Old Dominion University ODU Digital Commons CCPO Publications Center for Coastal Physical Oceanography 2018 The ncrI eased Risk of Flooding in Hampton Roads: On the Roles of Sea Level Rise, Storm Surges, Hurricanes, and the Gulf Stream Tal Ezer Old Dominion University, [email protected] Follow this and additional works at: https://digitalcommons.odu.edu/ccpo_pubs Part of the Climate Commons, and the Environmental Sciences Commons Repository Citation Ezer, Tal, "The ncrI eased Risk of Flooding in Hampton Roads: On the Roles of Sea Level Rise, Storm Surges, Hurricanes, and the Gulf Stream" (2018). CCPO Publications. 250. https://digitalcommons.odu.edu/ccpo_pubs/250 Original Publication Citation Ezer, T. (2018). The increased risk of flooding in Hampton Roads: On the roles of sea level rise, storm surges, hurricanes, and the Gulf Stream. Marine Technology Society Journal, 52(2), 34-44. doi:10.4031/MTSJ.52.2.6 This Article is brought to you for free and open access by the Center for Coastal Physical Oceanography at ODU Digital Commons. It has been accepted for inclusion in CCPO Publications by an authorized administrator of ODU Digital Commons. For more information, please contact [email protected]. PAPER The Increased Risk of Flooding in Hampton Roads: On the Roles of Sea Level Rise, Storm Surges, Hurricanes, and the Gulf Stream AUTHOR ABSTRACT Tal Ezer The impact of sea level rise on increased tidal flooding and storm surges in the Center for Coastal Hampton Roads region is demonstrated, using ~90 years of water level measure- Physical Oceanography, ments in Norfolk, Virginia. Impacts from offshore storms and variations in the Old Dominion University Gulf Stream (GS) are discussed as well, in view of recent studies that show that weakening in the flow of the GS (daily, interannually, or decadal) is often related to elevated water levels along the U.S. East Coast. Two types of impacts Introduction from hurricanes on flooding in Hampton Roads are demonstrated here. One type he National Water Level Obser- is when a hurricane like Isabel (2003) makes a landfall and passes near the vation Network (NWLON) operated Chesapeake Bay, causing a large but short-term (hours to a day) storm surge. T The second type is when Atlantic hurricanes like Joaquin (2015) or Matthew by National Oceanic and Atmospheric Administration (NOAA) (https:// (2016) stay offshore for a relatively long time, disrupting the flow of the GS tidesandcurrents.noaa.gov/nwlon. and leading to a longer period (several days or more) of higher water levels html) provides an essential source of and tidal flooding. Analysis of the statistics of tropical storms and hurricanes data to study both long-term sea level since the 1970s shows that, since the 1990s, there is an increase in the number rise (SLR) and short-term water level of days when intense hurricanes (Categories 3–5) are found in the subtropical variations and storm surges. These western North Atlantic. The observed Florida Current transport since the 1980s tide gauges data show that the rate often shows less transport and elevated water levels when tropical storms and of local SLR along some stretches hurricanes pass near the GS. Better understanding of the remote influence of of the U.S. East Coast (around the the GS and offshore storms will improve future prediction of flooding and help Chesapeake Bay and the Mid- mitigation and adaptation efforts. Atlantic coast in particular) is much Keywords: flooding, sea level, hurricanes, Gulf Stream faster than the global SLR; this is mostly due to land subsidence (Boon, 2012; Mitchell et al., 2013; Ezer & Norfolk, VA, on the southern side in Norfolk from ~90 years of tide Atkinson, 2015; Karegar et al., 2017), of the Chesapeake Bay (see Figure 1 for gauge records is ~4.6 mm/year (Ezer, with a potential recent acceleration its location), is a city that is already 2013), but the rate is increasing (i.e., in SLR due to climatic slowdown of battling an acceleration in flood- SLR is accelerating), so that the SLR ocean circulation (Boon, 2012; ing frequency and intensity (Ezer & over the last 30 years is ~5.9 mm/ Sallenger et al., 2012; Ezer & Corlett, Atkinson, 2014, 2015; Sweet & Park, year compared to ~3.5 mm/year in 2012). Variations in wind patterns 2014). This study will focus on this the previous 30 years (Ezer & Atkin- and atmospheric pressure (affecting sea city as an example that can apply to son, 2015); the recent local SLR is sig- level through the inverted barometer other coastal cities and communities nificantly larger than the global SLR effect) can significantly contribute to in the Hampton Roads area, where obtained from satellite altimeter data, coastal sea level variability along the efforts toward the development of ~3.2 mm/year (Ezer, 2013). SLR can U.S. East Coast (Piecuch et al., 2016; options for adaptation, mitigation, also escalate the damage from hurri- Woodworthetal.,2016),butthese and resilience to SLR have already canes, tropical storms, and nor’easters. effects are outside the scope of this been started (Considine et al., 2017; When high sea level today is added to study. Yusuf & St. John, 2017). Local SLR storm surges, weaker storms today 34 Marine Technology Society Journal FIGURE 1 and rivers (e.g., the Elizabeth River fl Mean sea surface height (SSH) from AVISO satellite altimeters are shown in color (in meters) and the Lafayette River cause ooding and the location of the GS is indicated by white arrows. The location of the FC measurement in Norfolk). across the Florida Strait is indicated by a red line, and the location of Norfolk, VA, is indicated by The connection between the flow a black star. The tracks of several storms, discussed in the paper, are shown with markers of the GS and sea level along the U.S. representing the location of the eye of the storm every 6 h. East Coast has been recognized early on from observations (Blaha, 1984) and models (Ezer, 2001), though due to the relatively short observed record of the GS identifying a persis- tent long-term trend in the GS trans- port is challenging (Ezer, 2015). Somewhat surprisingly, however, is the fact that this connection may be detected on a wide range of scales. On long-term decadal variability scales, for example, a potential climate-related slowdown of the Atlantic Meridional Overturning Circulation (AMOC) (Sallenger et al., 2012; McCarthy et al., 2012; Ezer et al., 2013; Ezer, 2013, 2015; Smeed et al., 2013; Srokosz & Bryden, 2015) may relate to acceler- would cause as much flooding as today, water level of a storm surge ated SLR and increased risk of flood- much stronger past storms that hap- would be expected to be ~40 cm higher, ing along the U.S. East Coast (Boon, pened when sea level was lower; this and many more streets would be 2012; Ezer & Corlett, 2012; Sallenger effect will be demonstrated here. flooded. In addition to the impact of et al., 2012; Mitchell et al., 2013; Yin There are some indications that warmer storm surges, Atlantic storms can also & Goddard, 2013; Goddard et al., ocean waters may be related to an have an indirect impact on the coast 2015; Ezer & Atkinson, 2014, 2015; increase in the potential destructive- by modifying ocean currents and caus- Sweet & Park, 2014). On short-term ness of Atlantic hurricanes and tropi- ing more mixing. If such storms af- time scales, there is now more evidence cal storms over the past 30 years fect the Gulf Stream (GS), coastal sea from data and models that even daily (Emanuel, 2005). However, with level could be affected as well (Ezer variations in the GS can cause var- strong interannual and decadal vari- & Atkinson, 2014, 2017; Ezer et al., iations in coastal sea level (Park & ability, finding a persistent trend in 2017), and this indirect impact will Sweet, 2015; Ezer, 2016; Ezer & storm activities over the past century be further investigated here. An addi- Atkinson, 2017; Ezer et al., 2017; or predicting future changes in hurri- tional indirect impact on coastal Wdowinski et al., 2016), including cane activities over the next century water level and coastal erosion is due unexpected “clear-day” flooding (i.e., are challenging (Knutson & Tuleya, to large swell from remote storms that unusual tidal flooding with no appar- 2004; Vecchi & Knutson, 2008; Vecchi can create wave runup (Dean et al., ent storm or local weather events). et al., 2008; Bender et al., 2010). De- 2005). Impact from wave runup can, These variations in the GS can be spite the difficultyofpredictingthe for example, increase coastal erosion due to natural variability and insta- changes in the frequency and inten- of barrier islands and coasts along the bility (Baringer & Larsen, 2001; sity of future storms, assessing the Atlantic Ocean (Haluska, 2017). Meinen et al., 2010) or variations in impact of SLR on storm surge is quite However, flooding in the Hampton the wind pattern (Zhao & Johns, straightforward—if a storm with the Roads is not affected that much by 2014), including impacts from tropical same intensity and track that hit waves and is mostly due to high storms and hurricanes passing near the Norfolk 90 years ago were to come water levels in the Chesapeake Bay GS (Oey et al., 2007; Kourafalou March/April/ 2018 Volume 52 Number 2 35 et al., 2016; Ezer & Atkinson, 2017). stormsurge)arearound±5–10 cm. website (http://www.aoml.noaa.gov/ Note that, on short-term scales, an im- As a reference water level, the mean phod/floridacurrent/); see the location portant mechanism transferring large- higher high water (MHHW) from in Figure 1. Estimated errors are ±1.6 Sv scale oceanic signals onto the shelf the datum centered on 1992 is used.