I have 30 years daily rainfall data. How can i calculate the mean monthly runoff, minimum monthly runoff and maximum monthly runoff with the available rainfall data using GIS?
I would like to use SCS curve number method for run off computation.
Presume you have no snowmelt and no baseflow to worry about? Curve numbers only give respones to rainfall events.
OTBE there are models that do this. Often/mainly out of USDA. Suggest AGWA for openers. Try SWAT.
This is a rather old question, however you might still like an aswer to it.
I don't think you can use a GIS-only approach for your problem. What you need is a precipitation / runoff model. If you want to use the SCS curve number method for runoff calculation, I could recommend the following model to you:
For this model you will need at least a DEM, a stream network, precipitation data, land use classes and discharge measurements for calibration. It runs on various time scales and has been used in many different locations worldwide. It's freeware / open-source and has a decent support community online.
There are a lot of similar models that perform tasks like this. In case you're looking for something different, please edit your question in order to let us know.