Exercise 4 Estimating the effects of sea level rise on coastlines by reclassification

Transcription

1 Exercise 4 Estimating the effects of sea level rise on coastlines by reclassification Due: Thursday February 1; at the start of class Goal: Get familiar with symbolizing and making time-series maps of one area. Note: You will turn in a powerpoint containing exports of part A and print part B. ALSO: Be reading Bolstad Chapter 3. Datasets: Exercise4a.zip world.sid MrSid format: image of the world etopo2 ESRI Grid format: elevation of the world\oceans worldrivers.shp ESRI shapefile format: major rivers of the world worldcities.shp ESRI shapefile format: major cities of the world Data can be downloaded from Make sure you UnZIP your data on your flash drive or under D:\GIS_myname\ so you can see them with ArcGIS. Origin of the etopo2 dataset: Assignment One very hot item at the moment is global warming. The current rapidly rising global temperatures are causing glaciers to melt. Consequently, the big volumes of glacial melt water are rising global sea level. Can we estimate how the world will look by the end of the century? Or in 1000 years? Which areas are in great danger? Where do many people live? Can you make a map to help illustrate this topic? Sea level information (from IPCC report a) Period m (round to 0.5m) b) The entire Greenland ice sheet (which would take > 1000 years) + 7 m Not directly from the report, but rough estimates for this exercise: c) Melt all ice in the world (Greenland & Antarctica) + 70 m? but try 25m too d) Pleistocene (18,000 years ago) m Part A. Map the Sea Level Change around the World Make a map of the world and overlay the IPCC sea level estimates on the current etopo2 bathymetry\topography (raster cells are 1 minute of latitude = 1 nautical mile, or km (so pretty big). Look at areas where sea level rise would have great consequences. Zoom in to a (low) area of interest and make some compelling exports of how the area you chose will change through time. (this is detailed below). 1

2 For the Pleistocene world, look at the land bridges that formed and where they are. Part B (below). How many people are actually affected by different amounts of sea level rise? Figure out how many people are affected by the different amounts of sea level rise in Louisiana. Part A Which areas in the world are most affected! 1. Assess your data and explore: Load the data in ArcMap 1. Load the data in ArcMap 2. Choose the following order in the Table of Contents: worldcities.shp (top) worldrivers.shp etopo2 (leave unchecked for now) world.sid (bottom) 3. Choose a blue color as the symbol for the world rivers. 4. Choose as symbology for the major cities something that highlights the population value (realize that the ranking is inverse (low rank is big symbol, high rank is small symbol)). Layer Properties > Symbology TAB > Quantities > Graduated Symbols Value = POP_Rank Color = Red Classes = 7 You can change the ranking by once-left click on the Symbol column > then selecting Flip Symbols to fix the inverse ranking problem. Or change the size to 18 to Analyze the data The main part of your analysis for this exercise is to play with the layer properties of the etopo2 layer and change the symbology. 1. Set the base value (0 m sea-level) for your sea level exercise: Realize that the grid cells are very coarse, so your coastline (0m sea level) is fairly general. The grid cell values are integers, or whole numbers. 0.5 meter sea level changes will be rounded to the nearest whole number. There are areas in the world that are actually already below sea level if you look at the elevation values. However with dike and levee systems, these areas are artificially kept dry and people live there. One of these areas is the Netherlands or New Orleans (see part B). The 0m sea level approach is not an accurate representation for those areas, yet it is interesting to see how those areas would look without human intervention. Layer Properties (etopo2) > Symbology TAB Select Classified (on the left) as coloring method. Select Classify (on the right) and select 2 classes(bins) 2

3 The histogram window should now open up: Manually change the upper value on the right to 0. Click OK 2. Back under the Symbology TAB, change the colors by double clicking on the box: Select a BLUE color for the upper symbol (the sea). Select NO COLOR for the lower symbol (the land). Click Apply (but not OK yet). 3. Back under the Display TAB (next to the Symbology TAB), change the transparency to 25% (use your own good taste, and see what looks best). 4. Click OK and look at the result in the map. Realize that we just simplified our bathymetry/topography data to show us just land OR sea. However we can decide where we want to define this land/sea boundary (i.e. the coastline). In case of 1m sea level rise, we can put this boundary 1 meter higher, etc. We will do this below: Prepare the rest of the sea level information: There are several ways to do this: 5. Either ADD a new version of etopo2 to your map, OR right-click on etopo2 and hit Copy. Then right-click on Layers (top of Table of Contents) and hit Paste Layer. The advantage is that your Symbology will already be set for 2 classes and the Transparency (Display TAB will be set as well). 6. Layer Properties (etopo2) > Symbology TAB. 7. Repeat the steps under II-1: Go to the histogram and change the number on the right side 3

4 to 1 (instead of 0 as mentioned above (and 0.5 is below the resolution of this topography dataset)). 8. Go back to your Symbology TAB and change the symbols to BLUE (upper symbol) and NO COLOR for the lower symbol. 9. Click OK and look at the result in the map. 10. It is now a good idea to RENAME your layer in the map to etopo2 1m: this can be done by double clicking (left) or once on the layer hit F2. This is recommended to keep track of which layer is which sea level! It is easy to get confused! 11. Order your etopo2 layers so you can see the succession and differences in coastline position. 12. Zoom in on areas you know that are quite low, like New Orleans, the Netherlands, Bangladesh, China, etc. The results will get more expressive with higher values: 13. Repeat steps 5 through 10, and fill out the symbology values to be 7m, 25m +100m and - 100m respectively and rename the map layers accordingly. 14. Find ONE example on your map that shows dramatic coastline changes. 15. You can Bookmark Areas you like and get back to these areas: Bookmarks > Create to mark your spot for later... and keep browsing around the world. 16. Right click on the layer worldcities and select Label Features 3. Export the Data 1. Zoom to your favorite coastal spot that has low elevation/coastal slopes. 2. Make sure you know which etopo2 layer represents which sea level value! 3. Go to View > Layout View (until now we have been working in the Data View and made simple screendumps, but for data reproduction, you can add legends, scalebars etc in your Layout View. 4. Go to Insert Menu (at the top) > Scalebar 5. Choose a scalebar to your liking: Choose a Division Value that makes sense! Choose a unit that makes sense (probably not inches) 4

5 See example below: 6. Choose a North Arrow via the Insert Menu too. Try to figure out how to do this (it works similar to the scale-bar). Pick a nice arrow you like. Please ask for help if you have problems with this step. Export each sea-level map one by one (so you will get 6 of your study area) 7. Now go to File > Export Map. 8. Choose *.png as export format (Portable Network Graphic, is like jpg). 9. Choose Clip Output to graphics extent, set your resolution to 180 dpi. 10. Choose a filename (sealevel0m.png) and location. 11. Repeat steps III-7 through 8 for each coastline. Be sure to name them appropriately. 12. MAKE SURE you don t zoom or pan (move your data while repeating the steps > this will cause wobbling of your powerpoint show). 13. Asses which areas in the world are at great danger of flooding. 4. Write your report The report will a compilation of your *.png exports in Powerpoint 1. Open Microsoft Powerpoint. 2. The easiest thing now is to go to INSERT > Picture > New Photo Album. Select all png files 3. In the preview window you can now order your sea-levels from Pleistocene to the future (- 100m to 0m, to 0.5, to 7, to 25, to 100m in succession). 4. Hit OK. 5. Check if your Powerpoint transitions smooth from one slide to the other and don t shift or wobble. To make it easier on the eye, the images should be exactly at the same spot, however with different coastlines. 6. Compress your images (double click on the picture). 7. Select compress all pictures in document: "apply compression settings now" and make sure box (for selected pictures only) is unchecked. 5

6 8. Add a textbox for each picture labeling the sea level change (-100, 0, 1m, +7, 25, and you can try 100m) so when you go through the slides you know which one you are looking at. 9. Also put your name and the place of interest on the 1st page. SAVE! Then upload to dropbox as Ex 4aLASTNAME.ppt. Part B - Analyze how many people are affected by sea level rise in Louisiana. Your dataset is now slightly more detailed and we will focus on Louisiana. The etopo2 dataset was too large to do a world-wide analysis. Download the Exercise 4B dataset (different than 4A) and open the layers in a new ArcMap document. Order your map document as follows (so you can see ). cities.shp ESRI shapefile (top) sealevel0m ESRI shapefile current sea level sealevel1m ESRI shapefile 1m sea level rise sealevel7m ESRI shapefile 7m sea level rise sealevel25m ESRI shapefile 25m sea level rise LA_censusblocks Louisiana census blocks (population data) shapefile luis_utmnad83 Digital elevation\bathymetry model ESRI GRID format AERONET_Stennis terra.img - MODIS image (in ERDAS img format) Methods 1. Assess your data by playing with the symbology of your layers: If needed, look at your notes for exercise 3! Go to Layer Properties > Symbology TAB Use: a) a UScities: Quantities > Graduated Symbols - for population b) sea levels: Features > Single Simbol - same color (blue?) for each one. c) LA_censusblocks: make a nice (sequential) choropleth map showing where the population is concentrated. d) luis_utmnad83: play with the different modes of classification to experiment with the data, however you can uncheck the layer s visibility (little check box next to the name). e) Check out the NASA MODIS 250m resolution satellite image, you will need it for your final display, but can uncheck if you think it enhances your map redrawing speed. For the analysis part you now have raster data (your luis_utmnad83 etopo2 bathymetry data) and vector data (your Louisiana censusblocks as polygons). How can you combine the raster and vector data to figure out how many people are affected? You can t! 6

7 You will have to convert the raster data to vector data to be able to make a spatial overlay. I did that for you, to save you some time and frustration as the methods might be slightly too advanced for now. The method was the following (in case you are interested and would like to try): 1) make the classification of the elevation data permanent (sea vs. land): > sea (raster value becomes 1 ~instead of elevation) or land (raster value becomes 0): Under the Spatial Analyst extension go to reclass > reclassify 2) convert each raster (i.e. the reclassified GRID) to polygons (one for land and one for sea). This you do via the Conversions>From Raster>Raster to Polygon 3) the result is the 4 sea level polygon shapefiles I gave you for this exercise. 2. Find out how many people in Louisiana are affected by the different amounts of sea level rise: How many people already lived below sea level (2000 data) How many people are affected by 1m sea level rise? How many people are affected by 7m sea level rise? How many people are affected by 25m sea level rise? Use the US censes block information (the LA_censusblocks shapefile) and the 4 different sea level shapefiles. A good method is the Select by Location tool. It can be accessed via the Selection Menu > Select by Location: Fill out the information as follows (see figure on next page!!): And click Apply (each time you do the analysis).!! What does Have their centroid in mean? Why would this be an option to use in this case? Look in the HELP to get your answer! What do the different options mean, and what different results will they give? 3. This will select a number of records in your LA_censusblocks table. Open the table (Right Click on the layer name, then Open Attribute Table). As we did in the earthquake exercise, Right Click on the field name POP2000 and select Statistics. This will give you the sum of the selected records, i.e. the total population below sea level. 7

8 4. Open the program Microsoft Excel. 5. For each of the four sea level values provided (i.e. 0, 1, 7 and 25 m) write down (rather copy) the number of total people selected and paste them into a little Excel table > >> Total LA Population 0m 1m 7m 25m Number of People Affected Percentage 6. Make a graph in Excel (like the one shown below) of your results, via the Chart Wizard. This is easiest when you have the sea level records of you Table selected. Try Insert > Chart > Column Chart Wizard Button: 8

9 If you cannot figure out how to do this, ask one of us for help! 7. Copy your entire graph into a Word Document (right click on graph > copy) 8. Copy your table with the underlying values into a Word Document, showing the absolute numbers and calculated percentages as well. 9. Arrange your layers; 9

10 Activate the satellite image Turn off the LA_censusblocks Show the UScities Choose a nice way to display your different coastlines (i.e. the sea level layers) so you can see them all at the same time o Suggestions are to play with the transparency of the layers (Can be found under Layer Properties > Display Transparency) OR you can play with the Symbology of the layers by making the Features > Single Symbol > No Color. o It is up to you to make something clear and good looking 10. Make a screendump of your best map. You don t need to be in Layout View, just a simple screen dump (ALT + Print Screen) will do for now. Paste it into your Word Document. 10

11 Something like below, but then with the sea levels shown: What to hand in? Part A: Upload a.pptx copy of your slides via D2L Dropbox so he can copy to a laptop. Part B: Send to Dropbox a Word Document with your answers and results. (Ex4LASTNAME.docx Summary: Added Data to ArcMap and symbolized your data Reclassified\Symbolized a raster file to show coastlines at different sea levels. Played with Display > Transparency settings of layers Worked briefly in Layout View Added a scalebar and North Arrow to your layout Exported your map as a series of images Imported your images all the same scale into Powerpoint to show a time series Worked with Excel and made a graph of the results 11