Meteorological records over the past five decades have shown that climate warming has been faster during the nighttime than during the daytime. However, the responses of vegetation development to asymmetric warming are not well understood due to the misinterpretation of phenology that have resulted from the snowmelt effect. We applied normalized difference vegetation index (NDVI) sources from Global Inventory Modeling and Mapping Studies (GIMMS:1982–2015) and Moderate Resolution Imaging Spectroradiometer (MODIS: 2000–2020) to reveal maximum greenness in high-mountain Asia (HMA). The snow-free normalized difference phenology index (NDPI), which is a 3-band vegetation index that designed to best contrast vegetation from soil and snow, was applied for estimating the start of the growing season (SOS). We found that alpine pastures in HMA generally became greener and the SOS was delayed. Preseason daytime temperatures ($T_{\mathit{day}}$) and nighttime temperatures ($T_{\mathit{night}}$) had opposite effects on maximum greenness, with $T_{\mathit{day}}$ being negative and $T_{\mathit{night}}$ being positive. The responses of SOS to $T_{\mathit{day}}$ and $T_{\mathit{night}}$ were highly related with the frequency of meteorological drought events during 2000–2020. In regions with lower frequency of drought events, both daytime and nighttime warming could advance SOS. In regions with higher frequency of drought events, daytime warming could delay SOS, but nighttime warming could advance SOS. The results of our study are of great significance to understand the responses of alpine ecosystems to asymmetric climate warming. Such an understanding is quite valuable for pasture management and future vegetation climate projections.

过去 5 年的气象记录表明，夜间气候变暖的速度比白天快。然而，由于融雪效应导致对物候的误解，植被发育对不对称变暖的响应尚不清楚。我们应用来自全球清单建模和制图研究 (GIMMS:1982–2015) 和中分辨率成像光谱仪 (MODIS: 2000–2020) 的归一化差异植被指数 (NDVI) 来源来揭示亚洲高山 (HMA) 的最大绿度。无雪归一化差异物候指数 (NDPI) 是一个 3 波段植被指数，旨在最佳地对比土壤和雪中的植被，用于估计生长季节 (SOS) 的开始。我们发现 HMA 的高山牧场普遍变绿，SOS 延迟。季前日白天温度（${吨}_{\mathit{天}}$) 和夜间温度 (${吨}_{\mathit{夜晚}}$) 对最大绿度有相反的影响，${吨}_{\mathit{天}}$消极和${吨}_{\mathit{夜晚}}$是积极的。SOS 的回应${吨}_{\mathit{天}}$和${吨}_{\mathit{夜晚}}$与 2000-2020 年气象干旱事件的发生频率高度相关。在干旱事件频率较低的地区，白天和夜间的变暖都可以促进 SOS。在干旱事件发生频率较高的地区，白天变暖可能会延迟 SOS，但夜间变暖可能会提前 SOS。我们的研究结果对于了解高山生态系统对不对称气候变暖的响应具有重要意义。这种认识对于牧场管理和未来植被气候预测非常有价值。