justify;"><strong>Conclusion</strong>: The results indicate that it should be possible to extrapolate a reference <strong>Ψ</strong><sub>PD</sub> value across a production region (syndicate/co-operative) defined on a similar soil type.</p><p style="text-align: justify;"><strong>Significance and impact of study</strong>: These intra-field relationships may minimise the need for <strong>Ψ</strong><sub>PD</sub> sampling to define irrigation/crop management in areas planted to similar soil types. The poor fit between fields with differing soil moisture regimes indicates that the original intra-field model may be flawed in larger fields or vineyards with heterogeneous soil moisture conditions.</p>

scholarly journals Trends in evapotranspiration and its drivers in Great Britain: 1961 to 2015

2018 ◽  
Author(s):  
Eleanor M. Blyth ◽  
Alberto Martinez-de la Torre ◽  
Emma L. Robinson
Keyword(s):  
Soil Moisture ◽  
Great Britain ◽  
Water Budget ◽  
River Flow ◽  
Potential Evapotranspiration ◽  
Evaporative Demand ◽  
East Anglia ◽  
Meteorological Forcing ◽  
Physically Based Model ◽  
Physically Based

Abstract. In a warming climate, the water budget of the land is subject to varying forces such as increasing evaporative demand, mainly through the increased temperature, and changes to the precipitation, which might go up or down. Using a verified, physically based model with 55 years of observation-based meteorological forcing, an analysis of the water budget demonstrates that Great Britain is getting warmer and wetter. Increases in precipitation (3.0 ± 2.0 mm yr−1 yr−1) and air temperature (0.20 ± 0.13 K decade−1) are driving increases in river flow (2.16 mm yr−1 yr−1) and evapotranspiration (0.87 mm yr−1 yr−1), with no significant trend in the soil moisture. The change in evapotranspiration is roughly constant across the regions whereas runoff varies greatly between regions: the biggest change is seen in Scotland (4.56 mm yr−1 yr−1), where precipitation increases were also the greatest (5.4 ± 3.0 mm yr−1 yr−1) and smallest trend (0.29 mm yr−1 yr−1) is seen in the English Lowlands (East Anglia and Midlands), where the increase in rainfall is not statistically significant (1.1 ± 0.7 mm yr−1 yr−1). Relative to their contribution to the evapotranspiration budget, the increase in interception is higher than the other components. This is due to the fact that it correlates strongly with precipitation which is seeing a greater increase than the potential evapotranspiration. This leads to a higher increase in actual evapotranspiration that the potential evapotranspiration, and a negligible increase in soil moisture or groundwater store.

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