Northern Virginia Hazard Mitigation Plan Update Executive Summary ........................................................................................................................ 1 Chapter 1: Introduction ................................................................................................................... 4 I. Background ...................................................................................................................... 4 A. Disaster Mitigation Act of 2000 ................................................................................... 5 II. Overview of Hazard Mitigation Planning ........................................................................ 6 III. Purpose of Plan ................................................................................................................ 7 IV. Authority .......................................................................................................................... 7 V. Summary of Plan Contents .............................................................................................. 8 Chapter 2: Planning Process ......................................................................................................... 10 I. Mitigation Advisory Committee .................................................................................... 11 II. Public Involvement and Citizen Input ........................................................................... 12 III. Incorporation of Existing Plans and Studies .................................................................. 14 Chapter 3: Regional Information ................................................................................................. 15 I. Northern Virginia Overview .......................................................................................... 15 A. Planning Region ......................................................................................................... 15 1. County Profiles ....................................................................................................... 17 2. City Profiles ............................................................................................................ 19 3. Town Profiles .......................................................................................................... 21 B. Geography, Hydrology, and Climate .......................................................................... 24 1. Geography ............................................................................................................... 24 2. Hydrology ............................................................................................................... 26 3. Climate .................................................................................................................... 27 C. Demographics, Population & Economic Growth ....................................................... 30 1. Projected Economic Growth ................................................................................... 32 2. Population ............................................................................................................... 34 3. Housing ................................................................................................................... 36 D. Land Use, Development & Zoning ............................................................................. 36 1. Land Use ................................................................................................................. 36 2. Development Trends ............................................................................................... 40 3. Zoning ..................................................................................................................... 41 Chapter 4: Regional Hazard Identification and Risk Assessment (HIRA) ................................... 47 I. Introduction .................................................................................................................... 47 II. Data Availability and Limitations .................................................................................. 48 Local Critical Facility and Building Data ..................................................................... 48 HAZUSMH MR4 .............................................................................................................. 56 Data................................................................................................................................ 62 III. Hazard Identification ..................................................................................................... 64 Federally Declared Disasters ........................................................................................ 65 NCDC Storm Events Database ...................................................................................... 67 NCDC Normalizing Data ............................................................................................... 70 NCDC Inflation Computation ........................................................................................ 71 NCDC Annualizing Data ............................................................................................... 71 NCDC Data Compilation ............................................................................................... 72 IV. Ranking and Analysis Methodologies ........................................................................... 74 HAZUSMH Methodology ................................................................................................. 74 Supplemental Annualized Loss Estimate Methodology ................................................. 75 i Northern Virginia Hazard Mitigation Plan Update Critical Facility and Building Risk ................................................................................ 75 2006 Ranking Methodology ........................................................................................... 76 2010 Ranking Methodology ........................................................................................... 78 Ranking Methodology .................................................................................................... 78 Population Vulnerability and Density ........................................................................... 79 Geographic Extent ......................................................................................................... 80 Annualizing the Data for Analysis ................................................................................. 82 Annualized Deaths and Injuries ..................................................................................... 82 Annualized Crop and Property Damage........................................................................ 83 Annualized Events .......................................................................................................... 83 Overall Hazard Ranking ................................................................................................ 84 Comparison of Methodologies ....................................................................................... 84 Additional Risk Assessments Completed for the Northern Virginia Region .................. 84 November 2008 NCR SHIELD....................................................................................... 86 September 2005 CIP MCR RBFRS ................................................................................ 86 V. Flood .............................................................................................................................. 87 A. Hazard Profile ............................................................................................................. 87 Sea Level Rise ................................................................................................................ 88 Erosion ........................................................................................................................... 91 B. Risk Assessment ....................................................................................................... 103 VI. Winter Storm (with extreme cold) ............................................................................... 123 A. Hazard Profile ........................................................................................................... 123 B. Risk Assessment ....................................................................................................... 128 VII. High Wind/ Severe Storms .......................................................................................... 136 A. Hazard Profile ........................................................................................................... 136 C. Risk Assessment ....................................................................................................... 143 D. Hurricanes and Tropical Storms ............................................................................... 145 E. Risk Assessment ....................................................................................................... 157 VIII. Tornadoes ..................................................................................................................... 172 A. Hazard Profile ........................................................................................................... 172 B. Risk Assessment ......................................................................................................