Evaluation of Radiation-Based Reference Evapotranspiration Models Under Different Mediterranean Climates in Central Greece

Eighteen radiation-based equations used to estimate reference evapotranspiration (ET_ref) were generalized into seven linear models. The general models were calibrated using the standard FAO-56 Penman-Monteith method. Model performance was evaluated under humid, sub-humid and semi-arid mediterranean climatic conditions in central Greece. Evaluation and comparison of the models was based on quantitative assessment of their ability to accurately estimate ET_ref values, generated by the FAO-56 Penman-Monteith equation. All models provided relatively accurate estimates of ET_ref. The Abtew model showed the best overall performance with respect to the data from all available climate stations of central Greece. The average error of the Abtew model in the monthly average daily ET_ref estimates was 0.24 mm, which corresponds to a relative error of 7.7 %. The Abtew method has not yet been tested under mediterranean climatic conditions. Based on our results, it seems to be a good choice for the estimation of monthly average daily ET_ref under different conditions in the mediterranean climate. An exception appears to be the mediterranean climate with relatively high humidity and low wind speed. Under these conditions the models of the Priestley-Taylor group, the Makkink group and the Jensen-Haise group performed better than the Abtew equation.     

遥感Penman-Monteith模型中土壤含水量与土壤蒸发的关系

土壤含水量是影响土壤蒸发的重要因素,分析土壤含水量变化对土壤蒸发的影响,对水资源管理有积极作用。遥感Penman-Monteith(P-M)模型是利用遥感手段进行蒸散发模拟的重要方法,且能分别对土壤蒸发和植被散发进行计算。利用遥感P-M模型对望都站的蒸散发进行模拟,并结合地表土壤含水量数据分析了土壤含水量变化对模型参数及土壤蒸发的影响。结果表明:(1)遥感P-M模型对望都站蒸散发取得较好效果,纳什效率系数(NSE)为0.559;(2)土壤含水量变化与遥感P-M模型的土壤蒸发系数间具有不确定性;(3)在本研究的模拟期内,与植被散发相比,土壤含水量变化与土壤蒸发间的一致性更强。     

内蒙古东部牧区缺测数据条件下适宜ET_0计算方法优选

内蒙古东部牧区多地处偏远边疆,气象站点有限,应用FA056 Penman-Monteith计算ET0相对困难。为了在缺测气象数据条件下准确计算ET0,本文依据该区内典型气象站点资料,以FAO56 Penman-Monteith为标准方法,以FAO17 Penman、Priestley-Taylor、Irmark-Allen拟合法、Hargreaves-Samani法为对照方法分别对ET0进行计算,并对4种方法适用性进行评价。结果表明:Priestley-Taylor与Hargreaves-Samani法计算值较FAO56 PM法计算结果偏大,不适于该地区ET0计算。FAO17 Penman法和Irmark-Allen拟合法与FAO56 PM法计算结果平均相对误差小于15%,计算精度较高,但Irmark-Allen拟合法仅需气温和日照时间气象资料,因此,Irmark-Allen拟合法适宜缺测气象条件下内蒙古东部牧区ET0计算。     

面板堆石坝应力变形计算中考虑土的各向异性

土体本构模型一般都将土体作为各向同性材料，应用于混凝土面板堆石坝应力变形计算时常带来不小的误差，本文以双曲线模型为例剖析了计算中存在的问题。该模型假定从大主应力方向加荷与从小主应力方向加荷弹性模量和泊松比都相同，但真三轴仪试验表明两者有显著差异。混凝土面板中的应力是水荷载引起的，而水荷载沿坝体的小主应力方向施加，无论弹性模量还是泊松比，与荷载从大主应力方向施加都有很大的不同。各向同性的本构模型忽略了它们的差异，仅仅用大主应力方向加荷的方法来确定弹性模量和泊松比，必然会有较大误差，对混凝土面板来说就可能是不能容许的误差。文中提出了一种考虑各向异性的本构模型，它是以E-ν模型为基础，作了某些修正处理。用其对面板坝进行计算，面板应力有明显改善。     

秸杆条带状覆盖条件下土壤水分运动的实验研究及数值计算

本文在开展了一系列室内外试验研究基础上，建立了有效根量密度分布函数，得到了较为切合实际的二维根系吸水率模型.同时通过田间不同条件下水面蒸发试验资料分析，得到了条带状覆盖时棵间无麦秸覆盖地和棵间麦秸覆盖地水面蒸发量(各布设20cm蒸发皿所观测的值)与大气水面蒸发量(试验场气象站位置布设的20cm蒸发皿观测值)之间的关系式.通过农田作物生理指标观测，得到了作物叶面积指数与水面蒸发量之间的关系.从而更合理地处理了条带状覆盖下上边界条件.并以此为基础，建立相应的数学模型，进行了数值模拟，实测值与计算值吻合较好，表明所建立的数学模型是可靠的，数值分析是可行的。     

植被覆盖的土质边坡土壤水分平衡模型及应用

土壤水分平衡模型在洪水预测、土壤湿度计算、灌溉设计管理以及全球气候变化影响的仿真分析上十分重要.以英格兰南部Newbury一个高速公路旁的边坡为例,介绍了土壤水分平衡模型的建立及应用.潜在蒸散量根据每日的气象观测资料,用FAO Penman-Monteith公式进行计算.在此基础上,建立了水分平衡模型并进行了校核,计算出的土壤湿度变化与时域反射仪(TDR)探头测量的数据一致.还利用建立的模型,模拟了2080年的气候条件变化对潜在蒸散量和土壤水分含量的影响.结果表明,该地区的日平均潜在蒸散量将增加10.7%,土壤水分消耗量将增加16.8 mm.     

A MODEL OF WATER, VAPOR AND HEAT FLOW IN POROUS MEDIA

ＡＭＯＤＥＬＯＦＷＡＴＥＲ，ＶＡＰＯＲＡＮＤＨＥＡＴＦＬＯＷＩＮＰＯＲＯＵＳＭＥＤＩＡ￥ＹａｎｇＪｉｎ－ｚｈｏｎｇ；ＣａＩＳｈｕ－ｙｉｎｇ（ＷｕｈａｎＵｎｉｖｅｒｓｉｔｙｏｆＨｙｄｒａｕｌｉｃａｎｄＥｌｅｃｔｒｉｃＥｎｇｉｎｅｅｒｉｎｇ，Ｗｕｈａｎ４...     

Evaluating and Calibrating Reference Evapotranspiration Models Using Water Balance under Hyper-Arid Environment

This research investigates five reference evapotranspiration models (one combined model, one temperature-based model, and three radiation-based models) under hyper-arid environmental conditions at the operational field level. These models were evaluated and calibrated using the weekly water balance of alfalfa by EnviroSCAN to calculate crop evapotranspiration (ET_c). Calibration models were evaluated and validated using wheat and potatoes, respectively, on the basis of weekly water balance. Based on the results and discussion, the FAO-56 Penman-Monteith model proved to be superior in estimating ET_c with a slight underestimation of 2 %. Meanwhile, the Hargreaves-Samani (HS) model (temperature-based) underestimated ET_c by 20 % and the Priestley-Taylor (PT) and Makkink (MK) models (radiation-based) had similar performances underestimating by up to 35 % of the measured ET_c. The Turc (TR) model had the lowest performance compared with other models, demonstrating values underestimated by up to 60 % of the measured ET_c. Local calibration based on alfalfa evapotranspiration measurements was used to rectify these underestimations. The surprisingly good performance of the calibrated simple HS model, with a new coefficient 0.0029, demonstrated its favorable potential to improve irrigation scheduling. The MK and PT models were in third and fourth rank, respectively, reflecting minor differences between one another. The new coefficients obtained for the MK and PT models were 1.99 and 0.963, respectively. One important observation was that the calibrated TR model performed poorly, with an increase in its coefficient from 0.013 to 0.034 to account for hyper-arid environmental conditions; moreover, it required additional seasonal calibration to adequately improve its performance.     

基于LAI的PM蒸散发计算模型及应用

采用空间分辨率为8 km×8 km、时间分辨率为15 d的美国航空航天局(NASA)全球监测与模型研究组发布的卫星GIMMS/NDVI数据,反演了褒河流域叶面积指数(LAI)的空间分布,引入基于LAI的Penman-Monteith模型,模拟了褒河流域蒸散发能力的时空分布,分析比较了不同植被覆盖下蒸散发能力的变化规律。结果表明:褒河流域植被蒸腾作用强于土壤蒸发,并且不同的植被覆盖对蒸散发能力的大小和时间分布有着显著的影响。     

Cross Comparison of Empirical Equations for Calculating Potential Evapotranspiration with Data from Switzerland

Earlier studies (Singh and Xu, 1997; Xu and Singh, 2000, 2001) have evaluated and compared various popular empirical evapotranspiration equations that belonged to three categories:(1) mass-transfer based methods, (2) radiation based methods, and(3) temperature-based methods; and the best and worst equations of each category were determined for the study regions. In this study a cross comparison of the best or representative equation forms selected from each category was made. Five representativeempirical potential evapotranspiration equations selected from the three categories, namely: Hargreaves and Blaney-Criddle (temperature-based), Makkink and Priestley-Taylor (radiation-based) and Rohwer (mass-transfer-based) were evaluatedand compared with the Penman-Monteith equation using daily meteorological data from the Changins station in Switzerland.The calculations of the Penman-Monteith equation followed theprocedure recommended by FAO (Allen et al., 1998). Thecomparison was first made using the original constant valuesinvolved in each empirical equation and then made using therecalibrated constant values. The study showed that: (1) theoriginal constant values involved in each empirical equationworked quite well for the study region, except that the valueof = 1.26 in Priestley-Taylor was found to be too high and therecalibration gave a value of = 0.90 for the region.(2) Improvement was achieved for the Blaney-Criddle method by addinga transition period in determining the parameter k. (3) The differences of performance between the best equation forms selected from each category are smaller than the differences between different equations within each category as reportedin earlier studies (Xu and Singh, 2000, 2001). Further examinationof the performance resulted in the following rank of accuracy ascompared with the Penman-Monteith estimates: Priestley-Taylor andMakkink (Radiation-based), Hargreaves and Blaney-Criddle (temperature-based) and Rohwer (Mass-transfer).     

Experimental Analyses of the Evaporation Dynamics in Bare Soils under Natural Conditions

In spite of recent progresses in evaporation estimate through advanced models and laboratory experiments, the drying process of bare soils through its successive stages remains difficult to predict. A study which addresses evaporation modeling in natural bare soils is presented. It relies upon hydro-meteorological measurements performed in a plot with a bare silt loam soil maintained in natural conditions. The following steps are involved: estimate of daily actual evaporation, E_a, through the hydrological balance, scaling with pan evaporation measurements, E_pan, and analysis of the relation of E_a/E_pan with the soil moisture vertical profile. The results enable us (1) to check the occurrence of the first stage of the evaporation process, characterized by not limited-soil water supply and high evaporative rates, and (2) to identify the transition from the first to the second stage, with decreasing soil water-limited E_a values. The last point requires the introduction of a soil water content threshold at 5 cm depth, that is associated with the soil field capacity. The adopted procedure provides insights on the soil water dynamics at depths differently involved through the successive stages of the evaporative process. Finally, indications on the use of pan evaporation measurements in evaporative rate estimate at least during the first stage of the process are also given.     

A Comparative Study of Daily Pan Evaporation Estimation Using ANN,Regression and Climate Based Models

Evaporation estimates are needed for efficient management of water resources at a farm scale as well as at a regional or catchment scale. This paper presents application of artificial neural networks (ANN), statistical regression and climate based models viz.: Penman, Priestley–Taylor and Stephens and Stewart, for estimation of daily pan evaporation. Six different measured weather variables comprising various combinations of maximum and minimum air temperature, sun shine hours, wind speed, relative humidity I and II were used. Randomly selected 1,096 daily records were used to develop the models of ANN and regression, and 365 daily records were used as independent data set for performance evaluation, which was not used previously in any of the model development process. The results of the developed ANN and multiple linear regression (MLR) models along with Penman, Priestley-Taylor and Stephens and Stewart models were compared statistically with observed pan evaporation values. Comparison showed that there is slightly better agreement between the ANN estimations and measurements of daily pan evaporation than other models.     

坡面径流阻力计算模式对比研究

坡面流是污染物迁移、土壤侵蚀、泥沙输移的主要动力因素,阻力系数是影响坡面流模拟的重要参数。为比较三种阻力计算模式(阻力系数为常数、以淹没度为变量的Lawrence模型和阻力分割模型)在裸坡、砾石覆盖坡面、植被覆盖坡面三种常见坡面上的适用程度,本文建立了坡面降雨径流模型,对不同类型坡面的产流进行了模拟。坡面径流模型采用扩散波模型,坡面降雨入渗模型采用考虑坡度影响的Green-Ampt模型,当存在植被时,考虑冠层降雨截留损失。结果表明:在裸坡上,三种阻力计算模式均适用;而在有砾石覆盖和植被覆盖的坡面上,考虑阻力系数时空变化的阻力分割模型模拟精度最高。阻力系数对坡面径流流量的影响在坡面汇流的涨水与退水阶段较大,而在稳定阶段很小。对有植被覆盖坡面,降雨强度存在阈值,大于阈值时,不同阻力模式对坡面流模拟结果影响甚微;反之,需选择合适的阻力计算模式,且坡长越长,坡度越缓,降雨强度阈值越大。     

A MACRO-SCALE SEMI-DISTRIBUTED HYDROLOGICAL MODEL AND APPLICATION TO THE DATONG RIVER VALLEY

1.INTRODUCTION TheYellowRiverisimportantwatersourcein north westChinaandtheHuabeiPlain.Therela tivearidclimateandunreasonablehumanactivities havemadewaterproblemsveryseveresuchas floodthreat,dryriverbedandenvironmentsdeg radation.Theproblemshinderthebasinfromsus tainabledevelopment.Soitisofsignificancetoresearchtheproblemsandmastertherulesofrunoff change.Hydrologicalmodelhasbeenplayinga veryimportantroleasatooltomodelrunoff.A numberofresearchershavedonemuchworkabout runoffsimulationand…     

厄瓜多尔区域水文平衡研究

采用厄瓜多尔147个气象站多年实测降水、温度、风速、湿度、日照等气象数据,分析研究了西部太平洋水系区、中部安第斯山区和东部亚马逊平原区降水、潜在蒸散发、土壤水分储存变化、实际蒸发量及土壤水的盈余或赤字量等水文平衡过程。研究方法基于Thornthwaite水平衡模型,需要输入降水量、潜在蒸散发量和土壤最大含水量等重要参数。潜在蒸散发量研究采用FAO-56 Penman-Monteith法和改进的Thornthwaite法。研究成果清晰展示了降水、蒸发、水量盈余或赤字的时空分布,对于研究该地区土壤水分的变化,优化农作物种植结构及播种、灌溉时机,水资源优化配置和水利工程规划可提供重要参考。     

Performance of Recalibrated Equations for the Estimation of Daily Reference Evapotranspiration

An accurate estimation of reference evapotranspiration (ET₀) is of paramount importance for many studies such as hydrologic water balance, irrigation system design and management, crop yield simulation, and water resources planning and management. In the present study, Blaney-Criddle, Jensen-Haise and Hargreaves (temperature based), Priestley-Taylor, Radiation and Makkink (radiation based) and, Pan Evaporation and Christiansen (pan evaporation based) methods have been evaluated and recalibrated with respect to FAO-56 Penman-Monteith method for estimating daily ET₀ in the semi-arid Tirupati, Nellore, Rajahmundry, Anakapalli and Rajendranagar sites of Andhra Pradesh, India. Recalibrated Blaney-Criddle (temperature based), Radiation (Radiation based) and Christiansen (Pan evaporation based) methods showed a satisfactory performance at the sites. Further, recalibrated Blaney- Criddle method showed relatively better performance than Radiation and Christiansen methods in the daily ET₀ estimation. Recalibrated Blaney- Criddle method may therefore be adopted at the sites selected for the present study and also at the sites with similar climatic conditions for satisfactory daily ET₀ estimation.     

基于Penman-Monteith公式的双源模型的改进

本文在Penman-Monteith公式的基础上，推导出能解析计算冠层蒸腾和土壤蒸发的双源模型，使之能广泛用于农田蒸腾和蒸发的计算.采用玉米田波文比-能量平衡(BREB)观测资料对模型进行检验，模拟的蒸散量与BREB的结果相当一致.模型 主要参数对蒸散的敏感性分析表明，这些参数变化±20%时，蒸散的响应小于±7%.     

基于Penman-Monteith公式的双源模型的改进

本文在Penman-Monteith公式的基础上，推导出能解析计算冠层蒸腾和土壤蒸发的双源模型，使之能广泛用于农田蒸腾和蒸发的计算.采用玉米田波文比椖芰科胶?BREB)观测资料对模型进行检验，模拟的蒸散量与BREB的结果相当一致.模型主要参数对蒸散的敏感性分析表明，这些参数变化±20%时，蒸散的响应小于±7%.     

大汶河流域陆面蒸发估算方法比较研究

区域陆面蒸散发的估算对于计算区域水资源总量,合理配置水资源具有重要意义。针对处于大汶河流域上游、受人类活动影响较小的雪野水库、黄前水库、东周水库控制子流域的实际特点,分别利用MODIS遥感方法、SWAT模型法、水面蒸发折算系数法对这三个子流域2000年-2008年的多年平均年陆面蒸发量及多年月平均陆面蒸发量进行估算,并基于水量平衡方程,结合各子流域的同期降雨与天然径流资料,对估算结果进行了分析比较。结果表明:在大汶河流域内,采用MODIS遥感方法估算实际陆面蒸散发的精度较低;水面蒸发折算系数法具有一定精度;SWAT模型法精度较高、适应性较好,估算误差仅在3%左右。研究结果可为半湿润区陆面蒸发估算方法的选择提供参考。     

葡萄根系分区交替滴灌的土壤水分动态模拟

在根系分区交替滴灌土壤水分动态和根系分布试验观测的基础上,提出了葡萄二维根系吸水模型,并确定了与土壤表层含水率有关的棵间土壤蒸发方程,然后在土壤水分运动基本方程的基础上结合交替滴灌的入渗特性,建立了根系分区交替滴灌的土壤水分动态模型(APRI-Model),模型考虑了该种灌水方式下棵间土壤蒸发和根系吸水的变化特征。通过与田间实测值进行比较,结果表明,模型的均方差在0.01~0.022cm3/cm3范围内,模拟值与实测值的平均相对误差在10%左右,因此,认为模型能很好的模拟干旱区蒸发力较大和作物根系分布不均匀条件下的土壤水分动态。