Land use regulations assessment on the impacts on urban river systems in Florianópolis, southern Brazil

Rapid urbanization is transforming small watersheds, amplifying flood risks and challenging sustainable water management worldwide. This study investigates how regulatory-driven urban expansion affects the hydrology of the Meio River watershed (4 km²) in Florianópolis, southern Brazil – a coastal, rapidly urbanizing area where the municipal Master Plan lacks explicit hydrological criteria. The watershed was chosen for its combination of intense urban growth and hydrological vulnerability, making it representative of similar coastal cities in Brazil and other regions globally. Using land-use and land-cover data from 2009, 2019, and a future scenario derived from the Master Plan, hydrological responses were simulated with a hydraulic-hydrological model for the period 1997–2020, focusing on peak and base flows as indicators of watershed resilience. Results show that base flows remain stable, while projected urban growth could increase peak flows by up to 25 %, signaling heightened flood risk and pressures on urban water systems. Limitations include the focus on a single watershed and the absence of water quality measurements, emphasizing the need for integrated and comparative studies. Future research should explore multiple watersheds, incorporate climate change scenarios, and evaluate stormwater management strategies, including Sustainable Drainage Systems, Water-Sensitive Urban Design, and Sponge City approaches. By linking empirical hydrological modeling with urban planning analysis, this research provides actionable insights for resilience-oriented urban policies, offering guidance to coastal cities worldwide facing similar hydroclimatic pressures. • Current urban planning increases peak flows by over 24 % in a small urban watershed. • Master Plan of Florianópolis lacks hydrological criteria for zoning decisions. • Land use scenarios modeled using HEC-HMS and high-resolution satellite images. • Study shows urban densification is a key driver of runoff intensification. • Results support integrating SuDS and WSUD into local planning regulations.