Fire damage: charred patches, glowing embers near 1.
Wear and destruction: cracks, missing patches, broken windows, potholes.
Snow cover on upward-facing surfaces (roofs, ledges, roads outside tyre tracks).
Rain: darker albedo, glossy surfaces, puddles on roads.
Weather and wear, each 0..1 (default 0). Hooks for a shared weather layer: set them per material group on CityOptions.weather, or per building with
City.setBuildingWeather; the larger of the two applies. All are shader uniforms or a small data texture: changing them costs nothing.