Yes—in most cases, a well-designed domed top does help keep rain out of urban trash bins, but it is not a perfect umbrella. The shape matters. A rounded or sloped top sheds water before it can collect on the lid, and a hood or overhang can protect the opening. If the opening is recessed, faces sideways, or sits under the dome, rain is much less likely to fall straight into the bin.
That said, domed tops work best when the whole design supports them. A dome with a wide gap around the opening, a shallow drip edge, or blocked drainage can still let water in. Wind-driven rain is the biggest exception: rain can blow sideways under the hood or drip from the rim onto the opening. Condensation and wet waste can also create moisture inside, even if direct rainfall is limited.
For cities, the practical benefits are real. A good domed-top bin can keep waste drier, reduce leachate at the bottom, make bags lighter, cut odors, and help with cleaner emptying. It can also make the bin less appealing to pests and less messy in freezing weather. But the design has to be sensible: a tight-fitting dome, a protected side opening, clear drainage, and regular maintenance all matter more than the dome shape alone.
So the short answer is yes, domed tops help—especially when they are combined with smart opening design and good drainage. They are a useful rain-protection feature for outdoor urban trash bins, but they should not be treated as completely rainproof.