Sponge basin could help prevent flooding

A devastating flash flood in a region between Nepal and Tibet has captured global attention, mirroring similar events that have occurred in various parts of Brazil over recent years. These extreme weather occurrences are increasingly frequent and intense, driven primarily by global warming. While urban areas require adaptation, Brazilian urban landscape architect Cecília Herzog emphasizes the need to consider the entire hydrological process and adapt watersheds.

Rather than merely adapting cities to absorb and reuse rainwater, Herzog proposes the implementation of a "sponge watershed" model. Drawing inspiration from the "sponge city" concept pioneered by Chinese architect Yu Kongjian, this approach focuses on managing river courses directly rather than altering cities to cope with rainfall.

Herzog explains that managing watersheds as a planning unit requires starting at the headwaters and extending all the way to the mouth, encompassing the entire watershed, not just the river itself and its immediate surroundings.

According to Juliana Baladelli Ribeiro, a nature-based solutions expert and Boticário Group Foundation manager, slowing runoff within the river system is more effective than concentrating solely on the effects of rainfall in urban areas. The excess rainfall causing disruptions in cities typically does not originate there; it accumulates throughout the watershed and flows into the rivers.

To implement this, Ribeiro advocates for protecting headwaters in the upper parts of watersheds and restoring forests along riverbanks to maintain natural vegetation connectivity across the landscape.

Ribeiro acknowledges that watershed interventions do not negate the need for city-level actions. Proper drainage systems must be established to handle the increased water volumes during heavy rains. Spaces such as urban parks, rain gardens, and wet squares can help retain water and allow it to gradually return to its natural flow, according to Ribeiro.

Experts agree that integrated watershed management based on the "sponge watershed" concept has proven successful in various countries. However, solutions must be tailored to local conditions, as simply importing models would not suffice. Cecília Herzog stresses the importance of co-creating resilient solutions with local knowledge to transform vulnerable landscapes into more resilient ones.