<p>This paper demonstrates that strategic application of ‘decentralised urban green infrastructure’ (DUGI) can alleviate flash flooding through adequate surface run off reduction using a combination of linear and dispersed components based on the perviousness of the sub catchments. As a first step, an assessment framework comprising of the following three steps is introduced: Site selection; DUGI implementation strategy; Impact analysis (hydrological, socio-economic, etc.). This is successfully implemented at a catchment site with medium-to-high risk of surface water flooding in Southampton, a coastal city in the south of England. We report peak runoff reductions of 10–75% in individual sub-catchments following effective DUGI implementation, compared to the business-as-usual scenario. Strategically placed DUGI is found to harmonise the link flows in the immediate aftermath of a rain event, demonstrating their potential for flash flood alleviation in the risk-prone lower sub-catchments of the study site. Socio-economic impact analysis demonstrated that certain intangible costs, potentially saved from flood risk alleviation as a result of DUGI implementation, outweighed the capital costs in setting up the DUGIs. Coordination and communication of the implementation plan with the key stakeholders is considered a crucial factor for maximising the flood alleviation potentials through strategic DUGI intervention, specifically in space-constrained cities with limited scope for retrofitting or regeneration.</p> Graphical abstract <p></p>