The Rainfall Map Tab.
This tab is where the average rainfall of a tile is determined. In
conjunction with the drainage tab, this map helps to determine what
biomes are present.

The Zoom Level control will zoom in all maps associated with this tab.
Zooming in will change the size of the edit brush so that the edit
reticle cursor always shows the extent of the brushes effect.
The ‘Percent Below Desert Threshold’ slider
controls the level of rainfall below which desert will occur.
The ‘Percent Below Grassland Threshold’ slider
controls the level of rainfall below which the grassland biome types
will occur. Any rain between this threshold and the desert threshold
will be grass.
The ‘Percent Below Forest Threshold’ slider
controls the level of rainfall below which forest will be created.
Above the grassland threshold and below this threshold, there should be
enough rainfall for forest biomes depending on temperature and
drainage. Above this threshold will also likely have forest, but as
much of the rainfall will occur on the windward side of mountain
biomes, this threshold was needed to ensure that areas of the highest
rain would occur below the mountains as well as in the mountains.
The ‘Wind Direction’ control governs the direction
of the prevailing winds over the map. This wind gathers moisture from
the oceans and drops it on to land.
The ‘Rain Shadow Map Weight’ slider controls the
amount of the rain shadow map is added to the final rainfall map.
The noise map control is the same as on other tabs.
The ‘weight’ slider governs how much of this noise
map is added to the final map.
The ‘Feature Size’ slider adjusts the size of the
features in the noise field. The higher the number, the smaller the
features get. If that seems awkward, the slider is actually controlling
‘frequency’ directly, and size indirectly as a
result of frequency.
The ‘Smoothness’ slider adjusts the smoothness of
the noise field.
The ‘Generate New’ buttons scramble the noise
inputs to create a new noise field.
You may also click and drag on the noise fields to adjust their
position in case you want a certain feature to appear in a specific
location.