flood_risk_in_buffer

Python Script to calculate average flood risk in a buffer around a point location. This is an application for Bangladesh.

In collaboration with Shaun Ashbury

1. Download SRTM 1 tiles.

Manually selected and downloaded 9 tiles from http://dwtkns.com/srtm30m/:

• N23E090.hgt
• N23E089.hgt
• N23E088.hgt
• N22E090.hgt
• N22E089.hgt
• N22E088.hgt
• N21E090.hgt
• N21E089.hgt
• N21E088.hgt

2. SRTM processing.

The below commands were ran in an Ubuntu 18.04 docker container with GDAL and dependancies installed:

Set project working directory.

cd PATH

Merge SRTM tiles.

gdal_merge.py -co BIGTIFF=YES -co COMPRESS=LZW -o output-data/sw-bangladesh-dem.tif $(ls input-data/*.hgt)

Set values <1 as water, to extract watercourses (only needed for visualization).

gdal_calc.py --calc=expression --calc "(A < 1)" --co BIGTIFF=YES --co COMPRESS=LZW --outfile=output-data/sw-bangladesh-water.tif -A output-data/sw-bangladesh-dem-filled.tif

Set values <1 to 0, and others to -1, to set a baseline water level.

gdal_calc.py --calc=expression --calc "((A < 1) - 1) + ((A >= 1) * A)" --co BIGTIFF=YES --co COMPRESS=LZW --outfile=output-data/sw-bangladesh-water-level.tif -A output-data/sw-bangladesh-dem-filled.tif

Calculate flood pixels at +1m, +2m, and +3m thresholds from the baseline.

gdal_calc.py --calc=expression --calc "(A <= 1)" --co BIGTIFF=YES --co COMPRESS=LZW --outfile=output-data/sw-bangladesh-1m-flood.tif -A output-data/sw-bangladesh-water-level.tif

gdal_calc.py --calc=expression --calc "(A <= 2)" --co BIGTIFF=YES --co COMPRESS=LZW --outfile=output-data/sw-bangladesh-2m-flood.tif -A output-data/sw-bangladesh-water-level.tif

gdal_calc.py --calc=expression --calc "(A <= 3)" --co BIGTIFF=YES --co COMPRESS=LZW --outfile=output-data/sw-bangladesh-3m-flood.tif -A output-data/sw-bangladesh-water-level.tif

3. Spatial analysis.

Run Python script to create buffered points in a virtualenv with GDAL installed as:

source ~/workspace/envs/gis/bin/activate

cd ~PATH

python3 PATH/calculate_flood_risk.py -i input-data/treatment_places.txt -o output-data/treatment_places_flood_risk.csv $(ls output-data/sw-bangladesh-[0-9]m-flood.tif)