Vapour Pressure Deficit and Moisture Stress in the CPE Framework: Joint Heat-Drought Conditions as the Strongest Climate-Finance Predictors

Paper 7 established heat stress thresholds as the strongest agricultural temperature predictor in the CPE
framework. This paper adds moisture stress variables — Vapour Pressure Deficit (VPD), precipitation, and
evapotranspiration — to the same 12 crop zones, generating 132 new predictors across 7 moisture stress
types. Across 7,040 tested configurations, 289 signals survive quality filters. Joint heat-and-drought
conditions — dry heat (heat stress AND precipitation <1mm/day) and combined heat+VPD (heat stress AND
VPD above crop threshold) — produce the highest lifts in the entire CPE series. EU Urban Energy dry heat
® UNG at 21 days achieves lift 2.02×, surpassing the previous maximum of 1.95×. A sign-flip permutation
test (N=10,000 per signal) confirms all 10 key signals at p£0.002 — seven at p<0.001. Event clustering
analysis shows the dry heat signal fires in 15 of 25 training years (well-distributed), while combined
heat+VPD and VPD_stress signals concentrate in 8 years, identifying specific drought-heat regime episodes.
A structural finding: VPD stress thresholds fire at near-zero frequency in temperate zones but at 1,000+
events in tropical zones (Brazil Soy, India Sugar), confirming VPD is a binding constraint only where
chronically hot and dry.