Climate Indices¶

The Open Climate Service exposes the full xclim indicator library — 179 peer-reviewed, CF-compliant climate extreme indices — as native openEO processes. Every indicator appears automatically in GET /processes and is callable by name from any openEO process graph or client, with no additional configuration.

What is available¶

All xclim indicator modules are covered:

Module	Domain	Examples
`atmos`	Atmospheric	SPI, CDD, CWD, TX days above, heat wave frequency, frost days, growing degree days, …
`land`	Land surface	Snow water equivalent, soil freeze/thaw, …
`seaIce`	Sea ice	Ice extent, concentration trends

Browse the full list from any connected client:

import openeo

conn = openeo.connect("http://your-instance:8000")
processes = conn.list_processes()
print([p.id for p in processes])

Or call GET /processes directly and search by keyword. In the openEO Web Editor, the search box filters by id and summary.

Standardized Precipitation Index (SPI)¶

SPI is the primary drought monitoring index. The window parameter selects the accumulation timescale:

Process call	Timescale
`spi(pr, window=1)`	SPI-1 — short-term moisture anomaly
`spi(pr, window=3)`	SPI-3 — seasonal drought
`spi(pr, window=6)`	SPI-6 — medium-term drought
`spi(pr, window=12)`	SPI-12 — long-term / groundwater recharge

Python client¶

import openeo

conn = openeo.connect("http://your-instance:8000")

precip = conn.load_collection(
    "chirps_rainfall_daily",
    temporal_extent=["2000-01-01", "2023-12-31"],
)

spi3 = precip.process("spi", arguments={
    "pr": precip,
    "window": 3,
    "cal_start": "2000-01-01",
    "cal_end": "2020-12-31",
})

job = spi3.save_result("Zarr").create_job()
job.start_and_wait()

Process graph (JSON)¶

{
  "process_graph": {
    "load": {
      "process_id": "load_collection",
      "arguments": {
        "id": "chirps_rainfall_daily",
        "temporal_extent": ["2000-01-01", "2023-12-31"]
      }
    },
    "spi": {
      "process_id": "spi",
      "arguments": {
        "pr": { "from_node": "load" },
        "window": 3,
        "cal_start": "2000-01-01",
        "cal_end": "2020-12-31"
      },
      "result": true
    }
  }
}

Parameters¶

Parameter	Type	Default	Description
`pr`	datacube	—	Daily precipitation (kg m⁻² s⁻¹ or mm/day)
`window`	integer	`1`	Accumulation window in months (1=SPI-1, 3=SPI-3, 6=SPI-6)
`cal_start`	string	start of record	Calibration period start (YYYY-MM-DD)
`cal_end`	string	end of record	Calibration period end (YYYY-MM-DD)
`freq`	string	`"MS"`	Output frequency — `"MS"` = monthly, `None` = pre-aggregated input

SPI values are standardised: 0 = climatological median, ±1 = moderate anomaly, ±2 = extreme anomaly.

Other common indices¶

Consecutive dry / wet days¶

# Annual maximum consecutive dry days (CDD)
precip.process("cdd", arguments={"pr": precip, "thresh": "1 mm/day", "freq": "YS"})

# Monthly maximum consecutive wet days (CWD)
precip.process("cwd", arguments={"pr": precip, "thresh": "1 mm/day", "freq": "MS"})

Days above temperature threshold¶

# TX days above 35°C per year
tmax.process("tx_days_above", arguments={"tasmax": tmax, "thresh": "35 degC", "freq": "YS"})

Heat wave frequency¶

# Annual count of heat waves (≥3 consecutive days with Tmax>35°C and Tmin>20°C)
tmax.process("heat_wave_frequency", arguments={
    "tasmin": tmin,
    "tasmax": tmax,
    "thresh_tasmin": "20 degC",
    "thresh_tasmax": "35 degC",
    "freq": "YS",
})

Customising an index¶

The auto-registered xclim processes can be overridden per-instance by placing a @process-decorated function with the same id in plugins_dir/processes/. This is useful for adjusting default parameters or adding domain-specific documentation without modifying shared code.

# plugins/processes/climate_indices.py
import xarray as xr
import xclim.indicators.atmos as xclim_atmos
from open_climate_service.process import process

@process(summary="Consecutive dry days (Rwanda threshold)")
def cdd(pr: xr.DataArray, thresh: str = "0.5 mm/day", freq: str = "MS") -> xr.DataArray:
    """CDD with a lower threshold suited to Rwanda's dry season definition."""
    return xclim_atmos.maximum_consecutive_dry_days(pr, thresh=thresh, freq=freq)

See Extensibility — Processes for the full @process decorator reference.