# Modelling extreme rainfall events: 'blanket approches' when considering soil infiltration

For my thesis on modelling an extreme rainfall event with a 2D surface runoff model I'm supposed to consider the effect of soil infiltration on the runoff: In my work description it says I'm supposed to "choose an appropriate approach to model soil infiltration because 'blanket approaches' (if its the correct english translation) have uncertainties". As an 'appropriate approach' I got recommended to use a software which computes a runoff-coefficient. But what are the 'blanket approaches'? I probably need to use one or more of those 'blanket approaches' and compare them with the results from the software. Any ideas what is meant?

I would be surprised if the rainfall-runoff relationship would show a linear relationship for extreme events. I would consider that to be a blanket approach, if you mean using a constant coefficient. So consider using a higher order relationship.

Another thing to consider is whether the rainfall runoff relationship depends on the soil moisture. Maybe check out how other models like SWAT deal with this.

To be honest, I think that the amount of soil infiltration will be insignificant for extreme rain events because it occurs too slowly compared to the rainfall rate and other uncertainties.

• ok, so the software I was adviced to use, takes a DEM as well as information on sealing, soil type, topography and land use as inputdata. Then, it gives me for each cell and time intervall a runoff coefficieant. Since it takes 4 parameters and spatial and temporal variability into consideration would you consider that a "higher order" relationship? A blanket approach would be to say that I have for each cell the same coefficient which doesn't change in time? And then I could do another simulation with SWAT and compare the results of all three model approaches. Did I get you right?
– DGIS
Commented Oct 30, 2019 at 21:54
• Oh and I also assume that soil infiltration will be insignificant actually but at this stage I think at this point its primarely about learning how develop a proper research design that could be applied to real sience.
– DGIS
Commented Oct 30, 2019 at 21:57
• seems that the parameters you described show spatial but not temporal variability. What changes with time and how is the change calculated? I personally wouldn't consider it a higher order relationship unless there was change with time or with precipitation rate. Good idea to compare to SWAT (either model might be inaccurate though) Commented Oct 31, 2019 at 0:30