The absence of a generic modeling framework in hydrology has long been recognized. With our current practice of developing more and more complex models for specific individual situations, there is an increasing emphasis and urgency on this issue. There have been some attempts to provide guidelines for a catchment classification framework, but research in this area is still in a state of infancy. To move forward on this classification framework, identification of an appropriate basis and development of a suitable methodology for its representation are vital. The present study argues that hydrologic system complexity is an appropriate basis for this classification framework and nonlinear dynamic concepts constitute a suitable methodology. The study employs a popular nonlinear dynamic method for identification of the level of complexity of streamflow and for its classification. The correlation dimension method, which has its base on data reconstruction and nearest neighbor concepts, is applied to monthly streamflow time series from a large network of 117 gaging stations across 11 states in the western United States (US). The dimensionality of the time series forms the basis for identification of system complexity and, accordingly, streamflows are classified into four major categories: low-dimensional, medium-dimensional, high-dimensional, and unidentifiable. The dimension estimates show some "homogeneity" in flow complexity within certain regions of the western US, but there are also strong exceptions.

The quantity of freshwater available per person in the world has been and continues to decrease due to a combination of factors, including population increase, water pollution, inadequate planning and management of transboundary and other shared waters, and inefficient operation of water supply and distribution systems. Consequently, there is an increasing potential for water scarcity, crisis and associated conflicts around the world in the future, especially in developing regions, if the current trend in water consumption and management practices continues. In this fast-changing and highly-interconnected world, the problems related to water crisis and conflicts are numerous, complicated and challenging. Efforts to effectively resolve these problems require a clear vision of the future water availability and demand as well as new ways of thinking, developing and implementing water planning and management practices. The present study attempts to offer a comprehensive account of the above issues and also some important guidelines for advancing research in this direction. Assessments of past, present and future statuses of the world's water are reviewed. Major water initiatives and their targets, successes and failures are highlighted. The urgent need for new ways of thinking, including an integrated framework (encompassing both the “hard sciences” and the “soft sciences”), water education and training and communication of the water issues and our studies to the different stakeholders in the water sector, is also discussed. Citation Sivakumar, B. (2011) Water crisis: From conflict to cooperation—an overview. Hydrol. Sci. J. 56(4), 531–552.