With precariously built homes and makeshift infrastructure, the city of Rio de Janeiro’s hillside poor neighborhoods, or favelas, are commonly the hardest hit during the summer’s heavy rain season. Residents say the government can do more to both flood-proof buildings here and warn people ahead of time.

Statistics collected by the Rio de Janeiro Budget People’s Forum, which monitors the local budget, showed that the city cut almost 80 percent of its spending on flood control in the last four years.

“This reduction shows authorities don’t prepare for these heavy rains,” said Luiz Mario Behnken, an economist with the forum. “Every year they are surprised by these rains.”

Rita de Cássia Smith, a community leader in Rocinha, one of the city’s largest favelas, pointed to faulty sewage and drainage systems, and the lack of trash collection, as some of the causes of the destruction.

“In Rio de Janeiro, we have tragedies and deaths every year,” Ms. Smith said. “This happens because all the building work is poorly done, so when the rain comes it knocks it all down.”

As she watched her street become a river rapid, Ms. Smith said she spent the night scared to death. Just down the road, dozens of residents spent the day trying to use ropes to lift more than 10 motorcycles that had fallen down a hillside.

Mauricio Ehrlich, an engineer and geotechnician at the Federal University of Rio de Janeiro, said there had been investments in the city’s drainage system in recent decades, but not enough.