NDMI Range Delta

Land Usev06.00 credits/per_km2

Responsible:Niccolò Calandri

NDMI Range Delta

Overview

The NDMI Range Delta compares the mean vegetation moisture between two consecutive time periods. The annual NDMI mean represents the average moisture index value over the period. By computing the difference between the means of two distinct periods, we obtain a measure of how leaf water content and vegetation moisture regime have changed over time.

Formula:

Delta = Mean_NDMI(period 2) - Mean_NDMI(period 1)
Mean_NDMI(period) = mean(NDMI, period)
NDMI = (NIR - SWIR1) / (NIR + SWIR1)

Positive delta: seasonal vegetation moisture variability has increased — potentially indicating more pronounced summer water stress (drought), changes in irrigation regimes, or shifts in vegetation composition toward less drought-resistant species.
Negative delta: moisture variability has decreased, suggesting leaf water content stabilization — possibly associated with introduction of irrigation systems, planting of more drought-resistant species, or more uniform climatic conditions.
Near-zero delta: vegetation moisture regime has remained stable between the two periods.

NDMI is a key indicator of vegetation water status and drought stress vulnerability. Seasonal range variations provide fundamental insights for forest management, agricultural irrigation planning, and fire risk monitoring.

Calculation Methodology

Data acquisition: Sentinel-2 images for both periods with cloud masks (SCL band).
NDMI calculation: computed using NIR (B8A, 20m) and SWIR1 (B11, 20m) bands.
Mean calculation for period 1: mean NDMI computed pixel-wise across all valid scenes of the first period.
Range calculation for period 2: same for year N+1.
Delta calculation: pixel-wise subtraction: Delta = Mean(period 2) - Mean(period 1).
Validation: pixels lacking valid data in either period masked as NoData.

Data Sources

Source Code	Name	Provider	Resolution	Availability
WRD_S2XXX_99	Sentinel-2 MSI L2A	ESA/Copernicus	20m (native B8A/B11)	From 2015

Technical Notes

20m resolution is native for the bands used (B8A and B11 in Sentinel-2).
NDMI is more sensitive to vegetation water content than NDVI, making it particularly suited for water stress monitoring.
Variations in rainfall regimes between the two years can significantly influence results.

References

Gao, B.C. (1996). "NDWI—A normalized difference water index for remote sensing of vegetation liquid water from space." Remote Sensing of Environment, 58(3), 257-266.
Ceccato, P., et al. (2001). "Detecting vegetation leaf water content using reflectance in the optical domain." RSE, 77(1), 22-33.

Data Sources & References

Sources

WRD_S2XXX_99

Methodology

Il delta del range dell'NDMI viene calcolato confrontando i range annuali dell'indice di umidità vegetale tra due periodi consecutivi. Per ciascun periodo si calcola la media dell'NDMI. Il delta è ottenuto tramite sottrazione pixel per pixel: Delta = Media(periodo 2) - Media(periodo 1). I dati provengono da Sentinel-2 (bande NIR B8A e SWIR1 B11) con risoluzione 20m.