# FAO-56 Penman-Monteith Irrigation Need Calculator

> FAO-56 Penman-Monteith Irrigation Need Calculator is a paid API for AI agents from natur.halowerk.com, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-11).

Computes daily crop water deficit using the FAO-56 Penman-Monteith reference evapotranspiration method, applies a crop coefficient, subtracts effective rainfall, and returns the daily and cumulative irrigation need.

## Facts

- Endpoint: POST https://natur.halowerk.com/v1/irrigation-need?utm_source=zero.xyz
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-11
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/fao-56-penman-monteith-irrigation-need-calculator-79623a45
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_82vE058GdeBEXiSNkR6-z

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability fao-56-penman-monteith-irrigation-need-calculator-79623a45 -d '<json body>'
```

Example prompt: Calculate how much irrigation my corn field (crop coefficient 1.15) needs today near Freiburg, Germany — use the Penman-Monteith method and subtract any effective rainfall, then give me the daily deficit and running total.

## When to prefer this

Choose this endpoint when you need agronomically rigorous irrigation scheduling that explicitly uses the FAO-56 Penman-Monteith standard — especially in windy or arid conditions where temperature-only methods diverge significantly. Prefer it over simpler ET calculators when the crop coefficient matters, when you need a running cumulative deficit, or when results must be comparable across different sites or studies using a named, standardized method.

## Known failure modes

- Missing or incomplete hourly forecast data for the requested location or time period
- Crop coefficient value out of plausible range causing rejected input
- Location coordinates resolving to an area with no available forecast data
- Invalid or missing date range parameters
- Network timeout if upstream forecast provider is slow
- Zero or negative effective rainfall values causing unexpected deficit spikes

## How this service works

Computes reference evapotranspiration by the FAO-56 Penman-Monteith method from hourly forecast data, applies a crop coefficient, subtracts effective rainfall and returns the resulting daily water deficit and its running total. The method is named because it matters: a simple temperature-based estimate and Penman-Monteith diverge substantially in windy or dry conditions, and a number without its method cannot be compared with anything.

## Output

Returns the computed FAO-56 Penman-Monteith reference evapotranspiration (ETo), the crop-adjusted evapotranspiration (ETc), effective rainfall subtracted, the resulting daily water deficit in millimeters, and a running cumulative deficit total — all clearly labeled by calculation method to enable cross-comparison.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "lat": {
   "type": "number",
   "maximum": 90,
   "minimum": -90
  },
  "lon": {
   "type": "number",
   "maximum": 180,
   "minimum": -180
  },
  "crop": {
   "enum": [
    "reference_grass",
    "maize",
    "wheat",
    "potato",
    "tomato",
    "vine",
    "lawn",
    "orchard"
   ],
   "type": "string",
   "default": "reference_grass"
  },
  "altitude_m": {
   "type": "number",
   "default": 100,
   "maximum": 5000,
   "minimum": -400,
   "description": "Site altitude; affects atmospheric pressure in the calculation."
  },
  "effective_rain_factor": {
   "type": "number",
   "default": 0.8,
   "maximum": 1,
   "minimum": 0.3,
   "description": "Share of rainfall that reaches the root zone rather than running off. An assumption, stated."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/fao-56-penman-monteith-irrigation-need-calculator-79623a45/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from natur.halowerk.com](https://www.zero.xyz/host/natur.halowerk.com/llms.txt)