The first method uses contingency workflows to provide information to WFOs or external partners, such as emergency managers, on how the river would respond if another event occurred.

In other words, the forecast is contingent on another event (typically precipitation or snowmelt) occurring.

Method

River Forecast Centers usually use output from quantitative precipitation forecast (QPF) ensembles as input to contingency forecasts. The forecaster selects the duration (0 to 120 hours) to make a contingency forecast.

This option only works if the CHPS Configuration Focal Points sets up contingency workflows to populate the QPF grids.

What-If Scenarios

Another option for scenario-based models run is called the What-If Scenario, an editor in CHPS. This tool can produce forecast time series for precipitation events or potential dam breaks.

Example: What happens to the flow time series when a user adds two inches of precipitation to a basin?

Types of What-If Scenarios

You can create one of four types of scenarios - transformation, user defined, module dataset, and module parameters.

Be prudent about which scenarios you save. Editing and deleting scenarios is difficult and not all users have permission to do so.

Hint: Export scenarios for use later, or import scenarios you think are analogs to the forecast event. Keep in mind, this option does import or export ALL of the scenarios. You may end up with a lot of scenarios.

Before moving on to the next page, use the following job sheet to practice creating, using, and managing What-If Scenarios.