Hydrothermal Balance and Diurnal Temperature Range Jointly Explain Maize Yield Variability in a Semi-Arid Region of North China

Hydrothermal variability, rising evaporative demand, and drought extremes increasingly threaten crop production in semi-arid regions, yet their relative contributions to maize yield variability remain unclear. Here, we examined maize yield responses to growing-season climatic conditions in Lyuliang City, North China, during 2005–2024 using yield statistics and ChinaMet climate data. Trend analysis, Pearson correlation, candidate regression models, standardized coefficients, and generalized additive models were used to identify dominant climatic predictors. Maize yield showed no significant temporal trend during the study period (Sen’s slope = 0.01 t ha−1 yr−1, p = 0.58), whereas growing-season potential evapotranspiration tended to increase (2.81 mm yr−1, p = 0.06). Diurnal temperature range declined significantly (−0.04 °C yr−1, p = 0.01), and minimum SPEI also decreased significantly (−0.04 yr−1, p = 0.01), indicating intensified extreme dry conditions. Maize yield was most strongly correlated with aridity index (r = 0.72, p < 0.001) and water deficit (r = 0.72, p < 0.001), suggesting that hydrothermal balance explained yield variability better than precipitation or temperature alone. The highest-ranked regression model included aridity index, growing-season temperature, diurnal temperature range, and minimum SPEI, explaining 70% of interannual yield variation. Aridity index was the strongest positive predictor, whereas diurnal temperature range had a significant negative association with yield. Although extreme dry conditions intensified over time, minimum SPEI was not directly associated with annual yield, implying that drought impacts may depend on drought timing, crop phenology, and management buffering. These findings highlight the importance of maintaining favorable hydrothermal balance and reducing risks from increasing evaporative demand and temperature variability to support climate-resilient maize production in Lyuliang City and climatically similar rain-fed semi-arid regions of North China.