Vitor Martinez, a 25-year-old musician and community organizer, lives in Porto Alegre, the capital of Rio Grande do Sul — the southernmost state in Brazil. Martinez’s neighborhood borders Guaíba Lake, around which Porto Alegre’s main attractions are clustered. On a sunny, 80-degree Fahrenheit day in late March, people biked, ran, and strolled along the promenade that surrounds the lake. Shoppers flocked to a mall on the bottom floor of a brand new Hilton DoubleTree hotel in the middle of the neighborhood. More than 23,000 people from all over the world gathered a few miles away at a conference center near the city’s historic downtown to talk about the future of technology and business in South America. That version of Porto Alegre — manicured and prosperous — is a distant memory now, Martinez said.
Last Friday, after a week of unrelenting…