Blue Green Infrastructure (BGI) has emerged as robust measures for managing stormwater, offering benefits such as reducing urban flooding, promoting groundwater recharge etc. However, recent studies highlight that these facilities often underperform during climate-induced intense rainfall events in urban areas. In addition, implementation of BGI in urban catchments is often challenging because many there are many different options and design considerations for BGI and commonly a lack of space. Therefore, there is greater need that 1) a more structured approach is applied during the selection, distribution and design of different BGI alternatives in urban catchments, and 2) facilities like bioretention are adapted to handle these intense events more effectively. The licentiate titled “Blue-green infrastructure for climate resilience - quantifying stormwater hydrology impact” focuses on advancing the understanding of design and implementation of Blue-Green Infrastructure (BGI) in catchment scale, with the explicit focus on design improvement of bioretention facilities by using modelling tools. 

The licentiate has an overall 3 scientific articles. Paper 1 develops different BGI alternatives by considering spatial scale and design complexity in urban environments having diverse land use characteristics. The study quantifies to what extent hydrological outcomes such as surface runoff, infiltration, and pre-development flow varies with different BGI alternatives in these catchments. One of the results obtained from this study showed that in residential areas, which offer more spaces for planned integration of stormwater control measures, engineered BGI alternatives showed the highest potential to reduce flooding while in densely built inner city catchments the more natural BGIs showed higher potential. Paper 2 evaluates the reliability of the SWMM model used in Paper 1 for bioretention modeling by comparing calibrated and uncalibrated models with observed data. The findings confirm that SWMM is a reliable tool for modeling bioretention systems, accurately capturing key hydrologic processes, especially after calibration. While first study is about how different BGIs can be combined to achieve various hydrologic benefits at catchments, the third study is about effect of different bioretention design variable in managing stormwater hydrology at local scale. Paper 3, by using the calibrated model in Paper 2, explores 54 different biofilter design options, to assess the impact of key design factors—ponding depth, hydraulic conductivity, filter media fraction and storage connection —on different stormwater performance indicators. In general, this study showed that a balanced approach is required while designing bioretention as there are trade-offs between optimizing for volume reduction during daily events (e.g. higher filter media fraction) and reducing overflow occurrences during high-intensity events (e.g. lower filter media fraction, high hydraulic conductivity).

Overall, this thesis provides valuable insights and practical recommendations for enhancing the effectiveness of BGI in urban catchments for climate adaptive stormwater management solutions, and with explicit focus on designing bioretention systems.