Biome fix: Temperature

So biomes presently leave something to be desired. They're scattered about with no regard to geographic location, and it's perfectly okay to find a frozen waste directly next to (or surrounding!) a desert.

Modeling temperature (and precipitation) would fix this, as well as add some neat features.

• Biomes would be appropriately large, and based on terrain elevation.
• Precipitation in the form of rain and snow would allow for lakes above and below "sea level", as well as snow drifts (avalanches?).
• Rivers would flow naturally, pool in lakes and create oceans. (requires a fix in the fluid physics)
• Temperature would have an effect on growth rate of plants
• Temperature would vary according to season
• Temperature could have an adverse affect on the player (too hot/cold)

However...I think it would require that the world be generated entirely in advance (is this such a bad thing)? A very large world in Dwarf Fortress currently takes me a few minutes to generate...but it also generates a population and simulates the passing of millenia, so I'm not sure how good that benchmark is.

Your thoughts?