The Water Year Method allows you to use historical data in a simplified form and to easily explore the effects of future changes in hydrological patterns. The Water Year Method projects future inflows by varying the inflow data from the Current Accounts according to the Water Year Sequence and Definitions specified in the Hydrology section. If you want to test a hypothetical event or set of events, or wish to approximate historic patterns, then you should probably select the Water Year Method. For example, you could use the Water Year Method to test the system under historic or hypothetical drought conditions. Hydrologic fluctuations are entered as variations from a Normal Water Year (the Current Accounts year is not necessarily a Normal water year). The Water Year Method requires data for defining standard types of water years (Water Year Definition), as well as defining the sequence of those years for a given set of scenarios (Water Year Sequence).
A water year type characterizes the hydrological conditions over the period of one year. The five types that WEAP uses--Normal, Very Wet, Wet, Dry, and Very Dry--divide the years into five broad categories based on relative amounts of surface water inflows.