Make rim braking efficient
I would look for contamination of the pads and wheels. Oil residue from the roadway may have gotten on to the brake surfaces. Try to clean them with a mild cleaner. I typically use the blue glass cleaner. If the brake pads are several years old they may be getting dried out or glazed. You can try to resurface the rubber face of the pad with a file. The improvement if any tends to be short lived. Avoid sanding the pads with sandpaper as the grit can imbed in the pad and damage the rim. Also consider some performance oriented brake pads. The pad materials have different characteristics such as wet stopping, dry stopping, durability and price.