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 identificati on of shifting relationships among hydrological variables. The methodology developed is applicable to many hydrological problems, such as identificati on of multiple stage-discharge relationships in a river section, data homog eneity analysis, analysis of temporal consistency of hydrological data, det ection 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 con siderations. Several statistical tests, as well as auxiliary information of physical conditions, are systematically combined to form an objective func tion to be optimised. This objective function represents the performance of a solution, (where a solution is a specific partitioning of a data set int o subperiods), in a manner, that holds in each subperiod a single relations hip among data values. It is shown that an exhaustive search of all candida te solutions is intractable. Therefore, a heuristic algorithm is proposed, which emulates the exploratory data analysis of the human expert. This algo rithm encodes a number of search strategies in a pattern directed computer program and results in an automatic determination of a satisfactory solutio n.