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Calculate Drought Stress Index (R3)

Source: R/indicators-risk.R
indicator_risk_drought.Rd

Computes drought stress combining a climate component (SPEI-3 index) and a topographic modulation (aspect, slope, TWI). Falls back to topographic-only assessment when SPEI is unavailable.

Usage

indicator_risk_drought(units, layers = NULL, dem = NULL, climate_data = NULL)

Arguments

units

An sf object with forest parcels.

layers

A nemeton_layers object. Used to extract DEM.

dem

A SpatRaster with digital elevation model (meters).

climate_data

Optional list with precip (monthly precipitation vector in mm) and temp (list with tmin and tmax monthly vectors in degrees C). If NULL, uses simulated data.

Value

The input sf object with added column:

  • R3: Drought stress (0-100). Higher = higher stress.

Details

**Climate component** (weight 0.6): Uses SPEI-3 (Standardised Precipitation-Evapotranspiration Index at 3-month scale) via SPEI. PET is computed with the Hargreaves method. R3_climat = (-SPEI_recent + 2) / 4, clamped to 0-1. Falls back to 0.5 without SPEI.

**Topographic component** (weight 0.4):

  • aspect_risk: south-facing = max risk

  • slope_risk: steep slopes = runoff = dry

  • twi_risk: low TWI = dry

topo_risk = 0.4*aspect_risk + 0.3*slope_risk + 0.3*twi_risk

R3 = (0.6 * climate + 0.4 * topo) * 100

See also

Other risk-indicators: indicator_risk_browsing(), indicator_risk_fire(), indicator_risk_storm()

Examples

if (FALSE) { # \dontrun{
library(nemeton)

data(massif_demo_units)
units <- massif_demo_units
dem <- rast("path/to/dem.tif")

result <- indicator_risk_drought(units, dem = dem)
summary(result$R3)
} # }