FA-71176 / Weather index computation / Open access

Hargreaves reference evapotranspiration: radiation equivalent evaporation · case 01

Irrigation demand is about 2.5 times too high.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Radiation in MJ/m2/day is used without the 0.408 mm-equivalent conversion.

THE FAILURE

Radiation in MJ/m2/day is used without the 0.408 mm-equivalent conversion.

Unsuccessful approach: Dividing by 0.408 applies the conversion in the wrong direction.

Case contract

Daily tmax/tmin degC (tmax >= tmin) and extraterrestrial radiation Ra in MJ/m2/day. Convert Ra to mm/day with 0.408. ET0 = 0.0023*Ra_mm*(Tmean+17.8)*sqrt(tmax-tmin), Tmean=(tmax+tmin)/2; negative results clamp to 0; round to 0.01 mm.

Why this case matters

Irrigation scheduling uses ET0 where full meteorological data are unavailable.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(tmax, tmin, ra_mj):
    tmean = (tmax + tmin) / 2
    et = 0.0023 * ra_mj * (tmean + 17.8) * math.sqrt(tmax - tmin)
    return round(max(et, 0.0), 2)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['tmax 30 tmin 15 Ra 10.0', [30, 15, 10.0], 1.46], ['tmax 30 tmin 15 Ra 25.0', [30, 15, 25.0], 3.66], ['tmax 30 tmin 15 Ra 40.0', [30, 15, 40.0], 5.86], ['tmax 35 tmin 20 Ra 10.0', [35, 20, 10.0], 1.65], ['tmax 35 tmin 20 Ra 25.0', [35, 20, 25.0], 4.12], ['tmax 35 tmin 20 Ra 40.0', [35, 20, 40.0], 6.59], ['tmax 10 tmin -2 Ra 10.0', [10, -2, 10.0], 0.71], ['tmax 10 tmin -2 Ra 25.0', [10, -2, 25.0], 1.77]], [['tmax 35 tmin 20 Ra 10.0', [35, 20, 10.0], 1.65], ['tmax 10 tmin -2 Ra 10.0', [10, -2, 10.0], 0.71], ['tmax 10 tmin -2 Ra 25.0', [10, -2, 25.0], 1.77], ['tmax 10 tmin -2 Ra 40.0', [10, -2, 40.0], 2.83], ['tmax -10 tmin -25 Ra 10.0', [-10, -25, 10.0], 0.01], ['tmax -10 tmin -25 Ra 25.0', [-10, -25, 25.0], 0.03], ['tmax -10 tmin -25 Ra 40.0', [-10, -25, 40.0], 0.04], ['tmax -12 tmin -30 Ra 10.0', [-12, -30, 10.0], 0.0]], [['tmax 10 tmin -2 Ra 10.0', [10, -2, 10.0], 0.71], ['tmax -10 tmin -25 Ra 40.0', [-10, -25, 40.0], 0.04], ['tmax -12 tmin -30 Ra 40.0', [-12, -30, 40.0], 0.0], ['tmax 25 tmin 25 Ra 10.0', [25, 25, 10.0], 0.0], ['tmax 25 tmin 25 Ra 25.0', [25, 25, 25.0], 0.0], ['tmax 25 tmin 25 Ra 40.0', [25, 25, 40.0], 0.0], ['tmax 40 tmin 18 Ra 10.0', [40, 18, 10.0], 2.06], ['tmax 40 tmin 18 Ra 25.0', [40, 18, 25.0], 5.15]], [['tmax 30 tmin 15 Ra 10.0', [30, 15, 10.0], 1.46], ['tmax -10 tmin -25 Ra 10.0', [-10, -25, 10.0], 0.01], ['tmax 22 tmin 8 Ra 10.0', [22, 8, 10.0], 1.15], ['tmax 22 tmin 8 Ra 25.0', [22, 8, 25.0], 2.88], ['tmax 22 tmin 8 Ra 40.0', [22, 8, 40.0], 4.61], ['tmax -5 tmin -20 Ra 10.0', [-5, -20, 10.0], 0.19], ['tmax -5 tmin -20 Ra 25.0', [-5, -20, 25.0], 0.48], ['tmax -5 tmin -20 Ra 40.0', [-5, -20, 40.0], 0.77]], [['tmax 30 tmin 15 Ra 10.0', [30, 15, 10.0], 1.46], ['tmax 30 tmin 15 Ra 25.0', [30, 15, 25.0], 3.66], ['tmax 30 tmin 15 Ra 40.0', [30, 15, 40.0], 5.86], ['tmax 35 tmin 20 Ra 10.0', [35, 20, 10.0], 1.65], ['tmax 35 tmin 20 Ra 25.0', [35, 20, 25.0], 4.12], ['tmax 35 tmin 20 Ra 40.0', [35, 20, 40.0], 6.59], ['tmax 10 tmin -2 Ra 10.0', [10, -2, 10.0], 0.71], ['tmax 40 tmin 18 Ra 10.0', [40, 18, 10.0], 2.06]]]
for label, args, expected in fixtures[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
tmax 30 tmin 15 Ra 10.0	`3.59`	`1.46`	Failed
tmax 30 tmin 15 Ra 25.0	`8.97`	`3.66`	Failed
tmax 30 tmin 15 Ra 40.0	`14.36`	`5.86`	Failed
tmax 35 tmin 20 Ra 10.0	`4.04`	`1.65`	Failed
tmax 35 tmin 20 Ra 25.0	`10.09`	`4.12`	Failed
tmax 35 tmin 20 Ra 40.0	`16.14`	`6.59`	Failed
tmax 10 tmin -2 Ra 10.0	`1.74`	`0.71`	Failed
tmax 10 tmin -2 Ra 25.0	`4.34`	`1.77`	Failed

SHA-256 / 4c0ac98d1cd34503e01d6fc8737831d7aef0c09ce5a83183f94ad178ff474347

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(tmax, tmin, ra_mj):
    tmean = (tmax + tmin) / 2
    et = 0.0023 * ra_mj / 0.408 * (tmean + 17.8) * math.sqrt(tmax - tmin)
    return round(max(et, 0.0), 2)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['tmax 30 tmin 15 Ra 10.0', [30, 15, 10.0], 1.46], ['tmax 30 tmin 15 Ra 25.0', [30, 15, 25.0], 3.66], ['tmax 30 tmin 15 Ra 40.0', [30, 15, 40.0], 5.86], ['tmax 35 tmin 20 Ra 10.0', [35, 20, 10.0], 1.65], ['tmax 35 tmin 20 Ra 25.0', [35, 20, 25.0], 4.12], ['tmax 35 tmin 20 Ra 40.0', [35, 20, 40.0], 6.59], ['tmax 10 tmin -2 Ra 10.0', [10, -2, 10.0], 0.71], ['tmax 10 tmin -2 Ra 25.0', [10, -2, 25.0], 1.77]], [['tmax 35 tmin 20 Ra 10.0', [35, 20, 10.0], 1.65], ['tmax 10 tmin -2 Ra 10.0', [10, -2, 10.0], 0.71], ['tmax 10 tmin -2 Ra 25.0', [10, -2, 25.0], 1.77], ['tmax 10 tmin -2 Ra 40.0', [10, -2, 40.0], 2.83], ['tmax -10 tmin -25 Ra 10.0', [-10, -25, 10.0], 0.01], ['tmax -10 tmin -25 Ra 25.0', [-10, -25, 25.0], 0.03], ['tmax -10 tmin -25 Ra 40.0', [-10, -25, 40.0], 0.04], ['tmax -12 tmin -30 Ra 10.0', [-12, -30, 10.0], 0.0]], [['tmax 10 tmin -2 Ra 10.0', [10, -2, 10.0], 0.71], ['tmax -10 tmin -25 Ra 40.0', [-10, -25, 40.0], 0.04], ['tmax -12 tmin -30 Ra 40.0', [-12, -30, 40.0], 0.0], ['tmax 25 tmin 25 Ra 10.0', [25, 25, 10.0], 0.0], ['tmax 25 tmin 25 Ra 25.0', [25, 25, 25.0], 0.0], ['tmax 25 tmin 25 Ra 40.0', [25, 25, 40.0], 0.0], ['tmax 40 tmin 18 Ra 10.0', [40, 18, 10.0], 2.06], ['tmax 40 tmin 18 Ra 25.0', [40, 18, 25.0], 5.15]], [['tmax 30 tmin 15 Ra 10.0', [30, 15, 10.0], 1.46], ['tmax -10 tmin -25 Ra 10.0', [-10, -25, 10.0], 0.01], ['tmax 22 tmin 8 Ra 10.0', [22, 8, 10.0], 1.15], ['tmax 22 tmin 8 Ra 25.0', [22, 8, 25.0], 2.88], ['tmax 22 tmin 8 Ra 40.0', [22, 8, 40.0], 4.61], ['tmax -5 tmin -20 Ra 10.0', [-5, -20, 10.0], 0.19], ['tmax -5 tmin -20 Ra 25.0', [-5, -20, 25.0], 0.48], ['tmax -5 tmin -20 Ra 40.0', [-5, -20, 40.0], 0.77]], [['tmax 30 tmin 15 Ra 10.0', [30, 15, 10.0], 1.46], ['tmax 30 tmin 15 Ra 25.0', [30, 15, 25.0], 3.66], ['tmax 30 tmin 15 Ra 40.0', [30, 15, 40.0], 5.86], ['tmax 35 tmin 20 Ra 10.0', [35, 20, 10.0], 1.65], ['tmax 35 tmin 20 Ra 25.0', [35, 20, 25.0], 4.12], ['tmax 35 tmin 20 Ra 40.0', [35, 20, 40.0], 6.59], ['tmax 10 tmin -2 Ra 10.0', [10, -2, 10.0], 0.71], ['tmax 40 tmin 18 Ra 10.0', [40, 18, 10.0], 2.06]]]
for label, args, expected in fixtures[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
tmax 30 tmin 15 Ra 10.0	`8.8`	`1.46`	Failed
tmax 30 tmin 15 Ra 25.0	`22.0`	`3.66`	Failed
tmax 30 tmin 15 Ra 40.0	`35.19`	`5.86`	Failed
tmax 35 tmin 20 Ra 10.0	`9.89`	`1.65`	Failed
tmax 35 tmin 20 Ra 25.0	`24.73`	`4.12`	Failed
tmax 35 tmin 20 Ra 40.0	`39.56`	`6.59`	Failed
tmax 10 tmin -2 Ra 10.0	`4.26`	`0.71`	Failed
tmax 10 tmin -2 Ra 25.0	`10.64`	`1.77`	Failed

SHA-256 / d208ebb009d8fe9311a6826be4520d38ad55828b6a6ab6df21709ec7870a5ffb

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This mechanism has 8 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

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Verification & scope

Stipulated deterministic teaching model of an operational weather index; coefficients and thresholds are fixed by the contract and no claim of standards conformance is made. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:48:27.337948+00:00.

Case digest / 5b19ece7c145f3966b1bbae30049c87db8f0f6f94a9247e2079c17e5d738caea