Rainfall Events

The Rainfall item is a type of Event.

There are two main types of rainfall data that can be used in InfoWorks ICM:

Data stored in the event includes:

See the Rainfall Event Editor topic for details on viewing and editing the data.


Rainfall events cannot be used in simulations in conjunction with Time Series Database objects.

Observed Rainfall

Observed (or recorded) rainfall data represents actual rainfall events. These events can cover a single storm or multiple storms over a long period of time. Recorded rainfall data would normally be used to calibrate the model and verify its correct operation against data collected during flow surveys or against flood records for large historical storms.

Rainfall data will often be available for several rain gauges. This is a great benefit because rainfall intensities can vary significantly across a catchment. For InfoWorks networks, InfoWorks ICM supports spatially varying rainfall by allowing rain gauge regions to be stored with each profile in a rainfall event. See Spatially Varying Rainfall for more information.

Similarly, in SWMM networks, rainfall profiles can be associated with a rain gage through the rain gage properties.

Long rainfall records

In some cases rainfall data covering many years of rainfall events may be available. You could use these long term records in two ways within InfoWorks ICM:

Design Rainfall

Design storms represent the statistical characteristics of rainfall. They are derived from analysis of many years of actual rainfall records. They are easier to use than observed rainfall and can approximate a region's rainfall in just a few storms.

Design rainfall is usually used during normal analysis and design work. However, long time-series observed rainfall (see above) may have advantages in some cases as it is likely to contain a wider range of conditions. In order to cover the same conditions using design storms, you will have to generate a large number of storms covering this wide range.

Design data can be edited in two ways:

When used in SWMM simulations, design rainfall events that have named catchments, such as RefH Rainfall, the name of a catchment identifier must match the name of the Rainfall profile in the rain gage properties.

Sub-Events and Profiles

Rainfall events, like many other types of event, are divided into:


In InfoWorks ICM, a rainfall value is applied from the timestep at which it is defined until the next timestep in the sub-event.

In this example, the 6mm/h falls between 6:54 and 6:56:

If the simulation covers a gap between two sub-events, InfoWorks ICM will generate intermediate values and give them a value of zero. Please note that this behaviour is specific to rainfall events and that it is very different from that applied to other events (e.g. Level, Inflow, etc). For more details on how InfoWorks ICM deals with sub-events and profiles, see the main Events topic.

Rainfall Initial Conditions

Both Observed and Design rainfall events contain initial conditions that can be used to refine the initial state of the model.

The following types of initial conditions are set up in the rainfall event in InfoWorks networks:


Importing and Exporting Rainfall Events

Design Rainfall Generators

Spatially Varying Rainfall

Using Rainfall Events