I have added an evaporation cycle following condensation that will stabilise water vapour in the atmosphere of a planet with liquid water at a level of:
Atmospheric Pressure * (Hydro Extent / 100) * 0.01 atm. For Earth that would be 1 * (70/100) * 0.01 atm = 0.007 atm
That atm * 20 is the % of the planet's surface that loses water. For Earth that would be 0.14%
As the water vapour is removed from the atmosphere, it will replenish from the surface water.
I'm confused about the hydro/atmo water balance. Is the 0.14% above a rate, or is it an equilibrium level? (I would vote for equilibrium level.) If it's an equilibrium level, then how does that square with what I think I read in the rules change, which is that 20% hydro requires 1 atmo of water (which seems way to high, given that Earth has 75% hydro without having 3.75 atmospheres of water vapor
Just thinking aloud here on the fly:
- there are 3 main reservoirs for water: atmo, hydro, and ice caps
- ideal gas law says Pressure = constant * density * temp. So as someone above mentioned, pressure should be proportional to temperature (in degrees kelvin
- hmmm - this (pressure scales with temperature) should actually apply to all gasses. So maybe the terrarforming pressures should be measured in "standard" atmospheres, then the "actual" pressure should be standard pressure * (temp/300 kelvin).
- can use Earth data to calibrate numerical constants, i.e. plug 75% in for hydro and pick constants so actual Earth atmo pressure comes out (think this is mentioned above).
- below ice cap temperature, all hydro should go to water.
- need a constant conversion factor that converts from 1 atmo of water vapor to x% surface coverage. This means you'd need to dump a LOT of water in the atmosphere to get any change in hydro (so atmo is essentially controlled by hydro %)
- Maybe hydro system shouldn't be controlled by terraforming at all (since it takes so much material). Either you take what you get (without being able to change), or one is able to drop asteroids/comets (whole new game mechanic that probably isn't worth it), or hydro percent change costs 10s of thousands (or even millions) times as much as gases when done through terrarforming.