Calculation of SSEBI and Evaporative Fraction from Raster Data

Calculates a modified Simplified Surface Energy Balance Index (SSEBI) and the Evaporative Fraction (EF) using geospatial raster data such as albedo and surface-air temperature difference (TS–TA). The SSEBI is computed from albedo and TS–TA to estimate surface moisture and evaporative dynamics, providing a robust assessment of surface dryness while accounting for atmospheric variations. Based on Roerink, Su, and Menenti (2000) .

ssebiEF Package

The ssebiEF package provides tools to calculate the Simplified Surface Energy Balance Index (SSEBI) and the Evaporative Fraction (EF) from raster data. It utilizes albedo and surface-air temperature difference (TS-TA) to generate the SSEBI or EF raster.

Installation

You can install the development version of ssebiEF directly from your local folder:

Requirements

• The input rasters (TS and TA) must have the same unit of measurement (Kelvin preferably) to ensure accurate calculations of TS-TA and Simplified Surface Energy Balance Index (SSEBI) or the Evaporative Fraction (EF).

• The input rasters (albedo and TS-TA) must:

  • Have the same Coordinate Reference System (CRS).
  • Cover the same geographic extent.

• If these conditions are not met, the function attempt to align the rasters automatically (with warnings).

Dependencies

The ssebiEF package automatically manages the following dependencies: - terra for raster manipulation. - dplyr for data manipulation. - stats for statistical calculations.

You do not need to load these packages manually; they are handled internally by ssebiEF

Examples Usage of the ssebiEF Package

To use the ssebiEF package, start by loading the necessary library in R.

• Define the paths to the input files (albedo and TS-TA rasters) and the output path for the calculated SSEBI raster.

  Load the necessary package

  library(ssebEF)

  Input raster paths

  albedo_path <- "path/to/albedo.tif" TS_TA_path <- "path/to/TS_TA.tif"

  Output raster path

  output_path <- "path/to/SSEBI.tif"

  Calculate SSEBI

  calculate_SSEBI( albedo_path = albedo_path, TS_TA_path = TS_TA_path, output_path = output_path, n_intervals = 20, percentile = 0.01 )

  Check the output

  SSEBI <- terra::rast(output_path) plot(SSEBI)

• Define the paths to the input files (albedo and TS-TA rasters) and the output path for the calculated EF raster.

  Load the necessary package

  library(ssebiEF)

  Input raster paths

  albedo_path <- "path/to/albedo.tif" TS_TA_path <- "path/to/TS_TA.tif"

  Output raster path

  output_path <- "path/to/EF.tif"

  Calculate EF

  calculate_EF( albedo_path = albedo_path, TS_TA_path = TS_TA_path, output_path = output_path, n_intervals = 20, percentile = 0.01 )

  Check the output

  EF <- terra::rast(output_path) plot(EF)