Aero-Thermodynamics of UAV Downwash for Dynamic Microclimate Engineering: Ameliorating Effects on Rice Growth, Yield, and Physiological Traits Across Key Growth Stages

A comprehensive investigation into the aero-thermodynamic impacts of UAV-generated airflow on the rice microclimate is essential to elucidate the complex relationships between wind speed, temperature, and temporal dynamics during the critical growth stages of rice. Focusing on the vulnerable stages of rice such as heading, panicle, and flowering, this research aims to advance the understanding of microclimatic influences on rice crops, thereby informing the development of UAV-based strategies to enhance crop resilience and optimize yields. By utilizing UAV rotor downwash, the research examines wind temperature and speed at three key diurnal intervals: 9:00 a.m., 12:00 p.m., and 3:00 p.m. At 9:00 a.m., UAV-induced airflow creates a stable microclimate with favourable temperatures (27.45–28.45 °C) and optimal wind speeds (0.0700–2.050 m/s), which promote and support pollen transfer and grain setting. By 12:00 p.m., wind speeds peak at 2.370 m/s, inducing evaporative cooling while maintaining temperature stability, yet leading to some moisture loss. At 3:00 p.m., wind temperatures reach 28.48 °C, with a 72% decrease in wind speed from midday, effectively conserving moisture during critical growth phases. The results reveal that UAV airflow positively influences panicle and flowering stages, where carefully moderated wind speeds (up to 3 m/s) and temperatures reduce pollen sterility, enhance fertilization, and optimize reproductive development. This highlights the potential of UAV-engineered microclimate management to mitigate stress factors and improve yield through targeted airflow regulation. Key agronomic parameters showed significant improvements, including stem diameter, canopy temperature regulation, grain filling duration, productive tillers (increasing by 30.77%), total tillers, flag leaf area, grains per panicle (rising by 46.55%), biological yield, grain yield (surging by 70.75%), and harvest index. Conclusively, optimal aero-thermodynamic effects were observed with 9:00 a.m. rotor airflow applications during flowering, outperforming midday and late-afternoon treatments. Additionally, 12:00 p.m. airflow during flowering significantly increased the yield. The interaction between rotor airflow timing and growth stage (RRS × GS) exhibited low to moderate effects, underscoring the importance of precise timing in maximizing rice productivity.