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NAME

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

KEYWORDS

raster, hydrology, curve number

SYNOPSIS

r.curvenumber
r.curvenumber --help
r.curvenumber landcover=name soil=name landcover_source=string [lookup=name] [hydrologic_condition=string] [antecedent_runoff_condition=string] 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,hc,cn (required if source=custom)
hydrologic_condition=string
Hydrologic condition (groundcover density affecting runoff potential)
Options: poor, fair, good
Default: fair
poor: increased runoff
fair: normal runoff
good: lower runoff
antecedent_runoff_condition=string
Antecedent Runoff Condition (the degree of wetness of a watershed before a rainfall event)
Options: i, ii, iii
Default: ii
i: dry
ii: average
iii: wet
output=name [required]
Curve number raster

Table of contents

DESCRIPTION

Generates a Curve Number (CN) raster using landcover and hydrologic soil group (HSG) rasters, along with user-specified hydrologic condition and antecedent runoff condition.

Landcover Source

Select the source of the landcover classification and corresponding lookup table:

For custom, the CSV must include the following columns:
lc,hsg,hc,cn

Hydrologic Soil Groups (HSG)

The HSG raster must contain only:

Curve Number increases from HSG A to D due to reduced infiltration associated with increasing clay content and compaction.

If you are using SSURGO soil data, Hydrologic Soil Group (HSG) values are typically provided directly. For other soil datasets that do not include HSG classifications, see Reference 1 (Chapter 7) for guidance on assigning HSGs based on soil texture, hydraulic conductivity, and water table depth. This information can be used to develop a custom HSG raster.

Hydrologic Condition (HC)

Hydrologic condition reflects the percentage of surface groundcover and affects runoff potential. Generally:

Curve Number decreases from poor to good due to improved infiltration with more vegetation.
See Reference 2 for further discussion.

Note: Curve Number for Cropland under fair hydrologic condition is provided as the average of the Curve Numbers for poor and good conditions.

Antecedent Runoff Condition (ARC)

The variability in Curve Number (CN) arises from factors such as rainfall intensity and duration, total precipitation, soil moisture conditions, vegetative cover density, growth stage, and temperature. These factors collectively define the Antecedent Runoff Condition (ARC), which is classified into three categories:

Curve Number increases from ARC I to ARC III as runoff potential rises.

A standard conversion table is used within the script to adjust CN values from ARC II to ARC I or ARC III, based on empirical relationships. This corresponds to Table 10-1 in Reference 3.

Sensitivity and CN Hierarchy

The CN is more sensitive to ARC than to HC.
Typical curve number values for a soil-cover complex follow this order:

CN Hierarchy

p_iii > f_iii > g_iii > p_ii > f_ii > g_ii > p_i > f_i > g_i

Where:

EXAMPLES

# Example 1: NLCD lookup (built-in)
r.curvenumber \
  landcover=nlcd \
  hsg=soil_hsg \
  landcover_source=nlcd \
  h_c=poor \
  arc=iii \
  output=cn_nlcd

# Example 2: ESA WorldCover lookup (built-in)
r.curvenumber \
  landcover=esa \
  hsg=soil_hsg \
  landcover_source=esa \
  h_c=fair \
  arc=ii \
  output=cn_esa

# Example 3: Custom CSV lookup
r.curvenumber \
  landcover=custom_lc_map \
  soil=custom_hsg_map \
  landcover_source=custom \
  lookup=cn_table.csv \
  h_c=good \
  arc=i \
  output=cn_custom
Example output from r.curvenumber

Figure: Example output from r.curvenumber

REFERENCES

AUTHOR

Abdullah Azzam, New Mexico State University

SOURCE CODE

Available at: r.curvenumber source code (history)

Latest change: Friday Jul 18 02:39:02 2025 in commit: 0d772326c6f475ad7ac0aecd64dd3669fc344604


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