The Development of Climate Change Indicator Maps to Improve Estimates of the Design Storm Across Virginia

Daniel Wilusz, CFM, PhD, Project Engineer, Dewberry

Joel Plummer, CFM, GIS Developer, Dewberry

Mathew Mampara, PE, Vice President, Dewberry

Siamak Esfandiary, PE, PhD, Associate Vice President, Dewberry

The design storm is a fundamental parameter for risk and vulnerability assessment of urban infrastructure.  It is traditionally determined from historic observations.  There is however growing recognition that design storm calculations based on historical data may misrepresent flood risk due to future climate change.  To determine if and when the design storm calculation should consider climate change, the U.S. Federal Highway Administration (FWHA) recommends calculating a Climate Change Indicator (CCI) at potential project sites (Kilgore et al, 2016).  The CCI is a dimensionless measure of the projected future change in the design storm relative to the uncertainty in estimates of historic rainfall.  When the CCI is greater than an action threshold of 0.8, the FWHA recommends using projected climate change scenarios to help determine the design storm.  The goals of this study were to calculate the CCI across Virginia, identify and analyze major regional trends, and produce statewide CCI maps. The USGS Geo Data Portal was used to download downscaled LOCA climate change projections from 14 GCMS at 1/16th degree resolution.  The CCI was calculated in each Virginia county for two emissions scenarios (RCP 4.5 and 8.5) and two future periods (mid- and late-century).  We found that rainfall during the 100-year 24-hour design storm event is projected to increase an average of 26% between now and late-century under the high emissions scenario.  Although CCI values vary significantly across counties and between GCMs, the average CCI is significantly greater than the action threshold in most counties.  Thus, the CCI maps reinforce the need to consider climate change in design storm calculations across most of Virginia.

Author Bio

Dano Wilusz has nearly 15 years of experience in water engineering, climate resiliency, and public sector project management. He leads flood modeling projects and risk assessments for local, state, and federal clients. From 2006-2012, Dano was a Foreign Affairs Officer at the U.S. Department of State, where he helped develop a U.S. government-wide Global Water Strategy. He has a PhD in water resources engineering from Johns Hopkins University and a Master of Policy from the University of California at Berkeley.