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Hazard Identification and Parish-Wide Risk Assessment

This section assesses the various risks that New Orleans faces in order to identify a strategy for mitigation. What follows details the major climatological and natural/human-influenced hazards by (1) defining them, (2) explaining how they are measured, (3) describing their geographic extent, (4) surveying their previous occurrences, and (5) evaluating their future likelihood of occurrences.

The Federal Emergency Management Agency (FEMA) requires that the City of New Orleans identify the natural hazards it faces. According to 44 CFR § 201.6[1] , Local Mitigation Plans must address the vulnerability of community assets and estimate potential losses, reflect changes in development since the last plan update, provide an overview of the future probabilities of hazard events, and detail a mitigation strategy and plan maintenance process.

[1] 44 CFR § 201.6 - Local Mitigation Plans. (2002, February 26). LII / Legal Information Institute.

Hazard Summary

Tables 10 and 11 provide an overview of the hazards that were profiled in the 2015 Orleans Parish Hazard Mitigation Plan, along with the hazards that were identified for the 2020 Hazard Mitigation Plan.

Table 10: 2015 and 2020 Hazard Mitigation Plan Hazards
2015 HMP Hazards 2020 HMP Hazards
Flooding Flooding (Stormwater/Storm Surge/Riverine)
Storm Surge
Tropical Cyclones High Wind (Tornadoes/Tropical Cyclones/Thunderstorms)
Coastal Erosion Coastal Land Loss
Subsidence Subsidence
Winter Storms Winter Weather
Drought1 -
Extreme Temperatures Extreme Heat
Thunderstorms (Hail and lightening) Severe Thunderstorms (Hail/Lightening)

1 Deleted as it is the analysis of the planning committee that 1) droughts are infrequent and their impacts are not severe enough to lead to a declared disaster, 2) the impacts of drought (drinking water quality and surficial soil oxidation are actively addressed through Sewage & Water Board of New Orleans standard water purification, The Environmental Protection Agency (EPA) administration of the Clean Water Act (CWA), and the City of New Orleans’ efforts to improve water management (flooding and subsidence).Man-made hazards are listed and addressed in alignment with the local all-hazards preparedness philosophy.

Man-made hazards are listed and addressed in alignment with the local all-hazards preparedness philosophy.

Table 11: 2015 and 2020 Man-Made Hazards*
2015 HMP Hazards 2020 HMP Hazards
Dam & Levee Failure -
Hazardous Materials (Spills/Contamination, Fixed Site & Transportation) Hazardous Materials (Spills/Release/Contamination)
Power Outages -
Terrorism Active Threats (Terrorism/Cyber Threat/Active Attack)
Infrastructure Failure Infrastructure Failure (Levee Failure/Building Collapse/Water Systems Failure/Power Outage)  
Building Collapse -
Civil Unrest11 -
Pandemic Infectious Disease Outbreak (Pandemic/Vector-Borne Disease)
  Economic Shock

* The Hazard Mitigation Plan Steering Committee considered including Climate Change as its own hazard. The committee ultimately felt it made more sense to evaluate it as a complicating factor in other natural hazards. The impacts of climate change on future risks are discussed in the profiles of individual hazards likely to be affected by climate change.

The revised list of hazards that are addressed in this updated plan reflect the current priorities of the community and are indicative of changes in perceived risks as well as political and financial circumstances. The emphasis on equity and climate change in this plan are in line with the values expressed in the Resilient New Orleans strategy including adapting to thrive in a changing environment, connecting people to opportunity, and transforming city systems to make New Orleans a dynamic and prepared city. This plan was updated during 2020, and the economic and public health impacts of the COVID-19 pandemic that developed during the planning process are reflected in this plan.

Previous Occurrences of Major Disasters

The most frequently occurring hazards in the City of New Orleans are tropical cyclones and flooding. 17 out of 28 (60.7%) of the Presidential Disaster Declarations that New Orleans has received have resulted from tropical cyclones. [1] Additionally, 25% (7 out of 28) of those declarations have resulted from flooding.

Table 12: Orleans Parish Major Disaster Declarations
Source: FEMA
Disaster & Date Nature of Event Description
FEMA-DR-208 9/10/1965 HURRICANE BETSY Category 3 Hurricane with landfall west of New Orleans. Estimated $1.4 billion in damage, 75 deaths, 800 injuries, and164,000 homes flooded.
FEMA-DR-272 8/14/1969 HURRICANE CAMILLE One of only two Category 5 hurricanes to make landfall on a US coastline. Hurricane Camille made landfall along the Mississippi coast near Bay St. Louis, MS, causing an estimated $1.4 billion in total damages and 259 deaths.
FEMA-DR-374 4/27/1973 SEVERE STORM,  FLOOD Spring rains caused flooding in large areas of Louisiana and along the Mississippi River for more than 1,500 miles.
FEMA-DR-448 9/23/1974 HURRICANE  CARMEN Category 4 Hurricane made landfall ten miles west of Grand Isle; six-foot storm surge. Orleans Parish damage estimates were reported at slightly less than $20 million
FEMA-DR-556 5/9/1978 SEVERE STORM,  FLOOD Torrential rains in excess of 10 inches, with rates of two inches per hour at times. Nearly all main arteries were flooded or inaccessible well into the evening hours.
FEMA-DR-616 4/9/1980 SEVERE STORM,  FLOOD Severe storms resulted in 10 inches of rain over several days. Drainage pumps throughout the Parish were overwhelmed and most shut down during the event.  Flooding occurred in low-lying areas.
FEMA-DR-679 4/20/1983 SEVERE STORM,  FLOOD Heavy rain overwhelmed drainage pumps throughout the Parish, with resulting moderate flooding in the low-lying areas.
FEMA-DR-752 11/1/1985 HURRICANE JUAN Category 1 storm made landfall in south-central Louisiana. Storm stalled over Louisiana for several days causing an estimated $38 million in damages in Orleans Parish.
FEMA-DR-849 11/19/1989 SEVERE STORM, FLOOD Heavy rain flooded residences and businesses.
FEMA-DR-956 8/26/1992 HURRICANE ANDREW Category 3 Hurricane, with winds of more than 100 miles per hour (mph) at the time it made landfall for the second time in Louisiana. Grand Isle and coastal areas were completely evacuated.
FEMA-DR1049 5/10/1995 SEVERE STORM, FLOOD Widespread rainfall of 8 to 12 inches in less than four hours overwhelmed the capacity of drainage pumps, with some of the most widespread and severe flooding reported in the City in the past 50 years. New Orleans damage estimated at $388 million.
FEMA-DR1246 9/13/1998 TROPICAL STORM FRANCES & HURRICANE GEORGE Category 3 hurricane that made landfall to the east of New Orleans. Widespread and deep flooding in the streets of the New Orleans metropolitan area.
FEMA-DR1380 6/11/2001 TROPICAL STORM ALLISON, FLOOD Slow-moving tropical storm caused widespread flooding; some locations received ten to 18 inches of rain.
FEMA-DR1437 10/03/2002 HURRICANE LILI Hurricane Lili made landfall on the central Louisiana coast as a category one hurricane. Property damages in Louisiana were estimated at $415 million.
FEMA-DR1548 9/15/2004 HURRICANE IVAN Impacted Orleans Parish as a hurricane on September 16, 2004 and then cycled back into the Gulf and came ashore again as a tropical depression on September 26, 2004.
FEMA-DR1601 7/5/2005 TROPICAL STORM CINDY The tropical storm came ashore just southwest of Grand Isle. Surge flooded low-lying coastal areas and high winds caused power outages across to an estimated 300,000 homes and businesses.
FEMA-DR1603 8/29/2005 HURRICANE KATRINA Made landfall as a Category 3 storm. Catastrophic flooding from storm surge and levee failures caused unprecedented flooding throughout New Orleans and the surrounding areas. A much longer discussion of the effects of Katrina can be found later in this section.
FEMA-DR1603 9/24/2005 HURRICANE RITA Made landfall as a strong Category 3 hurricane in extreme southwestern Louisiana.  Rita made landfall less than a month after Hurricane Katrina, while sections of the City of New Orleans were still being drained of floodwaters. An estimated 10,000 structures were flooded.
FEMA-DR1685 2/13/2007 SEVERE STORMS AND TORNADOES Tornadoes and severe storms impacted Jefferson, Orleans, and St. Martins Parishes. An EF2 Tornado moved through the City of Westwego and the Carrollton area of New Orleans. A total of 295 houses in New Orleans were damaged.  A total of 79 houses were destroyed.
FEMA-DR1786 9/2/2008 HURRICANE GUSTAV Made landfall along the Louisiana coast with 105 mph winds near Cocodrie, Louisiana. Surges of 12-13 feet occurred along the Louisiana coast southeast of New Orleans, with surges of 9-10 feet in other portions of southeastern Louisiana. The storm surge overtopped the levees and floodwalls in a few parts of the New Orleans metropolitan area.
FEMA-DR1792 9/13/2008 HURRICANE IKE Landfall as a Category 2 hurricane. A storm surge ranging from four to nearly eight feet above normal occurred along the southeast Louisiana coast with a storm surge around five feet above normal in Lake Pontchartrain
FEMA-DR4015 8/18/2011 FLOODING The historic Mississippi River Flood of 2011 resulted from above-normal snowfall over the Upper Mississippi Valley, elevated river levels from heavy rain events from February to April, and a very heavy rain event in the Mississippi watershed from the end of April to the beginning of May. 
FEMA-DR4041 10/28/2011 TROPICAL STORM LEE Lee made landfall in S. Louisiana on Sept. 4, 2011. The large, slow-moving system produced heavy rainfall with over 12.5 inches reported at New Orleans Lake Front Airport. Lee also generated strong winds and tornados
FEMA-DR4080 8/29/2012 HURRICANE ISAAC Isaac, a slow-moving system, made landfall twice in S. Louisiana, with sustained winds of 80 miles per hour. Storm surge in Orleans Parish was recorded at 4-8’ and up to 17’ in Plaquemines Parish. Over 20” of rain was recorded in New Orleans. 
FEMA-DR43002/11/2017 SEVERE STORMS, TORNADOES, STRAIGHT-LINE WINDS Governor John Bel Edwards requested an expedited major disaster declaration due severe storms, tornadoes, and straight-line winds on February 7, 2017. On February 11, 2017, President Trump declared that a major disaster exists in the State of Louisiana.  This declaration made Individual Assistance requested by the Governor available to affected individuals and households in Livingston and Orleans Parishes.  This declaration also made Hazard Mitigation Grant Program assistance requested by the Governor available for hazard mitigation measures statewide.
FEMA-DR4458 8/27/2019 HURRICANE BARRY Governor John Bel Edwards requested a major disaster declaration due to Hurricane Barry during the period July 10-15, 2019.  On August 27, 2019, President Trump declared that a major disaster exists in the State of Louisiana.  This declaration made Individual Assistance requested by the Governor available to state and eligible local governments and certain private nonprofit organizations on a cost-sharing basis for emergency work and the repair or replacement of facilities damaged by Hurricane Barry; debris removal and emergency protective measures (Categories A and B), including direct federal assistance under the Public Assistance program.  This declaration also made Hazard Mitigation Grant Program assistance requested by the Governor available for hazard mitigation measures statewide.

Probability of Future Hazard Events

The estimated probability of a hazard event occurring in the City of New Orleans is summarized below. The percent chance of an event happening during any given year was calculated by the following equation (Number of Events/Time Period) x 100, which is the standard method for calculating the probability for a FEMA Hazard Mitigation Plan. The event history and future probability of each hazard is discussed in more detail in the sections profiling each hazard.

Past events are not always reliable indicators of future trends. For example, changes to the climate and land-use patterns affect flooding by changing how water moves through the City. Many of the plans and tools used to inform this Risk Assessment incorporate climate change in their methods and assumptions. Locally, climate-related changes like sea-level rise, increasing temperatures, and less-frequent, but heavier precipitation are almost certain to increase stress on infrastructure, ecosystems, and populations[1].

The probability of future hazard reoccurrence, found in Table 13, was calculated using the National Oceanic and Atmospheric Administration NCDC/NCEI Database. There are limitations to this data. However, this is the best available data at the present moment, and it was used to calculate the probabilities below.

[1] U.S. Global Change Research Program. (2018). Fourth National Climate Assessment, Volume II (Chapter 19: Southeast). U.S. Government Publishing Office.

Table 13: Probability of Future Hazard Reoccurrence
Hazard Annual Probability
Flooding 100%
Tropical Cyclones 92%
Coastal Erosion 100%
Tornadoes 36%
Subsidence 100%
Winter Weather 36%
Extreme Heat 100%
Severe Thunderstorm 100%

Source: NCEI

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