Bioretention Performance Under Tropical Conditions: Experimental Analysis of Hydrological Controls and Design Implications

ABSTRACT Nature‐based solutions have proven effective in mitigating urban drainage problems, including floods and inundations. However, most research has focused on temperate climates, highlighting the need for studies in tropical regions, where data availability remains limited. The efficiency of runoff retention in bioretention systems is closely related to rainfall distribution. In tropical climates, precipitation tends to be more intense and concentrated, potentially influencing soil moisture, infiltration capacity, and overall system performance. This study evaluates the runoff retention efficiency of a bioretention cell located in a tropical urban area of Brazil. Over a 5‐month period, data from 50 natural rainfall events were collected and analysed to determine the system's water balance. Retention efficiency was assessed for four ponding depths. The results revealed that retention efficiency increased significantly with higher ponding depths, confirming the system's high performance at various storage levels. Approximately 78% of the monitored events achieved full (100%) retention efficiency at a ponding depth of 45 cm. The bioretention cell infiltrated up to 4.74 m of runoff, with an average infiltration layer of 0.78 m. Utilisation rates indicated that the system operated as designed, maintaining consistent infiltration capacity without evidence of clogging after 2 years of operation. Statistical analyses showed that runoff retention efficiency was mainly correlated with rainfall return period (−0.62), followed by total precipitation depth (−0.62), precipitation duration (0.46), average precipitation intensity (−0.44), and maximum precipitation intensity (−0.44). These findings enhance understanding of bioretention performance under tropical rainfall regimes and offer practical guidance for the design and implementation of sustainable urban drainage systems in similar climates.