The German topped the list, calculated according to results over the past 12 months, ahead of Swiss rider Steve Guerdat.
Ahlmann stands on 2585 points with Guerdat on 2365. There are 130 rankings points available for a World Cup Grand Prix victory.
While the top two stayed the same, there was a change just behind, with Dutchman Gerco Schröder jumping from eighth last month to third this time around.
Schröder's rise is largely thanks to a fourth-placed finish at the Hong Kong Grand Prix, third at the World Cup Grand Prix in Leipzig and fifth in the Basel Grand Prix.
Britain's Nick Skelton, swaps places with Schröder and drops to eighth, having competed in just three classes - in Wellington - last month.
The biggest mover is Maikel van der Vleuten of the Netherlands, who leaps up 16 places to 30th after his team and individual wins at the Grand Prix in Al Ain.
- Sports & Recreation