Climate - Rainforests?

[davoush]

(Sorry if this question is posted in the wrong forum, I wasn't sure where best to post it.)

I am currently trying to work out a climate map for my world in as 'realistic' a way as possible (in other words using the processes that seem to the determine the earth's climate as a guide). However, a few questions occurred to me regarding the placement of rainforests.

According to most climate maps, the rainforest in South America seems to be restricted to the West Coast-side, and becomes Savannah-like nearer the East Coast. Is there any reason or geographical feature which prevents the 'tropical rainforest' from covering the whole of the equatorial area there? (I've read that in East Africa the rainforest is limited because of the high altitudes in the East).

Thanks!

[Gamerprinter]

The mountains are both a barrier and the cause for the rain to fall in the first place. The winds that carry the rain clouds come form one direction or the other (depending on where it's located on Earth). As the rain clouds are forced upward against the mountain face, they cool and the water vapor collects and falls from the clouds as precipitation. All the water content of the clouds are exhausted in rain with no water content left once the clouds cross the barrier of mountains.

Look at Kauai the furthest west island of the Hawaiian chain. The north and west side is green and tropical from the rainfall, yet the south and east sides of Kawaii is almost a desert with practically no rainfall whatsoever - and this is an island 40 miles across, half tropical, half desert due to the same geologic/climatological reason.

[eViLe_eAgLe]

On a side note, this has been on my mind for a while, but is there an example of the opposite effect of the rainshadow? To where the extremely wet area is to the east, compared to it being on the West?

[waldronate]

On a side note, this has been on my mind for a while, but is there an example of the opposite effect of the rainshadow? To where the extremely wet area is to the east, compared to it being on the West?

It's the prevailing winds that determine the which side of mountains a rain shadow will be. if the wind is from the east, the rain shadow will be on the opposite side, to the west. If the rain is from the west, the rain shadown will be, again, on the opposite side, this time on the east.

[eViLe_eAgLe]

It's the prevailing winds that determine the which side of mountains a rain shadow will be. if the wind is from the east, the rain shadow will be on the opposite side, to the west. If the rain is from the west, the rain shadown will be, again, on the opposite side, this time on the east.

Thank you, that's what I thought.

[davoush]

Thanks, I understand that 'rainshadows' can cause areas of dryness next to seemingly wet areas. However, the amazon 'tropical rainforest climate' does not seem to reach the East coast, even though there are no mountains blocking it in that direction (at least according to the koppen climate map on Wikipedia). In comparison, the map shows the whole of Austronesia, as expected, being 'tropical rainforest'.

[Gamerprinter]

Well consider the distance of the east coast from the Andes. The dumping of rain occurs at the mountains, not a 1000 miles before the mountains (like the distance from the mountains to the east coast). So while the effective rainforest area is east of the Andes, it is only immediately east of the Andes, not everything east of the Andes...

[davoush]

Thanks. In relation to my own map, I have a range of mountains which runs North-South right through the equator, with roughly equal amount of land either side of the mountain range. Since a large part of the range falls within the ITCZ (so the prevailing winds would be calm), where would the rain be most likely to fall (and thus produce rainforest)?

Edit: Afterthought; since the air around the ITCZ is calm, and rainfall seems to be pretty uniform in those latitudes (except for mountainous areas), I imagine on my map it might end up being two large dry patches on both sides of the mountain, and then rainforest on both sides as the land flattens?

[waldronate]

Geometry of the terrain will make a huge difference for equatorial things. I suggest searching for and examining a Koppen climate classification map for insipration.

[Gamerprinter]

Whichever side of the mountains the prevailing wind is coming from will be where the rainforest exists. If the wind is from the west, the rainforest is west of the mountains.