高寒气候区生长季NDVI与昼夜不对称增温的Copula分析

Copula analysis of NDVI and diurnal-nocturnal asymmetric warming during the growing season in typical plateau climatic region

利用1982—2016年的青海地区归一化植被指数和气象数据,基于马尔科夫链蒙特卡罗的Copula函数方法,深入探索昼夜增温不对称性与植被活动之间的复杂关系,揭示了昼夜增温和NDVI之间的联合概率分布及其季节性差异。研究结果表明,昼夜增温与NDVI之间的关系在不同季节呈现显著差异。尤其在秋季,昼夜增温对NDVI的影响最为显著,其次是夏季和春季。通过Copula函数模型,发现昼夜增温与NDVI在特定温度区间内呈现正相关,表明适宜的温度条件下昼夜增温对植被生长具有促进作用。然而,当昼夜增温超过某一阈值时,其对NDVI的促进作用转变为抑制作用,从而限制了植被的生长。同时,还揭示了重现期与昼夜增温及NDVI之间的关系。在较低的重现期下,昼夜增温与NDVI的联合概率较高,表明在这些条件下,植被生长良好的情况出现的频率较高。反之,较高的重现期对应于昼夜增温与NDVI较低的联合概率,表明植被生长受到抑制。本研究通过Copula函数提供了一个全新的视角来理解昼夜增温与植被动态之间的相互作用,强调了气温变化对植被生长影响的复杂性。

In this study,utilizing the Normalized Difference Vegetation Index(NDVI)and meteorological data from 1982 to 2016 in the Qinghai region of China,we adopted a copula function method based on the Markov Chain Monte Carlo approach.Our goal was to explore the relationship between the NDVI and diurnal-nocturnal asymmetric warming during the growing seasons in the alpine climate zone of Qinghai Province from 1982 to 2016.The study results revealed the joint probability distribution and its seasonal differences between the diurnal-nocturnal warming and the NDVI.Initially,the paper presents the trends in seasonal diurnal-nocturnal temperatures and the NDVI over the years in the alpine climate region,followed by an analysis of diurnal-nocturnal temperatures using the copula function method to investigate the statistical characteristics between diurnal-nocturnal warming and the NDVI.It was found that the impact of diurnal-nocturnal warming on NDVI varies significantly from season to season,with the strongest correlation in autumn,followed by summer and spring.This suggests a clear seasonality in the influence of diurnal-nocturnal warming on vegetation growth.There is a specific temperature threshold between diurnal-nocturnal warming and the NDVI;when the diurnal-nocturnal warming is below this threshold,a positive correlation is observed,indicating that appropriate temperature increases promote vegetation growth.However,once this threshold is exceeded,the positive impact of diurnal-nocturnal warming on the NDVI becomes a suppression effect.Additionally,the paper examines the long-term impact of diurnal-nocturnal warming changes on vegetation growth by analyzing the joint probability distribution of diurnal-nocturnal warming and the NDVI during different recurrence periods.The results show that,in lower recurrence periods,the joint probability of diurnal-nocturnal warming with the NDVI is high,indicating more frequent favorable conditions for vegetation growth.Conversely,higher recurrence periods correspond to lower joint probabilities of diurnal-nocturnal warming with the NDVI,suggesting suppressed vegetation growth.This indicates that the relationship between diurnal-nocturnal warming and the NDVI becomes more complex within certain recurrence periods,which may be related to the regional climatic conditions,vegetation types,and other ecological factors.Overall,this study provides a new perspective on exploring the complex relationship between diurnal-nocturnal asymmetric warming and vegetation dynamics within the context of climate change.This is not only crucial for predicting and assessing the potential impact of future climate change on vegetation in alpine regions,but also provides a scientific basis for the management and conservation of these fragile ecosystems.