Vulnerability of Hampton Roads, Virginia to Storm-Surge Flooding and Sea-Level Rise

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<ul><li><p>Vulnerability of Hampton Roads, Virginiato Storm-Surge Flooding and Sea-Level Rise</p><p>LISA R. KLEINOSKY, BRENT YARNALw and ANN FISHERCenter for Integrated Regional Assessment, The Pennsylvania State University, University Park,</p><p>PA, 16802, USA</p><p>(Received: 1 February 2005; accepted: 8 January 2006)</p><p>Abstract. Sea-level rise will increase the area covered by hurricane storm surges in coastalzones. This research assesses how patterns of vulnerability to storm-surge ooding could</p><p>change in Hampton Roads, Virginia as a result of sea-level rise. Physical exposure to storm-surge ooding is mapped for all categories of hurricane, both for present sea level and forfuture sea-level rise. The locations of vulnerable sub-populations are determined through an</p><p>analysis and mapping of socioeconomic characteristics commonly associated with vulnera-bility to environmental hazards and are compared to the ood-risk exposure zones. Scenariosare also developed that address uncertainties regarding future population growth and distri-</p><p>bution. The results show that hurricane storm surge presents a signicant hazard to HamptonRoads today, especially to the most vulnerable inhabitants of the region. In addition, futuresea-level rise, population growth, and poorly planned development will increase the risk ofstorm-surge ooding, especially for vulnerable people, thus suggesting that planning should</p><p>steer development away from low-lying coastal and near-coastal zones.</p><p>Key words: storm-surge ooding, hurricanes, sea-level rise, climate change, coastal hazards,coastal development, vulnerability</p><p>1. Introduction</p><p>Global sea-level rise is a major impact of human-induced climate change.The Intergovernmental Panel on Climate Change (IPCC) projects a globalsea-level rise of 48 cm over the next century, with an uncertainty range of988 cm, resulting from thermal expansion of the oceans and glacial melt(Church and Gregory, 2001). Sea-level rise will be worse in regions experi-encing subsidence. For example, Najjar et al. (2000) estimated that thecoastline of the United States Mid-Atlantic region is sinking at the rate ofabout 2 mm per year due to crustal warping (Walker and Coleman, 1987),sediment compaction (Psuty, 1992; Nicholls and Leatherman, 1996), andgroundwater withdrawal (Leatherman et al., 1995). Because shorelines with</p><p>w Author for correspondence: Phone: +1-814-863-4894; Fax: +1-814-863-7943;</p><p>Natural Hazards (2007) 40:4370 Springer 2006DOI 10.1007/s11069-006-0004-z</p></li><li><p>shallow slopes, such as those found in the mid-Atlantic region, can be dra-matically aected by even small increases in sea level, low-lying coastalareas such as deltas, coastal plains, and barrier islands are especially vul-nerable to sea-level rise (McLean and Tsyban, 2001).</p><p>Although sea-level rise will aect coastal areas in many ways (McLeanand Tsyban, 2001), this study investigates one particular impact: more-severe storm-surge ooding (Flather and Khandker, 1993). When a hurri-cane passes over or near a coastal margin, it generates a storm surge thatcauses ooding in low-lying areas. Hurricane storm surge results from theinteraction of atmospheric pressure depression and wind shear stress onthe waters surface. That is, the intense low-pressure center of a hurricanelifts the water beneath it, forming a dome of water that the storms windspush onshore. The advancing surge combines with the normal tide to cre-ate the hurricane storm tide. In addition, superimposed on the storm tideare wind-driven waves. Together, storm tide and wind-driven waves cancause severe ooding in coastal regions (National Hurricane Center,2005a).</p><p>The degree of ooding depends on hurricane intensity, uctuations inastronomically generated tides, slope of the continental shelf, and rainfallamounts over land. More intense storms produce higher storm surges, andooding is worst when surges coincide with high tides. Flood severity isalso a function of water depth oshore and of location relative to the eyeof the hurricane. When shallow water is present oshore, the mound ofwater that builds as the storm approaches cannot disperse. In the North-ern Hemisphere, locations in the right-front quadrant of a hurricane expe-rience strong onshore winds and consequently the highest surge heights(National Hurricane Center, 2005a). It is important to note that tropicalcyclones can generate intense rainfall ahead of the storm, which can some-times cause more ooding than the surge. Worst-case ood scenarios occurwhen a river storm wave owing downslope combines with a storm tidemoving onshore.</p><p>The eect of a higher sea level is to move the eective shoreline land-ward, closer to existing structures and settlements. In addition, Tsybanet al. (1990) stress that sea-level rise, by increasing the mean sea-level heightupon which surges build, could by itself allow storm surges to increase inheight and thus penetrate farther inland (see also Wu et al., 2002; McInneset al., 2003; Gonnert, 2004). Thus, holding all other factors constant, ahurricane occurring at a higher sea level would cause more damage than ahurricane of equal intensity at present sea level simply because the shore-line would be further inland than today and storm surge would build froma higher base. Nicholls et al. (1999) estimate that an addition of 50 cm toglobal sea level would cause a sixfold increase in the number of peopleooded in a typical year by hurricane storm surges.</p><p>LISA R. KLEINOSKY ET AL.44</p></li><li><p>Because coastal zones are at risk of greater storm surges with sea-levelrise, it is important to analyze the vulnerability of crucial coastal zones tothe increased storm-surge ooding associated with sea-level rise. Vulnera-bility is a much-discussed concept in research on the human dimensions ofglobal environmental change (e.g., Clark et al., 2000; IHDP, 2001; Kasper-son and Kasperson, 2001). The IPCC denes vulnerability as the extentto which a natural or social system is susceptible to sustaining damagefrom climate change (Schneider and Sarukhan, 2001). It is a function ofthe exposure of the system to climatic hazards, the sensitivity of the systemto changes in climate, and the adaptive capacity of the system to moderateor oset the potential damages of climate change. The focus on vulnerabil-ity shifts attention from simple assessments of stressors (e.g., sea-level riseand hurricanes) and their impacts to an examination of the system understress and its ability to respond to the stress (Luers et al., 2003).</p><p>This paper uses Hampton Roads, a ten-city, sixteen-county area insoutheastern Virginia, as a case study to understand how sea-level rise willincrease the vulnerability of people and infrastructure to hurricane storm-surge ooding over the next century. It builds on vulnerability assessmentmethods developed by NOAA Coastal Services Center (1999), Cutter et al.(2000), and especially Wu et al. (2002). The study area of Hampton Roadsis described in Section 2. Section 3 assesses the overall vulnerability ofHampton Roads to present-day storm-surge ooding by determining itsexposure to storm surges from hurricanes of various intensities and bymapping social vulnerability throughout the region. In Section 4, the paperdescribes how exposure could change by mapping the expansion of storm-surge ood-risk zones with various sea-level rise scenarios. Section 5addresses uncertainty in future population growth and in population distri-bution patterns and provides credible future impact scenarios for the year2100. The paper concludes with the implications of this research for localplanners.</p><p>2. Study Area</p><p>2.1. REGIONAL CONTEXT</p><p>The metropolitan region of Hampton Roads consists of 10 cities and sixcounties in southeastern Virginia (Figure 1). The area covers approxi-mately 7500 km2 of low-lying coastal land at the conuence of the James,Nansemond, and Elizabeth Rivers with the Chesapeake Bay. It is home tomore than 1.5 million people and has intensely developed, densely popu-lated coastal frontages, making it an appropriate case study for under-standing the potential impacts of storm-surge ooding and sea-level rise.Understanding the vulnerability of the region to storm-surge ooding is</p><p>VULNERABILITY OF HAMPTON ROADS 45</p></li><li><p>also crucial for economic and national security reasons. Hampton Roads isnot only the second largest port on the East Coast and the center of Vir-ginias tourism industry, but also the location of the largest naval base inthe world.</p><p>Hampton Roads is composed of three geographic subdivisions (Hamp-ton Roads Planning District Commission, 2003). South Hampton Roadscontains the cities of Chesapeake, Norfolk, Portsmouth, Suolk, and Vir-ginia Beach. The Rural Southeastern Virginia region consists of the city ofFranklin and the counties of Isle of Wight, Southampton, and Surry. Thesubdivision known as the Peninsula is comprised of the cities of Hampton,Newport News, Poquoson, and Williamsburg as well as the counties of</p><p>Figure 1. Location of Hampton Roads, Virginia.</p><p>LISA R. KLEINOSKY ET AL.46</p></li><li><p>James City, York, and Gloucester. The northeastern quarter of SouthHampton Roads and the southern portion of the Peninsula are over-whelmingly urban, while the rest of the study area is dominated by for-ested and agricultural land. A few hundred square kilometers of wetlandsare also present, as well as a small amount of open water and barren land(Figure 2).</p><p>Hampton Roads is located entirely within the low-lying physiographicregion known as the Atlantic Coastal Plain (Bingham, 1991). Elevationrises slightly across the study area from east to west (Figure 3). Hampton</p><p>Figure 2. Land-cover distribution of Hampton Roads.</p><p>VULNERABILITY OF HAMPTON ROADS 47</p></li><li><p>Roads reaches a maximum elevation of about 54 m above sea level alongits western edge, while most of the eastern half of the study area is lessthan ten meters above sea level. Nearly all of South Hampton Roads is atelevations of less than 5 m, including heavily developed sections of Nor-folk, Portsmouth, Virginia Beach, and Chesapeake. The Great DismalSwamp, which occupies about 1500 km2 of southern Virginia and northernNorth Carolina, is also less than 5 m above sea level. Additionally, theeastern edge of the Peninsula is characterized by a bowl-shaped depressionknown as the Chesapeake Bay Impact Crater. The crater was createdabout 35 million years ago by a comet or meteorite (Powars, 2000). Todayit encompasses most of the cities of Poquoson and Hampton, as well asthe eastern portions of Gloucester and York counties.</p><p>The cities of South Hampton Roads have a very shallow slope andtherefore are particularly vulnerable to sea-level rise. It is important tonote Hampton Roads is still experiencing subsidence in reaction to theunloading of the Laurentide ice sheet from the North American continent,</p><p>Figure 3. Elevation of study area above sea level.</p><p>LISA R. KLEINOSKY ET AL.48</p></li><li><p>which exacerbates local sea-level rise. Data from the Sewells Point tidemonitoring station indicates that sea level has risen by 41 cm in HamptonRoads between 1933 and 2003 (Boon, 2004).</p><p>2.2. HURRICANE HISTORY</p><p>The Virginia Department of Emergency Management (2005) reports that25 hurricanes aected Hampton Roads in the 20th century, including ahurricane in 1933 that set the record high storm tide and storm surge forNorfolk (Table I). Most recently, in September 2003, Hurricane Isabel pro-duced an equal storm tide of approximately 2.4 m and a storm surge ofroughly 1.5 m (Boon, 2004).</p><p>The Chesapeake Bay-Potomac Hurricane of 1933 is an example of howeven a moderate hurricane can produce major storm-surge ooding.Although the storm was only a weakening Category 2 hurricane when itmade landfall, storm surge was particularly devastating due to an unusualstorm trajectory and associated pressure pattern (Cobb, 1991). A high-pressure system over Maine prevented the storm from curving to thenortheast; after making landfall near Nags Head, North Carolina, thestorm continued to move northwest directly over the Hampton Roadsarea. As the storm moved north of Norfolk, it encouraged the develop-ment of a high-breaking wave, known as a tidal bore, which moved up theChesapeake Bay. In Norfolk, bay and ocean waters combined to producea storm tide of 2.4 m above mean low water, but storm tides may havebeen as much as 3.7 m above mean low water in some narrow estuaries.</p><p>Although incomplete records exist, at least 15 hurricanes aected thearea in the 17th, 18th, and 19th centuries. Intensity and tide height forsome of those hurricanes might have far surpassed those of recent record.A hurricane in September 1667 might have had a storm tide that was1.7 m higher than that of the record 1933 hurricane. Moreover, a particu-larly violent hurricane in October 1749 may have had a storm tide approx-imately 2.3 m higher than the record storm tide (Virginia Department ofEmergency Management, 2005). Thus, storm-surge ooding is a signicanthazard in Hampton Roads.</p><p>Table I. Hurricanes striking Hampton Roads with signicant storm tides and storm surges.</p><p>Date Name Estimated storm tide (m) Estimated storm surge (m)</p><p>1667 Unnamed 4.1 ?</p><p>1749 Unnamed 4.7 ?</p><p>1933 Chesapeake Bay-Potomac 2.4 1.8</p><p>2003 Isabel 2.4 1.5</p><p>VULNERABILITY OF HAMPTON ROADS 49</p></li><li><p>3. Present Vulnerability to Storm-Surge Flooding</p><p>3.1. EXPOSURE</p><p>3.1.1. Methods</p><p>The study used output from the SLOSH (Sea, Lake, and Overland Surgesfrom Hurricanes) model of the National Hurricane Center to evaluate thepossible exposure of Hampton Roads to storm-surge ooding. TheSLOSH model was originally meant to make real-time forecasts for surgeheights of approaching hurricanes (Jelesnianski et al., 1992). When themodel is used to estimate surge from an actual hurricane, results are gener-ally accurate within plus or minus 20% (National Hurricane Center,2005a). In recent years, the SLOSH model also has been used to determinewhich coastal areas are at risk of storm-surge ooding (Jelesnianski et al.,1992; see Wu et al., 2002). SLOSH model output has become important tothe development of coastal hurricane evacuation plans (National HurricaneCenter, 2005a).</p><p>For SLOSH modeling, the National Hurricane Center has divided theUnited States coasts into a series of 38 elliptical basins, and each basin isdivided into hundreds of grid cells. To determine at-risk areas for stormsurge, the National Hurricane Center runs a series of hundreds of hypo-thetical hurricanes of various SarSimpson categories, forward speeds,landfall directions, and landfall locations for each basin. At the end ofeach model run, an envelope of water is generated, reecting the maximumsurge height obtained by each grid cell (National Weather Service, 2005).After all of the model runs, a composite called the Maximum Envelopes ofWater (MEOW) is formed. The MEOW contains the maximum surgeheight in a cell for a given hurricane category and storm track. A furthercomposite called a MOM (Maximum of MEOWs) represents the maxi-mum surge height in each cell for hurricanes of a particular SarSimpsoncategory, regardless of storm trac...</p></li></ul>