I've raced 110cc karts in the rain over 5 years, I'd say it was around 60/30 with the 10 in the middle being damp or drying...
I don't think Blancpain races at any deserts? I could be wrong but they race in America and that place has rain, I've been there and seen it for myself...
Europe, obviosly...
And even in Blancpain Asia, the race I went to at Sepang was damp and it did rain a bit during the race too.
UK kart tracks, (for some reason), are constantly wet and you rarely get a weekend where it's completely dry the whole way through, unless you're lucky.
Just look at Jenson, Lewis and Anthony, all pretty handy in the wet conditions, it's because during a race weekend you never know what you could face. The racing club I was in, and that a lot of the UK/European racing drivers have competed in at some point, used to run wet races with slicks. Don't like it, don't turn up. It taught you some incredibly valuable skills though.
I for one like racing in the rain, I even shared a trophy with two other guys for coming 2nd in an endurance race at Rye House which was an absolute downpour from start to finish, on slicks!
First time I've ever had team mates trying to get me to slow down from the pits...
I love it and hope we do more changing day/night/weather races here at RD, as someone said, we as a community have been asking for this to be implemented well in sim racing for a while now.