Water my field needs

Reference crop water use (ET0): FAO-56 Penman-Monteith monthly reference crop water use (ET0; Allen et al. 1998, Equations 6, 21–25, 37, 39, 43): monthly mean maximum and minimum temperature, relative humidity, wind at 2 m and solar radiation reaching the ground; the elevation is that of the POWER point. Period 2001–2025. Weather 0.5° latitude × 0.625° longitude (~55 km), solar radiation 1° × 1° (nearest radiation point); the village takes the nearest land point within 0.6° (POWER elevation above 5 m), otherwise the nearest point.

Crop factor (Kc) and growth stages: FAO, Irrigation Water Management: Training Manual No. 3 — Irrigation Water Needs (Brouwer and Heibloem, 1986), Chapter 3, Tables 7 and 8. Stage lengths in days are the average of the table's short and long rows; Kc is held constant within a stage and, following the FAO rule, lowered by 0.05 in humid, calm months and raised by 0.05 in dry, windy months (verbatim: “reduced by 0.05 if the relative humidity is high (RH > 80%) and the windspeed is low (u < 2 m/sec) … increased by 0.05 if the relative humidity is low (RH < 50%) and the windspeed is high (u > 5 m/sec)”).

Effective rain: FAO Training Manual No. 3, §4.2 — verbatim: “Pe = 0.8 P - 25 if P > 75 mm/month; Pe = 0.6 P - 10 if P < 75 mm/month”; “These formulae can be applied in areas with a maximum slope of 4-5%”; “Pe is always equal to or larger than zero; never negative”. Monthly rain is the 1991–2020 normal of the village's cell (CHIRPS v3.0); the dry year is the year, within the last 30 full calendar years, in which the cell got the least rain (measured, not estimated).

Irrigation efficiency: FAO, Irrigation Water Management: Training Manual No. 4 — Irrigation Scheduling (Brouwer, Prins and Heibloem, 1989), Annex I, Table 8 — “INDICATIVE VALUES OF THE FIELD APPLICATION EFFICIENCY (ea)”: surface 60%, sprinkler 75%, drip 90%; verbatim warning: “Lack of discipline may lower the values found in Table 8.”

Limits: the calculation does not know the soil's water-holding capacity, the slope, salinity, shade or the real moisture of the field; it uses the average climate, not this year's weather.

Source and attribution: © FAO 1986 and © FAO 1989 (FAO is the source and copyright holder; fao.org terms of use, verbatim: “may be copied, printed and downloaded for private study, research and teaching purposes, and for use in non-commercial products or services, provided that appropriate acknowledgement of FAO as the source and copyright holder is given” — https://www.fao.org/contact-us/terms/en/). The data was obtained from National Aeronautics and Space Administration (NASA) Langley Research Center's Prediction Of Worldwide Energy Resources (POWER) project funded through the NASA Earth Science Division. The data was obtained from the POWER Project's Monthly 2.10.0 version on 2026/11/05. CHIRPS v3.0, UCSB Climate Hazards Center, CC BY 4.0; Funk, C. et al. (2026), Scientific Data 13, 718, https://doi.org/10.1038/s41597-026-07096-4.