Decision Making could be defined as a process in which a decision maker makes a specific choice among several existing choices. Multi-Criteria Decision Making (MCDM) as its name suggests pertains to a decision making situation where the decision maker considers multiple criteria in order to make a choice. Benjamin Franklin is allegedly the earliest known person to create a simple method to solve this type of problems. As a result of the rapid growth of operations research during and after World War II, numerous methods have been invented to help decision makers face the challenge of MCDM problems. As an invaluable book on MCDM, Smart Choices by Hammond, Keeney, and Raiffa is strongly recommended to interested readers. Moreover, for a thorough description of MCDM history and other information and resources related to MCDM, you may have a look at MCDM Society website. I also spent some time working on developing a new method for solving MCDM problems with the use of fuzzy numbers, which enable more flexibility in taking account of uncertainties, and the results are published in a paper that might be of interest to you. With a simple search into literature, the variety of approaches and techniques to solve MCDM problems will be revealed.
MCDM techniques can be very helpful in solving water related problems due to the fact that most of the large-scale water related decisions impact multiple active components in a watershed system. (This concept was the base for the definition of Integrated Water Resources Management by Global WaterPartnership in 2000). If you have read the previous post, one of the applications of MCDM in water resources planning and management is in planning for reservoir operation. In fact, MCDM is somehow an impartible component of a Risk-informed Decision Making framework for reservoir operation during floods. I hope to be able to explain each of the components of such a framework through a number of posts in the future and explain how they connect and create a coherent framework in the end.