[GRASSLIST:5307] Getting rainfall data from DEMs?

[Antonio]

Hi.

I just finished obtaining my DEM of an area of Central Italy and I now
need to compute rainfall data. In this area there are 5 pluviometers at
elevation from 620m a.s.l. ---> 900m a.s.l.
The area is about 80Km^2 and the mean elevation is around 1050m a.s.l.
I've obtained a rainfall ditribution with s.surf.idw npoints=1;
s.surf.idw npoints=5; s.surf.rst (with non tunning).
The last two give similar results (maybe due to the fact that I only
have 5 meteo stations) even though I still have to learn how to tune
s.surf.rst parameters.
However I was thinking if it would have been polite to compute rainfall
starting from the DEM maybe using r.mapcalc. Obviuosly this means that I
would necessarily need a linear regression which interpolates the 5
stations and then would have to feed the DEM + linear interpolation to
r.mapcalc.
Is there anyone who has tried similar problems with r.mapcalc?
All this is done in consideration that having only 5 meteo stations with
large area (and what's more is that they are in mountainous region) does
not give good results.

Thanks and greetings.