Quantifying the Impact of Climate Change on Peak Stream Discharge for Watersheds of Varying Sizes in the Coastal Plain of Virginia

Civil infrastructure systems have traditionally been designed assuming stationarity in precipitation. However, climate change is making this assumption invalid, affecting both existing infrastructure designed assuming stationarity and the design of new infrastructure. Although many studies have analyzed potential increases in precipitation due to climate change, fewer have attempted to translate these changes into the impact of stream discharge in a way that could be incorporated into infrastructure design. Therefore, this study aimed to assess the potential impact of climate change on both rainfall and peak discharge to aid in bridge and road infrastructure design. Results showed that the median increase in model-derived rainfall intensity across the selected rainfall stations in Virginia was 10%–30% for the midcentury (centered on 2045) and 10%–40% for the end of the century (centered on 2085), with the higher increase for the Representative Concentration Pathway 8.5 (RCP8.5) scenario compared with the RCP4.5 scenario. A regression analysis was performed to relate peak discharge to watershed size for midcentury and end-of-century periods for the study area. In terms of peak discharge, smaller watersheds ($<25{\mathrm{km}}^2$) had a percent increase for a given return period that was independent of the watershed size. Considering both RCP4.5 and RCP8.5 scenarios, for a 100-year return period, the increase was 39% and 49%, respectively, for the midcentury periods and 36% and 52%, respectively, for the end-of-century periods. For larger watersheds ($>25{\mathrm{km}}^2$), the increase in peak discharge decreased as the watershed size increased, suggesting a dampening effect for larger watersheds in this coastal plain region of Virginia. For a watershed size of $\mathrm{1,700}{\mathrm{km}}^2$, the largest watershed included in the analysis, the percent increase in peak discharge for a 100-year return period was 14% and 39% during the midcentury, and 16% and 40% at the end of the century, for the two emission scenarios. These findings and the general methodology used in the study can aid transportation and water resources engineers in incorporating changing rainfall impacts into assessing current infrastructure and designing future infrastructure. They can also help to prioritize resources for more costly hydraulic analyses of potentially vulnerable infrastructure.

The study aims to understand better how climate change will impact future precipitation and how this change in precipitation will impact peak discharge for watersheds of various sizes. Using Virginia as a study region, the median increase in precipitation intensity was found to be between 10% and 30% for the midcentury and 10%–40% for the end of the century across the state. Smaller watersheds ($<25{\mathrm{km}}^2$) had an increase in peak discharge for a given return period that was independent of the watershed size. In comparison, larger watersheds ($>25{\mathrm{km}}^2$) had an increase in peak discharge, but the percent increase in peak discharge decreased as the size of the watershed increased, especially for the RCP8.5 emission scenario. Regression equations were developed to provide a first approximation of peak discharge based on the watershed area, the emission scenario, and the return period to aid decision-makers in the region when including climate change impacts when assessing existing or designing new hydraulic structures.