Calculating actual crop evapotranspiration under soil water stress conditions with appropriate numerical methods and time step     

Songhao Shang 《水文研究》2012,26(22):3338-3343

Calculation of actual crop evapotranspiration under soil water stress conditions is crucial for hydrological modeling and irrigation water management. Results of actual evapotranspiration depend on the estimation of water stress coefficient from soil water storage in the root zone, which varies with numerical methods and time step used. During soil water depletion periods without irrigation or precipitation, the actual crop evapotranspiration can be calculated by an analytical method and various numerical methods. We compared the results from several commonly used numerical methods, including the explicit, implicit and modified Euler methods, the midpoint method, and the Heun's third‐order method, with results of the analytical method as the bench mark. Results indicate that relative errors of actual crop evapotranspiration calculated with numerical methods in one time step are independent of the initial soil water storage in the range of soil water stress. Absolute values of relative error decrease with the order of numerical methods. They also decrease with the number of time step, which can ensure the numerical stability of successive simulation of soil water balance. Considering the calculation complexity and calculation errors caused by numerical approximation for different time step and maximum crop evapotranspiration, the explicit Euler method is recommended for the time step of 1 day (d) or 2 d for maximum crop evapotranspiration less than 5 mm/d, the midpoint method or the modified Euler method for the time step of up to one week or 10 d for maximum crop evapotranspiration less than 5 mm/d, and the Heun's third‐order method for the time step of up to 15 d. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Analytical and computational procedure for solving the consolidation problem of layered soils     

S. Sadiku 《国际地质力学数值与分析法杂志》2013,37(16):2789-2800

One‐dimensional consolidation analysis of layered soils conventionally entails solving a system of differential equations subject to the flow conditions at the bounding upper and lower surfaces, as well as the continuity conditions at the interface of every pair of contiguous layers. Formidable computational efforts are required to solve the ensuing transcendental equations expressing the matching conditions at the interfaces, using this method. In this paper, the jump discontinuities in the flow parameters upon crossing from one layer to the other have been systematically built into a single partial differential equation governing the space–time variation of the excess pore pressure in the entire composite medium, by the use of the Heaviside distribution. Despite the presence of the discontinuities in the coefficients of the differential equation, a closed‐form solution in the sense of an infinite generalized Fourier series is obtained, in addition to which is the development of a Green's function for the differential problem. The eigenfunctions of the composite medium are the coordinate functions of the series, obtained computationally through the application of the extended equations of Galerkin. The analysis has been illustrated by solving the consolidation problem of a four‐layer composite, and the results obtained agree very well with the results obtained by previous researchers. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Partial L-moments for the analysis of censored flood samples / Utilisation des L-moments partiels pour l’analyse d’échantillons tronqués de crues     

《水文科学杂志》2013,58(5)

Abstract

Abstract A parameter estimation method is proposed for fitting the generalized extreme value (GEV) distribution to censored flood samples. Partial L-moments (PL-moments), which are variants of L-moments and analogous to ?partial probability weighted moments?, are defined for the analysis of such flood samples. Expressions are derived to calculate PL-moments directly from uncensored annual floods, and to fit the parameters of the GEV distribution using PL-moments. Results of Monte Carlo simulation study show that sampling properties of PL-moments, with censoring flood samples of up to 30% are similar to those of simple L-moments, and also that both PL-moment and LH-moments (higher-order L-moments) have similar sampling properties. Finally, simple L-moments, LH-moments, and PL-moments are used to fit the GEV distribution to 75 annual maximum flow series of Nepalese and Irish catchments, and it is found that, in some situations, both LH- and PL-moments can produce a better fit to the larger flow values than simple L-moments.  相似文献   

我国月降水和气温网格点资料的处理和分析   总被引：14，自引：2，他引：14  

魏凤英  曹鸿兴 《气象》1994,20(10):26-30

用逐步搜索逼近法的客观分析技术计算出１９５１－１９９２年中国月降水量和月平均气温的格点资料，并利用图象识别原理对格点值和站点观测值进行了比较。  相似文献   

梅雨锋次天气尺度涡旋旋转风和辐散风动能收支   总被引：2，自引：3，他引：2  

汪钟兴  刘勇 《高原气象》1994,13(1):28-34

本文选取１９９１年７月５日２０：００－６日２０：００梅雨锋上移动性次天气尺度涡旋引起的长江中下游特大暴雨为实例。采用准拉格朗日球坐标系的旋转风和辐散风动能方程，计算得到次天气尺度涡旋发展和成熟两个阶段对流层各层旋转风动能和辐散风动能的收支特征为：在对流层高层（１００－４００ｈＰａ）两个阶段的旋转风动能源汇相同，辐散风动能源汇有异，即水平动能通量项和“摩擦”项符号相反；在中层（４００－７００ｈＰａ）  相似文献   

局地云量变化气候效应的数值模拟   总被引：3，自引：3，他引：3  

钱云  钱永甫 《高原气象》1994,13(2):169-177

本文用统计得到的东半球夏季平均云量资料，利用改进的云－辐射计算模式，在三维有限区域模式中模拟局地云量变化的气候效应。模拟结果表明，高原地区和热带辐合带云量变化造成的气候效应都主要表现在青藏高原地区。在低反照率时，高原地区云量减少使该地区地表加热，引起高低空气压系统加强；高反照率时结果相反。热带辐合带云量减少会引起青藏高原地区降温和气压系统减弱。  相似文献   

南北两极海冰的涛动关系          下载免费PDF全文

解思梅  包澄澜  郝春江 《极地研究》1994,6(3):41-55

本文将南极海冰分为４个区：ＳＰＩ１（０°－１２０°Ｅ），东南极海冰；ＳＰＩ２（１２０°Ｅ－１２０°Ｗ），以罗斯海为主体的海冰区；ＳＰＩ３（１２０°Ｗ－０°），以威德尔海为主体的海冰区；ＳＰＩ４，全南极海冰区。北极海冰区分为３个区：ＮＰＩ１（９０°Ｅ－１８０°－９０°Ｗ），太平洋侧冰区；ＮＰＩ２（９０°Ｗ－０°－９０°Ｅ），大西洋侧冰区；ＮＰＩ３，全北极冰区。本文使用了ＷＤＣ－Ａ的ＳＩＧＲＩＤ海冰资料，以分析南极和北极各冰区之间的相互关系。发现两极各冰区之间存在着非常复杂的相互作用。其中最突出的特征是：两极海冰之间相互作用的振源是ＮＰＩ２。ＳＰＩ３是影响南极海冰的正反馈中心。ＳＰＩ２则是南北两极海冰的负反馈中心。ＮＰＩ２，ＳＰＩ３和ＳＰＩ２之间的相互作用最强，形成涛动关系。这种涛动关系不是同时期的，而是有较长的滞后时间差。两极海冰形成周期变化，其周期为５－６年，正与ＮＰＩ２和ＳＰＩ３自身变化周期一致。另外还有更长的循环周期９－１１年  相似文献   

硅硼镁铝矿－柱晶石－电气石组合在南极的发现          下载免费PDF全文

任留东  刘小汉 《极地研究》1994,6(1):4-10

硅硼镁铝矿、柱晶石和电气石组合产于东南极拉斯曼丘陵，三种矿物相互接触并表现出特定的顺序：电气石（Ｔｒｎ１）→硅硼镁铝矿→电气石（Ｔｒｎ２）→柱晶石→电气石（Ｔｒｎ３），表明其产出是受Ｂ２Ｏ３、Ｈ２Ｏ活度的时间演化而不是空间变化所控制。这一组合的出现对于变质作用环境及过程中组分性质是一个很好的限定  相似文献   

CHINA''S REGIONAL DEVELOPMENT IN THE 1980s     

Liu Xiaojin 《地理学报(英文版)》1994,(Z1)

l.Introducti0nIntheseveraldecadestilltheendofthe1970s,therewasnoanyleastd0ubtthatChinahadbeenfollOwingabalancedregi0naldevelopmentstrategy.0bligedtotlledolnesticandinternationalsituationofthattime,capitalinvestlnentxvasn1ost1yf0rcedt0beputintotheundevel0pedarea(westeconomiczone),thisstrategyprovedtobelesseffectiveandincurredahugelossofinvestmentbenefit.Althoughthewestzoneisabundantinnatllralresources(mineral,energyresourcesetc.),thelevelofregionaldevel0pmentfromeastzonet0westzoneisgradua1lydec…  相似文献   

南极长城站至莫斯科和伊尔库茨克路径上时延的测量与传播路径研究          下载免费PDF全文

孙宪儒  王聚杰  杜军虎  杨维富 《极地研究》1994,6(1):61-65

本文介绍了利用在南极长城站接收来自ＲＷＭ（莫斯科）和ＲＩＤ（伊尔库茨克）台的授时信号的无线电波时延的测量方法，并依据１９９１年４月至１９９１年９月所测量的传播时延数据分析了电波传播路径。说明了沿长、短大圆路径的传播时段。判定存在着非大圆路径传播并阐明了关于非大圆路径传播的一些变化规律。对非大圆路径发生的条件进行了探讨  相似文献