Calculation of the Water Deficit Index (WDI) and the Evaporative Fraction (EF) on Rasters

Provides functions to calculate the Water Deficit Index (WDI) and the Evaporative Fraction (EF) using geospatial raster data such as fractional vegetation cover (FVC) and surface-air temperature difference (TS-TA). The package automates regression-based edge fitting and produces continuous spatial maps of surface moisture and evaporative dynamics.

wdiEF Package

The wdiEF package provides tools to calculate the Water Deficit Index (WDI) and the Evaporative Fraction (EF) from raster data. It utilizes fractional vegetation cover (FVC) and surface-air temperature difference (TS-TA) to generate the WDI or EF raster.

Installation

You can install the development version of wdiEF 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 the Water Deficit Index (WDI) or the Evaporative Fraction (EF).

• The input rasters (FVC 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 wdiEF 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 wdiEF

Examples Usage of the wdiEF Package

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

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

  Load the necessary package

  library(wdiEF)

  Input raster paths

  FVC_path <- "path/to/FVC.tif" TS_TA_path <- "path/to/TS_TA.tif"

  Output raster path

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

  Calculate WDI

  calculate_WDI( FVC_path = FVC_path, TS_TA_path = TS_TA_path, output_path = output_path, n_intervals = 20, percentile = 0.01 )

  Check the output

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

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

  Load the necessary package

  library(wdiEF)

  Input raster paths

  FVC_path <- "path/to/FVC.tif" TS_TA_path <- "path/to/TS_TA.tif"

  Output raster path

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

  Calculate EF

  calculate_EF( FVC_path = FVC_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)