High Tide Flooding
Data Limitations
The tide-gauge network is sparse, so there is a lack of tide data for many coastal communities and inconsistent periods of record for locations with gauges. Tide gauges are often placed in harbors and locations with protective housing that can reduce wave effects, preventing measurements of higher-frequency wave effects (Sweet et al. 2022). There is not a long-term record in many areas, and models that increase data coverage often underestimate water levels in areas with frequent tropical storms (Muis et al. 2016).
Definition and Description
Flooding that leads to public inconveniences such as road closures, occurring when tides reach anywhere from 1.75 to 2 feet above the daily average high tide and start spilling onto streets or bubbling up from storm drains (NOS 2021; NOAA 2022).
Coastal flooding may occur during high tides, even without a strong storm or hurricane. The combination of sea-level rise, land subsidence, and the loss of natural barriers contributes to an increased frequency of flooding capable of closing roads and damaging property. High-tide flooding may also contribute to flooding away from the immediate coast when stormwater systems cannot drain, such as from a thunderstorm occurring during a high-tide event. The frequency of high-tide flooding along the coast has doubled over the past 30 years (NOS 2021).
High tides occur when the moon is in alignment with the sun, at either a new moon or a full moon phase. This causes slightly higher tides than at other days in the month. If ocean waters are particularly warm or there is a nearby storm system, this can add to high tide levels through thermal expansion or wind and pressure effects.
Historical Data
Coastal Flood Exposure Mapper
National Oceanic and Atmospheric AdministrationThis interactive mapping tool shows areas susceptible to high tide flooding, water depth from sea level rise, storm surge from different hurricane categories, and FEMA flood zones. Users can overlay societal, infrastructure, and ecosystem exposures.
1. Click Get Started. 2. Zoom in to the area of interest. 3. Click the layers icon in the bottom-left corner to change the map. 4. To view areas susceptible to high tide flooding, click the High Tide Flooding option under Hazard Layers. 5. Click any of the exposure layers, such as Critical Facilities, to add additional information to the map.
Sea Level Rise Viewer
(High Tide: 1980-present in Louisiana) National Oceanic and Atmospheric AdministrationThis mapping tool visualizes the impacts of sea level rise and allows users to choose different water levels to view sea level rise projections, overlay community vulnerability, and view high tide flooding frequency. Note: this tool only includes 1 tide gauge in Louisiana.
1. Click Get Started. 2. Zoom into the area of interest. The default map is the current water level, where darker blues are greater water depths. 3. Click High Tide Flooding on the lefthand menu. Red areas represent shallow coastal flooding areas and tide gauges are shown at select locations (you may have to zoom in to view these). 4. Click the tide gauge icon on the map to view a graph of yearly high tide flooding events per year at that location. Note: access the legend by clicking the middle icon on the top right of the screen.
Gulf Tree
(Time frame varies by product) Northern Gulf of Mexico Sentinel Site Cooperative, Gulf of Mexico Climate Resilience Community of Practice, & Gulf of Mexico Alliance Resilience TeamThis decision support site guides users to the high tide/nuisance flooding tools and resources they need along the Gulf Coast through several filters of information, including how much time and effort they are willing to spend on the tool.
1. Choose a Filtered Search to look through all filter categories on one page or choose Guide My Search to walk through questions step by step to achieve what you’re looking for. 2a. If you chose the Filtered Search, first navigate to Geographic Scope. Click the Louisiana drop-down menu and choose Shoreline to select all coastal parishes or choose specific one(s). 2b. Under Tool Function, select what you’d like to use high tide flooding information for. You can leave this blank if you’re unsure which to choose. 2c. Under Cost, choose Free. 2d. Under Level of Effort, choose from low, moderate, or high (will determine how advanced the tool is). 2e. Under Climate Change Topics, select the drop-down for Flooding, then check the box for Nuisance Flooding. Explore other drop-down menus in this section to add more filters for additional topics. 2f. Click View Tool Matches on the top right to go to the results page. Click any of the tools or resources to go to that site.
3a. If you chose Guide My Search, Gulf Tree will walk you through the same filters by asking 6 questions. For step 1 (Tool Function), check the box for why you need a high tide flooding tool, then click Submit. If you’re not sure which option to use, you can Skip this step. 3b. Step 2 (Topic Area) includes a filter for what aspect of the topic you’re interested in. Click the drop-down menu for Flooding and check the box for Nuisance Flooding, then click Submit. 3c. On Step 3 (Location), click the Louisiana drop-down menu, then choose Shoreline to select all coastal parishes or choose specific one(s). Then, click Submit. 3d. For Step 4 (Level of Effort), choose how much effort you’d like to put into the tool, which will determine how advanced the tool is. Then, click Submit. 3e. For Step 5 (Tool Cost), choose Free, then click Submit. 3f. Click Leave Guided Search and View Matches to go to the results page or go back to a previous page on the left menu to change your selected options. Click any of the tools or resources to go to that site. 6. To create a new search, click Reset All Filters at the top right of the results page.
Climate Change Trends
As sea levels rise, coastal flooding is expected to increase, causing more frequent high tide flooding events that reach further inland (Sweet et al. 2022). The 2022 NOAA Sea Level Rise Technical Report (Sweet et al. 2022) analyzed high tide flooding from the mean higher high water (MHHW), which is the average height of the highest tide recorded at a tide station each day during the recording period. By 2050, minor/disruptive high tide events (0.5 m above MHHW) are projected to occur more than twice as often than in 2020, and major/often destructive events (1.2 m above MHHW) may occur five times more often along the western Gulf Coast (Sweet et al. 2022). The U.S. coasts are experiencing a flood regime shift, in which high tide flooding events have increased, and only 1-2 feet of sea level rise will transition more “nuisance” flooding events to more moderate to major flooding events. Read more about future high-tide flooding in Climate Change Science and Projection Resources.
Climate Explorer – High-Tide Flooding Tool
(1950-2099) NOAA Climate Program Office and National Environmental Modeling and Analysis CenterThe Climate Explorer is an interactive tool that provides the annual number of days with high-tide flooding for the historical period (up to 1950-present) and modeled projections (present-2099) under a lower and higher emissions scenario.
1. Type in the city or parish you are interested in. Click High-Tide Flooding. 3. Click a station (blue dot) on the map. Note: there is only one station available in Louisiana, near Grand Isle. 4. The resulting graph shows the annual days with high-tide flooding. The gray bars represent historical observations and the curves from the present year through 2099 represent the modeled/projected values, where red displays the higher emissions scenario and blue shows the lower emissions scenario. 5. Hover your mouse over the graph to view the observed or projected values.
