The six basic influencing parameters for the catch ratio as defined in Equation 3 are (1) building geometry (including environment topology), (2) position on the building envelope, (3) wind speed U, (4) wind direction ?, (5) horizontal rainfall intensity Rh, and (6) raindrop size distribution fh. The turbulent dispersion of raindrops is neglected in the present study. (Blocken, B. and Carmelie, J, 2001, Spatial and temporal distribution of driving rain on buildings: numerical simulation and experimental verification)