NDMI: Measuring the Water Inside the Canopy
NDMI is not about open water at all — it is about the moisture held in leaves and canopy. Because water absorbs shortwave-infrared strongly, the NIR-to-SWIR contrast tracks how hydrated vegetation is, often before stress becomes visible.
How it reads the surface
Turgid, well-watered leaves reflect NIR and absorb SWIR1; as they dry, SWIR1 reflectance rises and the index falls. That makes NDMI an early-warning indicator that leads visible browning by days to weeks.
The formula
where NIR is near-infrared reflectance, SWIR1 is shortwave-infrared 1 reflectance (~1.6 µm).
Reading the values
Higher = greater canopy / leaf moisture; low or negative = dry, stressed or non-vegetated surfaces.
Which bands to use
| Sentinel-2 | NIR B8 · SWIR1 B11 |
| Landsat 8/9 | NIR B5 · SWIR1 B6 |
In practice
It is used for drought monitoring, irrigation scheduling, forest-fire fuel-moisture assessment, and detecting canopy stress ahead of any NDVI decline.
Where it struggles
NDMI responds to canopy structure as well as water content, so treat it as a relative index — track its change over time on the same site rather than reading a single absolute value.
Compute NDMI on your own study area
Skip the code. Draw or upload a boundary and Spatial Research Suite runs NDMI on live Sentinel-2 or Landsat imagery — with cloud masking, exports and citations built in.
Run this analysis in GISforus →Frequently asked
What does a falling NDMI indicate?
Declining canopy or leaf moisture — an early sign of drought or water stress, often before the vegetation visibly browns.
Is NDMI the same as NDWI?
No. McFeeters NDWI (green/NIR) maps open water; NDMI (NIR/SWIR) measures moisture within vegetation.