{"uid":"cap_7j5mbQd0HihOF6ZCjhARM","slug":"farm-garden-calc-hargreaves-reference-evapotranspiration-et-3b4393b6","name":"Farm & Garden Calc – Hargreaves Reference Evapotranspiration (ET₀)","description":"Hargreaves reference evapotranspiration (mm/day) from max and min temperature, latitude and day of year.","url":"https://agri-calc.x402tookit.com/et0-hargreaves?utm_source=zero.xyz","method":"GET","headers":{},"bodySchema":{"type":"object","$schema":"https://json-schema.org/draft/2020-12/schema","required":["input"],"properties":{"input":{"type":"object","required":["type","method"],"properties":{"type":{"type":"string","const":"http"},"method":{"enum":["GET"],"type":"string"},"queryParams":{"type":"object","required":["tmaxC","tminC","latitude","dayOfYear"],"properties":{"tmaxC":{"type":"number","description":"Daily maximum air temperature, Celsius"},"tminC":{"type":"number","description":"Daily minimum air temperature, Celsius"},"latitude":{"type":"number","description":"Latitude in degrees, -90 to 90 (south negative)"},"dayOfYear":{"type":"number","description":"Day of year, 1 to 366"}}}},"additionalProperties":false},"output":{"type":"object","required":["type"],"properties":{"type":{"type":"string"},"example":{"type":"object","properties":{"asOf":{"type":["null","string"]},"source":{"type":["null","string"]},"reasons":{"type":["array","null"],"items":{"type":"string"}},"summary":{"type":["null","string"]},"verdict":{"type":["null","string"]},"degraded":{"type":["boolean","null"]},"meanTempC":{"type":["null","number"]},"disclaimer":{"type":["null","string"]},"notChecked":{"type":["array","null"],"items":{"type":"string"}},"tempRangeC":{"type":["null","number"]},"et0MmPerDay":{"type":["null","number"]},"et0InchesPerDay":{"type":["null","number"]},"extraterrestrialRadiationMmDay":{"type":["null","number"]},"extraterrestrialRadiationMJm2Day":{"type":["null","number"]}}}}}}},"responseSchema":null,"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.02","displayCostAsset":"USDC","priceDynamic":false,"priceHint":null,"priceStatus":"priced","priceSource":"probe","requiresHandshake":false,"reviewCount":0,"rating":{"score":"0.00","successRate":"0.00","reviews":0,"stars":null,"state":"unrated"},"availabilityStatus":"unknown","priceObserved":null,"sessionDeposit":null,"pricing":{"kind":"static","summary":"$0.02/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.02","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.02","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_hZiDXlTd5T7kZdm-a4YpD","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.02","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Calculates reference evapotranspiration (ET₀) in mm/day and inches/day using the Hargreaves method from daily max/min temperatures, latitude, and day of year.","exampleAgentPrompt":"What's the Hargreaves reference ET₀ for today at latitude 38.5°N, day of year 195, with a max temperature of 34°C and a min temperature of 18°C?","exampleUseCases":[{"title":"Daily irrigation scheduling for a crop farm","prompt":"I'm managing an alfalfa field at 36.8° latitude. Today is day 210 of the year, the high was 31°C and the low was 16°C — what's the reference ET₀ so I know how much to irrigate?"},{"title":"Seasonal water budget planning","prompt":"I need to estimate evapotranspiration for my vineyard in central California (latitude 37.2°N) on day 150 of the year, with a max temp of 28°C and min of 12°C. Can you calculate the ET₀ using the Hargreaves method?"},{"title":"Automated weather-driven irrigation trigger","prompt":"It's day 245 of the year at my farm (latitude 43°N). Yesterday's high was 26°C and low was 11°C. Calculate the Hargreaves ET₀ so I can decide whether to run the irrigation system today."}],"resultDescription":"Returns ET₀ in mm/day and inches/day, mean air temperature, temperature range, and extraterrestrial radiation in both MJ/m²/day and mm/day equivalents. Also includes metadata fields such as source, asOf timestamp, summary, disclaimer, and degraded flag.","failureModes":["Missing required query parameters (tmaxC, tminC, latitude, dayOfYear) results in a 400-level error","Out-of-range latitude (outside -90 to 90) or dayOfYear (outside 1–366) may return an error or degraded result","tminC greater than tmaxC may produce physically invalid results or a degraded flag","Payment not provided or insufficient USDC results in 402 Payment Required"],"whenToPreferThis":"Use this endpoint when you need a fast, formula-based ET₀ estimate using only temperature data and location — ideal when solar radiation data is unavailable. The Hargreaves method is well-suited for data-sparse environments. Prefer this over Penman-Monteith when you only have temperature and location as inputs. It is purpose-built for agricultural irrigation planning and water budget calculations at the field scale.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-10-29T13:08:16.345Z","isFirstParty":false,"canonicalSlug":"farm-garden-calc-hargreaves-reference-evapotranspiration-et-3b4393b6"}