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首页> 外文期刊>Journal of the American Water Resources Association >SENSITIVITY AND UNCERTAINTY OF GROUND-WATER DISCHARGE ESTIMATES FOR SEMIARID SHRUBLANDS
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SENSITIVITY AND UNCERTAINTY OF GROUND-WATER DISCHARGE ESTIMATES FOR SEMIARID SHRUBLANDS

机译：半干旱灌木丛的地下水排放估算值的敏感性和不确定性

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We proposed a step-by-step approach to quantify the sensitivity of ground-water discharge by evapotranspiration (ET) to three categories of independent input variables. To illustrate the approach, we adopt a basic ground-water discharge estimation model, in which the volume of ground water lost to ET was computed as the product of the ground-water discharge rate and the associated area. The ground-water discharge rate was assumed to equal the ET rate minus local precipitation. The objective of this study is to outline a step-by-step procedure to quantify the contributions from individual independent variable uncertainties to the uncertainty of total ground-water discharge estimates; the independent variables include ET rates of individual ET units, areas associated with the ET units, and precipitation in each subbasin. The specific goal is to guide future characterization efforts by better targeting data collection for those variables most responsible for uncertainty in ground-water discharge estimates. The influential independent variables to be included in the sensitivity analysis are first selected based on the physical characteristics and model structure. Both regression coefficients and standardized regression coefficients for the selected independent variables are calculated using the results from sampling-based Monte Carlo simulations. Results illustrate that, while as many as 630 independent variables potentially contribute to the calculation of the total annual ground-water discharge for the case study area, a selection of seven independent variables could be used to develop an accurate regression model, accounting for more than 96% of the total variance in ground-water discharge. Results indicate that the variability of ET rate for moderately dense desert shrubland contributes to about 75% of the variance in the total ground-water discharge estimates. These results point to a need to better quantify ET rates for moderately dense shrubland to reduce overall uncertainty in estimates of ground-water discharge. While the approach proposed here uses a basic ground-water discharge model taken from an earlier study, the procedure of quantifying uncertainty and sensitivity can be generalized to handle other types of environmental models involving large numbers of independent variables.
机译：我们提出了一种循序渐进的方法来量化通过蒸散量（ET）对三类独立输入变量进行地下水排放的敏感性。为了说明这种方法，我们采用了基本的地下水排放估算模型，在该模型中，ET流失的地下水量被计算为地下水排放率与相关面积的乘积。假定地下水排放速率等于ET速率减去局部降水量。这项研究的目的是概述分步进行的程序，以量化各个独立变量不确定性对地下水总排放量估计值不确定性的贡献；自变量包括单个ET单元的ET率，与ET单元相关的面积以及每个子流域的降水。具体目标是通过更好地将数据收集针对那些最负责地下水排放估算不确定性的变量，从而指导未来的表征工作。首先根据物理特性和模型结构选择要包含在敏感性分析中的有影响力的自变量。使用基于采样的蒙特卡洛模拟的结果来计算所选自变量的回归系数和标准化回归系数。结果表明，尽管多达630个独立变量潜在地有助于案例研究区域的年度地下水总排放量的计算，但可以选择七个独立变量来开发精确的回归模型，其中地下水排放总量变化的96％。结果表明，中等密度的荒漠灌木丛的ET速率变化约占总地下水排放估算值变化的75％。这些结果表明，需要更好地量化中等密度灌木林的ET率，以减少地下水排放量估算中的总体不确定性。尽管此处提出的方法使用了较早研究的基本地下水排放模型，但是可以将量化不确定性和敏感性的过程通用化，以处理涉及大量自变量的其他类型的环境模型。

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