| 基于三维Copula函数的滴灌硝态氮淋失风险评估方法 |
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| 引用本文： | 王 珍,李久生,栗岩峰.基于三维Copula函数的滴灌硝态氮淋失风险评估方法[J].农业工程学报,2013,29(19):79-87. |
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| 作者姓名： | 王 珍 李久生 栗岩峰 |
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| 作者单位： | 中国水利水电科学研究院流域水循环模拟与调控国家重点实验室，北京100038;中国水利水电科学研究院流域水循环模拟与调控国家重点实验室，北京100038;中国水利水电科学研究院流域水循环模拟与调控国家重点实验室，北京100038 |
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| 基金项目： | 国家自然科学基金项目（51179204） |
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| 摘 要： | 硝态氮淋失是滴灌系统设计和运行管理需要考虑的重要因素。该研究构建了滴灌条件下的水氮运移模型,利用HYDRUS-2D软件进行了求解,模拟分析了田间尺度砂壤土饱和导水率和初始含水率空间变异对NO3--N淋失率的影响,并利用三维Gumbel-Hougaard Copula函数构建了土壤饱和导水率、初始含水率和NO3--N淋失率的联合分布函数,分析了给定土壤饱和导水率和初始含水率条件下NO3--N淋失率超过某一阈值的条件概率。结果表明,NO3--N淋失率概率密度函数可用指数函数表示;土壤饱和导水率和初始含水率的空间变异会明显增加NO3--N淋失风险;NO3--N淋失率超过给定阈值（6.4%,均质土壤条件下的NO3--N淋失率）的条件概率基本随土壤饱和导水率和初始含水率的增大而增大。构建田间尺度土壤特性参数（如饱和导水率、初始含水率等）与NO3--N淋失率的联合分布函数为研究多变量空间变异条件下NO3--N淋失风险评估提供了参考。
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| 关 键 词： | 灌溉 土壤 水分 硝态氮淋失 饱和导水率 空间变异 三维Copula函数 |
| 收稿时间： | 2013/4/16 0:00:00 |
| 修稿时间： | 2013/8/23 0:00:00 |
Assessment method of nitrate leaching under drip irrigation using trivariate Copula |
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| Wang Zhen,Li Jiusheng and Li Yanfeng.Assessment method of nitrate leaching under drip irrigation using trivariate Copula[J].Transactions of the Chinese Society of Agricultural Engineering,2013,29(19):79-87. |
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| Authors: | Wang Zhen Li Jiusheng and Li Yanfeng |
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| Institution: | State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing 100038, China;State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing 100038, China;State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing 100038, China |
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| Abstract: | Abstract: Drip irrigation has been recognized as an efficient method to improve water and nitrogen use efficiency. Nitrate leaching is becoming an important consideration for the design, operation, and management of drip irrigation systems. Recent studies have indicated that soil properties such as soil texture and saturated hydraulic conductivity could impose a significant effect on nitrate leaching. However, most of these studies were conducted on an assumption of homogeneous soil. In the current study, the effect of the spatial variability of soil properties on nitrate leaching was evaluated by a model that was established and solved numerically by using the HYDRUS-2D package. In the simulation, the statistical distribution of the saturated hydraulic conductivity and the initial soil water content in the field were assumed to be able to be represented by a logarithmic normal distribution and a normal distribution function, respectively. A moderate variability for both saturated hydraulic conductivity and initial soil water content were considered with the coefficient of variation (CV) of 0.40 and 0.15, respectively. One hundred samples of the spatial varied saturated hydraulic conductivity and initial soil water content at a given CV value were generated randomly by the Monte Carlo method. The nitrate leaching ratios for these randomly generated parameters of saturated and initial soil water content were determined by the numerical model. After the positive correlation between the nitrate leaching ratio and the saturated hydraulic conductivity and the initial soil water content was confirmed, a joint distribution function of saturated hydraulic conductivity, initial soil water content, and nitrate leaching ratio was constructed using a Gumbel-Hougaard trivariate copula function. The maximum likelihood approach was used to determine the parameters for the Gumbel-Hougaard trivariate copula function and the Kolmogorov-Smirnov test indicated that the empirical distribution of the nitrate leaching ratios could be well represented by the trivariate copula function with a root mean square error (RMSE) value of 0.046. To quantify the risk of nitrate leaching, the conditional probability distribution function of the nitrate leaching ratio under given saturated hydraulic conductivities and initial soil water contents was estimated from the derived joint distribution function. The results indicated that the probability density function of the nitrate leaching ratio could be represented by an exponential function and the variability of saturated hydraulic conductivity and initial soil water content imposed an important effect on the nitrate leaching. For the sandy loam soil having medium variabilities of saturated hydraulic conductivity and initial soil water content, the simulated nitrate leaching ratio reached 13.2%, being more than double of the value for the homogeneous soil (6.4%). The probability under the condition that the nitrate leaching ratio exceeds a given threshold (6.4%) generally increases with an increasing saturated hydraulic conductivity and initial soil water content. It might be concluded that constructing a joint distribution function between the nitrate leaching and soil properties in the field (e.g., saturated hydraulic conductivity and initial soil water content) is a promising method to assess the risk of nitrate leaching while the spatial variability needs to be considered. |
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| Keywords: | drip irrigation soils moisture nitrate leaching saturated hydraulic conductivity initial soil water content spatial variability trivariate copula function |
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