Estimating Evaporation from Bare Soil Using Soil Moisture Data

A method is presented that uses continuous soil moisture measurements and hourly reference evapotranspiration data to estimate a soil hydraulic factor (β) for modeling soil evaporation. The β factor is used to assess the end of the energy limited soil evaporation phase (Stage 1) and the evaporation rate during the soil hydraulic limited phase (Stage 2) of a two-stage soil evaporation model. A previously developed and tested method to determine β uses an energy balance approach with sensible heat flux density estimated using the surface renewal method to obtain the continuous soil evaporation. A new method is presented, which uses a hydroprobe soil moisture measuring device to estimate the continuous soil evaporation. The estimation of evaporation with soil moisture sensors was simpler and less expensive when compared to the energy balance technique. The methods, evaluated in two field experiments, showed good agreement with evaporation data. Using the evaporation model and β derived from either method provided a good estimate of measured soil evaporation. Modeled daily soil evaporation, using either energy balance or soil measurements to obtain β, gave a root-mean-square error of 0.6 mm?day?1 when compared with soil evaporation measured using the energy balance method. When daily soil evaporation from soil moisture measurements was compared with soil evaporation estimated from energy balance measurements, the root-mean-square error was 1.3 mm?day?1. Direct soil monitoring method had bigger error, but the method is less costly.     

Measurement of Evaporation on Bare Soil and Estimating Surface Resistance

A new evaporation measuring device incorporating an evaporation chamber has been developed and checked for its accuracy. This device is unique that it uses a chamber that is completely open at one end and thereby minimizes the effect of the chamber on the natural profiles of temperature, humidity, and turbulence. It was used in estimating a newly formulated surface resistance to bare soil evaporation under dry topsoil conditions. A simple energy balance model incorporating the depth of evaporating surface, blended with a new approach for describing surface resistance was developed and successfully tested with a limited set of data obtained from a simple experiment, assuming ideal conditions. In addition to the newly formulated surface resistance, the depth of the dry soil layer was also estimated and was relatively comparable with measured value. The newly formulated surface resistance was found to be insignificant compared to the resistance imposed by the dry soil layer. The total surface resistance was modeled as a power function of soil moisture in the top 0–1 cm of soil, while the newly formulated resistance did not show any relation with the soil moisture.     

Estimating Evaporation from Bare Soil and the Crop Coefficient for the Initial Period Using Common Soils Information

The crop coefficient during the initial period (Kc?ini) varies with wetting frequency, evaporative demand, and water-holding capacity of the upper soil layer. It is possible to develop a semitheoretical integrated function to predict the average Kc?ini representing the initial period of a growing season when the soil is mostly bare and that incorporates these three factors. The function is based on a two-stage evaporation function as used in the Food and Agriculture Organization Irrigation and Drainage Paper No. 56 (FAO-56) dual crop coefficient method. Parameters in the integrated equation are soil based and can be calculated a priori without field measurements. The procedure can be used to produce graphical figures similar to that introduced in FAO-24 for Kc?ini. Similar to FAO-24, the function utilizes the mean time between wetting events and reference evapotranspiration. In this paper, the development of the procedure and figures for Kc?ini are described. Comparisons with measured evaporation and Kc?ini in southern California indicate relatively good performance by the function without calibration.     

Comparison of Measured and FAO-56 Modeled Evaporation from Bare Soil

This paper evaluates how well the FAO-56 style soil water evaporation model simulates measurements of evaporation (E) from bare soil. Seven data sets were identified from the literature and in all but one case, the individuals who took the measurements were contacted and they provided the writers with specific weather and soils data for model input. Missing weather and soils data were obtained from online sources or from the National Climatic Data Center. Simulations for three possible variations of soil data were completed and compared. The measured and the FAO-56 simulated E/ETo and cumulative evaporation trends and values were similar. Specifically, the average evaporation weighted percent difference between the measured and the simulated cumulative evaporation was between ?7.5 and ?0.5%. This evaluation suggests model accuracy of about ±15% with the use of sound weather data and a fairly generalized understanding of soil properties in the location being evaluated.     

FAO-56 Dual Crop Coefficient Method for Estimating Evaporation from Soil and Application Extensions

Crop coefficient curves provide simple, reproducible means to estimate crop evapotranspiration (ET) from weather-based reference ET values. The dual crop coefficient (Kc) method of the Food and Agricultural Organization of the United States (FAO) Irrigation and Drainage Paper No. 56 (FAO-56) is intended to improve daily simulation of crop ET by considering separately the contribution of evaporation from soil. The dual method utilizes “basal” crop coefficients representing ET from crops having a dry soil surface and separately predicts evaporation from bare soil based on a water balance of the soil surface layer. Three extensions to the evaporation calculation procedure are described here that are intended to improve accuracy when applications warrant the extra complexity. The first extension uses parallel water balances representing the portion of the soil surface wetted by irrigation and precipitation together and the portion wetted by precipitation alone. The second extension uses three “stages” for surface drying and provides for application to deep cracking soils. The third extension predicts the extraction of the transpiration component from the soil surface layer. Sensitivity and analyses and illustrations indicate moderate sensitivity of daily calculated ET to application of the extensions. The dual Kc procedure, although relatively simple computationally and structurally, estimates daily ET as measured by lysimeter relatively well for periods of bare soil and partial and full vegetation cover.     

Estimating Evaporation Using ANFIS

Water resources engineering assessment requires simple but effective evaporation estimation procedures, especially from readily measurable meteorological factors. Unfortunately, such approaches are rather scarce in the literature. In this paper, an adaptive neural-based fuzzy inference system (ANFIS) was applied to daily meteorology data from the Lake E?irdir region in the southwestern part of Turkey. Daily evaporation, solar radiation, air and water temperatures, and relative humidity measurements were used to develop the ANFIS method, which helps to assess possible contributions that each input variable has on the evaporation estimates. Such an assessment is not possible by any conventional procedure including the Penman method. However, the Penman method daily evaporation estimations were used as output data for the verification of the ANFIS approach. Classical evaporation estimation models treat the data individually. However, ANFIS models process past data collectively and then adaptively provide estimates as new sets of data become available. In the ANFIS architecture as developed in this paper, there are four measured input variables and one output variable to estimate evaporation. The estimation results from the ANFIS model had a high coefficient of determination of 0.98 when compared with the Penman method results and a low average performance error of 4.6% among other alternatives. The average performance error is less than the practically acceptable limit of 10%.     

Model for Estimating Evaporation and Transpiration from Row Crops

Accurate estimates of crop evapotranspiration ETc, that quantify the total water used by a crop, are needed to optimize irrigation scheduling for horticultural crops and to minimize water degradation. During early growth, accurate assessments of ETc are difficult in vegetable crops because of high soil evaporation due to frequent irrigation. A model to estimate ETc for vegetable crops, using only daily reference evapotranspiration data as an input parameter, was developed. It calculates crop transpiration and soil evaporation based on ground cover and daily radiation intercepted by the canopy. The model uses a two-stage soil evaporation method adapted to conditions of variable reference evapotranspiration. The model was evaluated against data using measurements from two seasons of lettuce crop, two tomato fields in the same season, and one season of broccoli crop production. Using all of the crop data, the root-mean-square error for measured versus modeled daily ETc was 0.72 mm day?1, indicating that the model works well.     

Simple Equation to Estimate Reference Evapotranspiration from Evaporation Pans Surrounded by Fallow Soil

Reliable estimates of reference evapotranspiration (ET0) are key elements for efficient water resource management, and estimating ET0, based on “Class ‘A’ pan evaporation” data is common in arid climates. A pan coefficient (Kp), which depends on the distance (or fetch) of green vegetation or fallow soil around the pan (F), wind run (U), and relative humidity (RH), is used to convert from pan evaporation to ET0. Several researchers have developed models for estimating Kp values for pans surrounded by green vegetated fetch, but there is only one equation to estimate Kp values for dry fetch conditions. The equation is complex, so the objective of this research was to develop a new simple equation to estimate Kp under fallow soil fetch conditions. The new Kp equation and the more complex equation were compared with tabular values published by the United Nations Food and Agriculture Organization. The new equation performed slightly better at matching the tabular Kp values than the complex equation. The equation derivation and evaluation are presented.     

Solute Transport through Unsaturated Soil due to Evaporation

A new method for predicting upward solute movement in unsaturated sand soil due to evaporation is developed and tested. Laboratory experiments were conducted in an unsaturated uniformly packed sand column with a cross section of 1.20 × 0.50 m2 and a constant shallow ground-water table. Evaporation was measured by a new ventilated chamber system. Solute movement from the ground water upward was monitored. Water and solute movement could be accurately reproduced by numerically solving Richards' equation and the convection-dispersion equation in one-dimension. The experimentally measured dispersivity for the unsaturated homogeneous sand agreed closely with the values which are available in the literature. This paper offers a new approach for investigating dispersion phenomena in unsaturated porous media exposed to evaporation.     

Estimating Soil Liquefaction in Ice-Induced Vibration of Bucket Foundation

The two suction foundation platforms installed in the Bohai Sea have vertical narrow columns passing through the water level. The continuous ice crushing on the columns and thereby the dynamic ice-structure interaction may usually happen during the ice season resulting in sustained violent vibrations of the structures. The paper first introduces the ice-induced vibration analysis of the suction foundation platform by using the self-excited vibration theory. Then the maximum dynamic shear stresses in the soil induced by ice are obtained from the analyses. By comparing the dynamic stresses to the cyclic strength of soil, which can be determined according to soil characteristics and features of the dynamic loading, the potential soil liquefaction is finally assessed.     

Field Investigation of Evaporation from Freshwater Tailings

Safe and economical storage of tailings is now a major consideration in the operation of many mining operations. Tailings in slurried form, particularly if they have a significant clay content, can take a very long time to consolidate under the action of self-weight consolidation alone. However, if the operation is located in an area of high potential evaporation, this can be used to accelerate the rate of tailings densification. This paper presents a study of the evaporation behavior of a clayey tailings slurry deposited into an evaporation pond in the southwest of Western Australia. Over a six-month period, the rate of evaporation from the tailings surface was monitored using the Bowen Ratio method and the microlysimeter method. This was compared with the evaporation from a Class A pan located nearby. The tailings underwent very significant cracking as drying proceeded, and it was found that these cracks had a significant influence on the overall rate of evaporation once the top surface of the deposit started to desaturate. A large strain consolidation model was used to model the behavior, and the algorithm used in this model to include the effects of evaporation is shown to provide a reasonable prediction of the observed evaporation behavior.     

Experimental Study of Evaporation from Saline Tailings

Many of the mining operations in Western Australia are located in arid and semiarid regions where there is a severe scarcity of freshwater. Most of the processing is carried out using ground water from paleochannels. Much of this ground water is very saline, with concentrations approaching saturation in many cases. The potential rates of evaporation in the region can be very high (over 3 m∕year). With careful management, tailings deposited subaereally in this region can achieve high strengths and densities due to evaporation. However, high salinity results in a severe reduction in the rate of evaporation from the tailings, thereby inhibiting consolidation due to evaporation. This paper presents the results of laboratory evaporation tests carried out to examine the mechanisms by which this reduction occurs. In these tests, all tailings samples with saline water formed salt crusts on the surfaces during evaporation, resulting in evaporation rates that were markedly low compared with those from equivalent freshwater tailings samples. This was the case even if the salinity was low. From measurements made on these samples, it is concluded that the most important mechanisms for reduction due to the salt crust are the increase in surface reflectivity and the increase in the surface resistance to moisture transfer. The vapor pressure reduction in the air due to the salinity of the tailings water is also a factor.     

Diagnostic Curve for Estimating Soil Dispersivity and Instantaneously Injected Mass

A diagnostic curve is developed for identification of dispersivity and injected mass in case of homogeneous and isotropic soil. The exit concentration from a soil column experiment is diagnostically plotted and matched to the diagnostic curve to yield the estimates of dispersivity and injected mass. A changed value of dispersivity can be identified during increasing versus decreasing concentrations. The new method is applicable for any value of the Péclet number or specific dispersivity. An estimate of the injected mass would be helpful in assessing the pollutant load from a point source. Thus, the new method would be useful for field application.     

Nearly 30% of Centrally-administered SOEs Suffer Losses from Overseas Investment

At the China Mining Congress, Tong Junhu, general manager of the Overseas Development Department of China National Gold Group Corp., told a reporter with Economic Information Daily that overseas M&A entailed a lot of uncertainties and huge risks, and enterprises should not act rashly because once they make payment, it would be difficult to control.     

Capillarity and Evaporation Exacerbated Seepage Losses from Unlined Channels

Steady, essentially two-dimensional, tension-saturated seepage from a flat-bottomed soil channel in an arid environment is studied analytically. Physically, the action of capillary spreading, evaporative drive to the atmosphere both from the near-channel banks and capillary fringe boundary, Darcian resistance of the matrix and gravity are juxtaposed and result in trifurcation of infiltrated water into deep percolation and semi-infinite evaporation “wings” with two hinge points on the soil surface and two dividing streamlines. Mathematically, free boundary problem is solved by conformal mappings and the Polubarinova-Kochina boundary-value problem method. The dependence of deep percolation losses and evaporative return flow on the channel width, conductivity, static capillary rise height, and intensity of evaporation is found.     

真空蒸发法从硫化锑渣中回收锑

针对锑工业生产过程中产生大量硫化锑渣的物料特性,通过理论分析研究,采用真空蒸发的方法处理硫化锑渣,并考察了物料粒径、体系压强、蒸发时间和蒸发温度对硫化锑渣蒸发率的影响。结果表明,在物料粒径0.106～0.075mm、体系压强50Pa、蒸发时间30min、蒸发温度923K的条件下,蒸余物中锑含量降至0.2%,硫化锑渣的蒸发率为27.9%,锑分离效率为98.6%。     

Estimating Soil Moisture Under Low Frequency Surface Irrigation Using Crop Water Stress Index

The present study investigated the relationship between the crop water stress index (CWSI) and soil moisture for surface irrigated cotton (Gossypium hirsutum, Delta Pine 90b) at Maricopa, Arizona during the 1998 season. The CWSI was linked to soil moisture through the water stress coefficient Ks that accounts for reduced crop evapotranspiration when there is a shortage of soil water. A stress recovery coefficient Krec was introduced to account for reduced crop evapotranspiration as the crop recovered from water stress after irrigation events. A soil water stress index (SWSI) was derived in terms of Ks and Krec. The SWSI compared reasonably well to the CWSI, but atmospheric stability correction for the CWSI did not improve comparisons. When the CWSI was substituted into the SWSI formulation, it gave good prediction of soil moisture depletion (fDEP; when to irrigate) and depth of root zone depletion (Dr; how much to irrigate). Disagreement was greatest for fDEP<0.6 because cotton is less sensitive to water stress in this range.     

Estimating country-specific cost-effectiveness from multinational clinical trials

Awareness of the insufficient degree to which mainstream research has created useful knowledge about women's health has drawn many researchers to feminist methodologies. Such approaches tend to privilege qualitative designs, emancipatory objectives, and cooperative strategies. They challenge the notions of expert power, the appropriation of voice, and ownership of the research products. By uncovering the extent to which power inequities are embedded in our research traditions, including such issues as who conducts research, which questions are studied, and how they are studied, feminist critique can be a powerful tool toward stronger research with more socially relevant findings. However, taken to extremes, feminist methodological requirements can immobilize and discourage active inquiry. In this paper, we articulate major directives of a feminist stance, explain the extremes at which they become problematic, and propose responsive options for women's health researchers. We intend such analysis to overcome divisiveness and promote inclusiveness without sacrificing excellence in research and action.