The purpose of the paper is to describe the climate modeling used to develop climate change scenarios and to describe the ecosystem modeling used to develop ecosystem impact scenarios. The paper has three main subjects. First, selected climate change models and their resulting impact scenarios are reviewed. Second, several main ecosystem models and their scenarios are described with emphasis on water and vegetation issues. Finally, water use models are reviewed. The method to achieve these objectives is through a critical literature review with emphasis on the last five years of published information. The climate change sections include descriptions of emission scenarios, criteria for climate change scenarios, types of climate scenarios, the uncertainties of emission and climate scenarios and how well they work. The various types of scaling were also discussed.