Knowledge of the global fresh water budget is presently poor, both with respect to the available fresh water flux, and to global fresh water storage. This lack of knowledge is an increasing problem, as the changing global fresh water resources under the effects of climate change are under increasing stress as the human population grows and places increasing demands of the availability of fresh water. The situation is being remedied. The technologies for an integrated measurement and modeling system for the major components of the global fresh water budget are presently known conceptually, and it is expectable that within the next decade, reliable measurement and modeling approaches will have been demonstrated with sufficient accuracy that a practical global fresh water budget monitoring system can built.

This paper describes the characteristics and feasibility of a future global fresh water budget monitoring system. Details of the required observations are developed, based on the required sampling characteristics of each component of the global fresh water budget system. These sampling requirements are evaluated in terms of hypothetical future global fresh water budget measurement and modeling approaches that are based, largely on a coordinated satellite remote sensing system, that is coupled to a dedicated earth fresh water budget data assimilation system, designed to produce fresh water budget analyses on global, continental and regional scales. The feasibility of building and operating such a system is evaluated in terms of the technology, the data communications, and the overall cost of operations, as compared with current earth observing systems.