Hierarchical Approach To Water Body Status Misclassification
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Within the context of assessing status of water bodies in EU countries, the Water Framework Directive (WFD) has introduced notions of confidence, precision and probability of misclassification (PoM). Although defined by WFD in a rather vague manner, the three measures of uncertainty have become compulsory elements of the reporting process. The EC requires all classifications of European water bodies to be accompanied by estimates of these uncertainty measures. The article describes the Hierarchical Approach introduced to assess PoM of riverine water bodies’ status using uncertain water quality monitoring data. The approach stems from the observation that uncertainty of higher level classifications (e.g. assessment of water body status) depends on uncertainties of lower order assessments, (e.g. assessments of chemical status and ecological status of that water body). Specifically, the Hierarchical Approach describes how uncertainties intrinsic for water quality measurements propagate through the stages of water body status classification. To assess PoM of a water body, twodimensional probability distributions are used sequentially. At every stage, they are derived by combining one-dimensional probabilities of committing statistical errors of the II-nd type when classifying corresponding elements of the lower stage. For instance, to assess PoM of status of some water body two onedimensional PoMs of its chemical and biological status are used. The proposed method of assessing PoM is also shortly discussed within the context of risks involved in water management decisions based on misclassified water bodies. Keywords: water body status, surface waters monitoring, classification, confidence, precision, probability of misclassification, Hierarchical Approach.
water body status, surface waters monitoring, classification, confidence, precision, probability of misclassification, Hierarchical Approach