黄土高原植被物候对季节性干旱的敏感性响应

Sensitive response of vegetation phenology to seasonal drought in the Loess Plateau

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。

Under the background of global warming,the increasing frequency and intensity of drought events significantly change the vegetation diversity in terrestrial ecosystems.Vegetation productivity,carbon storage,and the carbon cycle in terrestrial ecosystems are deeply affected by vegetation phenology.However,there are few studies on the effects of seasonal drought on different vegetation phenology due to the inherent complexity,uncertainty of drought,and differences in the resistance and resilience of different vegetation to drought.Therefore,based on the normalized differential vegetation index,landuse cover,and monthly temperature and monthly precipitation data,this study calculated the start of the season(SOS),end of the season(EOS),and standardized precipitation evapotranspiration index(SPEI)of vegetation on the Loess Plateau.Additionally,it analyzed the response of vegetation phenology changes to seasonal SPEI using the Ridge regression analysis method from 2001 to 2018.The results are as follows.(1)The vegetation SOS was delayed by the intensification of drought in summer and autumn of last year,whereas the SOS of vegetation was advanced by the weakening of drought in winter and spring of the same year.SPEI in the winter at the beginning of the year is more likely to delay vegetation EOS than SPEI in the spring and fall of the same year.An intensification of the summer drought could cause vegetation to stop growing earlier.(2)The EOS and SOS of vegetation showed obvious spatial heterogeneity in response to seasonal SPEI.The SOS of vegetation in the Loess Plateau will be advanced when the drought degree decreases at the beginning of winter in Qinghai.The intensification of drought in summer would lead to the premature end of most vegetation growth on the Loess Plateau.The response of most vegetation to drought at the end of the growth period was weaker than in other seasons.(3)The SOS of shrub was delayed,and the SOS of grassland was advanced due to SPEI in different seasons,and shrub was more susceptible to drought than forest and grassland.Droughts in winter at the beginning of the year have the greatest impact on the SOS of grassland than other seasons.Meanwhile,the growth of forests,shrubs,and grassland will end earlier with drought intensities in summer.This study revealed the response law of vegetation phenology to seasonal drought in the Loess Plateau.It provided a scientific basis for vegetation response to water stress and ecological environment protection.