We are adding rain next, it will affect both crops and critters/fish right at the start.
(Black Rain for testing)
There will be 3 rain levels:
low: water all outdoors tiles up to 24
medium: water all outdoors tiles up to 32
heavy: max out water tile content to 40 (this will overwater most crops)
Rain can water tiles above the crop water limit unlike the watering can and sprinklers, so get those flood resistance perks on your crops if you like keeping them permanently watered on sprinklers. Most of the time crops will be able to tank the overwatering with their damage buffers, but several heavy rains in a row will start damaging them.
Rain will affect critter and fish spawns too, here some of the planned changes
Fish that become more active on rain
mackerel, bass, catfish, trout
Critters that become less active outside on rain
flies, butterfly, dragonfly, moth, spider, poofah, faeriedragon, wasps, bees
Critters that become more active outside on rain
ants, roaches, frogs, slimes, slugs, snails
Critters that become more active in caves during rain
flies, dragonfly, moth, spider, ants, roaches, faeriedragon