A Comprehensive System for the Exploration and Analysis of Hydrological Data

A new approach is developed for the automatic (computer based) exploration and analysis of hydrological data, particularly focused on the identification of shifting relationships among hydrological variables. The methodology developed is applicable to many hydrological problems, such as identification of multiple stage-discharge relationships in a river section, data homogeneity analysis, analysis of temporal consistency of hydrological data, detection of outliers, and determination of shifts and trends in hydrological time series. Such problems are examined here as particular applications of the single methodology developed. A general mathematical representation of the data exploration problem is initially proposed, based on set theory considerations. Several statistical tests, as well as auxiliary information of physical conditions, are systematically combined to form an objective function to be optimised. This objective function represents the performance of a solution, (where a solution is a specific partitioning of a data set into subperiods), in a manner, that holds in each subperiod a single relationship among data values. It is shown that an exhaustive search of all candidate solutions is intractable. Therefore, a heuristic algorithm is proposed, which emulates the exploratory data analysis of the human expert. This algorithm encodes a number of search strategies in a pattern directed computer program and results in an automatic determination of a satisfactory solution. Copyright Kluwer Academic Publishers 1999