sara4r Vignette

Rafael Hernandez Guzman

2021-03-10

Introduction

sara4r is an easy way to calculate the rainfall-runoff relation using the Natural Resources Conservation Service - Curve Number method (NRCS-CN method) but includes modifications by Hawkins et al., (2002) about the Initial Abstraction. This graphical user interface follows the programming logic of a previously published software CN-Idris, Hernández-Guzmán et al., 2011 - CN-Idris: An Idrisi tool for generating curve number maps and estimating direct runoff. Environmental Modelling & Software, 26(12), 1764-1766, a raster-based GIS tool that outputs runoff estimates from Land use/land cover and hydrologic soil group maps. This package is under development at the Institute about Natural Resources Research (INIRENA) from the Universidad Michoacana de San Nicolás de Hidalgo and represents a collaborative effort between the Hydro-Geomatic Lab (INIRENA) with the Environmental Management Lab (CIAD, A.C.).

How to install

sara4r package is a Graphical User Interface developed in RGtk2 and depends on other libraries to run (raster, sp, rgdal). Thus, to make available sara4r in the R environment you must install RGtk2 first, then the raster, sp and rgdal packages.

First time

The first time you execute our tool, you will be asked to install RGtk+.

# Load the RGtk2 library
library(RGtk2)

Just type OK and wait until the program finished.

# Load the following libraries.
library(raster)
#> Loading required package: sp
library(rgdal)
#> rgdal: version: 1.5-23, (SVN revision 1121)
#> Geospatial Data Abstraction Library extensions to R successfully loaded
#> Loaded GDAL runtime: GDAL 3.2.1, released 2020/12/29
#> Path to GDAL shared files: C:/Users/Veirus/Documents/R/win-library/4.0/rgdal/gdal
#> GDAL binary built with GEOS: TRUE 
#> Loaded PROJ runtime: Rel. 7.2.1, January 1st, 2021, [PJ_VERSION: 721]
#> Path to PROJ shared files: C:/Users/Veirus/Documents/R/win-library/4.0/rgdal/proj
#> PROJ CDN enabled: FALSE
#> Linking to sp version:1.4-5
#> To mute warnings of possible GDAL/OSR exportToProj4() degradation,
#> use options("rgdal_show_exportToProj4_warnings"="none") before loading rgdal.
#> Overwritten PROJ_LIB was C:/Users/Veirus/Documents/R/win-library/4.0/rgdal/proj
library(sp)
library(sara4r)

Finally, to run our software, just type:

sara4r()

Data preparation

As you can see in the Menu - Help, there are the instructions to make all required files to use sara4r. If you go to the installed folder (sara4r), you will find the HowtoMake_CNindexFile.xlsx with all the instructions. In overall terms:

Land use and land cover map should be reclassified as follow:
LULC in the first place should be reclassified as 10
LULC in second place should be reclassified as 20
... and so on.
  As an example, Landuse file would be:
    10 Tropical dry forest
    20 Agriculture
    30 Mangrove
    40 Grassland
    50 Evergreen forest
    ...
    

While the Hydrologic Soil Group map should be reclassified as follow:

HSG A should be reclassified as 1
HSG B should be reclassified as 2
HSG C should be reclassified as 3
HSG D should be reclassified as 4
Thus, GSH map would be:
    1 A
    2 B
    3 C
    4 D

Finally,

The logic behind the method is:"
Landsoil is produced as the sum of LANDUSE and HSG maps. Thus, the possible values it can take are:"
  11 = Landuse 1 (reclassified as 10) with HSG A (reclassified as 1)
  12 = Landuse 1 (reclassified as 10) with HSG B (reclassified as 2)
  13 = Landuse 1 (reclassified as 10) with HSG C (reclassified as 3)
  14 = Landuse 1 (reclassified as 10) with HSG D (reclassified as 4)
  21 = Landuse 2 (reclassified as 20) with HSG A (reclassified as 1)
  22 = Landuse 2 (reclassified as 20) with HSG B (reclassified as 2)
  23 = Landuse 2 (reclassified as 20) with HSG C (reclassified as 3)
  24 = Landuse 2 (reclassified as 20) with HSG D (reclassified as 4)
  31 = Landuse 3 (reclassified as 30) with HSG A (reclassified as 1)
  ...
Thus, the CN index file would be (csv file):"
  11,12,CNvalue1
  12,13,CNvalue2
  13,14,CNvalue3
  14,15,CNvalue4
  21,22,CNvalue5
  22,23,CNvalue6
  23,24,CNvalue7
  24,25,CNvalue8
  31,32,CNvalue9
  ...
  ...
  ...

References:

CN-Idris, Hernández-Guzmán et al., 2011 - CN-Idris: An Idrisi tool for generating curve number maps and estimating direct runoff. Environmental Modelling & Software, 26(12), 1764-1766

SARA, Hernández-Guzmán and Ruiz-Luna, 2013. SARA – An enhanced curve number-based tool for estimating direct runoff. Journal of Hydroinformatics, 15(3), 881-887