Rain model (Water Overlay)

Rain is modeled as an amount of rain that falls within a defined period of time. So for example, 15 mm in 45 minutes. Internally this amount can be recalculated to an amount x per second. Moreover, the amount of rain per second that falls remains the same within the period it was defined for. At the end of the defined period of rain, it can be expected that the defined amount of rain should have fallen on each cell.

Rain is always added to the surface layer of a grid cell and each grid cell receives the same amount of rain per time step.

Dynamic rainfall

It is possible to add multiple consecutive periods of rainfall. 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. Negative values are rounded up to zero.
• 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.