Safe-to-Fail Climate Change Adaptation Strategies for Phoenix Roadways under Extreme Precipitation

As climate change continues to shift global climatological patterns with respect to temperatures and precipitation, builtinfrastructure is becoming more vulnerable. In the US Southwest, climate models predict hotter and drier... [ view full abstract ]

As climate change continues to shift global climatological patterns with respect to temperatures and precipitation, builtinfrastructure is becoming more vulnerable. In the US Southwest, climate models predict hotter and drier climates, and in some scenarios, an increased frequency of extreme precipitation events and urban flooding. Roads in highly urbanized desert cities like Phoenix, Arizona are particularly vulnerable to extreme precipitation events given the intensity and frequency of events. Due to the inherent uncertainty of extreme weather predictions, assessing future flooding damages and adapting road infrastructure to manage them remains a difficult task. Currently, there is limited work focused on assessing climate change impacts on roadway infrastructure, and the few urban flooding studies largely overlook the US Southwest. More importantly, there is no systematic way to assess the effectiveness of roadway flooding solutions to manage unforeseen events into the future. In order to be useful over a wide range of potential future threats, flooding solutions themselves must be developed such that their failure to manage water does not compromise the rest of the urban system, e.g., designed according to a paradigm of “safe-to-fail”. Traditional “fail-safe” systems provide robust protection to infrastructures when the risks are accurately predicted and inflicted within the range of a designed safety factor. However, if the system receives a shock that is not foreseen with the historical data, it may lead to a shutdown of the entire system and thus cause an unmanageable and cascading failure. Moreover, the risks and uncertainties faced by urban infrastructures are becoming so great due to climate change that the “fail-safe” paradigm is quickly becoming economically and technically unsustainable. Coupling spatially-explicit flooding forecasts with site- and context-specific “safe-to-fail” strategies can help infrastructure managers make decisions with high uncertainties coming from non-stationary and the unpredictable characteristics of extreme weather events. In this study, we link climate and urban drainage models to predict future roadway vulnerability using the EPA Storm Water Management Model (SWMM) and assess potential flooding solutions based on multiple “safe-to-fail” criteria for Phoenix. The simulation results indicate increased flooding intensity at drainage junctions are the most vulnerable type of road. From the literature, we score 31 separate roadway flooding solutions based on the roadway types that they impact and 19 “fail-safe” and “safe-to-fail” criteria they may possess. The “safe-to-fail” scorecard and a multi-criteria decision analysis (MCDA) analytic hierarchy process (AHP) algorithm are used to rank flooding solutions for Phoenix. Different weight schemes for “safe-to-fail” and “fail-safe” infrastructure characteristics give various flooding solutions in MCDA, which implies that MCDA provides a framework for city governments to make decisions considering various factors that are not easily captured by climate models and/or

engineering design criteria for more “safe-to-fail” infrastructure development.