Map hurricane storm surges

Create a new project and obtain elevation data

To map any kind of flooding, you'll need to know the elevation of the land in your study area. ArcGIS Living Atlas of the World provides global elevation data you can use to conduct your analysis. You'll create a project in ArcGIS Pro and acquire elevation data.

  1. Open ArcGIS Pro.
    Note:

    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. In the Create a New Project window, for Name type StormSurge and click OK.
  4. On the ribbon, on the Map tab, in the Inquiry group, click the Locate button.
    Locate button
  5. In the Locate pane, type New York City and press Enter.

    The map navigates to New York City.

    Topographic basemap of New York City

    The default Topographic basemap helps you identify the different areas of New York City, such as Manhattan.

  6. Close the Locate pane.

    Close the Locate pane

  7. Zoom in to Manhattan with the mouse wheel button, and pan to obtain the extent displayed in the example image.

    Zooming in on Manhattan

    The extent shows the island of Manhattan, as well as parts of other New York City boroughs like Brooklyn to the south and Queens to the east. You'll now add the elevation data.

  8. On the ribbon, on the View tab, in the Windows group, click Catalog Pane.

    Catalog Pane button

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

    Living Atlas tab on the Portal tab of the Catalog pane

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

  10. In the Catalog pane, in the search box, type Terrain owner:esri, and press Enter.

    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

  11. Right-click the Terrain layer and choose Add To Current Map.

    Add To Current Map button

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

    Global terrain layer

    A raster layer is made of a grid where each cell is called a pixel and has a numeric value. In the case of the Terrain layer, the value of each pixel represents elevation in meters. The pixels with the highest values, for instance, for the highest mountain peaks, appear in white. The pixels with the lowest values, for instance, for depressions below sea level, appear in dark gray or black.

  12. On the ribbon, on the Map tab, in the Navigate group, click Previous Extent once 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 generally low when compared to the entire world. You'll change the display of the terrain layer to better see the differences in elevation in the New York City area.

  13. In the Contents pane, verify that the Terrain layer is selected.

    Selecting the Terrain layer

  14. On the ribbon, click the Appearance tab. In the Rendering group, click DRA.

    DRA button

    DRA stands for dynamic range adjustment. In this mode, the color tones on the map are selected strictly based on the range of values in the current map view. After a few seconds, the view is updated, and you can now visually discern the local variation in elevation values.

    Terrain for Manhattan and surroundings symbolized with DRA rendering

  15. On the Quick Access Toolbar, click Save to save the project.

    Save button on the Quick Access Toolbar

In this section, you created a project in ArcGIS Pro and added the Terrain imagery layer from ArcGIS Living Atlas, which provides elevation data for the whole world.

Export an elevation 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.

    Export Raster menu option

    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 still centered on Manhattan as before. In the Export Raster pane, for Clipping Geometry, choose Current Display Extent.

    The four coordinates that define the bounding box to clip the raster update.

  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.
    Tip:

    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, Terrain.tif, is added to the map, it is drawn with a similar new range of black to white as the previous DRA display.

  5. Close the Export Raster pane.

    You'll now remove the original world-wide Terrain layer, as you don't need it any longer.

  6. In the Contents pane, right-click the Terrain layer and choose Remove.

    Remove menu option

    You'll check some of the elevation values on your map.

  7. On the map, click anywhere within the Terrain.tif layer.

    The Pop-up pane appears, displaying the elevation value for the specific pixel you clicked, for instance 23.12 meters.

    Pop-up showing an elevation value of 23.12 meters.

  8. Click several other points to see how the elevation varies across your area of study.
  9. Close the pop-up.
  10. Press Ctrl+S to save the project.

In this section, you saved a clipped raster, which provides elevation data for your area of study.

Map a 3-meter surge

Now that you have elevation data, you can use it to find low-lying coastal lands and predict which areas of New York City may flood when hit with a hurricane. First, you'll start with the scenario where a hurricane produces a water surge of 3 meters (or 9.8 feet). Considering that the water surrounding New York City sits at an elevation of 0 meters, all the areas in the city that have an elevation of up to 3 meters would be flooded.

To find all areas with an elevation of 3 meters or less, you'll use the Remap tool applied to the Terrain.tif layer.

  1. On the ribbon, on the Imagery tab, in the Analysis group, click the Raster Functions button.

    Raster Functions button

    Note:

    Raster functions are operations that apply processing directly to the pixels of raster datasets in memory, without writing out a new raster to disk. Since no intermediate datasets are created, these processes can be applied quickly.

  2. In the Raster Functions pane, search for and open the Remap tool.

    Searching for the Remap tool

    The Remap tool allows you to change or reclassify the pixel values of a raster and produce a new raster layer with the new values.

  3. In the Remap tool, on the Parameters tab, for Raster, choose Terrain.tif. For Remap Definition Type, keep List.

    Remap Properties parameters

    In the Remap table, you'll define the reclassification rules.

  4. Based on the legend for the Terrain.tif layer in the Contents pane, you can see that the lowest value possible for that layer is about -22.9 meters and the highest is 96.5 meters.

    Terrain.tif legend

  5. In the Remap table, for the first rule, click in each cell of the first row and enter -23 for Minimum, 3 for Maximum, and 1 for Output.

    Creating the first Remap rule

    This rule means that any pixel with a value between -23 and 3 meters should get a value of 1 in the new raster. Those are the flooded areas.

  6. For the second rule, click the star to create a new row. Then, in the cells of the new row, enter 3 for Minimum, and 97 for Maximum. Leave 0 for Output and uncheck the NoData check box.

    Creating the second Remap rule.

    This rule means that any pixel with a value between 3 and 97 meters should have no data. Those are the areas that are not flooded, and you are not interested in them, so you won't represent them with any data.

  7. Click Create New Layer.

    A new layer, Remap_Terrain, symbolized in gray, is added. You'll make some changes to the display to make the layer easier to see. First, you'll turn off the elevation layer.

  8. In the Contents pane, turn off the Terrain.tif layer by unchecking the box.

    Turn off the Terrain layer

    You'll rename the new layer.

  9. In the Contents pane, click the Remap_Terrain layer twice, type Storm surge 3 m and press Enter.

    Next, you'll change its symbology.

  10. Right-click the color ramp for the layer, expand the drop-down list, and check Show Names. Scroll down the list of color ramps, and choose the Red-Purple (Continuous) ramp.

    Choose the Red-Purple (Continuous) ramp.

    Because the only pixel value in this raster is 1, only one median color from that ramp will be used, and the layer changes to a uniform pink color.

  11. In the Contents pane, ensure that the Storm surge 3 m layer is selected. On the ribbon, on the Appearance tab, in the Effects group, change the Transparency slider to 40.0%.

    Transparency slider

    The map now shows in light pink the areas of the city that may be flooded by a 3-meter storm surge.

    Map of the 3 meter storm surge

  12. On the Appearance tab, in the Compare group, click Swipe.

    Turn the Swipe tool on

  13. On the map, with the Swipe tool on, drag the map from side to side to reveal the basemap below and compare the flood areas to the preflood water boundaries.

    You can also zoom in and pan to see in more detail which areas of Manhattan and surrounding neighborhoods appear flooded.

    Swipe pointer

  14. On the ribbon, on the Map tab, in the Navigate group, click the Explore button to exit swipe mode.

    Explore tool

    In October 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.

  15. On the ribbon, on the Map tab, in the Layer group, click Add Data.

    Add Data button

  16. In the Add Data window, under Portal, click ArcGIS Online. Search for and select Hurricane Sandy Inundation Zone owner: Learn_ArcGIS.

    Add the Hurricane Sandy layer.

  17. Click OK.

    A new layer appears on the map. This feature layer comes from the New York City Open Data portal and displays the areas inundated in the city of New York during Hurricane Sandy in 2012.

    Hurricane Sandy flood overlaid on top of the 3-meter storm surge layer

  18. In the Contents pane, if necessary, click the Hurricane Sandy layer to select it. On the ribbon, on the Appearance tab, in the Compare group, click Swipe. Explore the map with the Swipe tool.

    How well does your 3-meter storm surge model match the real storm surge of Hurricane Sandy? The model is fairly close, but it looks like overall the surge from Hurricane Sandy was slightly larger than 3 meters.

  19. When you're done, on the ribbon, on the Map tab, in the Navigate group, click the Explore button to exit swipe mode.
    Note:

    Optionally, you can use the Remap tool again to generate a 3.5-meter storm surge layer, and see if the result matches the Hurricane Sandy layer more closely.

  20. Press Ctrl+S to save the project.

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 lifetimes. However, while a unique combination of weather factors made Sandy particularly destructive, storms with larger surges have hit the city in the past.

In this section, you used elevation data to create a flood map corresponding to a 3-meter storm surge, and then you compared it to the flood caused by Hurricane Sandy in 2012.

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 submerge 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. On the ribbon, on the Imagery tab, in the Analysis group, click the Raster Functions drop-down arrow to expand the list, and choose History.

    Open the Raster Functions History

    The History pane appears, showing the process you performed previously in this project.

  2. In the History pane, double-click Remap.

    Choose Remap in the History pane.

    The Remap tool opens with all the information you had previously entered to create the Storm surge 3 m layer.

  3. On the Parameters tab, for Raster, make sure that Terrain.tif is selected. In the table, replace the value 3 with 9 for both rules.

    Change the parameters in the Remap pane.

  4. Click Create new layer.

    A new layer, Remap_Terrain, symbolized in gray, is added. You'll make some changes to the display to make the layer easier to see.

  5. In the Contents pane, click Remap_Terrain twice, and rename it Storm surge 9 m.
  6. Right-click the color ramp for the layer, and expand the drop-down list to pick the Yellow-Orange-Brown (Continuous) ramp.

    The layer's color changes to orange.

  7. In the Contents pane, ensure that the Storm surge 9 m layer is selected. On the ribbon, on the Appearance tab, in the Effects group, change the Layer Transparency slider to 40.0%.
  8. In the Contents pane, turn off the Hurricane Sandy Inundation Zone layer. Drag Storm surge 3 m above the Storm surge 9 m.

    Reorder the layers.

    The map now shows in orange the parts of the city that may be flooded by a 9-meter storm surge. For reference, you can compare with the 3-meter storm surge flood area displayed in pink.

    Final map

  9. In the Contents pane, click Storm surge 9 m to select it. On the Appearance tab, in the Effects group, click Swipe, and explore the map.

    Because New York has historically seen a storm surge this high, it is not unreasonable to plan for such an event in the future.

  10. When you're done, on the ribbon, on the Map tab, in the Navigate group, click the Explore button to exit swipe mode.
  11. Press Ctrl+S to save the project.

In this lesson, you completed three steps to map the potential extent of a large storm surge in New York City. You obtained elevation data by adding the Terrain layer from ArcGIS Living Atlas to your map and exporting the extent of interest to a local raster. You used the Remap raster function to find the areas that are below certain elevations. Finally, you symbolized the new layers to visualize the flood areas.

Because the Terrain imagery layer covers the entire world, you can use this same workflow for any coastal area. You can also use this process to model sea level rise. The Intergovernmental Panel on Climate Change (IPCC) has predicted that average global sea level could increase by 60 to 110 centimeters by 2100 if greenhouse gas emissions continue to increase significantly. What does a coastline near you look like when you flood elevations below 1.1 meters? Remember that storm intensity, surge levels, and sea level rise are all different in different areas.

You can find more lessons like this on the Introduction to Imagery & Remote Sensing page.