# Garden Watering Need

> Litres of water per bed for the coming week from the MET Norway forecast and FAO-56 crop water use. Estimates how much to water each garden bed over the next days: FAO-56 Penman–Monteith reference evapotranspiration from the MET Norway forecast, times the crop coefficient of each planting and its growth stage, minus the rain that reaches the roots — in millimetres and litres, with a suggested number of waterings.

Part of usefulweb.site (https://usefulweb.site/). Part of [Hearth](https://hearth.usefulweb.site/) (ownerApp: hearth). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://hearthwateringneed.usefulweb.site/ (interactive tool at https://hearthwateringneed.usefulweb.site/tool)
- JSON API: POST https://hearthwateringneed.usefulweb.site/api/v1/calculate with a JSON object of inputs (schema: https://hearthwateringneed.usefulweb.site/api/v1/tool)
- OpenAPI: https://hearthwateringneed.usefulweb.site/openapi.json
- MCP (Streamable HTTP): https://hearthwateringneed.usefulweb.site/mcp - tool `hearth_watering_need`

## Inputs
- place (text, required): Place (latitude, longitude) - Decimal degrees such as “52.47, 13.40”. Rounded to 0.01° (about 1 km).
- timeZone (text): Time zone of the place
- days (integer): Days ahead
- plantings (table): Plantings

## Method
- Fetches the MET Norway Locationforecast 2.0 for the place (rounded to 0.01°, cached until MET’s Expires time) and groups the hours into local days; only complete days count (at least 20 forecast hours).
- Per day: maximum and minimum temperature and humidity, mean wind (10 m wind reduced to 2 m, FAO-56 eq. 47) and mean cloud cover. Solar radiation is estimated from the clear-sky radiation and the cloud fraction C with Kasten & Czeplak (1980): Rs = Rso (1 − 0.75 C^3.4).
- Reference evapotranspiration ET0 is the FAO-56 Penman–Monteith equation (eq. 6) with net radiation from eq. 38–40 and the height MET reports for the point; a test reproduces FAO-56 example 18 (Brussels, 6 July: 3.9 mm/day).
- Crop water use ETc = Kc × ET0 with FAO-56 Table 12 coefficients; with a planting date the Kc follows the FAO single-coefficient curve over a season of 1.25 × the days to harvest (20 / 30 / 35 / 15 % initial, development, mid-season, late), otherwise the mid-season value of an established crop. Plantings sown after a day do not count that day.
- Rain under 2 mm a day is lost to leaves and evaporation; 80 % of larger amounts reach the roots. Need = ETc − effective rain over the period (not below zero); litres = millimetres × square metres. One watering per about 12 mm of need (soaking, not sprinkling).

## Limits
- An estimate for open beds: sandy soil, wind, containers and greenhouses need more water; mulch and heavy soil less. Check the soil a finger deep before watering.