(CNN) Floods displaced more than 150,000 people in Argentina, Brazil, Uruguay and Paraguay this week after days of torrential rains blamed on El Niño.
In Paraguay, which was the hardest-hit, more than 130,000 people were evacuated. In Alberdi city, residents fled as walls holding back water appeared on the verge of collapse, authorities said.
Argentina had 20,000 evacuees, half of them from Concordia city, which President Mauricio Macri will visit Sunday.
At least 38 cities were inundated in Brazil, with Rio Grande do Sul state the most affected, authorities said.
Uruguay had at least 9,000 evacuees, mostly in Salto.
El Niño is a warming of the eastern Pacific Ocean and affects global climate fluctuations. The phenomenon is especially strong this year, and may lead to the worst effects in 15 years, scientists say.
A strong El Niño heats up the atmosphere and changes circulation patterns around the globe, especially the jet stream over the Pacific. With the changes, it dumps more rains and intense storms over the western U.S. and west coast of South America.