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Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.

NAME - Computes subday design precipitation totals.


raster, hydrology, precipitation

SYNOPSIS --help map=name return_period=name[,name,...] rainlength=integer [area_size=float] [--help] [--verbose] [--quiet] [--ui]


Print usage summary
Verbose module output
Quiet module output
Force launching GUI dialog


map=name [required]
Vector map of location under analysis
Or data source for direct OGR access
return_period=name[,name,...] [required]
Rainfall raster maps of required return period
Options: N2, N5, N10, N20, N50, N100
rainlength=integer [required]
Design rainfall length in minutes
Options: 0-1439
Maximum area size to be processed (in km2, -1 for no limit)
Default: 20

Table of contents

DESCRIPTION computes subday design precipitation totals based on Hradek's method of reduction of daily maximums to chosen duration.

The tool uses methods of zonal statistics to compute average values of 24 hours precipitation amounts of specified return period for a provided area or a spot. Rasters of daily maxima were derived from statistics published by Samaj et al. in 1985, which were based on precipitation series observed in 1901-1980. Calculated average value (in millimeters) is then reduced to the chosen length of design rain event.


Subday design precipitation series are important for hydrological modelling and soil erosion problems in a small catchment scale when designing common measures for promoting water retention, landscape drainage systems, flood mitigation measures etc.

First automatization has been implemented by well-known method which is based on reduction of 24 hours design precipitation to shorter time. GIS can used for spatial supervised classification of point values of specified return periods (2, 10, 20, 50 and 100 years).

Figure: Basins (in orange) with orthophoto
on background
Figure: Return periods (2, 10, 20, 50 years)
in the area of the Czech Republic

Figure: IV.order basins colored by mean H_N2T60 value (in millimeters)

EXAMPLE map=basin return_period=N2,N5,N10,N20 rainlength=60



This work has been supported by the research project QJ1520265 - "Variability of Short-term Precipitation and Runoff in Small Czech Drainage Basins and its Influence on Water Resources Management".


v.rast.stats, v.what.rast


Martin Landa, GeoForAll (OSGeoREL) Lab, Czech Technical University in Prague, Czech Republic
The module is inspired by Python script developed for Esri ArcGIS platform by M. Tomasu in 2013.


Available at: source code (history)

Latest change: Monday Jan 30 19:52:26 2023 in commit: cac8d9d848299297977d1315b7e90cc3f7698730

Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.

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