Monthly TerraClimate in netCDF format#

This section will explain on how to download TerraClimate’s precipitation (ppt) and potential evapotranspiration (pet) monthly data in netCDF format and prepare it as input for SPI/SPEI calculation.

Download TerraClimate data#

  • There are 2 files contains link for downloading ppt (Precipitation) and pet (Potential Evapotranspiration).

  • Download both files and put it in the same location with your working directory.

  • Navigate to downloads/terraclimate/ppt/nc_original and downloads/terraclimate/pet/nc_original folder in the working directory. Download all TerraClimate in netCDF format from Jan 1958 to Dec 2020 using wget (this is lot of data, ppt ± 7.7GB and pet ± 6.4GB, please make sure you have bandwidth and unlimited data package). Paste and Enter below script in your Terminal.

    If you are in downloads/terraclimate/ppt/nc_original then execute below command.

    sh data_ppt.sh

    If you are in downloads/terraclimate/pet/nc_original then execute below command.

    sh data_pet.sh

Extract data based on area of interest#

Next step will be extract data using a bounding box based on area of interest and merge netCDFs into single netCDF.

Note

Below guideline provide example on how to use CDO and NCO to do some data extraction process, you can choose which one is suits you.

  • Clip your area of interest using bounding box. We will use Sao Tome and Principe (STP) as the example case.

    Example: STP bounding box with format lon1,lon2,lat1,lat2 is 5.75,8.05,-0.35,2.15.

    Precipitation: Navigate your location to /downloads/ppt/nc_original.

    Software

    Script

    CDO

    for fl in *.nc; cdo sellonlatbox,5.75,8.05,-0.35,2.15 $fl ../nc_subset/"stp_cli_"$fl; done

    NCO

    for fl in *.nc; ncks -d latitude,-0.35,2.15 -d longitude,5.75,8.05 $fl -O ../nc_subset/"stp_cli_"$fl; done

    Potential Evapotranspiration: Navigate your location to /downloads/pet/nc_original.

    Software

    Script

    CDO

    for fl in *.nc; cdo sellonlatbox,5.75,8.05,-0.35,2.15 $fl ../nc_subset/"stp_cli_"$fl; done

    NCO

    for fl in *.nc; ncks -d latitude,-0.35,2.15 -d longitude,5.75,8.05 $fl -O ../nc_subset/"stp_cli_"$fl; done

  • Merge all annual netcdf in a folder into single netcdf.

    Precipitation: make sure you are in /downloads/ppt/nc_subset.

    Software

    Script

    CDO

    cdo mergetime stp_*.nc ../nc_merge/stp_cli_terraclimate_ppt_1958_2020.nc

    NCO

    Before merging the data, NCO required all the data has time dimension, we will use ncks command to make time the record dimension/variable used for concatenating files. Then use ncrcat to concatenate it.

    • for fl in *.nc; do ncks -O --mk_rec_dmn time $fl $fl; done
    • ncrcat -O -h stp_*.nc ../nc_merge/stp_cli_terraclimate_ppt_1958_2020.nc

    Potential Evapotranspiration: make sure you are in /downloads/pet/nc_subset.

    Software

    Script

    CDO

    cdo mergetime stp_*.nc ../nc_merge/stp_cli_terraclimate_pet_1958_2020.nc

    NCO

    Before merging the data, NCO required all the data has time dimension, we will use ncks command to make time the record dimension/variable used for concatenating files. Then use ncrcat to concatenate it.

    • for fl in *.nc; do ncks -O --mk_rec_dmn time $fl $fl; done
    • ncrcat -O -h stp_*.nc ../nc_merge/stp_cli_terraclimate_pet_1958_2020.nc

Check variable and attribute#

As explain in above step, we need to check the variable and attribute on above result to make sure all meet the requirements.

  • Navigate to /downloads/ppt/nc_merge folder in the working directory. Then execute below command.

    ncdump -h stp_cli_terraclimate_ppt_1958_2020.nc

    ncdump ppt

  • Navigate to /downloads/pet/nc_merge folder in the working directory. Then execute below command.

    ncdump -h stp_cli_terraclimate_pet_1958_2020.nc

    ncdump pet

  • As you can see from above picture, all the requirement is completed: unit is in mm, order dimension for each variables is lat, lon, time, and time dimension is in UNLIMITED. Once this has completed, the dataset can be used as input to climate-indices package for computing SPI/SPEI.