Integrating socioeconomic data and biophysical data

In this exercise we will integrate census data and weather data to get insight into how the

effects of a weather system might be distributed spatially. Along the way, we’ll point out

several key data resources available online, as well as important tools in ArcMap for

integrating datasets.

1. In 1999, a number of strong cyclones hit the eastern coast of India. Go to

http://weather.unisys.com/hurricane/ and select “North Indian” to navigate to the

“Indian Ocean Cyclone Tracking Data by Year” webpage. Click “1999” to see the

paths of cyclones that year.

2. We’ll focus on the fourth cyclone. Scroll down the page to see the exact dates when

the storm was a cyclone.

3. By clicking on “Tracking information” you can access data on the position and wind

speed of the cyclone through time. That might be a very useful resource for certain

research applications. For this exercise, however, we are only interested in the dates.

They are 15-18 October, 1999.

Now go to the TRMM Online Visualization and Analysis System website:

http://disc.sci.gsfc.nasa.gov/precipitation/tovas/. This website is a portal to

precipitation data records. Scroll down and click on the link to “Daily TRMM and

Other Rainfall Estimates”.

4. In the map, draw a bounding box that includes most of eastern India. Alternately, you

may enter N E S W coordinates.

5. In the next panel, add the cyclone dates: 15 October 1999 – 18 October 1999. In the

“Select Visualization” panel, select “Lat-Lon map, Time-accumulated”.

6. Click “Generate Visualization”. This may take a minute. A heat map of accumulated

precipitation will appear.

7. Click “Download Data” and on the next page, select the “ASC” box for the “Two

Dimensional Map Plot”. Then click “Download in Batch”

8. On the next page, click the tar.gz file to download it. It should be a relatively small

file. Unzip the file and open it in a text editor.

9. Looks a little messy - we’ll fix that. Delete everything up to (and including) “(Lon:

76.375E - 92.875E)”. The text should begin with “latitude longitude

precipitation”. Save and close the file. Open excel, and import the text file. This

dialog box will appear:

10. Select “fixed width”, and click “Next”. Make sure the breaks are between the

columns, and click “Finish”.

11. Delete the second column. Then save the file. Sometimes ArcMap has trouble

importing xlsx files. Save the file as an Excel 97-2003 Workbook.

12. Close Excel. Open ArcMap. Add the Excel file as a map layer.

13. Right-click on the layer, and select “Display X-Y Data”.

14. Change the “Z field” to “precipitation” and click OK.

15. The lattice of points that appears represents a sample of precipitation estimates. We

will now interpolate the values between those points. Using the “Search” function,

find the “Kriging (Spatial Analyst)” tool. Before clicking on it, make sure that Spatial

Analyst is enabled (“Customize” “Extensions”).

In the “Kriging” dialog window, select the precipitation layer, select “precipitation”

as the “Z value field” and chose a name and location for the output file. Also, change

the “Output cell size” to “0.0083333333” (more on that later).

16. Click “OK”. The interpolation data will appear. You may wish to unselect the

TRIMM point data to see it better.

17. Now we have interpolated accumulated precipitation for a cyclone that hit the eastern

coast of India in 1999. How many people were affected? We’ll now add another

dataset to help put this weather event in more context. The NASA SEDAC website is

a very good resource for a range of socioeconomic and biophysical data. We’ll

download population data for India. Go to

http://sedac.ciesin.columbia.edu/data/set/grump-v1-population-count/data-download.

Choose “India”, “Population Density Grid”, “Grid”, “30””, and “2000” from the

fields. When you click “Download” you will be prompted to log in, or register.

18. Once you have logged in, and clicked “Download”, the zipped data files will begin to

download. Unzip them, and open the dataset in ArcMap.

19. Now we’ll do a rough calculation of the values of both raster layers to get some

insight into how the effects of the storm’s heavy precipitation might have been

distributed across the landscape. Using the search utility, open the “Raster Calculator

(Spatial Analyst)” tool. For this exercise we are going to simply multiply the values of

the population density raster cells by the values of the precipitation raster cells.

However, a more deliberate analysis would include several intermediate steps to

normalize or otherwise transform the distribution of cell values for both rasters, so

that a calculation would be more meaningful—and the calculation itself might not

necessarily involve multiplication.

20. Create an equation by clicking on one raster layer, then the “*” button, then the other

raster layer. The equation should look like this: "induds00ag" * "precip_interp". Then

choose a name and location for the output file. Click OK.

21. If you wish, you may change the color of the new raster layer, set it to be semi-

transparent, or change the symbology in some other way. You may also wish to

unselect the precipitation layer.