Flood Hazard Mapping with Nonstationary Extreme Values under Changing Climate for Cagayan De Oro River Basin

Flood hazard mapping is vital for forecasting, early warning, and planning for flood disasters. Flood inundation modeling and simulation is conducted to describe the spatial extent and distribution of flood waters over time, for a given hydrologic design flood. Engineers use the ‘return period’ or probability of occurrence as the basis for designing flood management schemes or control structures to protect vulnerable communities. However, with the changing climate and urbanization, the flood frequency analysis should be performed in the framework of nonstationary extreme value analysis rather than treating the river flow process as stationary in time which is the usual practice. This chapter applies flood hazard mapping with nonstationary extreme values under a changing climate for the Cagayan de Oro River Basin which was devastated during Typhoon Sendong in December 2011. This chapter presents several policy implications: first, for the engineering practice of DPWH to utilize nonstationary extreme value analysis over stationary analysis. Second, policies and decisions should be based on actual trends or shifts from observed data rather than just relying on climate change design parameters and projections that depend on scenarios, storylines, and global climate models that may not be appropriate for Philippine climate conditions. A strategic policy that should be adopted is piecewise engineering or optimal project sequencing and staging that considers the evolutionary nature and uncertainty of climate change.