Rainfall

Rainfall inflows apply a spatially uniform rainfall intensity over a polygon within the domain.

Properties

Property	Type	Description
type	string	Must be "Rainfall"
data	string or array	Intensity in mm/hr (constant or time-varying)

Constant rainfall

Set data to a single numeric value (as a string):

"data": "50.0"

This applies 50 mm/hr for the entire simulation duration.

Time-varying rainfall

Set data to a JSON array of timestamp/value pairs:

[
    {"timestamp": "2024-01-01T00:00:00Z", "value": 0},
    {"timestamp": "2024-01-01T00:30:00Z", "value": 50},
    {"timestamp": "2024-01-01T01:00:00Z", "value": 0}
]

ANUGA interpolates linearly between data points using forward-fill for missing timesteps.

Design storms

A design storm is a rainfall hyetograph for a chosen return period (for example a 100 year ARI / 1% AEP event) over a set duration. Hydrata applies a design storm the same way as any other time-varying rainfall: the timestamp/value array above is the hyetograph, with each value being the storm's rainfall intensity (mm/hr) at that point in the event.

To build one:

1. Pick the return period and storm duration your study requires.
2. Derive the intensity profile from your jurisdiction's IDF (intensity-duration-frequency) data and temporal pattern (for example ARR, NOAA Atlas 14, or a local standard). This step happens in your own IDF tooling or spreadsheet, not in the map editor.
3. Enter the resulting timestamp/intensity pairs as the data array on the rainfall polygon.

The mesh-area total rainfall is whatever your hyetograph integrates to, so the choice of return period and temporal pattern is yours to make and document. Hydrata does not pick a design standard for you.

How it works

Internally, rainfall polygons are applied as Polygonal_rate_operator instances with a conversion factor of 1.0 x 10^-6 (converting mm/hr to m/s, the units ANUGA uses internally).