Dear Mr. Bertram,
As far as i know the classification of different driving rain regions is based on the yearly amount of precipitation and the surrounding area. Maybe you can check it with the englisch version of the DWD climate atlas.
http://www.dwd.de/bvbw/appmanager/bvbw/ ... 8654463391
Furthermore the classification is, in accordance to the german standard 4108-3 :2012:
1) yearly sum of precipitation < 600mm/a and a sheltered location
2) 600 mm/a < yearly sum of precipitation < 800mm/a and an exposed location
3) yearly sum of precipitation > 800mm/a and an exposed location (e.g. coast line or the alps)
Hope this helps,
Kind regards,
Tobias Schöner