Soil moisture anomalies

Product overview¶

Soil moisture observations describe current conditions but do not indicate whether those conditions are typical or extreme. Soil moisture anomaly products provide this context by comparing current observations with long-term climatological records.

Anomalies are computed as the difference between a short-term (rolling window) median and a long-term (climatological) median for the same calendar period.

Anomaly types¶

Type	API value	Description	Unit
Difference	`diff`	Absolute difference between the short-term and long-term median	m³/m³
Percentile rank	`prank`	Percentile rank of the current value within the climatological distribution	percentile (0–100)

Climatological reference periods¶

Reference	API value	Description
10-year	`10y`	Based on the preceding 10 years of data
30-year	`30y`	Based on the preceding 30 years of data

Aggregation windows¶

Window	API value	Description
7-day rolling	`r7day`	Rolling 7-day median
30-day rolling	`r30day`	Rolling 30-day median

Available anomaly products¶

Anomalies are available for all standard, NRT, and forecast products:

d-mssm-anom — Standard D-MSSM anomalies
d-essm-anom — Standard D-ESSM anomalies
d-hssm-anom — Standard D-HSSM anomalies
d-mssm-nrt-anom — NRT D-MSSM anomalies
d-essm-nrt-anom — NRT D-ESSM anomalies
d-hssm-nrt-anom — NRT D-HSSM anomalies
d-mssm-fc-anom — Forecast D-MSSM anomalies
d-essm-fc-anom — Forecast D-ESSM anomalies
d-hssm-fc-anom — Forecast D-HSSM anomalies

When querying anomalies, the parameters anom_type, clim_ref, and clim_window must be provided alongside the product name.

Anomaly netCDF4 structure¶

Anomaly netCDF files contain a single data variable instead of the standard soil moisture variable:

Variable	Description	Dims	Type	Fill value	Scale factor	Unit
`diff`	Difference between long- and short-term soil moisture medians	(y, x)	int16	-9999	0.005	m³/m³
`y`	Latitude coordinate	(y)	float64	NaN	—	degrees_north
`x`	Longitude coordinate	(x)	float64	NaN	—	degrees_east
`spatial_ref`	Coordinate reference system	()	int64	—	—	—

Additional global attributes¶

Attribute	Example value
`description`	“Soil moisture anomaly difference with respect to 30y climatological reference, aggregated over a ‘r7day’ time window.”
`source`	D-MSSM v02.00
`data_level`	L4
`feed`	standard

Anomaly JSON (point API) response¶

Example (d-mssm-anom, diff, r7day, 30y):

{
  "data": [
    {
      "location": {
        "coordinates": {
          "lat": 14.0,
          "lon": 100.5
        }
      },
      "times": {
        "valid_time": "2026-02-10 12:00:00"
      },
      "values": {
        "lat": 14.0,
        "lon": 100.5,
        "diff": -0.045,
        "feed": "standard"
      }
    }
  ],
  "meta": {
    "message": null
  }
}

Anomaly file naming¶

Anomaly files embed the type, window, and reference period in the product name:

smi.YYYYMMDD.t12z.<resolution>.d-mssm-anom-<anom_type>-<clim_window>-<clim_ref>.<region>.vMAmi.nc

Where:

diff or prank — anomaly type
r7day or r30day — aggregation window
30y or 10y — climatological reference

Example: smi.20260210.t12z.6000m.d-mssm-anom-diff-r7day-30y.global.v0200.nc

Further details: Introducing Spire’s Soil Moisture Insights: Anomalies & Contextual Intelligence