Overview

This script produces a local drain direction (LDD) map (in netCDF-4 format) based on 90-m MERIT Hydro upstream area data for a particular region at a particular resolution. The script is entirely self-containing and only requires one to specify the path of the clone map and several output folders.

The script:

1. downloads and extracts the MERIT Hydro upstream area data;
2. resamples the data using a maximum filter (to retain the river network);
3. uses the resampled upstream area (inverted) as elevation; and
4. computes the LDD.

System requirements

The script can be run on a normal desktop PC (Windows and Linux). The download of the MERIT data requires ~45 GB of free disk space. The download will be performed only once.

Instructions

If you're using Windows, install the cross-platform wget and tar utilitie. Add the location of the utilities to the environment variables, so they can be executed from any location.

Clone the repository:

git clone https://github.com/hylken/create_ldd_from_merit
cd create_ldd_from_merit

Modify config.cfg with the correct paths and folders. res should match the resolution of the clone map. The clone map should contain lat and lon variables and a data variable (any name).

Register at the MERIT Hydro website using the Google form. You will receive credentials to download the data. Make a file called merit_user_pw.txt with the user name on the first line and the password on the second line.

Create and activate a Conda environment and run the script as follows:

conda create --name <env> --file requirements.txt
conda activate <env>
python create_ldd_from_merit.py

If the environment creation step fails, we recommend creating the environment and installing the packages as follows:

conda create -n <env> -c conda-forge h5py pandas numpy netcdf4 matplotlib rasterio scikit-image pcraster