BACKGROUND:
I have been working on a game called Rise: The Vieneo Province.
Vieneo is a terrestrial moon (all details can be found here) but we have an atmospheric composition we arrived on from another question:
N, SO2, O, and trace CH4, NH3, H2O, Ne, N2, CO... Nitrogen 98.4% 2589 mb Sulfur Dioxide 1.0% 26 mb and Oxygen 0.6% 16 mb
We have a perpetually overcast sky and a lot of rain in the game (like tropical environments on Earth) ... I am being told that we need more water vapor in the air because of the small hydrosphere of 13%. But with an average global temperature of 7.7 Celsius we are too cold.
The middle of the cloud layer averages about 9.25 km above sea level and are about 2.5 km thick on average.
QUESTION:
What is the minimum increase in water vapor percentage and global temperature that will make the the described cloud layer and tropical precipitation work? I would like to remove the SO2 altogether in favor of the water vapor explaining the persistent cloud layer.
Thanks in advance!