Projections of the Advance in the Start of the Growing Season during the 21st Century Based on CMIP5 Simulations

It is well-known that global warming due to anthropogenic atmospheric greenhouse effects advanced the start of the vegetation growing season （SOS） across the globe during the 20th century. Projections of further changes in the SOS for the 21st century under certain emissions scenarios （Representative Concentration Pathways, RCPs） are useful for improving understanding of the consequences of global warming. In this study, we first evaluate a linear relationship between the SOS （defined using the normalized difference vegetation index） and the April temperature for most land areas of the Northern Hemisphere for 1982-2008. Based on this relationship and the ensemble projection of April temperature under RCPs from the latest state-of-the-art global coupled climate models, we show the possible changes in the SOS for most of the land areas of the Northern Hemisphere during the 21st century. By around 2040-59, the SOS will have advanced by -4.7 days under RCP2.6, -8.4 days under RCP4.5, and -10.1 days under RCPS.5, relative to 1985-2004. By 2080-99, it will have advanced by -4.3 days under RCP2.6, -11.3 days under RCP4.5, and -21.6 days under RCP8.5. The geographic pattern of SOS advance is considerably dependent on that of the temperature sensitivity of the SOS. The larger the temperature sensitivity, the larger the date-shift-rate of the SOS.

Effect of seasonal snow on the start of growing season of typical vegetation in Northern Hemisphere

Under global warming, seasonal snow takes faster melting rate than before, which greatly changes the hydro-logical cycle. In this study, by targeting three typical seasonal snow-covered land types (i.e., open shrubland,evergreen needleleaf forest and mixed forest) in the Northern Hemisphere, the start of growing season (SGS) hasbeen found obviously advanced in the past years, greatly contributed by the faster melting rate of seasonal snow.It is manifested that significantly positive correlation has been found between SGS and May snow depth for openshrubs, March and April snow depth for evergreen needleleaf forests and March snow depth for mixed forests.However, such close association is not appeared in all the climate conditions of same vegetation. In the future,as the rate of melting snow becomes faster in the high emission of greenhouse gasses than the current situation,continuously advanced SGS will accelerate the change of vegetation distribution in the Northern Hemisphere.These findings offer insights into understanding the effect from seasonal snow on vegetation and promote thesustainable utilization of regional vegetation in the Northern Hemisphere.

Variations of the thermal growing season during the period 1961–2015 in northern China

Researching into changes in thermal growing season has been one of the most important scientific issues in studies of the impact of global climate change on terrestrial ecosystems. However, few studies investigated the differences under various definitions of thermal growing season and compared the trends of thermal growing season in different parts of China. Based on the daily mean air temperatures collected from 877 meteorological stations over northern China from 1961 to 2015, we investigated the variations of the thermal growing season parameters including the onset, ending and duration of the growing season using the methods of differential analysis, trend analysis, comparative analysis, and Kriging interpolation technique. Results indicate that the differences of the maximum values of those indices for the thermal growing season were significant, while they were insignificant for the mean values. For indices with the same length of the spells exceeding 5°C, frost criterion had a significant effect on the differences of the maximum values. The differences of the mean values between frost and non-frost indices were also slight, even smaller than those from the different lengths of the spells. Temporally, the starting date of the thermal growing season advanced by 10.0–11.0 days, while the ending dates delayed by 5.0–6.0 days during the period 1961–2015. Consequently, the duration of the thermal growing season was prolonged 15.0–16.0 days. Spatially, the advanced onset of the thermal growing season occurred in the southwestern, eastern, and northeastern parts of northern China, whereas the delayed ending of the thermal growing season appeared in the western part, and the length of the thermal growing season was prolonged significantly in the vast majority of northern China. The trend values of the thermal growing season were affected by altitude. The magnitude of the earlier onset of the thermal growing season decreased, and that of the later ending increased rapidly as the altitude increased, causing the magnitude of the prolonged growing season increased correspondingly. Comparing the applicability of selected indices and considering the impacts of frost on the definitions are important and necessary for determining the timing and length of the thermal growing season in northern China.

Co-influence of the start of thermal growing season and precipitation on vegetation spring green-up on the Tibetan Plateau

The climate in the Tibetan Plateau(TP)has undergone significant change in recent decades,mainly in thermal and water conditions,which plays a crucial role in phenological changes in vegetation spring phenology.However,how the start of the thermal growing season(SOS-T)and the start of the rainy season(SORS)as key climatic factors affect vegetation green-up remains unclear.Given that these factors characterize thermal and water conditions required for vegetation green-up,this study investigated changes in the SOS-T and SORS from 1961 to 2022,using observation-based datasets with long time series.We found that the SOS-T and SORS have advanced across the TP in 1961-2022 and have shown a spatial pattern of advancement in the east and delay in the west in 2000-2022.Further,the co-effect of temperature and precipitation change on the start of vegetation growing season(SOS-V)in 2000-2022 was observed.Averaged across TP,the SOS-V had an early onset of 1.3 d per decade during 2000-2022,corresponding to advanced SOS-T and SORS.Regionally,the SOS-V generally occurred nearly at the same time as the SOS-T in the high-altitude meadow region.A substantial delay in the SOS-V relative to the SOS-T was observed in the desert,shrub,grassland and forest regions and generally kept pace with the SORS.Furthermore,for 50%of the vegetated regions on the TP,inter-annual variation in the delay in the SOS-V relative to the SOS-T was dominated by precipitation change,which was profound in warm-climate regions.This study highlights the co-regulation of precipitation and temperature change in the SOS-V in different vegetation cover regions in the TP,offering a scientific foundation for comprehending the impact of climate change and prospects for vegetation phenology on the TP.

Changing Spring Phenology Dates in the Three-Rivers Headwater Region of the Tibetan Plateau during 1960–2013

The variation of the vegetation growing season in the Three-Rivers Headwater Region of the Tibetan Plateau has recently become a controversial topic. One issue is that the estimated local trend in the start of the vegetation growing season(SOS)based on remote sensing data is easily affected by outliers because this data series is short. In this study, we determine that the spring minimum temperature is the most influential factor for SOS. The significant negative linear relationship between the two variables in the region is evaluated using Moderate Resolution Imaging Spectroradiometer–Normalized Difference Vegetation Index data for 2000–13. We then reconstruct the SOS time series based on the temperature data for 1960–2013.The regional mean SOS shows an advancing trend of 1.42 d(10 yr)during 1960–2013, with the SOS occurring on the 160th and 151st days in 1960 and 2013, respectively. The advancing trend enhances to 6.04 d(10 yr)during the past 14 years. The spatiotemporal variations of the reconstructed SOS data are similar to those deduced from remote sensing data during the past 14 years. The latter exhibit an even larger regional mean trend of SOS [7.98 d(10 yr)] during 2000–13. The Arctic Oscillation is found to have significantly influenced the changing SOS, especially for the eastern part of the region,during 2000–13.

蒙古高原干旱时空特征及对植被物候的累积影响

蒙古高原是中国北方重要的生态安全屏障,为厘清蒙古高原干旱时空动态及对植被物候的影响,利用SPEIbase 2.9数据集和基于累积NDVI的Logistic曲线曲率极值法反演的植被物候数据集,分析1982—2022年蒙古高原干旱时空特征及干旱对植被返青期和枯黄期的累积影响。结果表明:(1)不同尺度SPEI均呈显著下降趋势,随着时间尺度的增加干旱化趋势加剧、干旱化面积明显增大,中部和西部地区干旱化尤为严重。(2)植被返青期提前和推迟的面积占比分别为50.03%和49.97%,枯黄期推迟和提前的面积占比分别为67.85%和32.15%;荒漠草原返青期和枯黄期主要表现为推迟趋势,针叶林和森林草原北部返青期显著提前、枯黄期呈推迟趋势。(3)蒙古高原(荒漠除外)79.62%的区域植被返青期与1~12个月尺度SPEI呈最大正相关,干旱尺度主要为中期尺度,尤其7~9个月尺度的干旱对植被返青期影响明显;54.15%的区域植被枯黄期与SPEI呈最大负相关,干旱尺度主要为1~3个月尺度。其结果对防御蒙古高原干旱及对植被物候和生产力的影响具有重要意义。

Start of vegetation growing season on the Tibetan Plateau inferred from multiple methods based on GIMMS and SPOT NDVI data

In this study, we have used four methods to investigate the start of the growing season （SGS） on the Tibetan Plateau （TP） from 1982 to 2012, using Normalized Difference Vegetation Index （NDVI） data obtained from Global Inventory Modeling and Mapping Studies （GIMSS, 1982-2006） and SPOT VEGETATION （SPOT-VGT, 1999-2012）. SGS values esti- mated using the four methods show similar spatial patterns along latitudinal or altitudinal gradients, but with significant variations in the SGS dates. The largest discrepancies are mainly found in the regions with the highest or the lowest vegetation coverage. Between 1982 and 1998, the SGS values derived from the four methods all display an advancing trend, however, according to the more recent SPOT VGT data （1999-2012）, there is no continu- ously advancing trend of SGS on the TP. Analysis of the correlation between the SGS values derived from GIMMS and SPOT between 1999 and 2006 demonstrates consistency in the tendency with regard both to the data sources and to the four analysis methods used. Com- pared with other methods, the greatest consistency between the in situ data and the SGS values retrieved is obtained with Method 3 （Threshold of NDVI ratio）. To avoid error, in a vast region with diverse vegetation types and physical environments, it is critical to know the seasonal change characteristics of the different vegetation types, particularly in areas with sparse grassland or evergreen forest.

中国中高纬地区植被物候对干旱的响应特征研究

植被物候直接影响其生物量,调控生态系统碳循环过程。目前,气候变化(尤其干旱)对中国中高纬度植被物候的影响依然不清楚。因此,文章基于GIMMS NDVI3g数据集,提取中国30°N以北地区中多种植被类型生长季的开始日期(Start of the Season,SOS)与结束日期(End of the Season,EOS)两物候参数。然后结合野外观测数据,验证提取物候参数结果可靠性,并结合饱和水汽压差(Vapor Pressure Deficit,VPD)与改进后的标准化降水蒸散指数(Standardized Precipitation Evapotranspiration Index,SPEI)探究植被物候对干旱的响应特征规律。结果表明:(1)不同地区的植被物候变化呈现明显的差异性,单季植被与双季植被第1个生长季的SOS集中在每年的第30~180天,而双季植被第2个生长季的SOS集中在每年的第200~220天。单季植被与双季植被第1个生长季的EOS主要集中在每年的第180~300天,双季植被第2个生长季的EOS主要集中在每年的第260~300天。(2)森林季前VPD的上升导致植被的SOS提前及EOS延迟;草地季前VPD上升导致植被的SOS滞后以及EOS提前。(3)研究区内大部分地区的SPEI与植被的SOS、EOS均呈正相关,即干旱促使该地区植被的SOS、EOS提前。

基于遥感植被指数的青藏高原生长季开始时间分析和模拟

青藏高原是重要的牧草产地、生态屏障和水源涵养区,其植被生态过程可以直接牵动中国乃至东亚的变化。随着全球变暖,青藏高原植被物候期不断改变,通过碳循环、水热循环等影响着气候和生态系统,物候变化及其影响因素研究成为关键问题,构建可以实现未来物候预测的模型具有重要科学意义。本文基于2000-2020年卫星获取的归一化差值植被指数(MODIS NDVI),利用动态阈值法提取青藏高原植被生长季开始时间(SOS),并结合植被类型分析其时空变化规律,构建SOS与气温、土壤水分的多种物候模型,探究不同区域、种类植被开始生长所需水热条件。结果表明:(1)2000-2020年,青藏高原SOS整体呈提前趋势,东部最为显著,提前速率超过10d·(10a)^(-1),针叶林、灌丛、草甸和高山植被覆盖区SOS提前比例较高,草原有约50%的轻微延后区域;(2)青藏高原东部和北部区域有明显的暖湿化趋势,年均温上升速率约为0.36℃·(10a)^(-1),年均土壤水分增加速率约为每年3.8×10^(-4) m^(3)·m^(-3)(p<0.01);(3)四个物候模型参数率定结果均显示,青藏高原东部和南部植被开始生长对水热条件要求更高,南部植被SOS的主控因子为气温,而北部则为土壤水分,不同植被类型生长季开始的气温、土壤水分阈值和主控因子也与其空间分布位置密切相关;(4)文中构建的积温-累积土壤水分阈值模型对于青藏高原主要植被类型(草原、草甸和高山植被)模拟效果最好,均方根误差仅在8天左右,对于青藏高原未来SOS预测、物候与气候之间的相互作用机制等相关研究具有参考意义。

Characterizing Spatial Patterns of Phenology in Cropland of China Based on Remotely Sensed Data

This study used time-series of global inventory modeling and mapping studies （GIMMS） normalized difference vegetation index （NDVI） datasets at a spatial resolution of 8 km and 15-d interval to investigate the spatial patterns of cropland phenology in China. A smoothing algorithm based on an asymmetric Gaussian function was first performed on NDVI dataset to minimize the effects of anomalous values caused by atmospheric haze and cloud contamination. Subsequent processing for identifying cropping systems and extracting phenological parameters, the starting date of growing season （SGS） and the ending date of growing season （EGS） was based on the smoothed NVDI time-series data. The results showed that the cropping systems in China became complex as moving from north to south of China. Under these cropping systems, the SGS and EGS for the first growing season varied largely over space, and those regions with multiple cropping systems generally presented a significant advanced SGS and EGS than the regions with single cropping patterns. On the contrary, the phenological events of the second growing season including both the SGS and EGS showed little difference between regions. The spatial patterns of cropping systems and phenology in Chinese cropland were highly related to the geophysical environmental factors. Several anthropogenic factors, such as crop variety, cultivation levels, irrigation, and fertilizers, could profoundly influence crop phenological status. How to discriminate the impacts of biophysical forces and anthropogenic drivers on phenological events of cultivation remains a great challenge for further studies.

2001—2020年蒙古高原昼夜非对称变暖对植被返青期的影响

基于2001—2020年归一化植被指数(NDVI)、增强型植被指数(EVI)2种遥感植被指数以及蒙古高原94个气象站点的月最高、最低温和降水量数据,利用累积NDVI的Logistic曲线曲率极值法和动态阈值法2种物候识别方法提取蒙古高原植被返青期,分析蒙古高原昼夜非对称变暖的时空变化及其对植被返青期的影响。结果表明:(1)2001—2020年蒙古高原生长季开始前6个月(上一年11月—当年4月)平均最高温[0.7℃·(10a)-1]和最低温[0.3℃·(10a)-1]均呈上升趋势,最高温的变暖速率是最低温的2.3倍。(2)季前昼夜非对称变暖对植被返青期均产生提前作用,但与最高温相比,最低温对返青期的影响程度更大,且影响范围更为广泛。(3)季前昼夜非对称变暖对不同植被类型返青期产生不同影响,白天变暖对灌丛、农田和稀疏植被返青期的影响更明显,夜间变暖对森林和草地返青期的影响更强,特别是森林地区(25.5%)。研究白天和夜间非对称变暖对蒙古高原植被物候的影响,对揭示温度对春季植被物候的影响机制有重要意义。

内蒙古植被春季返青期和秋季枯黄期的气候敏感性研究

春季返青期和秋季枯黄期是植被生长过程中两个重要的物候指标,其变化对气候,尤其对温度敏感性的大小及其差异十分不清楚。利用2001-2019年MODIS NDVI和气象数据,在气象台站和像元尺度上分别计算内蒙古植被春季返青期和秋季枯黄期,并以生长度日(GDD)和冷却度日(CDD)为影响返青期和枯黄期的温度指标,研究两个物候指标对气候敏感性的空间格局及其大小。结果表明,2001-2019年内蒙古植被返青期主要集中在第110~135 d,整体呈提前趋势(2.6 d·10 a^(-1));枯黄期主要集中在第260~280 d,整体呈微弱的推迟趋势(0.7 d·10a^(-1))。返青期对GDD和枯黄期对CDD的敏感性主要以负敏感性为主,分别占研究区总面积的68.1%和56%。从两个物候指标对降水的敏感性看,植被物候对降水敏感性主要以正敏感为主。气象台站尺度的研究结果总体与像元尺度的研究结果基本一致。在气象台站尺度上对比显示有65%的站点枯黄期对温度的敏感性大于返青期,94%的站点返青期对降水的敏感性大于枯黄期,在气候不断变化的条件下,敏感性的研究可促进生态系统可持续管理的能力,对物候模拟以及生态系统气候的评估具有重要参考价值。

蒙古国冬春季气候非对称变暖及其对植被返青期和春季NDVI的影响

基于2001—2020年NDVI和EVI两种遥感植被指数及蒙古国60个气象站点的气温和降水数据,利用累积植被指数的Logistic曲线曲率极值法和动态阈值法提取蒙古国植被返青期,并结合偏相关分析方法探讨二者与冬春季昼夜气温非对称变化之间的关系。结果表明:(1)近20 a来,最高气温在冬春季的变暖速率分别为0.07℃·a^(-1)、0.15℃·a^(-1)(P<0.05,R^(2)=0.33),最低气温在冬春季的变化速率分别为-0.01℃·a^(-1)、0.04℃·a^(-1),冬春季气温日较差的变化速率分别为0.08℃·a^(-1)、0.11℃·a^(-1)(P<0.05,R^(2)=0.52),存在明显的季节性差异。(2)蒙古国植被返青期对冬春季气候变暖的季节性响应是非对称的,冬季最高气温和气温日较差的影响大,而春季则是最低气温影响大,且均表现为负相关。(3)蒙古国气候变暖对植被NDVI产生的非对称影响主要表现在春季,即春季最高气温和气温日较差对植被NDVI主要表现为负相关,而春季最低气温对植被NDVI主要表现为正相关。研究结果可为进一步了解全球气候变暖背景下植被春季物候及植被后期生长的季节性影响提供重要参考价值。

The relative controls of temperature and soil moisture on the start of carbon flux phenology and net ecosystem production in two alpine meadows on the Qinghai-Tibetan Plateau

Aims Variations in vegetation spring phenology are widely attributed to temperature in temperate and cold regions.However,temperature effect on phenology remains elusive in cold and arid/semiarid ecosystems because soil water condition also plays an important role in mediating phenology.Methods We used growing degree day(GDD)model and growing season index(GSI)model,coupling minimum temperature(T_(min))with soil moisture(SM)to explore the influence of heat requirement and hydroclimatic interaction on the start of carbon uptake period(SCUP)and net ecosystem productivity(NEP)in two alpine meadows with different precipitation regimes on the Qinghai-Tibet Plateau(QTP).One is the water-limited alpine steppe-meadow,and the other is the temperature-limited alpine shrub-meadow.Important Findings We observed two clear patterns linking GDD and GSI to SCUP:SCUP was similarly sensitive to variations in preseason GDD and GSI in the humid alpine shrub-meadow,while SCUP was more sensitive to the variability in preseason GSI than GDD in the semiarid alpine steppe-meadow.The divergent patterns indicated a balance of the limiting climatic factors between temperature and water availability.In the humid meadow,higher temperature sensitivity of SCUP could maximize thermal benefit without drought stress,as evidenced by the stronger linear correlation coefficient(R2)and Akaike’s information criterion(AIC)between observed SCUPs and those of simulated by GDD model.However,greater water sensitivity of SCUP could maximize the benefit of water in semiarid steppe-meadow,which is indicated by the stronger R2 and AIC between observed SCUPs and those of simulated by GSI model.Additionally,although SCUPs were determined by GDD in the alpine shrub-meadow ecosystem,NEP was both controlled by accumulative GSI in two alpine meadows.Our study highlights the impacts of hydroclimatic interaction on spring carbon flux phenology and vegetation productivity in the humid and semiarid alpine ecosystems.The results also suggest that water,together with temperature should be included in the models of phenology and carbon budget for alpine ecosystems in semiarid regions.These fi ndings have important implications for improving vegetation phenology models,thus advancing our understanding of the interplay between vegetation phenology,productivity and climate change in future.

内蒙古主要草原类型植物物候对气候波动的响应

物候是气候变化的指示者,由于不同地区植被类型不同,导致其对气候波动的响应方式不同。利用2004—2013年内蒙古草原区生态监测站群落优势种物候观测资料和同时段的气象资料,分析了不同草原类型区优势种物候期变化及其与气候因子间的相互关系,结果表明:(1)2004—2013年内蒙古草原区各时段气候波动趋势均不显著,返青前以气温降低、降水增加趋势为主;黄枯前草甸草原、典型草原以气温降低、降水增加趋势为主,荒漠草原变化趋势相反。(2)2004—2013年典型草原植物返青期平均提前4.01 d,黄枯推后10.35 d,生长季延长14.36 d;草甸草原返青期提前2.04 d,黄枯期推后12.68 d,生长季延长14.72 d;荒漠草原物候变化趋势最小,返青期平均提前了1.32 d,黄枯期平均推后了9.58 d,生长季延长了10.90 d。(3)内蒙古草原区植物返青期主要受气温波动的影响,草甸草原返青期与前3个月平均气温的负相关最为显著,气温每升高1℃,返青期约提前1.123 d;典型草原、荒漠草原返青期与前2个月平均气温的负相关最为显著气,气温每升高1℃,返青期约提前1.137 d和1.743 d。(4)典型草原区植物黄枯期受前1—2月平均气温和累积降水的共同影响,与夏季平均气温和当月降水量的相关最为显著,夏季气温每升高1℃,黄枯期约提前2.250 d,当月降水每增加1 mm,黄枯期约推后0.119 d。草甸草原、荒漠草原植物黄枯期与各时段降水、气温的相关均不显著,影响黄枯机制比较复杂。

过去20年中国耕地生长季起始期的时空变化

多时相遥感数据能够较好地描述区域尺度的植被物候和生长季节的变化特征。利用NDVI时序数据,采用非对称性高斯函数拟合方法重建平滑曲线,分别提取了我国20世纪80年代初、90年代初和21世纪初等3个时期为我国耕地第一生长季起始期,计算3个时期平均生长起始期,并分析了我国耕地第一生长季起始期的区域空间分异规律;然后,从区域和省份两个尺度分析了20世纪80年代初至90年代初和20世纪90年代初至21世纪初两个阶段我国耕地生长季起始期动态变化趋势和空间格局。结果表明,我国不同区域耕地第一生长季起始期存在十分明显的空间差异,清楚地呈现出一个从南向北逐渐推迟的空间特征;从不同区域看,在20世纪80年代初至90年代初和20世纪90年代初至21世纪初两个时期,我国耕地第一生长季起始期变化都是提前和推迟并存,不同区域变化程度不一;从不同省份看,在过去20年间,我国绝大多数省份耕地第一生长季起始期都表现为总体提前的趋势,但不同省份的起始期变化具有差异性。影响我国耕地生长季起始期变化的因素很多,如何区别气候变化等自然因子和人类活动因子对耕地生长季起始期变化的影响是一个值得深入研究的问题。

季节性气候对不同草地植被物候变化的影响

草地广泛分布于干旱区和半干旱区,对季节性气候变化的响应十分敏感,但目前针对草地物候对季节性气候变化响应的研究仍较为薄弱。文章以内蒙古为例,基于不同草地类型的NDVI数据,辅以动态阈值、趋势分析和偏相关方法研究了2001—2020年草地物候时空动态、变化趋势及其随海拔梯度、气温和降水变化特征。结果表明内蒙古地区:(1)随纬度、海拔升高,草地生长季始期(start of growing season,SOS)逐渐推迟,生长季末期(end of growing season,EOS)缓慢推迟,生长季长度(length of growing season,LOS)呈不规律性变化趋势。(2)SOS集中在4月上旬到5月下旬,71.3%呈显著提前趋势,速率为0~2.0 d/a。EOS集中在9月下旬到10月中旬,69.98%呈推迟趋势。LOS持续在110~230 d,50.31%呈变长趋势。(3)在海拔500~2500 m的区域,随海拔上升,SOS推迟、EOS提前、LOS延长。(4)SOS与夏、秋、冬的气温为显著负相关关系,与春、秋、冬降水为显著负相关关系,与春季气温和夏季降水呈显著的正相关关系。EOS与春、夏、秋降水以不显著负相关性为主,与冬季降水以不显著正相关为主,与四季气温以负相关关系为主。LOS与春、夏、冬气温以负相关为主,秋季气温与LOS的正负相关参半。以上研究结果对内蒙古草地生长监测和应对气候异常提出保护策略、制定行之有效的防灾减灾措施、构建稳定的生态屏障具有指导意义。

1971～2013年我国四季开始日期及生长期长度的变化特征分析

利用中国气象局国家气象信息中心提供的中国584个气象站点1971~2013年的逐日气温数据,采用线性倾向估计和经验模态分解(EMD)等方法,以地理信息系统为数据处理平台,分析我国43年来四季起始日以及生长期的变化特征。结果表明:新疆、云南和四川地区的四季起始日变化呈现明显的南北差异;全国大部分地区春、夏季起始日提前,春季比夏季提前趋势更明显,江苏、安徽、湖北大部和云南北部春季提前显著,提前率为4.1~7.2 d/10 a;夏季提前的区域更广,新疆东部、甘肃西部、华南大部和云南南部夏季提前显著,提前率为2.9~4.6 d/10 a;全国大部分地区秋、冬季起始日推迟,秋季比冬季推迟的范围更大,新疆南部和四川西部秋季推迟明显,推迟率为4.4~8.6 d/10 a;冬季推迟趋势更显著,新疆东南部和青海大部冬季推迟明显,推迟率为4.7~13.8d/10 a;全国各地区生长期均有延长,最显著的是云川交界处和新疆东南部地区,延长率为20.1 d/10 a。EMD和线性倾向估计的结果基本一致,但EMD得到的春季起始日推迟地区的范围更大,夏、秋、冬季起始日以及生长期的变化趋势更显著。

中国温带草原和荒漠区域春季物候的变化及其敏感性分析

[目的]在全球气候变化背景下,分析中国温带草原和荒漠区域春季物候变化趋势,探索该区域春季物候与气候因子之间的关系。[方法]利用1982—2015年归一化植被指数(NDVI)数据集,提取中国温带草原和荒漠区域植被生长季开始日期(SOS),评估整个研究区及草甸、草原和荒漠SOS的线性趋势。利用偏相关和多元线性回归方法,分析SOS与季前(5月—上一年11月)温度和季前降水的关系,并分析SOS对气候变化响应的空间模式。[结果]1982—2015年中国温带草原和荒漠区域SOS以0.14d·a^-1的速率显著提前。空间上,68%的地区呈提前趋势,32%的地区呈延迟趋势。SOS与不同季前时期的平均温度和降水均呈负相关,且与季前平均温度的相关性更显著。SOS分别与季前40d平均温度和季前200d降水的相关性最大。1982—2015年,季前(40d)平均温度上升1℃,SOS显著提前1.31d;季前(200d)降水增加10mm,SOS提前0.44d。空间上,长期平均季前(200d)降水增加10mm,SOS温度敏感性增加0.093d·℃^-1,SOS降水敏感性降低0.019d·10mm^-1。[结论]过去34年中国温带草原和荒漠区域SOS表现提前趋势。季前平均温度是控制SOS变化的主要因子。季前平均温度升高和季前降水增加会导致SOS提前。季前降水决定SOS温度敏感性和SOS降水敏感性的空间格局。季前降水越多的地区,SOS对季前平均温度越敏感;季前降水越少的地区,SOS对季前降水越敏感。

Variations of Vegetation Phenology Extracted from Remote Sensing Data over the Tibetan Plateau Hinterland during 2000–2014

How vegetation phenology responds to climate change is a key to the understanding of the mechanisms driving historic and future changes in regional terrestrial ecosystem productivity. Based on the 250-m and 8-day moderate resolution imaging spectroradiometer(MODIS) normalized difference vegetation index(NDVI) data for 2000-2014 in the Three-River Source Region(TRSR) of Qinghai Province, China, i.e., the hinterland of the Tibetan Plateau, we extracted relevant vegetation phenological information(e.g., start, end, and length of growing season) and analyzed the changes in the TRSR vegetation in response to climate change. The results reveal that, under the increasingly warm and humid climate, the start of vegetation growing season(SOS) advanced 1.03 day yr-1 while the end of vegetation growing season(EOS) exhibited no significant changes, which led to extended growing season length. It is found that the SOS was greatly affected by the preceding winter precipitation, with progressively enhanced precipitation facilitating an earlier SOS. Moreover, as the variations of SOS and its trend depended strongly on topography, we estimated the elevation break-points for SOS. The lower the elevations were, the earlier the SOS started. In the areas below 3095-m elevation, the SOS delay changed rapidly with increasing elevation;whereas above that, the SOS changes were relatively minor. The SOS trend had three elevation break-points at 2660, 3880, and 5240 m.