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.
Rainfall Tab Screenshot

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.