This volume contains selected up-to-date professional papers prepared by specialists from various disciplines related to geosciences and water resources. Thirty papers discuss different aspects of environmental data modeling. It provides a forum bringing together contributions, both theoretical and applied, with special attention to Water in Ecosystems, Global Atmospheric Evolution, Space and Earth Remote Sensing, Regional Environmental Changes, Accessing Geoenvironmental Data and Ecotoxicological Issues. "Geosciences and Water Resources: Environmental Data Modeling" is now the fourth volume in the Series "Data and Knowledge in a Changing World". Launched by CODATA after the 14th International Conference of the Committee on Data for Sciences and Technology, in Chambery, the purpose of this new Series is to collect from widely varying fields a wealth of information pertaining to the intelligent exploitation of data in science and technology and to make that information available to a multidisciplinary community. The present series encompasses a broad range of contributions, including computer-related handling and visualization of data, to the major scientific, tech nical, medical and social fields. The titles of the previous published volumes are: The Information Revolution: Impact on Science and Technology. Modeling Complex Data for Creating Information. Industrial Information and Design Issues.