Please note that I said "non-Essaential reasons"
I am a firm believer of "less magic is better" when trying to justify the making of a world. As a result, I try to find mundane, real-world physics reasons why the world would be as it is.
After a quick brainstorming session based on the oceanic currents and prevailing winds chart provided in Eidolon sourcebook for Emer, I tried to match the provided data with the climate patterns provided in MA4 and had to change a handful of things :
- SW Emer (Uj) is mostly OK if you assume that the southwesternmost peninsula is a mountain range of significant height. Most rainfall occurs on the western and southern coastline, and the interior, especially at higher elevations (Charn Plateau, eastern desert) suffers from prevailing winds that have "dried up".
- SE Emer (Rael, Onar, Khum-Kaan, Namar-Tol) is basically OK. I would add a prevailing wind pattern running from the Circular Sea along the southern coast of Rulaash, then bending northwards to sweep coastal Lygaar, skirting the inland. This would provide much moisture on the coastal area but much less inland, creating savannah-like vegetation. An interesting side effect is that Namar-Tol is noticeably cooler on its eastern side than on its western side.
- NE Emer is changed : first, the prevailing winds go northwards in Tai-Emer and in the Sea of Tears - these are the same winds as in Khum-Kaan, but the winds are drier because most humidity was dropped in Lygaar and on the southern slopes of the Peligris. This explains why southern Tai-Emer is very dry.
Second, the current and prevailing winds that run along the eastern Silaar coast, the Sel archipel and Praeten are reversed : instead of coming from the northwest and circling clockwise, they come from the southeast and go counterclockwise, running along the northern Haestran coastline, including Danarchis. Since the cold currents coming from the north on both sides of Jaiman still exist, this creates very intense weather conditions in the Melurian Straits (the current running southwards along Urulan is bent eastward towards Orbis, and the one coming along Ly-Aran curls back up into the Elysean Bay). This also matches the fact that there is a very sharp difference between climates along the northern edge of Emer and climates in southern Jaiman north of the Melurian heights.
- Likewise, the current running along the western Haestran coastline is reversed : it runs along the northern side of the Komaren, then bends northwards towards Danarchis and the Barrier Isles. Another arm of this current curls back around Barellis and Rashelles and meets the cold flow that comes from the north along the southern edge of the Barrier Isles. The interesting thing is that the wind patterns come from the northwest (Thesmoq) and hit the Haestran coastline along its mountain edge, dropping huge amounts of precipitation on the western side of the Gold Mountains and the northern Scorpion Ridge. The interior is drier.
The remaining problem is the inland Haestran climate, which is much cooler than everything around. The easiest way to meet this behaviour is to make Haestra into a plateau that slopes down from the Spine of Emer towards the sea. It is probably quite high, perhaps 2000ft or more. Stroane and eastern Miir would be the coldest areas. Vornia would be warmer because of its slightly lower mean altitude and influx from the Bay of Izar. Bodlea would be fairly cool, but wet because there is no mountain range to stop cloud-born humidity incoming from the sea. The Sea of Votania would likely be a collapse basin, with a nice altitude drop all along the Stroane coast which would be quite steep most of the time.
Note that I did not include Coriolis-induced wind patterns.
I will try to scrounge up the old MA1 maps to see if they provide more global trends.
