What is the natural disaster that befalls the family in "We're very poor"?

A storm came unexpectedly, “in great waves of water,” without giving the family time to bring any of the harvest inside. All they could do was sit under their roof watching the water. On top of these misfortunes, we are told that the cow that the father had given to the narrator’s twelve-year-old sister Tacha for her birthday has been swept away by the river.