Short answer: usually yes—but not automatically. A domed top is better at shedding rain than a flat lid, so it reduces standing water, pooling around seams, and drips that can run into the can when the lid sags. In a city, that matters because flat lids often collect water in shallow puddles. That water can seep through rust spots, welds, hinge gaps, or a slightly warped rim. A dome encourages water to roll off before it finds those weak points.
But the shape alone doesn't keep rain out. Most urban trash cans don't have a simple lift-off lid; they have side openings, push flaps, swing doors, or hooded mouths. If rain can blow sideways into the opening, a domed top won't help much. Wind-driven rain is the real test. A flat lid with a good overhang, tight seal, sloped surface, and drainage channels can outperform a poorly designed dome with an exposed mouth.
Also, openings need to stay usable. A dome that covers the opening too much can make it awkward to throw away coffee cups or fast-food bags. That's why many city bins use a domed hood over a side opening or a curved top with a rain lip. The best designs combine three things: a slope or dome to shed water, an overhang to protect the opening, and drainage holes or channels so any water that gets in can escape. Liners and internal baskets help too, because soggy trash is heavier and smellier.
Flat lids are not doomed. A flat lid can work well if it's sealed, slightly pitched, and paired with a recessed opening or rain shield. The problem is that flat surfaces are less forgiving. If the lid is dented, the gasket is worn, or the opening faces the prevailing wind, water will find a way in. Domed lids are more forgiving because they don't let water sit on top in the first place.
So, do domed tops really keep rain out better? In general, yes—especially in open, windy, rainy places. But the dome is only one part of the system. A well-sealed flat lid can beat a bad dome, and a good dome with an exposed opening will still let rain in. If you're choosing a public trash can, look at the opening, overhang, drainage, and maintenance access before you judge the lid by its shape alone. The dome helps; it just isn't a rainproof guarantee.