干旱是由水分亏缺引起的一种水资源短缺现象，其频率高、影响广、持续时间长。在全球气候变化的背景下，干旱风险的增加引发了更为严峻的生态问题，对陆地生态系统造成严重影响。金沙江流域地处我国西南地区，拥有丰富的自然资源，地形复杂，是典型的生态敏感区和脆弱区。近年来，该地区极端气候事件频发，经历了多次严重的干旱事件，对区域植被产生一定的影响。因此，本研究对金沙江流域气候要素、气象干旱以及植被的时空演变进行了研究，分析评价了近23年金沙江流域气象干旱特征与演变规律，综合考虑植被覆盖与植被物候期两方面内容探究植被对气象干旱的响应，并以2011年伏秋至2012年初的典型干旱事件为例，探讨在典型干旱期间植被生长变化特征及其响应规律，以期为区域生态保护和恢复提供科学依据。研究结果如下：

（1）研究期间，金沙江流域呈现“湿润-干旱-湿润”的阶段特征，春季和夏季的阶段变化最为明显。2000年以来金沙江流域气温升高，上游高寒草甸草原生态区和寒温性针叶林生态区升高趋势最大，下游气温升高趋势较小。降水和潜在蒸散发具有阶段趋势特征，2011年之前降水量呈减少趋势，潜在蒸散发呈增加趋势，2011年之后相反。基于此，标准化降水蒸散发指数（SPEI）在2011年之前波动下降，区域处于变干趋势，2011年之后波动上升，区域干旱缓解逐渐湿润化。干旱影响面积比平均在10.93%~42.87%之间，秋季最易发生气象干旱且干旱烈度最大，而夏季的干旱峰值强度最大。

（2）金沙江流域多年平均归一化植被指数（NDVI）在空间上呈现由东南向西北递减的分布特征。2000-2022年研究区植被生长状况改善，植被绿度增加，下游NDVI增加趋势大于上游。植被生长开始期（SOS）主要集中在3月初至5月初，由东南向西北延迟，下游SOS呈延迟趋势，上游呈提前趋势。植被生长结束期（EOS）主要集中在9月至11月下旬，空间上高寒草甸草原生态区西部和下游发生较早，寒温性针叶林生态区EOS发生较晚，变化趋势无明显空间集聚特征。生长季长度（LOS）平均为150-268天，由东南向西北逐渐缩短，上游LOS呈延长趋势，下游LOS呈缩短趋势。

（3）SOS、EOS、LOS与SPEI1在95%以上的区域表现为正相关关系，上游相关系数大于下游。随SPEI时间尺度的增大，相关系数逐渐减小，呈正相关关系的面积占比逐渐减小，下游部分区域由正相关转为负相关。在短时间尺度气象干旱的影响下，植被SOS、EOS提前，生长季长度LOS缩短，受长期干旱影响，植被经历严重的水分限制和胁迫，导致植被生长受到更大的影响，下游部分区域植被SOS、EOS延迟，LOS延长。

（4）基于SPEI时间序列和历时资料记载，选取2011年5月至2012年4月连续干旱作为典型干旱事件，在此期间，降水量表现为负距平，潜在蒸散发表现为正距平。本次干旱事件的峰值出现在2011年8月，但同期NDVI并非最小，9月NDVI距平显著减小，表明植被对干旱的响应存在滞后性。流域下游干旱严重且持续时间长，植被受到影响，上游干旱程度小且持续时间短，并未对植被造成明显影响。在极端干旱的影响下，2011年下游农林复合生态区和常绿阔叶林生态区EOS普遍延迟，受前一年累积干旱的影响，2012年农林复合生态区、常绿阔叶林生态区和寒温性针叶林生态区SOS普遍延迟。

Drought, a water scarcity phenomenon resulting from a water deficit, is characterized by high frequency, widespread impact, and long duration. In the context of global climate change, the heightened risk of drought has led to more severe ecological challenges, significantly affecting terrestrial ecosystems. The Jinsha River basin, situated in the southwest of China, boasts abundant natural resources and intricate topography, making it a prime example of an ecologically sensitive and fragile region. In recent years, this area has witnessed frequent extreme climatic events and numerous severe drought occurrences, impacting regional vegetation to a certain extent. This study delves into the climatic factors, meteorological droughts, and spatial and temporal changes in vegetation within the Jinsha River basin. By analyzing and evaluating the characteristics and evolutionary trends of meteorological droughts over the past 23 years, the research aims to understand the response of vegetation to droughts in the region. Specifically, it focuses on the vegetation cover, vegetation phenology, and the impact of typical drought events from autumn 2011 to early 2012. By exploring the process of vegetation growth changes and its response during these events, the study seeks to provide a scientific foundation for regional ecological protection and restoration. The results of the investigation are as follows:

(1) During the study period, the Jinsha River Basin exhibited a phase characteristic of ‘wet-dry-wet’, with the most significant phase changes occurring in spring and summer. Since 2000, the temperature in the Jinsha River Basin has been rising, with the highest increasing trend in the alpine meadow grassland ecological zone and the cold temperate coniferous forest ecological zone in the upper reaches, while the temperature rise in the lower reaches is relatively smaller. Precipitation and potential evapotranspiration show phase trend characteristics, with a decreasing trend in precipitation and an increasing trend in potential evapotranspiration before 2011, and the opposite trend after 2011. Based on this, the Standardized Precipitation Evapotranspiration Index (SPEI) fluctuated downward before 2011, indicating a drying trend in the region, while it fluctuated upward after 2011, indicating a gradual shift from drought to wetter conditions in the region. The area affected by drought ranges from 10.93% to 42.87% on average, with autumn being the most susceptible to meteorological drought and experiencing the most severe drought intensity, while the peak intensity of drought occurs in summer.

(2) The multi-year average Normalized Difference Vegetation Index (NDVI) in the Jinsha River Basin displayed a spatial distribution pattern of decreasing from southeast to northwest. Vegetation growth in the study area exhibited improvement from 2000 to 2022, resulting in an increase in vegetation greenness. Notably, the trend of increasing NDVI in the lower reaches surpassed that in the upper reaches. The Start of Season (SOS) during the vegetation growth initiation phase predominantly occurred from early March to early May, with a delayed progression from southeast to northwest. The downstream SOS exhibited a delayed trend, while the upstream showed an advancement. Conversely, the End of Season (EOS) for the vegetation growth initiation phase mainly fell between September to late November. Spatially, EOS occurred earlier in the western and downstream regions of the alpine meadow grassland ecoregion, and later in the cold-temperate coniferous forest ecoregion. The change trend did not exhibit distinct spatial clustering characteristics. The Length of Growing Season (LOS) averaged between 150-268 days, gradually shortening from southeast to northwest. There was a lengthening trend in the upstream LOS and a shortening trend in the downstream LOS.

(3) SOS, EOS, and LOS, along with SPEI1, exhibited a positive correlation in over 95% of the areas, with higher correlation coefficients observed in the upstream regions compared to the downstream. As the time scale of SPEI increased, the correlation coefficients gradually decreased, leading to a reduction in the proportion of areas displaying positive correlations. In certain downstream areas, the correlation even shifted from positive to negative. During periods of short-term meteorological drought, vegetation SOS and EOS advanced, while the LOS shortened. Prolonged drought conditions imposed severe water stress and growth constraints on vegetation, resulting in a more pronounced impact on vegetation growth. This led to delayed vegetation SOS and EOS, along with a lengthening of LOS in certain downstream regions.

(4) The period of consecutive drought from May 2011 to April 2012 was identified as a significant drought event, characterized by below-average precipitation levels and above-average potential evapotranspiration rates. The peak of this drought event occurred in August 2011; however, NDVI did not reach its minimum during the same period. Notably, the NDVI exhibited a substantial decrease in September, indicating a delayed vegetation response to the drought conditions. The severity and duration of the drought were more pronounced in the lower part of the basin, leading to significant vegetation stress. In contrast, the upper part of the basin experienced a milder and shorter-lived drought, with minimal impact on vegetation. During the extreme drought, EOS of the downstream agroforestry complex ecoregion and evergreen broadleaf forest ecoregion were generally delayed in 2011. Additionally, SOS for the vegetation growth initiation phase in the agroforestry complex ecoregion, evergreen broadleaf forest ecoregion, and cold-temperate coniferous forest ecoregion was delayed in 2012 due to the lingering effects of the cumulative drought from the previous year.