Intensifying droughts under global climate change threaten vegetation and regional ecological security. Understanding vegetation responses to drought is essential for future ecosystem dynamics prediction and adaptive management. However, most studies relied singly on correlation analysis to examine vegetation responses to drought, which may not fully capture actual response processes. Here we integrated and compared both correlation-based and event-based approaches to comprehensively investigate the drought dynamics and vegetation responses across the Lancang-Mekong River Basin (LMRB) during 1990–2022, using the Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI) and Standardized Leaf Area Index (SLAI). Our results revealed an intensification of drought in the LMRB, and short-duration droughts, defined as events lasting no more than 3 months, accounted for 85.4%–89.3% of all drought events. Comparison between the two methods showed that the event-based approach detected shorter vegetation response times of 3.2–3.8 months, whereas the correlation-based approach estimated longer response times of 6.2–6.7 months. In addition, the average vegetation recovery time was 6.1–6.3 months. Drought duration and intensity were positively correlated with vegetation anomaly duration and intensity but negatively correlated with vegetation response time. While, vegetation recovery time was negatively correlated with drought duration but positively correlated with drought intensity. Among all vegetation types, croplands and grasslands exhibited lower resilience and weaker recovery capacity, as indicated by shorter response times and longer recovery times. Overall, this study provides quantitative insights into vegetation–drought relationships and offers a scientific basis for vegetation drought risk assessment in the LMRB.

Understanding vegetation responses to drought is essential for future ecosystem dynamics prediction and adaptive management under the intensified climate change. However, most studies relied singly on correlation analysis to examine vegetation responses to drought, which may not fully capture actual response processes. Here we integrated and compared both correlation-based and event-based approaches to comprehensively investigate drought dynamics and vegetation responses across the Lancang-Mekong River Basin (LMRB) during 1990–2022, using the Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI) and Standardized Leaf Area Index (SLAI). Our results revealed an intensification of drought in the LMRB by SPEI and SPI, while short-duration droughts (duration ≤ 3 months) accounted for 85.4%–89.3% of all drought events. Comparison between the two methods showed that the event-based approach detected shorter vegetation response times of 3.2–3.8 months, whereas the correlation-based approach estimated longer response times of 6.2–6.7 months, and also detected an average vegetation recovery time of 6.1–6.3 months. Based on event-based approach, drought duration and intensity were positively correlated with vegetation anomaly duration and intensity but negatively correlated with vegetation response time. In contrast, vegetation recovery time was negatively correlated with drought duration but positively correlated with drought intensity. Among all vegetation types, croplands and grasslands exhibited lower resilience and weaker recovery capacity, as indicated by their shorter response times and longer recovery times. Overall, this study provides quantitative insights into vegetation–drought relationships and offers a scientific basis for vegetation drought risk management in the LMRB.

Understanding the drought propagation from meteorological drought (MD) to hydrological drought (HD) can help assist in the drought early warning and reduce drought related losses. Propagation time is a significant variable in describing drought propagation. In this study, we identify the MD and HD using the three-dimensional drought identification method to reflect the drought characteristics over temporally continuous periods and spatially adjacent areas. Then, we calculate the drought propagation time by considering the spatio-temporal overlaps between MD and HD events, which can provide further insight to reveal the drought propagation process in both time and space. Specifically, we consider the propagation time of interval of the start (Delta T-s), peak (Delta T-p), and end (Delta T-e) time between a paired MD event and HD event, respectively. The propagation process from MD to HD is investigated during 1961-2015 in the Yangtze River basin, China. Results indicate that the majority (>70%) of HD events are well matched with the majority (>70%) of MD events, and there are decomposed effect and joint effect during the propagation process from MD to HD. A stronger link between HD events and MD events with higher matching rate of MD and HD events is observed in autumn (SON) than the remaining three seasons. We find that the MD events in Yangtze River basin generally need 2 to 4 months to propagate to the HD events, and such response time from MD to HD events is becoming longer in most subbasins as the propagation time (Delta T-s,Delta T-p, and Delta T-e) show a significant increasing trend. The results in our study can help understand the drought development and the drought propagation, and are also helpful for water managers to make rational water resources management decisions.

基于黄土高原1983-2015年间的植被状况指数(VCI)与1～48个月尺度的标准化降水蒸散发指数(SPEI)和标准化降水指数(SPI),利用Pearson相关系数法、线性回归法和Mann-Kendall趋势检验法等方法研究了黄土高原地区植被对气象干旱的多时间尺度时空响应特征.结果表明:(1)1983-2015年,黄土高原植被状况整体趋于改善,但黄土高原整体干湿状况变化趋势不大.(2)黄土高原绝大部分区域植被变化与气象干旱指数呈现显著正相关关系,表明植被活动受到水分的限制较强.但是,过去几十年,黄土高原地区植被受到水分限制的影响程度有逐渐减轻的趋势.(3)黄土高原植被对短时间尺度的水分盈亏变化相对敏感,尤其是耕地和草地对1～4个月的SPEI更为敏感,而林地对SPEI的响应时间尺度较为分散.黄土高原VCI与SPEI、SPI的最大相关系数均主要出现在生长季(4-10月),表明水分条件在生长季对植被活动的影响较为显著.

为了分析未来时期(2020-2099年)长江中下游区域气象干旱演变特征,选取跨行业影响模式比较计划(ISI-MIP)的4个全球气候模式,基于不同代表性浓度路径(RCP)的排放情景(RCP-2.6、RCP-6.0和RCP-8.5),分别计算了标准化降水指数(SPI)和标准化蒸散发指数(SPEI),探讨了两种指数对研究区气象干旱的刻画能力,分析了研究区未来气象干旱变化规律.研究结果表明:未来时期SPI整体呈增加趋势,汉江流域和洞庭湖水系西北区域增加幅度较大,说明该区域干旱减缓趋势明显;SPEI呈显著减小趋势,且随着排放浓度的增加,减小幅度逐渐增加,洞庭湖水系和鄱阳湖水系东南区域减小趋势较大,说明该区域未来时期干旱增加趋势明显;不同情景下SPI减小的区域SPEI也呈减小趋势且减小幅度更大;研究区SPI与SPEI的相关性从北到南、从西到东逐渐增强;SPI与SPEI的整体相关性随着排放浓度的增加逐渐减弱.研究成果有助于预估未来长江中下游区域干旱发生演变规律.

全球变化背景下,干旱事件频发给区域水资源管理和社会经济可持续发展带来了巨大挑战,科学合理地辨识干旱发生发展过程一直是干旱研究领域的前沿与难点.该研究将图像三维连通性识别方法应用于气象干旱事件的识别和提取.在长江流域的应用表明此方法识别出的干旱事件与历史记录的吻合度较高,能有效识别气象干旱事件.基于1960—2015年标准化降水蒸散发指数(Standardized Precipitation Evapotranspiration Index,SPEI),长江流域共发生281场气象干旱事件,其中长历时干旱事件(历时大于4个月)64场.长历时干旱事件在流域中部发生次数多于东部和西部,2000年之后的发生频次、干旱面积和干旱强度大于2000年之前,单场事件发展方向以西北和东南为主.整体上,干旱事件发生频次和干旱强度在长江流域中部呈增加趋势,在流域东部和西部呈减小趋势.该研究有助于探索长江流域干旱事件发展演变规律.

本文基于泾河流域1960—2018年共59年的径流资料和气象数据,定量分析了气候变化和人类活动对泾河流域径流变化的影响.结果表明:泾河流域年径流呈现显著减少趋势,年径流在1996年存在突变.基于Budyko假设的归因分析方法表明人类活动对泾河流域径流减小的贡献率为84.73％,是导致流域年径流减少的主要原因;而气候变化对泾河流域径流减少的贡献为15.27％,其中,相较于降水,蒸散发对径流变化的影响更大,其贡献率为14.67％.本文研究结果为泾河流域水资源管理提供一定的科学支撑,对该地区制定可持续发展策略具有重要实际意义.

The Three-North Shelterbelt Project (TNSP) is one of the largest ecological restoration projects of the world. Although its important role in regulating the ecosystem of northern China has been acknowledged, how this project affects the surface water-energy balance deserves further evaluation. This study characterizes spatiotemporal variation of climate variables and vegetation coverage/density over the Three-North Region (TNR) of China using multiple datasets since the implementation of the TNSP. Of particular importance is that effects of vegetation restored during the TNSP on surface water-energy budget are examined for the study domain. Our results show that accompanied by a significant enhancement of vegetation coverage and density in the TNR, its annual air temperature and precipitation have increased 1.46 degrees C and 89.1 mm, respectively from 1982 to 2015. We find such rise in the air temperature and precipitation plays a positive role in the TNR's vegetation restoration in a sense that the vegetation dynamics show positive correlation with its regional air temperature and precipitation, while more sensitive to precipitation. We also find carbon sequestration of the TNR increases at the cost of greater water consumption through evapotranspiration since the TNSP commences. In some arid regions, revegetation accelerates the water deficit due to an excessive rate of restoring vegetation; yet, no substantial water imbalance occurs as a result of enhanced precipitation and water use efficiency during this period. Although the solar radiation increases with decreases in surface albedo over the last few decades, our results do not reveal an appreciably increasing trend in the land surface temperature of the TNR. This is because the improved vegetation can assimilate CO2 (mitigating greenhouse gas emissions) and transpire water by photosynthesis, thereby increasing latent heat flux and reducing the warming effect. This study highlights a mixed consequence of the TNSP by inducing both positive and negative effects on the surface water-energy balance over the TNR.