This tutorial shows you how to calculate stream-specific freshwater variables by relating the upstream e.g. land cover to any given downstream location using the GRASS GIS add-ons r.stream.watersheds & r.stream.variables . The original 1km data and publication are available here - see also the original code from spatial-ecology.net . This example contains the following steps: Download an exemplary digital elevation model (DEM) Extract the stream network from the DEM Delineate major drainage basins Crop data to a sub-basin Calculate the sub-watersheds for each stream grid cell ( r.stream.watersheds ) Calculate contiguous stream-specific variables ( r.stream.variables ) The add-ons have been tested in the Linux environment. Microsoft Windows users: consider installing the OSGEO-Live Virtual machine that has GRASS GIS 7 already installed and is ready to use. Alternatively you can run the add-ons via QGIS. Create and enter the folder where the data will be stored: export INDIR=HOME/grasshydromkdirHOME/grass_hydro mkdir INDIR cd INDIR Download the script cd ~ wget "http://www.spatial-ecology.net/ost4sem/exercise/basic_adv_grass/stream_variables.sh" rstudio stream_variables.sh & Download and unzip a DEM from WorldClim : wget -O INDIR/alt_16_tif.zip "http://biogeo.ucdavis.edu/data/climate/worldclim/1_4/tiles/cur/alt_16_tif.zip" unzip -o INDIR/alt16tif.zip−dINDIR/alt_16_tif.zip -d INDIR/dem gdalinfo INDIR/dem/alt_16.tif # check data If needed, first install the latest GRASS GIS version: sudo add-apt-repository ppa:ubuntugis/ubuntugis-unstable sudo add-apt-repository ppa:grass/grass-devel sudo apt-get update sudo apt-get install grass grass-gui grass-dev subversion gdal-bin libgdal-grass libalgorithms1 libbase1 libgdal-dev Create the GRASS GIS data base and enter GRASS: grass78 -text -c INDIR/dem/alt_16.tif INDIR/grasslocationReaddataintoGRASS:r.in.gdalinput=INDIR/grass_location Read data into GRASS: r.in.gdal input=INDIR/dem/alt_16.tif output=elevation r.info elevation # check data Open GUI and visualize the layers: g.gui wxpython Run hydrological conditioning: g.extension extension=r.hydrodem # download extension # if you get an error run: sudo apt install grass-dev subversion r.hydrodem input=elevation output=elevation_cond Extract drainage direction and stream network r.watershed --h # see help regarding the options and flags r.watershed elevation=elevation_cond drainage=drainage stream=stream accumulation=accumulation threshold=100 --o Get drainage basins (last downstream segment: -l flag) g.extension extension=r.stream.basins r.stream.basins direction=drainage stream_rast=stream basins=basins_last -l --o Categorize the single basins: r.clump -d input=basins_last output=basins_cat --o Extract the data for one basin: r.mapcalc "drainage_sub = if (basins_cat==798, drainage, null() ) " --o r.mapcalc "stream_sub = if (basins_cat==798, stream, null() ) " --o Write files to disk: r.out.gdal input=drainage_sub output=INDIR/drainagesub.tiftype=Int32nodata=−9999−−o−ccreateopt="COMPRESS=LZW,ZLEVEL=9"r.out.gdalinput=streamsuboutput=INDIR/drainage_sub.tif type=Int32 nodata=-9999 --o -c createopt="COMPRESS=LZW,ZLEVEL=9" r.out.gdal input=stream_sub output=INDIR/stream_sub.tif type=Int32 nodata=-9999 --o -c createopt="COMPRESS=LZW,ZLEVEL=9" Create stream-specific variables, and limit the calculation only to a single basin. Download and install the GRASS add-ons. Work-around (December 2019) for grass78: mkdir HOME/.grass7/addons/scriptswget−OHOME/.grass7/addons/scripts wget -O HOME/.grass7/addons/scripts/r.stream.watersheds "https://raw.githubusercontent.com/domisch/grass-addons/master/r.stream.watersheds" chmod 777 HOME/.grass7/addons/scripts/r.stream.watershedswget−OHOME/.grass7/addons/scripts/r.stream.watersheds wget -O HOME/.grass7/addons/scripts/r.stream.variables "https://raw.githubusercontent.com/domisch/grass-addons/master/r.stream.variables" chmod 777 HOME/.grass7/addons/scripts/r.stream.variablesAdd−on1:Calculatethesub−watershedandsub−streamsectionsforeachstreamgridcellusing2processors:r.stream.watershedsstream=streamsubdrainage=drainagesubcpu=2Add−on2:Createstream−specificvariablesbasedonelevationr.stream.variablesvariable=elevationoutput=cells,min,max,range,mean,stddev,coeffvar,sumarea=watershedscale=1cpu=2Renamethe“elevationcells”to“flowaccumulation”andcheckvariables:r.mapcalc"flowaccummulation=elevationcells"−−or.infoflowaccummulationr.infoelevationrangeGetstreamlength(similarprocedureasabove):r.stream.variablesvariable=elevationoutput=cellsarea=streamscale=1cpu=2r.mapcalc"streamlength=elevationcells"−−or.infostreamlengthCalculatetheamountofrainfallwithinthebasin:wget−OHOME/.grass7/addons/scripts/r.stream.variables Add-on 1: Calculate the sub-watershed and sub-stream sections for each stream grid cell using 2 processors: r.stream.watersheds stream=stream_sub drainage=drainage_sub cpu=2 Add-on 2: Create stream-specific variables based on elevation r.stream.variables variable=elevation output=cells,min,max,range,mean,stddev,coeff_var,sum area=watershed scale=1 cpu=2 Rename the “elevation_cells” to “flow_accumulation” and check variables: r.mapcalc "flow_accummulation = elevation_cells" --o r.info flow_accummulation r.info elevation_range Get stream length (similar procedure as above): r.stream.variables variable=elevation output=cells area=stream scale=1 cpu=2 r.mapcalc "stream_length = elevation_cells" --o r.info stream_length Calculate the amount of rainfall within the basin: wget -O INDIR/prec_16_tif.zip "http://biogeo.ucdavis.edu/data/climate/worldclim/1_4/tiles/cur/prec_16_tif.zip" unzip -q -o INDIR/prec16tif.zip−dINDIR/prec_16_tif.zip -d INDIR/prec r.in.gdal input=INDIR/prec/prec6_16.tif output=prec6 # rainfall in June r.stream.variables variable=prec6 output=sum area=watershed scale=1 cpu=2 Run all 12 months in a loop: for var in (seq 1 12); do r.in.gdal input=INDIR/prec/precINDIR/prec/prec{var}_16.tif output=precvarr.stream.variablesvariable=precvar r.stream.variables variable=precvar output=sum area=watershed scale=1 cpu=2 done Other useful add-ons for hydrological applications: http://grasswiki.osgeo.org/wiki/Hydrological_Sciences Other examples Get the stream order: r.stream.order stream_rast=stream direction=drainage strahler=str_order --o Get only streams and basins >=3rd order r.mapcalc "str_order_3rd = if(str_order >=3, str_order, null() ) " --o r.stream.basins direction=drainage stream_rast=str_order_3rd basins=basins_3rd_last -l --o Stream distance - Calculates distance to and elevation above streams and outlet g.extension extension=r.stream.distance r.stream.distance stream_rast=stream direction=drainage elevation=elevation_cond method=downstream distance=str_distance difference=str_elevation_diff --o Stream order statistics - Calculates Horton’s statistics for Strahler and Horton ordered networks created with r.stream.order Print only order statistics: g.extension extension=r.stream.stats r.stream.stats stream_rast=stream direction=drainage elevation=elevation_cond output=str_stats_o.txt --o more INDIR/strstatso.txtPrintonlycatchmentstatistics:r.stream.statsstreamrast=streamdirection=drainageelevation=elevationcondoutput=strstatsc.txt−cmoreINDIR/str_stats_o.txt Print only catchment statistics: r.stream.stats stream_rast=stream direction=drainage elevation=elevation_cond output=str_stats_c.txt -c more INDIR/str_stats_c.txt See also these useful GRASS-GIS commands for hydrological applications: https://grass.osgeo.org/grass78/manuals/topic_hydrology.html https://grasswiki.osgeo.org/wiki/R.stream .*_modules https://grasswiki.osgeo.org/wiki/Hydrological_Sciences