  Current approaches to design flood-sensitive infrastructure typically assume
a stationary rainfall distribution and neglect many uncertainties. These
assumptions are inconsistent with observations that suggest intensifying
extreme precipitation events and the uncertainties surrounding projections of
the coupled natural-human systems. Here we demonstrate a safety factor approach
to designing urban infrastructure in a changing climate. Our results show that
assuming climate stationarity and neglecting deep uncertainties can drastically
underestimate flood risks and lead to poor infrastructure design choices. We
find that climate uncertainty dominates the socioeconomic and engineering
uncertainties that impact the hydraulic reliability in stormwater drainage
systems. We quantify the upfront costs needed to achieve higher hydraulic
reliability and robustness against the deep uncertainties surrounding
projections of rainfall, surface runoff characteristics, and infrastructure
lifetime. Depending on the location, we find that adding safety factors of 1.4
to 1.7 to the standard stormwater pipe design guidance produces robust
performance to the considered deep uncertainties. The insights gained from this
study highlight the need for updating traditional engineering design strategies
to improve infrastructure reliability under socioeconomic and environmental
changes.
