biome_percipitation

uniform int biome_precipitation;

This uniform identifies what type of precipitation occurs in this biome: 0 is no precipitation, 1 is rain, 2 is snow. The following defines can also be used: PPT_NONE, PPT_RAIN, PPT_SNOW. For more information on biomes, see the Minecraft Wiki.

This uniform functions similarly to the value available for custom unfiroms in Optifine, however Iris additionally provides them as standard uniforms.