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On the mechanisms of two composite methods for construction of multivariate drought indices

机译：两种综合方法构建多元干旱指数的机理研究

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摘要

Droughts are comprehensive and complex issues that need to be characterized from a multivariate perspective. In recent years, a number of composite indices have been proposed for drought characterization. However, rare studies have systematically compared similarities and dissimilarities of these indices, and they have provided little insights into the combination mechanisms. To address this issue, two widely used combination approaches, namely the principal component analysis (PCA) and copula based joint probability distribution were employed, with the corresponding integrated product denoted as the Aggregate Drought Index (ADI) and Joint Drought Deficit Index (JDI). Five constituents for constructing ADI and JDI were derived from the variable infiltration capacity model (VIC) monthly simulations over the Yellow River basin (YRB), China, including precipitation (P), actual evapotranspiration (ET), soil moisture of top two layers, and runoff (during 1961-2012). Results showed that the behavioral patterns of ADI and JDI may not be easily influenced by the variation of one single element, and they represented comprehensive moisture status well. A further comparison between these two composite indices suggested that ADI and JDI behaved similarly inmost areas of YRB, with some dissimilarities in the source region. The particular behavior of ET was responsible for the inconsistency. Comparing to other regions, an enhanced role of potential evapotranspiration (PET) was imposed on ET in the source region, leading to a poor relationship of ET with P and other hydrological variables. Accordingly, when constructing composite drought indices, the drought information indicated by ET was more easily abandoned by ADI but reserved in JDI. This study clearly demonstrates the mechanisms of two common integrated approaches in blending different drought information, which has significant implications for composite drought indices construction and application, and potentially provides some valuable references for the improvement of monitoring techniques in future drought related researches. (c) 2018 Elsevier B.V. All rights reserved.
机译：干旱是一个综合而复杂的问题，需要从多方面角度加以表征。近年来，已经提出了许多用于干旱特征的综合指数。但是，很少有研究系统地比较了这些指标的相似性和相异性，并且他们对组合机制的了解很少。为了解决此问题，采用了两种广泛使用的组合方法，即主成分分析（PCA）和基于copula的联合概率分布，相应的综合产品称为总干旱指数（ADI）和联合干旱赤字指数（JDI） 。 ADI和JDI的五个构成要素来自中国黄河流域（YRB）的月度可变渗透能力模型（VIC），包括降水量（P），实际蒸散量（ET），顶层两层土壤湿度，和径流（1961-2012年）。结果表明，ADI和JDI的行为模式可能不会轻易受一个元素变化的影响，它们很好地表现了综合水分状态。这两个综合指数之间的进一步比较表明，ADI和JDI在YRB的大多数区域中表现相似，但在源区域​​中有些不同。 ET的特定行为是造成不一致的原因。与其他地区相比，源区ET的潜在蒸散量（PET）作用增强，导致ET与P和其他水文变量之间的关系不佳。因此，在建立综合干旱指数时，由ET表示的干旱信息更容易被ADI抛弃，但保留在JDI中。这项研究清楚地说明了两种常见的综合方法在融合不同干旱信息方面的机制，这对综合干旱指数的建立和应用具有重要意义，并可能为今后干旱相关研究中监测技术的改进提供一些有价值的参考。 （c）2018 Elsevier B.V.保留所有权利。

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