In the context of global change, urban drainage infrastructures must be planned considering future challenges such as new climate change and urban growth scenarios. Large cities require master plans to properly rank and schedule infrastructure development. The flood mitigation measures proposed in previous plans must be revised and updated to address future urban challenges with special regard to climate scenarios. Regarding risk assessment, there is no linear relationship between an increase in rainfall and an increase in risk value. For risk management, the relationship between an increase in rainfall increase and the budget for mitigation measures is even more complex. To investigate this relationship and the economic impact of the aforementioned update, a new plan should be elaborated. Urban drainage master plans have been developed in Barcelona city for the last 50 years. In terms of rainfall, the impact of climate change has been established to be an increase of 7–26% at peak intensity, depending on rainfall duration. The Integral Drainage Master Plan of Barcelona (PDISBA) addresses these new challenges. The modification of rainfall scenario planning and the typology of mitigation measures result in an important rise in investment budget, infrastructure life cycle, and operation and maintenance budgets for said infrastructure. The total cost of the planned measures outlined in the PDISBA has risen to €1.442 million, nearly double that of the previous plan developed in 2006.