Years and Time Steps

Time Horizon

Enter the Current Accounts Year and Last Year of Scenarios. WEAP performs a monthly analysis from the first month of the Current Accounts Year through the last month of the Last Year. The Current Accounts Year is usually the most recent year for which reasonably reliable and complete data are available and from which future demand projections can be made. The Current Accounts year data comprise the Current Accounts, which all scenarios use as the basis for their projections.

Time Steps per Year

The time step can be set anywhere from one day to 365 days. Each year and scenario in an area must have the same time step.  

Checking Add Leap Days? will add an extra day in leap years (e.g., 2000, 2004, 2008) to the timestep that includes February 28 (e.g., the February timestep in a monthly analysis).  For daily models there will be 366 time steps in leap years, 365 time steps in all other years.  This would be useful if you have datasets, such as river streamflow gauges, that include data for leap days.

Time Step Boundary

The user has the option to have time steps be based on (a) the calendar year, (b) all time steps are equal, or (c) the time step lengths are entered manually.

Water Year Start

Any particular time step (for example, a particular month) can be designated as the starting point for the "Water Year."  WARNING: You should not change Water Year Start after you have begun entering data and expressions, because it might change some of your expressions.  Some functions, such as MonthlyValues, store their parameters by number instead of name.  For example, if you have an expression MonthlyValues(Jan, 10, Jul, 40) that was created when the Water Year Start was January, changing the Water Year Start to October will change the expression to MonthlyValues(Oct, 10, Apr, 40).

Time Step Names

In the grid on the right, the user can change the title and abbreviation of the time steps. If the Time Step Boundary is set to "Set time step length manually," the length can be set in the grid.

Menu Option: General: Years and Time Steps