I wanted some time ago to make a mod that had 6 seasons, with a different caravan in each.
I would like seasons to be imported to the raws.
First, you would have the year raw itself. Let's suppose we wanted to have a 360 day year, with each day taking up 1500 frames of game time.
[YEAR:360:1500]
Next, you would have the months. Let's do 18 months of 20 days each. I'll just use random stone names with no bearing on the real calendar.
[GRANITE:1:20]
[DACITE:21:40]
[LIMESTONE:41:60]
[MICROCLINE:61:80]
[ORTHOCLASE:81:100]
[SANDSTONE:101:120]
[SILTSTONE:121:140]
[MUDSTONE:141:160]
[CLAYSTONE:161:180]
[GABBRO:181:200]
[SLATE:201:220]
[SHALE:221:240]
[OBSIDIAN:241:260]
[MARBLE:261:280]
[HEMATITE: 281:300]
[MALACHITE:301:320]
[TETRAHEDRITE:321:340]
[LIMONITE:341:360]
That rounds out the year.
Now we've got to do the seasons. Unfortunately, 18 isn't divisible by 4, so we're clearly not dealing with a temperate climate! I'll deal with how this relates to climate itself- freezing and evaporating-later, but for now:
[SEASON: SPRING]
[GRANITE]
[DACITE]
[LIMESTONE]
[MICROCLINE]
[ORTHOCLASE]
[SANDSTONE]
[SEASON: SUMMER]
[SILTSTONE]
[MUDSTONE]
[CLAYSTONE]
[GABBRO]
[SLATE]
[SHALE]
[SEASON: FALL]
[OBSIDIAN]
[MARBLE]
[HEMATITE]
[MALACHITE]
[TETRAHEDRITE]
[LIMONITE]
Note that if you change the season raws, you'll also have to go into the entity raws to change the way caravans work.