Rain model (Water Overlay)

Rain can be implicitly activated and deactivated by defining an appropriate period of rainfall as weather effect. If a period with no rainfall is defined, that period is simulated but no rain is simulated.

Currently, during a period in the simulation where rainfall is defined, water is uniformly added to the surface for each cell in the project area. During any single defined period of rain, the amount of rain is consistent. At the end of the defined period of rain, exactly the defined amount of rain should have fallen on each cell.

Dynamic rainfall

It is possible to add multiple consecutive rain periods. See the table below:

Time key (minutes)	Amount of rainfall (mm/m2)
35	15
42	19
120	5

This format can be interpreted as followed:
The first period is starts at t=0 minutes and ends at t=35 minutes. In this first period, 15 mm/m² of rain will fall. Uniformly this gives 15 / ((35 - 0) * 60) = 0.00714 mm per second.
The second period starts at t=35 minutes and ends at t=42 minutes. In this period, 19 mm/m² of rain will fall. Uniformly this is 19 / ((42 - 35) * 60) = 0.04524 mm rain per second.
The last period starts at t=42 minutes and ends at t=120 minutes. In this period, 5 mm/m² of rain will fall. Uniformly this is 5 / ((120 - 42) * 60) = 0,00107 mm rain per second.
In total it can be expected that per m² 15 + 19 + 5 = 39 mm rain has fallen in a total simulation time of 120 minutes.

Notes

• The rainfall table is stored as an attribute array in the Weather selected by the Water Overlay
• The time keys in seconds.
• Zero rain within a period is allowed, but negative is not.
• The next time key should always be larger than the previous time key, else the rain calculation model will stop from that moment on.
• The last time key also determines the total simulation time.