Like numerous other cities, Beijing and Copenhagen are experiencing more frequent urban flooding due to increased impervious cover and climate change. Consequently, huge investments are foreseen to maintain resilience. Analyses of planning documents and interviews with key stakeholders reveal that in their climate resilience strategies both cities do employ alternative approaches based on on-site retention-detention of stormwater runoff. However, when there is an emergency situation with heavy downpours, both cities rely heavily on conventional concepts involving deep tunnels for rapid discharge. The applied alternative solutions tend to be more engineering-based, like underground tanks in Beijing and detention-discharge plazas in Copenhagen. More nature-based solutions lag behind. Both cities are simultaneously targeting specific additional sustainability goals. Nevertheless, other potential goals seem to be neglected, like livability improvements in Beijing and biodiversity support and water footprint reduction in Copenhagen. The main barriers for implementing more nature-based solutions with greater sustainability potentials were a combination of time constraints caused by external political pressures for rapid problem solving, lack of routines for the innovation and documentation of solutions for dense urban areas, and insufficient multi-sectorial collaboration. These factors limit the propagation of alternative solutions and tip the balance of current investments towards a conventional approach.