2001—2020年北半球中高纬度植被生长峰值期和峰值对气候的敏感性研究

Sensitivity of the peaking time of the growing season and peak EVI to climate at the middle and high latitudes of the Northern Hemisphere during 2001-2020

植被夏季生长峰值期和峰值是植被极为重要的物候和生长指标,对年生产力的大小具有决定性作用。论文利用2001—2020年MODIS EVI数据和双Logistic四参数模型,识别北半球中高纬度植被生长峰值期与EVI峰值时空变化特征及其对气候的敏感性。研究结果表明:(1)在过去20年间,植被生长峰值期主要发生在6—8月,并随着纬度的升高呈先提前后推迟趋势,但如果忽略70°N以北地区的少部分陆地,植被峰值期随着纬度升高呈提前趋势。植被EVI峰值主要介于0.2~0.6之间,整体上高纬度的值低于低纬度。(2)区域平均植被生长峰值期呈不显著提前趋势(0.12 d/a,p>0.05)。在空间上呈提前趋势(60.3%)的像元占比大于呈推迟趋势(39.7%)的占比。EVI峰值以0.01/10 a(p<0.01)的速率呈显著增加趋势。在空间上,研究区74.5%地区的植被EVI峰值呈增加趋势。(3)2001—2020年间,春夏季气温、降水量和云覆盖对植被生长峰值期(EVI峰值)的影响最广泛,其中气温对植被生长峰值期和EVI峰值的影响最强,在高纬度地区对两者产生不对称作用,在低纬度地区气温的升高可能通过干旱等事件将降低EVI峰值。而降水量和云覆盖对峰值期和EVI峰值的影响在空间分布上相对复杂,空间异质性强。研究结果可为阐明北半球中高纬度地区植被物候和生长变化规律及其对气候变化的响应特征,以及对生态系统的影响过程和预测提供数据支撑。

The peaking time and peak Enhanced Vegetation Index(EVI)are important indicators of vegetation phenology and growth that play a decisive role in annual productivity.Using MODIS EVI(MOD13C1)data and a double logistic four-parameter model,we quantified the spatial and temporal variations of peaking time of vegetation growth and peak EVI,and their sensitivities to climate at the middle and high latitudes of the Northern Hemisphere during 2001-2020.The results show that:1)During the 20 years,the peaking time of vegetation growth occurred between June and August.It first advanced and then delayed with the increase in latitude.Discounting land north of 70°N,the peaking time tended to advance with increasing latitude.Peak EVI ranged between 0.2 and 0.6,with higher EVI in high latitudes.2)The spatially averaged peaking time of vegetation growth in the study area showed a nonsignificant advancing trend during the study period(0.12 d/a,p>0.05).The percentage of pixels showing advancing trend(60.3%)was larger than that with delaying trend(39.7%).Peak EVI showed a significant increasing trend,with an increase of 0.01/10 a(p<0.01).Spatially 74.5%of the study area showed an increasing trend in peak EVI.3)During 2001−2020,the impacts of changing temperature,precipitation,and cloud cover in the spring and the summer were widespread.Temperature had the strongest effect on the peaking time and peak EVI of vegetation growth,with asymmetric effects at high latitudes.At low latitudes,a rise in temperature was likely to decrease peak EVI through events such as droughts.In contrast,the effects of precipitation and cloud cover on the peaking time and peak EVI of vegetation growth were relatively complex and spatially heterogeneous.The results of our study may provide data and information to elucidate the mechanisms that drive vegetation phenology and growth patterns and their responses to climate change at the middle and high latitudes of the Northern Hemisphere,and to predict the impacts on ecosystem changes.