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Research was conducted to develop a method for obtaining floating pan evaporation rates in a small (less than 10,000 m~2) wetland, lagoon, or pond. Floating pan and land pan evaporation data were collected from March 1 to August 3...
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Research was conducted to develop a method for obtaining floating pan evaporation rates in a small (less than 10,000 m~2) wetland, lagoon, or pond. Floating pan and land pan evaporation data were collected from March 1 to August 31, 2005, at a small natural wetland located in the alluvium of the Canadian River near Norman, Oklahoma, at the U.S. Geological Survey Norman Landfill Toxic Substances Hydrology Research Site. Floating pan evaporation rates were compared with evaporation rates from a nearby standard Class A evaporation pan on land. Floating pan evaporation rates were significantly less than land pan evaporation rates for the entire period and on a monthly basis. Results indicated that the use of a floating evaporation pan in a small free-water surface better simulates actual physical conditions on the water surface that control evaporation. Floating pan to land pan ratios were 0.82 for March, 0.87 for April, 0.85 for May, 0.85 for June, 0.79 for July, and 0.69 for August.
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The most precise equation in order to estimate the evapotranspiration (ET) of crops is the Penman-Monteith (PM). However, the PM equation needs specific data that, in the majority of Mexico's irrigation districts, it is not availa...
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The most precise equation in order to estimate the evapotranspiration (ET) of crops is the Penman-Monteith (PM). However, the PM equation needs specific data that, in the majority of Mexico's irrigation districts, it is not available because there are few automated weather stations. For this reason, it is convenient to develop simple methods that allow to precise estimation of ET. A reliable way to estimate ET is by using the pan evaporation that, according to the revised literature, continues to be used nowadays. Investigators like to include its use in irrigation water management projects in various parts of the world. However, this method uses Kp from the FAO that is not calibrated in Mexico. The use of FAO Kp affects the precision of the results, since some variables like radiation, wind, temperature and relative humidity vary from place to place; therefore ET is under estimated or overestimated. This paper presents an original contribution across method to estimate "Kp pan evaporation and ETo monthly maps", using information from 60 weather observatories included in The Climate Normals (1941-1970) from Mexico, based on the PM method and the class A pan evaporation. Once the Kp values were obtained from each weather observatory, the Kringing method was used. This way, by interpolating data of the triad "latitude, longitude and Kp" and "latitude, longitude and ET", monthly normalized maps of Kp and ET were established for Mexico, except the upland areas (Sierra Madre Occidental and Sierra Madre Oriental), as well as other highland zones above 2700 meters over sea level, for the highest observatory is located in Toluca, State of Mexico (key 14-0039), at 2680 m over sea level.
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As an important constituent of hydrological cycle, estimation of Reference Evapotranspiration (ETo) is essential for planning of projects related to water resources. This article compares the results obtained from the available pa...
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As an important constituent of hydrological cycle, estimation of Reference Evapotranspiration (ETo) is essential for planning of projects related to water resources. This article compares the results obtained from the available pan evaporation based equations to estimate ETo from pan evaporation (E-p) and proposes a new simplified methodology for estimation of ETo, which needs only the data of relative humidity (H). The resulting model is based upon the collected meteorological data of a selected study area i.e. Nagpur District in Maharashtra State, which lies in western plateau and hills region of India. In the proposed methodology, E-p rates are adjusted to the values expected for 50 % relative humidity. Then, the relationship between ETo and the adjusted E-p is established. The validation of the proposed new model has been carried out by comparing its results with the results obtained by the pan evaporation method, for the study area as well as for the data set of another area. This new model is found to be reasonably accurate for estimation of reference evapotranspiration for the study area and as such, is expected to be applicable to the river basins located in the regions having climatic conditions similar to that of the study area. Although, if the conditions are different then another site specific model can be developed by adopting the methodology proposed in this article.
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Declining trends in pan and lake evaporation have been reported. It is important to study this trend in every region to evaluate
the validity of the trend and water management implications. Data from nine pan evaporation sites in ...
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Declining trends in pan and lake evaporation have been reported. It is important to study this trend in every region to evaluate
the validity of the trend and water management implications. Data from nine pan evaporation sites in South Florida were
evaluated to see if there is a trend and if the quality of the data is sufficient for such analysis. The conclusion is that pan
evaporation measurements are prone to too many sources of errors to be used for trend analysis. This condition is demonstrated
in South Florida and in other regions by differences in magnitude and direction between spatially related pan stations and
unexplainable observations. Also, potential evapotranspiration (ETp) was estimated with the Simple (Abtew equation) and the
Penman–Monteith method. Both cases indicated no decline in evapotranspiration for the period of analysis. Based on the
decline in humidity and the increasing trend in vapor pressure deficit for the short period of analysis, 1992–2009, it appears
that South Florida is experiencing increase in evaporation and evapotranspiration at this time assuming no systematic error in
the weather stations’ observations.
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Pan evaporation decrease has been reported worldwide over the past decades. A recent increasing pan evaporation trend has been found globally. Remarkably, most studies on Chinese pan evaporation change were based on simulations in...
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Pan evaporation decrease has been reported worldwide over the past decades. A recent increasing pan evaporation trend has been found globally. Remarkably, most studies on Chinese pan evaporation change were based on simulations involving meteorological variables, including temperature, radiation (sunshine duration [SSD]), wind speed, and relative humidity (RH), due to the pan evaporation observation inconsistency caused by the micro-pan (D20) replacement with large pan (E601) around 2002. In addition, a large-scale humidity sensor replacement across China occurred since the 2000s can cause an inconsistency of RH and in turn lead to that of simulated pan evaporation. Therefore, the recent pan evaporation trends independent of the observed RH in China should be revisited. In this study, we (a) generate merged D20 pan evaporation from 1988 to 2017 according to E601 observations under the constant conversion coefficient assumption between the evaporation observations of these pans in the same month of every year at each station, and (b) propose a framework based on the PenPan-D20 model to attribute pan evaporation change into specific humidity (instead of RH or vapor pressure deficit in previous studies), SSD, air temperature, and wind speed, since RH and vapor pressure deficit are not independent from air temperature. The results show a significant 2.68 mm/a/a upward pan evaporation trend (p < 0.05) across China from 1988 to 2017, which was primarily driven by the rising air temperature. Humidity sensor replacement causes an ~2.2% inconsistency in RH, which produces nonnegligible errors in simulated pan evaporation trend.
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The Budyko, Bouchet, and Penman hypotheses together describe, using different formulae, the tight connections and feedbacks between water - energy balances and the landscape. The discrepancy between the Penman and Bouchet hypothes...
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The Budyko, Bouchet, and Penman hypotheses together describe, using different formulae, the tight connections and feedbacks between water - energy balances and the landscape. The discrepancy between the Penman and Bouchet hypotheses is usually highlighted in non-humid regions. In this paper, using Fu's equation for annual water-energy balances at the catchment scale, which was derived phenomenologically and mathematically on the basis of the Budyko hypothesis, consistency among the three hypotheses is explained. In non-humid regions, change of actual evaporation is dominated by change in precipitation rather than potential evaporation, and the Bouchet complementary relationship between actual evaporation and potential evaporation comes about because actual evaporation and potential evaporation are correlated via precipitation. The annual water balances in 108 non-humid catchments of China have been examined as part of this study, and the results supported the complementary relationship. In humid regions, change in actual evaporation is controlled by change in potential evaporation rather than precipitation, and this is identical to the Penman hypothesis.
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The effect of pan size on evaporation rates, pan coefficient, and reference crop evapotranspiration is not clearly understood. Evaporation rates (mm/day) were therefore measured using the standard class a pan, a half-standard pan ...
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The effect of pan size on evaporation rates, pan coefficient, and reference crop evapotranspiration is not clearly understood. Evaporation rates (mm/day) were therefore measured using the standard class a pan, a half-standard pan (half the diameter of the class A pan), and quarter-standard pan between February 1 and April 30, 2000, at St. Augustine, Trinidad. Evaporation rates were highest in the quarter-standard pan, followed by the half-standard and then the standard pan. Heat transfer analysis showed that while the total heat absorbed by the water in the pans increased, the resulting total heat absorbed per surface area decreased with increasing pan diameter, thereby explaining the trend in the measured evaporation rates. Measured evaporation rates from each pan were correlated with reference crop evapotranspiration rates predicted with the Penman-Monteithformula. This article demonstrates that pans smaller than the class A could be used to measure evaporation rates, provided that calibrations are carried out to determine the pan coefficients relating measured evaporation rates to evapotranspiration rates. This would result in substantial cost reductions in situations where a dense evaporation network is needed.
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摘要 :
The effect of pan size on evaporation rates, pan coefficient, and reference crop evapotranspiration is not clearly understood. Evaporation rates (mm/day) were therefore measured using the standard class A pan, a half-standard pan ...
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The effect of pan size on evaporation rates, pan coefficient, and reference crop evapotranspiration is not clearly understood. Evaporation rates (mm/day) were therefore measured using the standard class A pan, a half-standard pan (half the diameter of the class A pan), and quarter-standard pan between February 1 and April 30, 2000, at St. Augustine, Trinidad. Evaporation rates were highest in the quarter-standard pan, followed by the half-standard and then the standard pan. Heat transfer analysis showed that while the total heat absorbed by the water in the pans increased, the resulting total heat absorbed per surface area decreased with increasing pan diameter, thereby explaining the trend in the measured evaporation rates. Measured evaporation rates from each pan were correlated with reference crop evapotranspiration rates predicted with the Penman-Monteith formula. This article demonstrates that pans smaller than the class A could be used to measure evaporation rates, provided that calibrations are carried out to determine the pan coefficients relating measured evaporation rates to evapotranspiration rates. This would result in substantial cost reductions in situations where a dense evaporation network is needed
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An assessment of effects of drip irrigation and nutrition treatments on growth parameters of mango, fruit yield, total soluble solids (TSS) and acidity in a semi-arid Alfisol at Hyderabad has been studied during May 2001 and Septe...
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An assessment of effects of drip irrigation and nutrition treatments on growth parameters of mango, fruit yield, total soluble solids (TSS) and acidity in a semi-arid Alfisol at Hyderabad has been studied during May 2001 and September 2006. The studywas conducted with 4 levels of drip irrigation (control, 0.25,0.5 and 0.75 Evaporation Replenishment Rates(Ep)) and 5 levels of nutrition (control, FYM @ 75 kg/tree, 100% recommended NPK, 100% recommended NPK + FYM @ 75 kg/tree and 50% NPK + FYM @ 37.5 kg/tree). Based on Analysis of Variance, irrigation treatments differed significantly in influencing only fruit yield in 2003,2004 and 2005; and weight of single fruit in 2002 and 2006. The nutrition treatments were significantly superior in influencing tree height, collar diameter, canopy spreadin September 2006, and fruit yield in 2002, 2004 and 2006; weight of single fruit in 2002, 2003 and 2006; and TSS. Among irrigation treatments, 0.5 Ep drip was superior with a significantly higher fruit yield in2004 and 2005 and weight of single fruit in 2006. The nutrition treatment - 100% NPK + FYM @ 75 kg/tree was superior with a significantly higher tree height, collar diameter and canopy spread in September 2006; fruit yield in 2002,2003 and 2004; and weight of single fruit in 2003. Application of FYM @ 75 kg/tree was superior with a significantly higher fruit yield in 2006 and TSS. The study indicated that drip irrigation at 0.5 Ep together with 100% recommended NPK + FYM @ 75 kg/tree was efficient for attaining a significantly higher net returns of Rs.48,159/ha with a benefit-cost ratio of 1.37 under semi-arid Alfisols.
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