Patos Lagoon – Macromicro

Patos Lagoon, located in the southern Brazilian state of Rio Grande do Sul, is the largest coastal lagoon in South America. Its vast expanse has historically supported the region’s economic development, providing a rich ecosystem for fisheries, fertile lands for agriculture, and a vital crossroads for maritime trade through the port of Rio Grande. Today, however, this immense and complex hydrological system has become one of the continent’s most vulnerable areas in the face of climate change impacts, transforming water from a driver of prosperity into a constant threat.

The territory is defined by a long and narrow sandy peninsula that separates the lagoon’s fresh and brackish waters from the Atlantic Ocean. Along its shores lie densely populated cities and industrial settlements, often built at very low elevations or even at the same level as the water. In recent years, sea-level rise at the estuary’s mouth and, above all, the increasing frequency and intensity of extreme rainfall across the watershed have disrupted the lagoon’s delicate hydrological balance, accelerating shoreline erosion and heightening the risk of prolonged flooding.

The catastrophic floods of spring 2024 revealed the fragility of this region with dramatic clarity: torrential rains swelled the tributary rivers, pushing the lagoon’s water level far beyond historical thresholds. With its outflow toward the ocean obstructed and driven inland by strong southern winds, the water overtopped embankments, inundating large areas of cities such as Pelotas, Rio Grande, and São Lourenço do Sul. As climate anomalies intensify, extreme events of this magnitude may occur more frequently, threatening hundreds of thousands of residents and paralyzing critical infrastructure.

To address these growing risks, authorities and researchers are rethinking territorial management: efforts are underway to modernize outdated drainage and pumping systems, strengthen shoreline defenses, and implement more sophisticated early warning networks. The challenge for Rio Grande do Sul—whose economy and social identity revolve around this vast body of water—will be to develop structural and nature-based adaptation strategies capable of protecting communities while preserving the ecosystem in a future marked by increasing climate instability.