1982-2012年全球干旱区植被变化及驱动因子分析

基于长时间序列卫星遥感数据GIMMS3g NDVI(1982-2012年),分析了全球干旱区(包括亚湿润干旱区、半干旱区、干旱区和极端干旱区)植被时空变化及其对气候和人文等非气候因子的响应.结果表明:①全球干旱区NDVI总体呈显著增长趋势(P＜0.001),增长速率为0.0005·a-1,略低于全球植被增长速率.显著上升区域和显著下降区域分别占全球植被显著变化区域面积的27.0％和7.7％(P＜0.05).显著退化面积最大区域为半干旱区.②降水作为干旱区植被变化的主要影响因子,主要表现在对干旱区和半干旱区植被的影响上,对亚湿润干旱区和极端干旱区影响较小.③全球不同干旱区植被变化及驱动因子存在较大差异.如澳大利亚南部主要受到季节降水的影响,植被改善;而南美和欧亚大陆中部则主要受到人为因素的影响,植被退化.     

新疆伊犁河流域植被变化动态监测与评价

基于2000-2013年MODIS/NDVI数据和研究区内气象站点资料,分析了伊犁河流域植被生长季NDVI时空变化特征及其与气候因子的关系。结果表明:1)研究区植被整体呈微弱的退化趋势,年退缩率为-0.8×10-3a-1,其中草原的退化趋势较草甸、灌丛和林地略显著。2)2000-2013年研究区植被退化区面积占研究区总面积的11.45%,主要分布在特克斯河中下游、巩乃斯河周边地区;植被改善面积占全区总面积的8.38%,主要分布在伊宁市及霍尔果斯河周边地区。3)研究区伊宁站周边植被生长季NDVI与同期气温及降水存在不显著相关性,昭苏站周边植被生长季NDVI与同期气温及降水分别存在显著负相关和极显著正相关。气候的暖干化趋势可能是导致伊犁河流域植被生长退化的主要原因。     

1961-2017年青藏高原东北部雨季降水量变化及其贡献度分析

利用53个气象观测站1961—2017年5—9月逐日降水资料,分析了青藏高原东北部雨季降水量的变化特征,以及不同等级降水变化在降水量增量中的相对贡献。结果表明:1961—2017年青藏高原东北部干旱区雨季降水量呈增加趋势,半干旱区和半湿润区降水量的极端性增强。大部分地区的降水强度普遍增加。进一步分析可知,青藏高原东北部雨季降水量变化主要由降水强度的变化引起,同时中雨等级降水增加贡献大于其他等级降水。半湿润区和半干旱区东部降水极端化趋势明显增强。该结果有助于进一步理解和认识青藏高原东北部生态环境变化的气候效应。     

1982-2006年新疆植被活动的年际变化及其季节差异

利用1982-2006年NOAA/AVHRR归一化植被指数(NDVI)时间序列,结合植被、地形和气候等资料,研究新疆植被活动的年际变化及其季节差异.结果表明:过去的25年,占新疆植被面积27%的地区生长季(4～10月)NDVI显著增加(P＜0.05),其中近一半地区年增加速率大于0.003,而显著减少地区的面积仅占4%...     

基于GIMMS NDVI数据的北方13省荒漠化趋势评价

北方13省处在干旱、半干旱和半湿润地区,植被对气候变化和人类活动最为敏感,一直是荒漠化研究的热点地区。基于GIMMS NDVI和降水数据,使用一元线性回归方法对北方13省1982年-2006年ΣNDVI和降水的年际变化趋势及其相关性进行了分析,并对ΣNDVI和降水的变化趋势差异做进一步分析。研究结果表明:从总体上来看,中国北方13省在25年间荒漠化趋势变缓,即植被覆盖度呈显著上升趋势,其中显著增加的像元数为35.3%,而显著降低的像元数仅占7.2%。从ΣNDVI与降水的斜率散点象限图来看,ΣNDVI和降水的差异主要在第二象限和第三象限,说明尽管降水在北方地区植被覆盖度变化中起到主要作用,但是降水并不能完全解释植被覆盖度的变化趋势,人类活动如植树造林等是植被覆盖度增加的重要驱动力。内蒙古自治区东北部和东北地区的三江平原呈现出荒漠化趋势,在大部分地区与降水的相关性不显著,表明在该地区降水的影响作用较弱,主要是人类活动等因素导致的。     

中国西北干旱区1981～2001年NDVI对气候变化的响应分析

气候变化在不同的区域有着不同的特征,对植被也带来不同的影响,对不同地区气候变化特征的认识及植被变化的相应分析,可使我们对全球变化对干旱区的影响有更深入的认识。本文通过定量分析西北干旱区1981~2001年NOAA/AVHRR数据和同期的气象资料,借助于遥感技术和数理统计知识,分析了1981~2001年我国西北干旱区NDVI变化及其与气候变化的关系。结果显示:1981-2001年间西北干旱区年际最大NDVI的变化与气候变化具有明显的相关性,尤其是对新疆的南、北疆来说,NDVI的变化受到年降水量、年均温和空气相对湿度的影响比较显著,NDVI与年降水量和相对湿度的相关程度要明显比与年均温的相关程度高。甘肃内蒙古的河西走廊和青海的柴达木地区NDVI没有明显的变化趋势,同时这两个地区也是年降水量变化最小的地区。从而得出一个结论:降水资源是我国西北干旱区植被生长和生态建设的最重要气象因子,只有充分、合理地利用"降水"这种天然水资源才能最终实现中国西北干旱区环境、社会与经济的可持续发展。     

基于GIMMS NDVI的中亚干旱区植被覆盖时空变化

选用1982—2013年GIMMS NDVI数据,运用变异系数法、Theil-Sen median趋势分析耦合Mann-Kendall检验以及Hurst指数法,研究了中亚干旱区植被覆盖的空间格局、不同维度的空间变异性、时间变化特征和未来趋势预测。同时,结合CRU降水、气温资料和MODIS土地覆盖数据,对植被覆盖时空格局及其变化的驱动因素进行分析。结果表明:1 1982—2013年中亚干旱区植被覆盖有较强的空间异质性,有植被覆盖的区域占总面积的85.32%,无植被覆盖的区域占14.68%。受降水量控制,植被覆盖呈山区高平原低、西部高东部低、北部高南部低的特点;受河流和人工灌溉的影响,绿洲区的植被覆盖高于荒漠区。2近32 a全区植被覆盖的波动变化较明显,各变异程度的面积比例:中等波动变化相对较高的波动变化高波动变化相对较低的波动变化低波动变化。受降水变率和人工种植的影响,植被覆盖的高波动变化主要在荒漠区和诸流域绿洲区;低波动变化主要在植被生长良好的区域。3 32 a间全区NDVI呈增长趋势,NDVI距平的变化率为0.01·(10a)~(-1)。基于像元尺度的分析也表明,全区植被覆盖变化趋势以增加为主,各类变化趋势的面积比例:轻微增加显著增加轻微减小显著减小无法确定。植被改善是区域气候增湿增暖和绿洲土地覆盖变迁所致。4全区NDVI的Hurst指数均值为0.63,Hurst指数大于0.5的范围所占比例为75.17%,即未来全区植被覆盖的变化趋势以持续性增加为主,其中25.23%的区域未来变化趋势无法确定。     

近10 a来祁连山植被覆盖变化研究

NDVI作为植被生长状况及植被覆盖度的最佳指示因子,被认为是监测地区或全球植被和环境变化的最有效指标。基于2000-2011年250 m分辨率的MODIS NDVI数据并结合气候资料,采用最大值合成法、均值法、斜率分析法、相关分析法,研究祁连山生长季植被覆盖的时空变化及其与气候因子的相关性。结果表明：祁连山植被覆盖总体上自西向东递增,呈现东多西少的分布格局;植被覆盖变化存在明显的空间差异,表现为中西部植被覆盖增加,增加面积为79 149 km2,占祁连山总面积的52.93%;东部植被覆盖减少,减少面积为22 865 km2,占祁连山总面积的11.09%。近10 a来植被覆盖整体上呈增加趋势,生长季各月植被覆盖整体上呈增加趋势,全球气候变暖导致的降水增加是祁连山植被覆盖增加的主要原因。NDVI与气温、降水的相关性较高并存在一定的滞后性,6、7月NDVI分别与前期1月和前期2月的降水显著相关,相关系数分别为0.788和0.684;8、9月NDVI分别与当月、前期1月的气温极显著相关,相关系数分别为0.825和0.829。     

近30年内蒙古自治区植被变化趋势及影响因素分析

基于NOAA和MOD IS数据,以生长季累计NDVI为植被表征指标,采用基于像元的趋势分析方法,对过去近30年内蒙古自治区的植被变化进行了系统分析(分为1983～1999年和2000～2009年两个时段),确定了植被发生趋势性变化的区域,并利用气候和社会经济统计资料确定了影响植被变化的主要因素。研究结果表明:近30年来,内蒙古自治区72.1%的地区植被未发生明显的趋势性变化;5.5%的地区(科尔沁沙地以南和鄂尔多斯东北部)植被状况两个时期均持续好转,13.9%的地区(锡林郭勒盟草原、科尔沁沙地以南、后套平原和土默川平原)植被前期好转,后期一直保持平稳状态;0.6%的地区(科尔沁沙地北部)植被前期变差,后期无明显变化趋势;1.8%的地区(大青山山脉北侧的乌盟后山及大兴安岭的部分地区)植被前期未发生明显变化,后期明显变差。除锡林郭勒植被好转和大青山山脉北侧的乌盟后山地区植被变差主要受降水影响外,研究期内植被活动显著增强的大部分地区主要受人为因素的影响。西辽河沿岸平原、土默川平原、后套平原、科尔沁沙地以南等耕作区的植被变化主要与农作物产量的变化有关,鄂尔多斯地区和乌兰布和沙漠东部边缘的磴口县等草原区NDVI的显著增加与区域草原开垦、持续植树种草、禁牧轮牧等防沙治沙等活动有关,大兴安岭部分地区的NDVI显著减少与森林火灾有关。     

西藏青稞需水关键期降水的气候变化特征

利用1961-2000年西藏不同气候型农区旬降水量资料,分析了青稞生育期的降水特征及趋势变化。结果表明：青稞拔节～孕穗期降水变率较大,此时温暖半干旱农区、温暖半湿润农区易出现旱情;抽穗～乳熟期半湿润农区多数年份的降水能够满足青稞需求,且还有盈余。过去40a青稞全生育期的降水量,在温暖半干旱农区,1980年以前呈显著的减少趋势,1981年开始表现为显著的增加趋势;温暖半湿润农区呈明显的增加趋势,而温凉半湿润农区表现为不显著的减少趋势。     

甘肃东部气候变化及冬小麦生长发育响应特征

分析发现1971年以来陇东黄土高原变暖特征明显,其中西峰半湿润塬区1971～2005年增温线性趋势0.0525℃/a,环县半干旱川区增温线性趋势0.0367℃/a,平凉半湿润半干旱过渡地区增温线性趋势0.0411℃/a.除了环县川区夏季增温不明显,其余各区域四季增温均比较显著,西峰塬区四季增温幅度最大,增温趋势最明显,平凉次之.增温表现出夏季、秋季、春季、冬季依次增强的趋势.西峰半湿润塬区年降水量呈减少的趋势,环县半干旱川区年降水量呈增加的趋势,处于半湿润和半干旱过渡带的平凉年降水量则没有明显变化,不同区域秋季降水量均呈现出减少的趋势.气候变暖对陇东不同气候区域冬小麦生态影响既有相同之处,也有不同之处,相同之处主要表现在停止生长期和乳熟期均没有明显变化,起身期提前趋势明显.不同之处体现在西峰播种期明显推迟,返青期明显提前,而环县和平凉播种期和返青期均没有明显变化;西峰、平凉分蘖期明显推迟,抽穗期明显提前,而环县分蘖期和抽穗期没有明显变化;西峰、环县成熟期显著提前,全生育期日数显著缩短,而平凉成熟期和全生育期日数则没有明显变化;另外,西峰、平凉冬前及早春分蘖减少,越冬死亡率大幅度下降,产量显著增高,西峰、环县灌浆期显著延长,成熟期显著缩短,环县越冬死亡率较高时段对应秋春季降水偏少时段,产量增幅不大,增产趋势不明显.综合分析认为,西峰半湿润塬区气候变暖特征最明显,气候变暖对冬小麦的生态影响最显著.     

天水旱作区自然降水生产潜力的适度开发对策

通过10年的定点资料统计,分析了天水旱作地区自然降水生产潜力开发程度、适宜开发程度及可开发程度;并就资源和环境条件对水分生产潜力开发的制约问题进行了讨论,分阶段分层次提出了生产潜力适度开发对策措施。     

Assessment of desertification in Eritrea: land degradation based on Landsat images

Remote sensing is an effective way in monitoring desertification dynamics in arid and semi-arid regions. In this study, we used a decision tree method based on NDVI(normalized difference vegetation index), SAVI(soil adjusted vegetation index), and vegetation cover proportion to quantify and analyze the desertification in Eritrea using Landsat data of the 1970 s, 1980 s and 2014. The results demonstrate that the NDVI value and the annual mean precipitation declined while the temperature increased over the past 40 a. Strongly desertified land increased from 4.82×10~4 km~2(38.5%) in the 1970 s to 8.38×10~4 km~2(66.9%) in 2014: approximately 85% of the land of the country was under serious desertification, which significantly occurred in arid and semi-arid lowlands of the country(eastern, northern, and western lowlands) with relatively scarce precipitation and high temperature. The non-desertified area, mostly located in the sub-humid eastern escarpment, also declined from approximately 2.1% to 0.5%. The study concludes that the desertification is a cause of serious land degradation in Eritrea and may link to climate changes, such as low and unpredictable precipitation, and prolonged drought.     

Drought trend analysis in a semi-arid area of Iraq based on Normalized Difference Vegetation Index,Normalized Difference Water Index and Standardized Precipitation Index

Drought was a severe recurring phenomenon in Iraq over the past two decades due to climate change despite the fact that Iraq has been one of the most water-rich countries in the Middle East in the past.The Iraqi Kurdistan Region(IKR)is located in the north of Iraq,which has also suffered from extreme drought.In this study,the drought severity status in Sulaimaniyah Province,one of four provinces of the IKR,was investigated for the years from 1998 to 2017.Thus,Landsat time series dataset,including 40 images,were downloaded and used in this study.The Normalized Difference Vegetation Index(NDVI)and the Normalized Difference Water Index(NDWI)were utilized as spectral-based drought indices and the Standardized Precipitation Index(SPI)was employed as a meteorological-based drought index,to assess the drought severity and analyse the changes of vegetative cover and water bodies.The study area experienced precipitation deficiency and severe drought in 1999,2000,2008,2009,and 2012.Study findings also revealed a drop in the vegetative cover by 33.3%in the year 2000.Furthermore,the most significant shrinkage in water bodies was observed in the Lake Darbandikhan(LDK),which lost 40.5%of its total surface area in 2009.The statistical analyses revealed that precipitation was significantly positively correlated with the SPI and the surface area of the LDK(correlation coefficients of 0.92 and 0.72,respectively).The relationship between SPI and NDVI-based vegetation cover was positive but not significant.Low precipitation did not always correspond to vegetative drought;the delay of the effect of precipitation on NDVI was one year.     

Estimation of spatial and temporal changes in net primary production based on Carnegie Ames Stanford Approach (CASA) model in semi-arid rangelands of SemiromCounty,Iran

Net primary production (NPP) is an indicator of rangeland ecosystem function. This research assessed the potential of the Carnegie Ames Stanford Approach (CASA) model for estimating NPP and its spatial and temporal changes in semi-arid rangelands of Semirom County, Iran. Using CASA model, we estimated the NPP values based on monthly climate data and the normalized difference vegetation index (NDVI) obtained from the MODIS sensor. Regression analysis was then applied to compare the estimated production data with observed production data. The spatial and temporal changes in NPP and light utilization efficiency (LUE) were investigated in different rangeland vegetation types. The standardized precipitation index (SPI) was also calculated at different time scales and the correlation of SPI with NPP changes was determined. The results indicated that the estimated NPP values varied from 0.00 to 74.48 g C/(m²?a). The observed and estimated NPP values had different correlations, depending on rangeland conditions and vegetation types. The highest and lowest correlations were respectively observed in Astragalus spp.-Agropyronspp. rangeland (R²=0.75) with good condition and Gundeliaspp.-Cousiniaspp. rangeland (R²=0.36) with poor and very poor conditions. The maximum and minimum LUE values were found in Astragalus spp.-Agropyronspp. rangeland (0.117 g C/MJ) with good condition and annual grasses-annual forbs rangeland (0.010 g C/MJ), respectively. According to the correlations between SPI and NPP changes, the effects of drought periods on NPP depended on vegetation types and rangeland conditions. Annual plants had the highest drought sensitivity while shrubs exhibited the lowest drought sensitivity. The positive effects of wet periods on NPP were less evident in degraded areas where the destructive effects of drought were more prominent. Therefore, determining vegetation types and rangeland conditions is essential in NPP estimation. The findings of this study confirmed the potential of the CASA for estimating rangeland production. Therefore, the model output maps can be used to evaluate, monitor and optimize rangeland management in semi-arid rangelands of Iran where MODIS NPP products are not available.     

甘肃省季节性干旱综合指数的特征

利用甘肃省71个气象站1971-2013年月降水量资料,借助Z指数构建了基于干旱频率、干旱强度的干旱综合指数评价指标,从季节性干旱以及季节性连旱着手分析了不同时间尺度的干旱特征。结果表明:研究区季节性趋旱程度(MK0)和趋旱范围(DR,%)差异显著,其中春季陇东高原为-0.154(100%),重旱为灵台(-0.238*)、宁县(-0.180)、镇原(-0.178);夏季河西走廊为-0.081(73.7%),重旱为马鬃山(-0.271*)、安西(-0.255*)、敦煌(-0.171);秋季陇中高原为-0.017(50.9%),重旱在会宁(-0.186)。季节性干旱综合指数重旱时段显示,春季为1995年(陇东0.481),夏季为1997年(陇南0.405),秋季为1972年(甘南0.366),冬季为1998年(陇东0.586)和2009年(甘南0.449)。两季连旱高值区在白银、会宁、古浪、玛曲、灵台、永登、华池、静宁等地(0.030),其中秋冬连旱最为严重(0.0274);三季连旱高值区为会宁、古浪、静宁、白银、永登等地(0.020),其中夏秋冬连旱最为显著(0.017 5);四季连旱高值区为会宁、古浪、西峰、灵台、泾川等地(0.015),即除了冬春夏秋连旱外,其余季节性连旱程度均比较显著(0.009)。     

Can climate change influence agricultural GTFP in arid and semi-arid regions of Northwest China?

There are eight provinces and autonomous regions (Gansu Province, Ningxia Hui Autonomous Region, Xinjiang Uygur Autonomous Region, Inner Mongolia Autonomous Region, Tibet Autonomous Region, Qinghai Province, Shanxi Province, and Shaanxi Province) in Northwest China, most areas of which are located in arid and semi-arid regions (northwest of the 400 mm precipitation line), accounting for 58.74% of the country's land area and sustaining approximately 7.84×10⁶ people. Because of drought conditions and fragile ecology, these regions cannot develop agriculture at the expense of the environment. Given the challenges of global warming, the green total factor productivity (GTFP), taking CO₂ emissions as an undesirable output, is an effective index for measuring the sustainability of agricultural development. Agricultural GTFP can be influenced by both internal production factors (labor force, machinery, land, agricultural plastic film, diesel, pesticide, and fertilizer) and external climate factors (temperature, precipitation, and sunshine duration). In this study, we used the Super-slacks-based measure (Super-SBM) model to measure agricultural GTFP during the period 2000-2016 at the regional level. Our results show that the average agricultural GTFP of most provinces and autonomous regions in arid and semi-arid regions underwent a fluctuating increase during the study period (2000-2016), and the fluctuation was caused by the production factors (input and output factors). To improve agricultural GTFP, Shaanxi, Shanxi, and Gansu should reduce agricultural labor force input; Shaanxi, Inner Mongolia, Gansu, and Shanxi should decrease machinery input; Shaanxi, Inner Mongolia, Xinjiang, and Shanxi should reduce fertilizer input; Shaanxi, Xinjiang, Gansu, and Ningxia should reduce diesel input; Xinjiang and Gansu should decrease plastic film input; and Gansu, Shanxi, and Inner Mongolia should cut pesticide input. Desirable output agricultural earnings should be increased in Qinghai and Tibet, and undesirable output (CO₂ emissions) should be reduced in Inner Mongolia, Xinjiang, Gansu, and Shaanxi. Agricultural GTFP is influenced not only by internal production factors but also by external climate factors. To determine the influence of climate factors on GTFP in these provinces and autonomous regions, we used a Geographical Detector (Geodetector) model to analyze the influence of climate factors (temperature, precipitation, and sunshine duration) and identify the relationships between different climate factors and GTFP. We found that temperature played a significant role in the spatial heterogeneity of GTFP among provinces and autonomous regions in arid and semi-arid regions. For Xinjiang, Inner Mongolia, and Tibet, a suitable average annual temperature would be in the range of 7°C-9°C; for Gansu, Shanxi, and Ningxia, it would be 11°C-13°C; and for Shaanxi, it would be 15°C-17°C. Stable climatic conditions and more efficient production are prerequisites for the development of sustainable agriculture. Hence, in the agricultural production process, reducing the redundancy of input factors is the best way to reduce CO₂ emissions and to maintain temperatures, thereby improving the agricultural GTFP. The significance of this study is that it explores the impact of both internal production factors and external climatic factors on the development of sustainable agriculture in arid and semi-arid regions, identifying an effective way forward for the arid and semi-arid regions of Northwest China.     

1982—2015年中国北方生长季NDVI变化及其对气温极值的响应

基于GIMMS NDVI 3g v1.0数据集和日值气象数据，结合极端气温指数，辅以极点对称模态分解、趋势分析、Mann-Kendall趋势检验、相关分析等方法，探讨中国北方生长季植被覆盖及极端气温的变化特征，研究植被覆盖对气温极值的响应状况。结果表明：① 1982—2015年中国北方生长季NDVI以0.002·（10a）^-1的速率上升（P<0.05），ESMD（极点对称模态分解方法）显示生长季NDVI波动上升；针叶林、灌丛、荒漠植被、草地以及栽培植被呈增长趋势，栽培植被增速最快，针阔混交林、落叶阔叶林和高山植被呈不显著减少趋势。② 空间上，NDVI显著增加区域超过全区的33%，主要分布在天山、塔里木盆地北部、祁连山、陇南山区、黄土高原、河套平原、吕梁山和太行山、大别山以及辽西丘陵地区；显著下降区域仅占12%，主要分布在大兴安岭、小兴安岭和长白山区。③ 极端气温指数中，除TNmean（日最低气温平均值）和TNn（日最低气温极低值）呈上升趋势外，其余冷极值指数均呈下降趋势；所有暖极值指数均呈上升趋势；其他指数中，DTR（气温日较差）呈减小趋势，GSL（生长季日数）呈增加趋势。④ 中国北方NDVI与极端气温指数的相关性表明，冷极值指数中NDVI与FD0（霜冻日数）、TN10p（冷夜日数）、TX10p（冷昼日数）呈显著负相关（P＜0.05），与TNmean呈显著正相关（P＜0.01）；NDVI与所有暖极值指数呈正相关，与TR20（热夜日数）、TXmean（日最高气温平均值）、TX90p（暖昼日数）以及TN90p（暖夜日数）存在显著相关性（P＜0.05）；NDVI与GSL呈显著正相关（P＜0.05）。⑤ 天山、塔里木盆地北缘、祁连山区、河套平原、黄土高原、太行山和吕梁山区等NDVI显著增加区域对极端气温指数的响应强烈。NDVI显著增加区主要对FD0、TNmean、TN90p、GSL等指数响应较强。NDVI显著减少区域对指数的响应各异，主要与SU25（夏季日数）呈显著负相关（P＜0.05）。     

Attribution analysis and multi-scenario prediction of NDVI drivers in the Xilin Gol grassland,China

Grassland degradation is influenced by climate change and human activities, and has become a major obstacle for the development of arid and semi-arid areas, posing a series of environmental and socio-economic problems. An in-depth understanding of the inner relations among grassland vegetation dynamics, climate change, and human activities is therefore greatly significant for understanding the variation in regional environmental conditions and predicting future developmental trends. Based on MODIS (moderate resolution imaging spectroradiometer) NDVI (normalized difference vegetation index) data from 2000 to 2020, our objective is to investigate the spatiotemporal changes of NDVI in the Xilin Gol grassland, Inner Mongolia Autonomous Region, China. Combined with 12 natural factors and human activity factors in the same period, the dominant driving factors and their interactions were identified by using the geographic detector model, and multiple scenarios were also simulated to forecast the possible paths of future NDVI changes in this area. The results showed that: (1) in the past 21 a, vegetation cover in the Xilin Gol grassland exhibited an overall increasing trend, and the vegetation restoration (84.53%) area surpassed vegetation degradation area (7.43%); (2) precipitation, wind velocity, and livestock number were the dominant factors affecting NDVI (the explanatory power of these factors exceeded 0.4). The interaction between average annual wind velocity and average annual precipitation, and between average annual precipitation and livestock number greatly affected NDVI changes (the explanatory power of these factors exceeded 0.7). Moreover, the impact of climate change on NDVI was more significant than human activities; and (3) scenario analysis indicated that NDVI in the Xinlin Gol grassland increased under the scenarios of reduced wind velocity, increased precipitation, and ecological protection. In contrast, vegetation coverage restoration in this area was significantly reduced under the scenarios of unfavorable climate conditions and excessive human activities. This study provides a scientific basis for future vegetation restoration and management, ecological environmental construction, and sustainable natural resource utilization in this area.     

Spatial-temporal dynamics of desert vegetation and its responses to climatic variations over the last three decades:a case study of Hexi region in Northwest China

Analysis of spatial-temporal variations of desert vegetation under the background of climate changes can provide references for ecological restoration in arid and semi-arid areas.In this study,we used the Global Inventory Modeling and Mapping Studies(GIMMS)NDVI data from 1982 to 2006 and Moderate Resolution Imaging Spectroradiometer(MODIS)NDVI data from 2000 to 2013 to reveal the dynamics of desert vegetation in Hexi region of Northwest China over the past three decades.We also used the annual temperature and precipitation data acquired from the Chinese meteorological stations to analyze the response of desert vegetation to climatic variations.The average value of NDVImax(the maximum NDVI during the growing season)for desert vegetation in Hexi region increased at the rate of 0.65×10–3/a(P0.05)from 1982 to 2013,and the significant increases of NDVImax mainly appeared in the typical desert vegetation areas.Vegetation was significantly improved in the lower reaches of Shule and Shiyang river basins,and the weighted mean center of desert vegetation mainly shifted toward the lower reaches of the two basins.Almost 95.32% of the total desert vegetation area showed positive correlation between NDVImax and annual precipitation,indicating that precipitation is the key factor for desert vegetation growth in the entire study area.Moreover,the areas with non-significant positive correlation between NDVImax and annual precipitation mainly located in the lower reaches of Shiyang and Shule river basins,this may be due to human activities.Only 7.64% of the desert vegetation showed significant positive correlation between NDVImax and annual precipitation in the Shule River Basin(an extremely arid area),indicating that precipitation is not the most important factor for vegetation growth in this basin,and further studies are needed to investigate the mechanism for this phenomenon.