Projected Crop-Calendar Shifts and Burning-Window Ventilation in Mainland Southeast Asia by Mid-Century: Implications for Residue Collection and Burning Management

Crop-residue burning in mainland Southeast Asia wastes a bioresource and coincides with the region’s worst air quality. We asked how projected crop-calendar shifts change the overlap between residue burning and stagnant weather by mid-century (2041–2060). Burning windows from harvest to the next planting, validated against satellite cropland fire detections, were projected with 15 bias-corrected CMIP6 models under SSP2-4.5 and SSP5-8.5 and combined with two stagnation indices: calm days and poorly ventilated afternoons. Rice harvests advance by 6–9 days, but the calendar shift changes the share of residue burning on stagnant days by less than 0.5 percentage points in the ensemble mean, whether burning follows the harvest or the next planting, because burning peaks in late February and March, when the frequency of stagnant days changes little from week to week. The shift instead removes one to two dry days from the first month after the rice harvest, when straw is collected. The change in the ventilation climate is larger but uncertain, because models disagree on near-surface wind, and it differs between and within countries. Crop-calendar shifts are therefore unlikely to increase the exposure of residue burning to stagnant conditions.