Need data on rainfall intensity and sandy clay permeability calculation in North Goa

My query is how to calculate rainfall intensity when you know average annual rainfall.

We are harvesting roof top water as part of a project and further the water will be treated and used for domestic purposes.
As per my calculation I need the intensity of rainfall, but I tried browsing but what I could finally get is the Average Annual Rainfall of
North Goa is around 3000-3250mm.

The soil type is:
Top surface Strata : Brownish Sandy clay.
Underlain Strata : Brownish laterite Gravels

For few soil Texture i could find the permeability factors but not for sandy clay. How can the same be calculated?

Average permeability for different soil textures in cm/hour
Sand                    5.0
Sandy loam        2.5
Loam                   1.3
Clay loam           0.8
Silty clay              0.25
Clay                      0.05
Ranjini V