Soil Moisture, Not Daily Rainfall, Marks the Location of Monsoon Road-Landslide Closures in Uttarakhand: A Low-Cost, Reproducible Validation Using Government Road-Closure Records

Monsoon road-landslides cause recurrent loss of life and connectivity across the Indian Himalaya, yet real-time, spatially resolved risk information rarely reaches those most exposed. Treating 1,900+ distinct road-closure records published by the Uttarakhand Public Works Department (PWD) as ground truth, we find that at sites where roads closed, soil moisture sat at approximately the 62nd percentile of the day's hill-point distribution (chance = 50th), whereas rainfall reached only the 55th–57th. The result replicated across nine independent samples, with a significance exceeding 6σ. A live test on 10 August 2026 (112 closures): 74% of located closures fell within flagged elevated-risk areas, 77% within 5 km, most flagged two days in advance. An independent, preliminary field-GPS check (77 exact-coordinate sites, July–September) reproduced this pattern: mean soil percentile 67.6, 75% within 5 km. We make no claim of novel discovery — the role of antecedent moisture is established science. Our contribution is threefold: a low-cost, reproducible validation method; measured negative results (seven correction strategies that failed); and an honest characterisation of limits. The tool is available without login, on a phone, in Hindi — reaching communities that larger systems often do not. The signal resolves the dangerous valley (~5 km), not the exact slope, and does not detect cloudbursts, flash floods, tunnel failures, or earthquakes. Uttarakhand is presented as a pilot; the framework can be extended across the Himalayan belt, provided each region is re-validated against its own ground truth.