Map hurricane storm surges

Find elevation data

To map any kind of flooding, you'll need to know the elevation of the land in your study area. Living Atlas provides global elevation data you can use to conduct your analysis.

  1. Open ArcGIS Pro.

    If you don't have ArcGIS Pro or an ArcGIS account, you can sign up for an ArcGIS free trial.

  2. On the start page, under New, click Map.

    New Map button on the Settings page

  3. Name the project StormSurge and click OK.
  4. On the ribbon, on the Map tab, in the Inquiry group, click Locate.
  5. In the Locate pane, search for New York City.

    The map navigates to New York City.

    Topographic basemap of New York City

  6. In the Catalog pane, on the Portal tab, click the Living Atlas button.

    Living Atlas tab on the Portal tab of the Catalog pane

    Living Atlas is a curated collection of geographic information, including maps, apps, and data layers.

  7. In the Catalog pane, search for Terrain.

    The list of search results contains an imagery layer named Terrain. It provides elevation data for the entire world at different resolutions as you zoom in and out.

    Terrain imagery layer in the Portal list

  8. Drag the Terrain imagery layer onto the map.

    The map view zooms out to show a raster layer that covers the entire world.

    Global terrain layer

    The value of each pixel in this raster represents elevation in meters. The lightest pixels are for the highest mountain peaks and the darkest are for depressions below sea level.

  9. On the ribbon, on the Map tab, in the Navigate group, click Previous Extent to return the map view to New York City.

    Previous Extent button on the Map tab of the ribbon

    The entire map appears black. This is because the elevation of New York is low when compared to the entire world.

  10. Click anywhere on the map.

    A pop-up appears. It contains an elevation value for the pixel you clicked.

    Pop-up showing an elevation value of 6.77 meters

  11. Close the pop-up.
  12. On the Quick Access Toolbar, click Save to save the project.

    Save button on the Quick Access Toolbar

Export a raster

Next, you'll export a file-based raster from the Terrain imagery layer that only covers your area of interest, so you can perform analysis with it.

  1. In the Contents pane, right-click Terrain, point to Data, and choose Export Raster.

    The Export Raster pane appears. You do not want to export a raster of the entire world, only for New York City.

  2. Make sure your map is centered on Manhattan. For Clipping Geometry, choose Current Display Extent.
  3. Under Cell Size, change both X and Y to 10.

    Cell Size X and Y both set to 10

    The cell size determines the resolution of the output raster. In this case, each pixel will cover a piece of the earth that is 100 square meters.

  4. Accept all of the other defaults and click Export.

    If you receive a warning that the output raster dataset exceeds the size limitation, you can either zoom in so your map covers a smaller area or increase the cell size.

    When the new raster is added to the map, it is drawn with a new range of black to white and you are able to visually discern the local variation in elevation values.

    New terrain layer with water in black and higher elevations in white

  5. Close the Export Raster pane and the Locate pane.
  6. In the Contents pane, right-click the original Terrain layer and choose Remove.

    Unlike the imagery service layer covering the entire earth, the exported raster can be used for analysis.

Map a storm surge

Now that you have elevation data, you can use it to find low-lying coastal lands and predict which areas might flood when hit with a hurricane.

  1. On the ribbon, on the Analysis tab, in the Geoprocessing group, click Tools.
  2. In the Geoprocessing pane, search for and open the Con tool.

    You can use the Con tool in either the Spatial Analyst or Image Analyst toolboxes.

    The Con tool creates a new raster that categorizes pixels as either true or false based on a condition. You'll use this tool to find areas in New York that would be flooded if it was hit by a 3-meter storm surge.

  3. For Input conditional raster, choose Terrain.tif.
  4. Click New expression.
  5. Use the menu controls to construct the following clause: Where VALUE is less than or equal to 3.

    Expression in the Con tool

  6. For Input true raster or constant value, type 1.
  7. For Input false raster or constant value, type 0.
  8. For Output raster, type StormSurge_3m.

    Con tool with parameters filled in

    This tool is now set up to perform the following actions:

    • If a pixel has an elevation of 3 meters or less, assign it a value of 1 (flooded).
    • Otherwise, assign it a value of 0 (not flooded).

  9. Click Run.

    A new raster layer is added to your map, with two randomly chosen colors. The Con tool reclassified your raster into two categories, which you'll symbolize to show low-lying areas.

  10. In the Contents pane, turn off Terrain.tif. In the Geoprocessing pane, leave the Con tool open.
  11. Under StormSurge_3m, right-click the legend patch next to 0.

    Those cells that didn't meet the condition of being at an elevation less than or equal to 3 meters were assigned a value of 0. Since these areas aren't important to your analysis, they don't need to be shown on the map.

  12. In the color picker window, click No Color.

    No Color option at the top of the color picker

  13. On the ribbon, on the Appearance tab, in the Effects group, change the Transparency slider to 50.0 percent.

    Transparency slider set to 50.0 percent on the ribbon

    The map now shows which parts of the city might be flooded by a 3-meter storm surge.

    Map with all low-lying areas in orange

Map flooding from Hurricane Sandy

In October of 2012, Hurricane Sandy passed through Jamaica, Cuba, and Bermuda. It caused extensive damage to most of the east coast of the United States as it traveled north, before combining with a separate high-pressure storm from the north and making landfall in New York and New Jersey. More than 230 people were killed in the Caribbean, the United States, and Canada.

Next, you'll compare your 3-meter storm surge map to a map of actual flooding from Hurricane Sandy.

  1. On the ribbon, on the Map tab, in the Layer group, click Add Data. In the Add Data window, click All Portal. Search for and select Hurricane Sandy Inundation Zone owner: Learn_ArcGIS.

    Add Data window

  2. Click OK.

    A new layer appears on the map. This is a feature layer from the New York City Open Data Portal displaying the areas inundated during Hurricane Sandy in 2012.

  3. Explore the map. How well does your 3-meter storm surge model match the real storm surge of Hurricane Sandy?

    Part of the map showing the orange hypothetical storm surge layer over the blue Hurricane Sandy layer

    The model is fairly close, but it looks like overall the surge from Hurricane Sandy was larger than 3 meters.

    Most people in New York and New Jersey were caught by surprise by this storm, not expecting that their homes were at risk of flooding. Such a large storm had not been seen in their lifetime. However, while a unique combination of weather factors made Sandy particularly destructive, storms with larger surges have hit the city in the past.

Map a 9-meter storm surge

In 1893, New York City was hit by a hurricane that brought with it a 30-foot (9-meter) storm surge. This storm was powerful enough to almost completely remove Hog Island, a former island along the Rockaway shore. Next, you'll map what such a large surge would look like in the present-day city.

  1. In the Geoprocessing pane, open the Con tool.
  2. Change the clause to read Where VALUE is less than or equal to 9.

    New expression in the Con tool

  3. Change the name of the Output raster to StormSurge_9m.
  4. Click Run.
  5. In the Contents pane, for the StormSurge_9m layer, change the color of value 0 to No color. Change the transparency to 50 percent.

    Map showing the 9-meter storm surge in pink over the previous surge layers

  6. Explore the map to see which parts of the city might be flooded. Because New York has historically seen a storm surge this high, it is not unreasonable to plan for such an event in the future.
  7. Save the project.

In this lesson, you completed three steps to map the potential extent of a large storm surge in New York City:

  • Export a raster from the Living Atlas Terrain layer.
  • Use the Con tool to find those areas that are below a certain elevation.
  • Symbolize the new layer to visualize the flood.

Because the Terrain imagery layer covers the entire world, you could use this same workflow for any coastal area. You could also use this process to model sea level rise. The Intergovernmental Panel on Climate Change (IPCC) has predicted that average global sea level will increase between 26 and 82 centimeters by 2100. What does a coastline near you look like when you flood elevations below 0.82 meters? Remember that storm intensity, surge levels, and sea level rise are all different in different areas.

You can find more lessons in the Learn ArcGIS Lesson Gallery.