Large gullies in dryland landscapes are often indicators of land degradation by surface runoff. However, under conditions where gully systems are hydrologically arrested by restoration interventions that increase water residence time-most notably check dams and ponds-they may also function as hydrologically active zones of groundwater recharge and subsurface connectivity. In China's Loess Plateau, we assess these functions in the Nianzhuang Catchment using a multi-indicator, process-based approach that integrates stable isotopes (delta H-2, delta O-18), chloride concentrations, and groundwater level fluctuations. Our results show that precipitation is the dominant source of recharge for shallow pore water within engineered gully zones, while deeper fissure water is replenished more slowly through percolation. Hydrological arrest through ecological engineering interventions acts as focal points for groundwater infiltration, enhancing recharge in otherwise limited dryland systems. Estimated annual recharge in the monitored gully-zone pore aquifer (238-241 mm) is equivalent to about 43 % of the mean annual precipitation at the site, a site-specific recharge magnitude that far exceeds reported catchment-wide recharge rates observed in nearby tableland and hilly areas. Our results indicate that engineered gully systems can act as focused recharge zones rather than solely degraded landforms. By linking runoff convergence and ponding to measurable recharge responses, the study provides a process-based framework for assessing groundwater dynamics in managed semi-arid landscapes.

Check dams are known to support sediment retention and erosion control for water and soil conservation; however, their hydrological role in perched groundwater recharge remains mechanistically unresolved. To address this gap, we integrated water level monitoring, iodide-bromide tracer tests, water table fluctuation (WTF) calculations, and cumulative sum (CUSUM) analysis to investigate perched groundwater dynamics associated with check dams in the Yangjuangou Catchment of the Loess Plateau in China. We find that the perched groundwater levels exhibit distinct spatiotemporal variability, with recharge-dominated areas located in the middle and tail sections above check dams and discharge-dominated zones occurring near the check dam head. Iodide-bromide tracer tests identified both vertical and lateral subsurface water movement, with rates of 6.4 cm & sdot;day-1 and 7.1 m & sdot;day-1, respectively. Recharge totaled 207.3 mm, representing 48.4% of the annual rainfall, and included contributions from both infiltrating precipitation and lateral water inflow. Recharge response lagged rainfall by approximately 9 days and followed a nonlinear relationship. Collectively, these findings support development of a new conceptual model focused on the "precipitation-driven-perched groundwater" relationship, challenging the traditional view of check dams as static storage. They reveal the formation, migration, and precipitation response mechanisms of perched groundwater, establishing its role as "dynamic hydrological regulators". This process-based framework enhances assessment of groundwater recharge, lateral connectivity, and hydrological regulation within check-dam systems in semi-arid environments.

Check dams are widely used across the Loess Plateau to control erosion and retain water, yet their effects on groundwater recharge remain poorly quantified. Using stable isotopes, residence-time analysis, and mixing models, we investigated groundwater recharge pathways in a check-dam catchment. Check-dam construction created two new recharge reservoirs-pond water and perched groundwater. These engineered water bodies became dominant recharge intermediaries for both pore and fissure groundwater. Together, they contributed approximately 81% of pore-groundwater recharge and about 50% of fissure-groundwater recharge. Mean residence times increased from pore groundwater (307 days) to fissure groundwater (591 days), indicating slower renewal and greater hydrological buffering in the fractured system. Seasonal isotope analyses further showed that pore groundwater receives substantial dry-season recharge, consistent with delayed infiltration from stored water behind check dams. Fissure groundwater is recharged primarily during the rainy season. These results demonstrate that check dams establish a dominant focused recharge pathway mediated by engineered surface-water storage. Meanwhile, diffuse precipitation recharge remains an important wetting component of the groundwater recharge system. The findings highlight an important but often overlooked role of check dams in groundwater regulation and hydrological-cycle modification in semi-arid landscapes.

The vertical soil moisture heterogeneity in the rhizosphere affects the way vegetation absorbs water, resulting in hydraulic lift (HL). However, quantifying and resolving HL is difficult due to the unpredictability of subsurface components and complex plant-soil interactions. In this study, we investigated the HL occurrence in tree species (Acer truncatum Bunge and Pinus tabuliformis Carrie`re) in the mountainous areas of Beijing by pot experiments through the addition of heavy water (2H2O) to create a soil moisture gradient. The results indicated that soil moisture differences (0.107-0.204 cm3 cm- 3 for A. truncatum, 0.048-0.145 cm3 cm-3 for P. tabuliformis, respectively) led to a significant occurrence of HL in both broadleaf (A. truncatum) and conifer species (P. tabuliformis). The total HL was up to 4767 and 2735 cm3, with daily fluxes of 64-1,49 and 84-1133 cm3 d- 1 for A. truncatum and P. tabuliformis, respectively. The flux of HL in P. tabuliformis was lower and appeared later than that of A. truncatum. This is because P. tabuliformis will respond to drought by preferentially decreasing stomatal conductance (Gs) and transpiration rate (Tr) compared to A. truncatum. As the Tr of A. truncatum and P. tabuliformis decreased, the probability of HL occurring increased, but the fluxes gradually declined. The occurrence of HL increased the likelihood of plant water uptake from deep soils, helping to alleviate drought stress in shallow soils. This study will help to understand the water acquisition and allocation strategies of plants under drought stress.

Extreme, dry events have major impacts on vegetation phenology worldwide. However, the differential responses of vegetation phenology to climatic elements during these extreme events remain unclear. We investigated the response of vegetation phenology to climatic factors during extreme events in arid and semi -arid regions of the Chinese Loess Plateau, using the climate water deficit method, to identify extremely dry and wet events. The results revealed that extremely wet events extended the vegetation growth periods in addition to global warming, whereas extremely dry events did not completely counteract this effect. During different extreme events, phenological changes in vegetation on the Loess Plateau were primarily influenced by the interactive effects of climatic factors. During extremely dry events, a 100 mm increase in precipitation advanced the start of the season by 3.0, 9.2, and 16.7 days in forest, shrubland, and grassland, respectively. During extremely wet events, a 1 degrees C rise in temperature delayed the end of the season by 1.6, 0.6, and 3.8 days in forest, shrubland, and grassland, respectively. These findings provide crucial guidance for improving predictions of plant phenology changes under extreme climatic events and unraveling biosphere -atmosphere feedback cycles.

Groundwater is a critical moisture source for the growth and survival of dryland forests. Spatiotemporal variations in water table depth (WTD) affect soil water availability in the root zone, which influences canopy transpiration (E-c). However, to date, relatively few studies have been conducted on how changes in WTD regulate E-c. We measured the meteorological variables, volumetric water content (VWC), sap flow, and WTD in 2022 and 2023 from April to October in three Mongolian pine plantations located in Mu Us Sandy Land, China. The initial WTDs were 4 m (WTD4), 9 m (WTD9), and 13 m (WTD13), respectively. The mean VWC did not differ significantly between WTD4, WTD9, and WTD13 in the 0-50 cm layer. However, there was a significant decrease in the mean VWC with increasing WTD in the 50-200 cm layer (p < 0.05). E-c decreased significantly with increasing WTD (p < 0.01), with mean daily E-c of 1.25, 0.75, and 0.28 mm day(-1) for WTD4, WTD9, and WTD13, respectively. Under soil drought conditions, E-c decreased significantly at WTD9 and WTD4 (p < 0.05). Meanwhile, E-c at WTD13 did not vary significantly under the different soil moisture conditions. At WTD9 and WTD13, E-c was mainly influenced by VWC. Meanwhile, at WTD4, E-c was influenced by the vapor pressure deficit and solar radiation. The diameter at breast height and leaf area index at WTD13 were significantly lower than those at WTD9 and WTD4 (p < 0.05). Although Mongolian pine could alleviate soil drought by adjusting E-c through morphological and physiological adaptations, it still suffered from the adverse effects of reduced water availability at deep WTD sites. This study establishes a basis for predicting the response of forests in semi-arid areas to changes in WTD. It contributes to the optimization of silvicultural design in similar areas and reduces ecological risks from the over-exploitation of groundwater.

Study regionLoess Plateau (LP), ChinaStudy focusEvapotranspiration (ET) is crucial in the terrestrial hydrological cycle and serves as a vital indicator of water resource availability. However, the interactions between ET and vegetation, climate, and soil on the LP have been left unexplored, especially during the growing season and regarding ET thresholds for different land-use types. Therefore, we used ridge regression and geographic detector model to analyze ET response to fractional vegetation coverage (FVC), temperature, precipitation, land surface temperature (LST), and temperature vegetation dryness index (TVDI). Additionally, the elastic coefficient was used to determine the ET thresholds for dominant factors in different land-use types.New hydrological insight for the regionThe study reveals FVC as the dominant factor driving ET changes, while also highlighting the synergistic effects of temperature, precipitation, LST, and TVDI with FVC. The synchronization of ET and FVC change trends in vegetation unchanged and restored areas underscores the significance of vegetation cover in regulating regional water cycles. Furthermore, the study provides valuable insights into the regional water cycle dynamics and offers a certain level of guidance for water management strategies tailored to different land-use types.

植被物候动态是多重因子影响的结果,尤其在对外界扰动响应敏感的青藏高原草地生态系统.本研究利用2000-2020年MODIS 16 d合成的归一化植被指数(normalization difference vegetation index,NDVI)数据,选用动态阈值法提取了青藏高原逐年的植被物候期,探究了青藏高原草地物候动态变化及其对驱动因子的响应.结果表明:1)2000-2020年青藏高原草地生长季始期(start of the growing season,SOS)从西北向东南呈提前趋势,每年提前约0.19 d;草地生长季末期(end of the growing season,EOS)整体呈推迟趋势,每年推迟约0.19 d;草地生长季长度(length of the growing season,LOS)由西北向东南逐渐增长.2)风速和连续5 d最大降雨(yearly maximum five-day precipitation,RX5day)是影响草地LOS的主要因素,且因子间两两交互作用要强于单个因子对植被物候的影响,尤其表现在RX5day与温度和风速与温度之间的交互.3)草地LOS与风速和RX5day的回归系数有明显的空间异质性.藏北高原草地LOS随风速增大而变长,随RX5day增大而变短.青海高原和藏南谷地的草地LOS随风速增大而变短.川藏高山峡谷区草地LOS随RX5day增大而变长.综上,本研究可为研究区内生态系统保护和畜牧业的发展提供一定科学依据.

石羊河流域是河西典型的干旱内陆河流域,其生态本底极为敏感脆弱,探究该地区草地植被净初级生产力(NPP)数量和分布变化及其对气候的响应,对该地区草地管理等具有重要意义.本研究基于草原综合顺序分类系统(CSCS)改进的CASA模型模拟了 2000-2020年石羊河流域草地NPP,并辅以Sen's斜率、变异系数(CV)和Hurst指数探究了 NPP时空动态、变化趋势、变化稳定性、未来变化趋势,并通过偏相关分析方法分析了积温和降水与NPP之间的相关关系.结果表明:1)草地年均NPP为170.24g·(m2·a)-1,10年NPP增量为28.96 g·m-2,呈波动上升趋势,未来一段时间内NPP还会有所增加.2)草地类中,年均NPP最高的是山地草甸类(ⅡE30),年均548.74 g·(m2·a)-1;其次为山地草甸草原类(ⅡD23),年均为454.50 g·(m2·a)-1;年均NPP最低的是温带荒漠类(ⅣA4),年均91.65 g·(m2·a)-1.3)石羊河流域草地整体稳定,中波动草地占据主体地位,仅温带典型草原类(ⅢC17)存在较高波动.4)多数草地NPP增加的主导因素是降水,对降水响应敏感的区域占流域面积的24.93％,仅两类荒漠草地(ⅢA3和ⅣA4)对降水响应关系不明显;草甸类草地NPP对积温响应最为敏感,荒漠类草地与积温呈现一定的负相关关系.

使用机器学习算法快速、准确、大范围监测草地地上生物量(AGB)是目前研究热点,但不同机器学习算法因训练样本、超参数设置不同而存在较大差异.基于实测草地AGB和同期遥感数据、气象数据、地形数据,选择与草地AGB相关性较强的13个因子作为深度神经网络(DNN)、随机森林算法(RF)、梯度提升回归树(GBRT)、支持向量机(SVR)、人工神经网络(ANN)和高斯过程回归(GPR)算法的输入变量,建立草地AGB预测模型并从模型预测精度、稳定性、样本敏感性等方面综合评价6种模型应用潜力,分析2020年天祝藏族自治县生长季(4-9月)内草地AGB时空变化特征及其对气候的响应.结果表明:1)DNN估算草地AGB的综合性能最佳,但稳定性较差,对样本敏感性较高;GPR综合性能次于DNN,稳定性和精度均较好;GBRT、RF模拟精度较高,稳定性差;SVR和ANN精度相对其他模型较差,SVR稳定性较高,ANN稳定性较差.2)天祝藏族自治县草地AGB集中在50～250 g·m-2,不同月份草地AGB空间异质性较大,整体表现为从西北向东南呈下降趋势.3)山地草甸、高寒草甸和温性草原中的AGB变化与气温表现出较为明显的正相关关系.降水量对高寒草甸、温性草原和山地草甸的影响不明显,但对温性荒漠草原类的影响较大,AGB随降水量减少呈现减少态势.以上研究结果可为监测草地生物量的方法选择和参数设置提供一定技术支持和参考依据.

在全球变暖的背景下,干旱事件发生频率和强度的增加导致陆地生态系统中植被多样性发生重大变化,研究植被物候对季节性干旱的响应对保护黄土高原的生态系统具有重要意义.基于MODIS遥感归一化植被指数(MODIS NDVI:MOD13Q1)数据及降水和气温逐月格点数据,采用岭回归分析方法,探讨黄土高原植被物候对季节性干旱的敏感性响应.结果表明:(1)上年夏季干旱指数(Standardized precipitation evapotranspiration index,SPEI)和上年秋季SPEI会延迟植被生长季始期(Start of the season,SOS),年初冬季SPEI和当年春季SPEI导致植被SOS提前.年初冬季SPEI相比于当年春季SPEI和当年秋季SPEI更容易延迟植被生长季末期(End of the season,EOS),而当年夏季SPEI会导致植被EOS提前.(2)黄土高原植被物候对季节性SPEI具有明显的空间异质性.青海境内年初冬季干旱程度减弱时,会造成植被SOS提前;当年夏季干旱程度加剧会导致黄土高原大部分植被提前结束生长.(3)黄土高原不同植被物候对季节性SPEI响应差异明显,灌木SOS相比于森林SOS和草地SOS更容易受干旱的影响,草地SOS最易受年初冬季干旱的影响.该研究可为黄土高原植被应对季节性干旱提供一定的科学依据.

Studying the impact of regional or seasonal drought on vegetation water-use efficiency (WUE) can identify an effective theoretical basis by which vegetation can cope with future climate change. Based on remote sensing data and climate grid data, in this study, we calculated the ecosystem WUE and standardized precipitation evapotranspiration index (SPEI), analyzed the temporal and spatial divergence of seasonal drought and WUE, and explored the relationship between WUE and seasonal drought in the Loess Plateau. The results indicate that from 2001 to 2019, the humidity in spring and summer on the Loess Plateau shows an increasing trend, and the aridity in fall also shows an increasing trend. Averaged over four seasons, WUE presents distribution characteristics of “high in the southeast and low in the northwest”, with the highest WUE in summer. However, the geological distribution of the sensitivity of WUE to seasonal drought was significantly different. Spring drought increased WUE, whereas summer drought led to a decrease in WUE. When fall drought was less severe, the WUE increased; WUE response to winter SPEI was negative, but the sensitivity did not change with variation of drought degree. The sensitivity of WUE to the magnitude of seasonal drought was affected by regional dry and wet conditions. A clear seasonal divergence was found in four climate regions, along with increased drought intensity, and the sensitivity of WUE to drought magnitude in arid areas was generally higher than that in semi-arid, semi-humid areas, or humid areas. With this study, we deeply explored how ecosystems deal with the water supply strategy of seasonal drought, which is of great significance in the understanding of the coupling relationship between the carbon–water cycle and climate change.

环境变化引起的植被变化对生态系统过程产生了重大影响.然而,目前对植被生长及其对多影响因素响应的研究仍不够深入.本文采用Theil-Sen中位数趋势分析、Mann-Kendall检验、变异系数、岭回归分析和结构方程模型等方法,探究了青藏高原草地归一化差值植被指数(Normalized difference vegetation index,NDVI)时空变化特征及其对驱动因子的响应.结果表明:青藏高原2001-2020年草地NDVI从东南向西北呈下降趋势,年际变化呈上升趋势,坡度较小区域的草地分布较集中,阴坡草地生长情况较好.另外,区域内草地受水分利用效率(Water use efficiency,WUE)升高和温度升高而生长情况变好,且草地WUE是影响草地NDVI变化的主导因子.本研究提高了我们对多变量如何共同影响草地生长的认知,也强调了 WUE对草地生长的重要性.

Grassland degradation has emerged as a serious socio-economic and ecological problem, endangering both long-term usage and the regional biogeochemical cycle. Climate change and human activities are the two leading factors leading to grassland degradation. However, it is unclear what the degradation level caused by these two factors is. Using the normalized difference vegetation index (NDVI) and coefficient of variation of NDVI (CV NDVI ), the spatial distribution features of grassland degradation or restoration were analyzed in Qilian County in the northeast of the Qinghai–Tibet Plateau. The dominant climate variables affecting NDVI variation were selected through the combination of random forest model and stepwise regression method to improve the residual trend analysis, and on this basis, twelve possible scenarios were established to evaluate the driving factors of different degraded grasslands. Finally, used the Hurst index to forecast the trend of grassland degradation or restoration. The results showed that approximately 55.0% of the grassland had been degraded between 2000 and 2019, and the area of slight degradation (NDVI slope > 0; CV NDVI (slope) > 0; NDVI value > 0.2) accounted for 48.6%. These regions were centered in the northwest of Qilian County. Climate and human activities had a joint impact on grassland restoration or degradation. Human activities played a leading role in grassland restoration, while climate change was primarily a driver of grassland degradation. The regions with slight degradation or re-growing (NDVI slope > 0; CV NDVI (slope) > 0), moderate degradation (NDVI slope < 0; CV NDVI (slope) > 0), and severe degradation or desertification (NDVI slope < 0; CV NDVI (slope) < 0) were dominated by the joint effects of climate and anthropogenic activity accounted for 34.3%, 3.3%, and 1.3%, respectively, of the total grassland area. Grasslands in most areas of Qilian County are forecasted to continue to degrade, including the previously degraded areas, with continuous degradation areas accounting for 54.78%. Accurately identifying the driving factors of different degraded grassland and predicting the dynamic change trend of grassland in the future is the key to understand the mechanism of grassland degradation and prevent grassland degradation. The findings offer a reference for accurately identifying the driving forces in grassland degradation, as well as providing a scientific basis for the policy-making of grassland ecological management.

Ecosystem water use efficiency (WUE) is an important parameter of carbon-water coupling, which connects the carbon cycle and water cycle. It is crucial to understand the spatial and temporal distribution of WUE in degraded grassland and its influencing factors for predicting land surf-atmosphere interactions and the dynamic changes of terrestrial ecosystems. Thus, combining the Moderate Resolution Imaging Spectroradiometer (MODIS) normalized difference vegetation index (NDVI), gross primary production (GPP) and evapotranspiration (ET), this study investigated the spatial and temporal variation of grassland degradation and WUE from 2001 to 2020 on the Qinghai-Tibet plateau (QTP) by Theil-Sen trend method and Mann-Kendall test, and identified the sensitivity response of grassland WUE to degradation, temperature, wind speed and precipitation within different degradation gradients by ridge regression analysis and generalized linear model. The results showed that (1) the WUE gradually decreases from southeast to northwest, and the interannual variation showed an increasing trend. The grassland degradation on the QTP gradually increases from southeast to northwest, and the grievous severe degradation (GSD) and severely degradation (SD) grassland accounted for 61.59% of the total grassland area. (2) The sensitivity of grassland WUE to temperature (γTEM) and precipitation (γPRE) were generally negative in the whole region, the opposite results were found in wind speed and degradation. (3) Temperature was the main factor affecting WUE in degraded grassland, and the growth trend of WUE becomes faster with the increase of the degree of degradation.

研究耕地资源时空变化及驱动因子,对于提高区域粮食安全,严守耕地保护红线,制定耕地保护政策和措施具有重要的实践意义.以甘肃省1995年、2005年、2015年和2020年4期土地利用数据为基础,在ArcGIS和Geo-Da等技术的支持下,从栅格、格网和县域尺度全面分析了甘肃省近25 a耕地时空变化特征,并利用地理探测器对引起耕地变化的主要驱动因子进行了探测.结果表明:(1)甘肃省1995—2020年间耕地减少幅度达1.6％,1995—2005年耕地面积增加,2005—2020年耕地面积递减,且耕地主要流向草地、林地和建设用地,而未利用地主要向耕地和草地转移.(2)耕地空间分布呈"东南多、西北少"的典型特征.耕地空间分布受自然因素和社会经济因素的共同作用,其中,人口和土地开发强度的交互作用是1995年、2005年和2015年甘肃省耕地空间分布差异性的主要原因,而2020年温度和降水的交互作用成为影响耕地的主导因素.研究结果可为甘肃省耕地保护管理提供科学依据.

As one of the extreme climatic events, the frequency and intensity of drought have great impacts on regional water resource. Water is a main limiting factor for plant growth in arid and semi-arid regions. Therefore, it is of great scientific significance to explore the spatiotemporal variations and future tendency of drought for the ecological environment in the Loess Plateau. Based on grid data of monthly precipitation and temperature from 1986 to 2019, we calculated standardized precipitation evapotranspiration index (SPEI) and drought frequency. The spatiotemporal patterns and its variations were analyzed at the seasonal and annual scales in the Loess Plateau using the Mann-Kendall test and Sen's slope estimation method. Finally, the future trend of drought was analyzed in the Loess Plateau by the NAR neural network combined with Hurst index. Results showed that the trend of aridification became more significant in the Loess Plateau, and that the frequency of droughts events exhibited great spatial variations at the interannual and seasonal scales during the study period. Specifically, the highest frequency of drought in the interannual, spring and winter was found in the southeast and west of the Loess Plateau, whereas the frequency of drought in summer and autumn was higher in the northwest. The frequency of moderate drought was the highest in summer compared with other seasons while the frequency of slight drought was the highest in interannual and other seasons. The Loess Plateau showed a trend of aridification in spring and summer, but this trend in autumn and winter became weaker in most areas of the study area. The SPEI value in the interannual, spring, and summer exhibited a decline trend in a future period in the Loess Plateau. The aridification would be enhanced. The Hurst index value was the largest and the persis-tence of its change remained stronger in summer. The possibility of continuous drought in summer would be higher than that in other seasons in the future.

受气候变化影响,全球范围内植被物候发生了显著变化,而目前针对不同植被分区类型下（荒漠草原区、典型草原区、森林草原区、落叶栎林区、落叶栎林亚区）植被物候变化及其对季节性气候变化响应的研究尚少。因此基于MODIS遥感归一化差值植被指数（MODIS NDVI:MOD13Q1）数据、中国植被区划数据及135个气象站点插值数据,利用Sen′s斜率估计、Hurst指数和高阶偏相关分析等方法,研究黄土高原2001—2018年植被物侯变化及其对季节性气候变化的响应。结果表明:（1）黄土高原植被生长季始期（SOS, Start of Growing Season）主要集中在第96—144天,子植被分区由西北向东南方向,逐渐呈现提前趋势,71.0%的像元植被SOS整体提前0—2 d/10a（α=0.05）,且在未来一段时间66%的像元植被SOS继续呈现提前趋势;植被生长季末期（EOS, End of Growing Season）主要集中在第288—304天,各子植被分区植被EOS变化基本保持一致,87.6%的像元植被EOS整体延迟0—3 d/10a（α=0.05）,且在未来一段时间有80%的像元植被EOS继续呈现推迟趋势。（2）黄土高原植被SOS主要受各季节温度的影响;当年春季降水导致植被SOS提前,主要分布在黄土高原中部;上年夏季和上年秋季降水增加会导致植被SOS推迟;当年春季、上年秋季和年初冬季的温度升高均会导致植被SOS提前;各子植被分区植被SOS对不同季节降水的响应存在差异,而对不同季节温度的响应具有一致性。（3）黄土高原植被EOS主要受各季节降水和秋季温度的影响;不同季节降水增加均会导致大部分植被EOS推迟;当年秋季温度导致整体区域植被EOS推迟,且各子植被区植被EOS对当年秋季温度响应具有一致性。该研究可为大尺度植被物候影响因素提供新的认识,也为植被适应未来气候变化提供借鉴。

Climate changes, especially increased temperatures, and precipitation changes, have significant impacts on vegetation phenology. However, the response of vegetation phenology to the extreme climate in the Loess Plateau in Northwest China remains poorly quantified. The research described here analyzed the spatial change in vegetation phenology and the response of vegetation phenology to climate change in the Loess Plateau from 2001 to 2018, using data from seven extreme climate indices based on the ridge regression method. The results showed that extreme climate indexes, TNn (yearly minimum value of the daily minimum temperature), TXx (yearly maximum value of the daily maximum temperature), and RX5day (yearly maximum consecutive five-day precipitation) progressively increased from 2001 to 2018 in the Loess Plateau region, but decrease trend was found in DRT (diurnal temperature range). The start of the growing season (SOS) of vegetation gradually advanced with precipitation from northwest to southeast, and the rate was +0.38 d/a. The overall vegetation end of the growing season (EOS) was delayed, and the trend was −2.83 d/a. The sensitivity of the different vegetation phenology to different extreme weather indices showed obvious spatial differences, the sensitivity coefficient of SOS being mainly positive in the region, whereas the sensitivity coefficient of EOS was negative generally. More sensitivity was found in the EOS to extreme climate indexes than in the SOS. Forest, shrubland and grassland have similar responses to DRT and TNn; namely, both SOS and EOS are advanced with the increase in DRT and delayed with the increase in TNn (the sensitivity coefficient is quite different) but have different responses to RX5day and TXx. These results reveal that extreme climate events have a greater impact on vegetation EOS than on vegetation SOS, with these effects varying with vegetation types. This research can provide a scientific basis for formulating a scientific basis for regional vegetation restoration strategies and disaster prediction on the Loess Plateau.

了解草地覆盖动态在生态环境保护和建设上有重要意义.基于GIMMS NDVI3g数据、气象数据和高程数据分析了1982—2015年中国北方草地NDVI时空动态及对气候变化的响应.结果表明:(1)1982—2015年中国北方草地NDVI以增加趋势为主(占76％),增速为0.002/10 a.其中,坡地草地的增加速率最大(增长速率为0.001/10 a),高山亚高山平原草原变化速率最小,其他4种草地类型速率为平原草地NDVI增长速率>高山亚高山草甸>荒漠草原>草甸;(2)NDVI变异系数均值为0.078,变化相对稳定(Cv<0.15);(3)Hurst指数均值为0.42,结合NDVI变化趋势结果发现未来草地NDVI变化趋势主要以下降为主(0<H<0.5,占79.8％);(4)降水是影响北方草地生长的主要气候因子.除昆仑山脉、青海高原东坡坡底及小兴安岭等海拔较高区域外,其他地区(占92.4％)的降水与NDVI呈显著相关关系.温度与草地NDVI主要以正相关为主(占62.7％),呈负相关关系的区域集中在内蒙古高原、黄土高原西南部、准噶尔盆地和塔里木盆地等较为干旱地区.以上研究结果可为草地资源管理、生态环境保护、荒漠化防治提供重要参考信息.