Investigating Impacts of Projected Climate Change on Flood Hazard in Urban Areas Located Along River Channels

Abstract

Hurricane Florence, which generated flooding in the Carolinas in 2018, caused an estimated $38 - 50 billion in property damage (Rocco, 2018). There is scientific data supporting the hypothesis that the intensity of natural disasters is increasing, as are the associated damages. The goal of this study is to evaluate how increases in monsoon intensity might influence the risk of potential flooding in urban areas located along river channels. To accomplish this, an ArcMap model was created for a 588,800 acres (920 square miles) watershed located approximately 90% in Pima County and about 10% in Santa Cruz County. The river of interest in the watershed, Rillito Wash, runs through a residential area. The watershed was generated using the automated geospatial watershed assessment (AGWA) tool in ArcMap. Data from three storm events, 1996, 2008 and 2010, were used to simulate the watershed in ArcMap via the kinematic runoff and erosion (KINEROS 2) model. Present and future precipitation data entered into the model were based on a 24-hour, 100-year event. KINEROS2 returns flowrates from which water level depths can be determined. An assessment conducted on three different data sets obtained from various storms with the same occurrence interval provides indications of expected flood risk. Watershed calibration was successful, and the calibration accuracy was surprising. There were limitations when using the AGWA and KINEROS2 models. KINEROS2 is better suited for smaller watersheds, less than 97 miles2, to control precipitation over planes, and AGWA uses one soil moisture over the entire watershed, enhancing or mitigating the affects in specific regions. Initial soil moisture throughout the watershed affected the flood hazard. The greatest affects are seen in less intense storms such as IDF data decreased by 10% and current IDF data.