FA-71186 / Weather index computation / Open access

Hargreaves reference evapotranspiration: cold day clamp · case 01

Deep-cold days report negative evapotranspiration.

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

ROOT CAUSE

The result is not clamped at zero when Tmean < -17.8.

VERIFIED REPAIR

Clamp negative ET0 to zero.

Unsuccessful approach: Taking the absolute value turns frost into positive water demand.

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 * 0.408 * ra_mj * (tmean + 17.8) * math.sqrt(tmax - tmin)
    return round(et, 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 -12 tmin -30 Ra 10.0', [-12, -30, 10.0], 0.0], ['tmax -12 tmin -30 Ra 25.0', [-12, -30, 25.0], 0.0]], [['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 -12 tmin -30 Ra 25.0', [-12, -30, 25.0], 0.0], ['tmax -12 tmin -30 Ra 40.0', [-12, -30, 40.0], 0.0]], [['tmax -12 tmin -30 Ra 10.0', [-12, -30, 10.0], 0.0], ['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 40 tmin 18 Ra 40.0', [40, 18, 40.0], 8.24]], [['tmax -12 tmin -30 Ra 10.0', [-12, -30, 10.0], 0.0], ['tmax -12 tmin -30 Ra 25.0', [-12, -30, 25.0], 0.0], ['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 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 -12 tmin -30 Ra 10.0', [-12, -30, 10.0], 0.0]]]
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	`1.46`	`1.46`	Passed
tmax 30 tmin 15 Ra 25.0	`3.66`	`3.66`	Passed
tmax 30 tmin 15 Ra 40.0	`5.86`	`5.86`	Passed
tmax 35 tmin 20 Ra 10.0	`1.65`	`1.65`	Passed
tmax 35 tmin 20 Ra 25.0	`4.12`	`4.12`	Passed
tmax 35 tmin 20 Ra 40.0	`6.59`	`6.59`	Passed
tmax -12 tmin -30 Ra 10.0	`-0.13`	`0.0`	Failed
tmax -12 tmin -30 Ra 25.0	`-0.32`	`0.0`	Failed

SHA-256 / 1ff917afb235dc54c5e59efa099c5a6b1460386cceafd63e33d599bd5e0dddd6

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 * 0.408 * ra_mj * (tmean + 17.8) * math.sqrt(tmax - tmin)
    return round(abs(et), 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 -12 tmin -30 Ra 10.0', [-12, -30, 10.0], 0.0], ['tmax -12 tmin -30 Ra 25.0', [-12, -30, 25.0], 0.0]], [['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 -12 tmin -30 Ra 25.0', [-12, -30, 25.0], 0.0], ['tmax -12 tmin -30 Ra 40.0', [-12, -30, 40.0], 0.0]], [['tmax -12 tmin -30 Ra 10.0', [-12, -30, 10.0], 0.0], ['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 40 tmin 18 Ra 40.0', [40, 18, 40.0], 8.24]], [['tmax -12 tmin -30 Ra 10.0', [-12, -30, 10.0], 0.0], ['tmax -12 tmin -30 Ra 25.0', [-12, -30, 25.0], 0.0], ['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 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 -12 tmin -30 Ra 10.0', [-12, -30, 10.0], 0.0]]]
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	`1.46`	`1.46`	Passed
tmax 30 tmin 15 Ra 25.0	`3.66`	`3.66`	Passed
tmax 30 tmin 15 Ra 40.0	`5.86`	`5.86`	Passed
tmax 35 tmin 20 Ra 10.0	`1.65`	`1.65`	Passed
tmax 35 tmin 20 Ra 25.0	`4.12`	`4.12`	Passed
tmax 35 tmin 20 Ra 40.0	`6.59`	`6.59`	Passed
tmax -12 tmin -30 Ra 10.0	`0.13`	`0.0`	Failed
tmax -12 tmin -30 Ra 25.0	`0.32`	`0.0`	Failed

SHA-256 / 3068738c3ff3806a19aba4ed02cebd6a0f1cdfe740439cd1e630162c134a7e2e

3 / The verified repair

Exit 0

"""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 * 0.408 * 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 -12 tmin -30 Ra 10.0', [-12, -30, 10.0], 0.0], ['tmax -12 tmin -30 Ra 25.0', [-12, -30, 25.0], 0.0]], [['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 -12 tmin -30 Ra 25.0', [-12, -30, 25.0], 0.0], ['tmax -12 tmin -30 Ra 40.0', [-12, -30, 40.0], 0.0]], [['tmax -12 tmin -30 Ra 10.0', [-12, -30, 10.0], 0.0], ['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 40 tmin 18 Ra 40.0', [40, 18, 40.0], 8.24]], [['tmax -12 tmin -30 Ra 10.0', [-12, -30, 10.0], 0.0], ['tmax -12 tmin -30 Ra 25.0', [-12, -30, 25.0], 0.0], ['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 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 -12 tmin -30 Ra 10.0', [-12, -30, 10.0], 0.0]]]
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	`1.46`	`1.46`	Passed
tmax 30 tmin 15 Ra 25.0	`3.66`	`3.66`	Passed
tmax 30 tmin 15 Ra 40.0	`5.86`	`5.86`	Passed
tmax 35 tmin 20 Ra 10.0	`1.65`	`1.65`	Passed
tmax 35 tmin 20 Ra 25.0	`4.12`	`4.12`	Passed
tmax 35 tmin 20 Ra 40.0	`6.59`	`6.59`	Passed
tmax -12 tmin -30 Ra 10.0	`0.0`	`0.0`	Passed
tmax -12 tmin -30 Ra 25.0	`0.0`	`0.0`	Passed

SHA-256 / d0c04cc6a97dcf7b97e35f96e09d48159ed907f7f7633d1d197da868d3f0f431

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 2026-09-29T14:48:27.416634+00:00.

Case digest / 41de98641ac445bd3a304f22f583a16455df56fe7de7ed4a21185a7fb18daae0