Evaluating the Potential Impacts from Climate Change on Compound Flooding at a Coastal Watershed

Coastal watersheds are exposed to compound flooding during tropical cyclones, as they are subjected to the joint occurrence of peak inland flow, heavy precipitation, and storm surge. Meanwhile, these factors are all affected by climate change. A comprehensive evaluation is needed to investigate the potential impacts of future climate change on the compound flooding caused by tropical cyclones. The objective of this study is to develop an integrated modeling framework for exploring how the flooding induced by Hurricane Harvey would have been different under projected future climate conditions. The high-resolution modeling framework consists of a regional Earth system model (Regional Community Earth System Model, R-CESM), a hydrological model (Distributed Hydrology Soil Vegetation Model, DHSVM), and a hydrodynamic model (Two-dimensional Runoff Inundation Toolkit for Operational Needs, TRITON). A case study is carried out at a coastal watershed near Houston (the Clear Creek watershed) under climatically modified Hurricane Harvey scenarios. First, an ensemble of R-CESM downscaling simulations of future Hurricane Harvey under Representative Concentration Pathway 8.5 (RCP8.5) are conducted. Considering that the R-CESM simulated cyclone tracks can affect the flood results in the small watershed significantly, different approaches will be tested to identify the best option for best representing the modifications of Hurricane Harvey precipitation under future climate change. In addition, the approach limitations are to be explored. By driving the hydrologic-hydraulic model with the changed precipitation and sea level rise, the flood inundation in the watershedincluding extent, depth, and durationcan be evaluated. Final results from this study can be used to improve our understanding of coastal flood risks under a changing climate, and thus support future water coastal adaptation planning.