r.curvenumber.py - GRASS GIS manual

NAME

r.curvenumber.py - Generates the Curve Number raster from the landcover and hydrologic soil group rasters

KEYWORDS

SYNOPSIS

r.curvenumber.py

r.curvenumber.py --help

r.curvenumber.py landcover=name soil=name landcover_source=string [lookup=name] output=name [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

--overwrite: Allow output files to overwrite existing files
--help: Print usage summary
--verbose: Verbose module output
--quiet: Quiet module output
--ui: Force launching GUI dialog

Parameters:

landcover=name [required]: Landcover raster
soil=name [required]: Hydrologic Soil Group raster
landcover_source=string [required]: Lookup table source; Options: nlcd, esa, custom
lookup=name: CSV with columns lc,hsg,cn (required if source=custom)
output=name [required]: Curve number raster

DESCRIPTION
EXAMPLES
REFERENCES
AUTHOR

DESCRIPTION

r.curvenumber computes a Curve Number (CN) raster from a landcover classification raster and a Hydrologic Soil Group (HSG) raster. The Curve Number is a value that represents the runoff potential of a soilâ€“landcover combination and is a key input in the USDA SCS Curve Number methodâ€”a widely adopted practice in hydrology to estimate runoff.

It supports the lookup tables for curve number values for the following datasets and provides:

Built-in NLCD lookup (use the parameter source=nlcd)
Built-in ESA WorldCover lookup (use the parameter source=esa)

For custom lookups, use the parameter source=custom, and lookup=/path/to/table.csv. The CSV must have the header lc,hsg,cn. Pass the custom lookup as a file or paste the values in the dialogue box.

Your HSG raster must contain only the following values:

1, 2, 3, 4 for Hydrologic Soil Groups A, B, C, D.
11, 12, 13, 14 for Dual HSGs A/D, B/D, C/D, D/D.

No other values are allowed.

The curve numbers used in r.curvenumber are based on values published by the United States Department of Agriculture, Natural Resources Conservation Service (2004). While these values serve as a widely accepted reference, users should assess and, if needed, modify them to suit the specific requirements, assumptions, and spatial scale of their hydrologic studies or engineering designs.

EXAMPLES

# Example 1: NLCD lookup (built-in)
r.curvenumber \
  landcover=nlcd2019 \
  hsg=soil_hsg \
  ls=nlcd \
  output=cn_nlcd

# Example 2: ESA WorldCover lookup (built-in)
r.curvenumber \
  landcover=esa2020 \
  hsg=soil_hsg \
  ls=esa \
  output=cn_esa

# Example 3: Custom CSV lookup
r.curvenumber \
  landcover=my_lc_map \
  soil=my_hsg_map \
  ls=custom \
  lookup=cn_table.csv \
  output=cn_custom

Figure: Example output from r.curvenumber

REFERENCES

United States Department of Agriculture, Natural Resources Conservation Service. (2004). National Engineering Handbook, Part 630 Hydrology: Chapter 9 Hydrologic Soil-Cover Complexes (210-VI-NEH).

AUTHOR

Abdullah Azzam, New Mexico State University

SOURCE CODE

Available at: r.curvenumber source code (history)

Accessed: Tuesday Jul 01 15:34:48 2025