基于MODIS遥感数据的福建植被生产力时空分布与干旱响应分析

Spatio-temporal Dynamics of Vegetation Productivity and Drought Impacts in Fujian Province Using MODIS Data

全球升温导致干旱发生的范围和强度增加,但干旱对生态系统碳循环的影响还不明确。基于MODIS遥感数据,采用Sen趋势分析及Mann-Kendall检验、Pearson相关性分析等方法,通过干旱对植被生产力标准化异常的影响等信号,分析了2001-2021年福建省植被总初级生产力(Gross Primary Productivity,GPP)、净初级生产力(Net Primary Productivity,NPP)的时空变化特征与干旱对其的影响及累积/滞后效应。结果表明,1)空间上,福建省植被GPP、NPP多年平均空间分布均呈现“东南高,西北低”的特征,区域平均差异分别为37.4%、65.1%;近21年以来,有近80.8%的区域GPP呈现增长趋势,主要分布在福建省南部、东南部少部分地区,主要指被类型为农田,多为热带经济水果种植的集中区域;另外,超过59.7%的区域NPP呈现下降趋势,主要出现在福建省中部及内陆山区的常绿阔叶林地和稀树草原。2)时间上,植被GPP年际波动明显,总体呈现弱增长趋势[4.86 g∙m^(−2)∙a^(−2)(以C计,下同),p=0.130],空间上,6.7%的区域年增速显著超过15 g∙m^(−2)∙a^(−2);而NPP年际变化总体呈现弱下降趋势(−1.05 g∙m^(−2)∙a^(−2),p=0.396),4.9%的区域年降速显著超过6 g∙m^(−2)∙a^(−2)。3)研究时段内福建省出现的干旱过程主要以中等干旱为主(52.5%),其次是轻旱(34.0%)。植被GPP、NPP年标准化异常指数与干旱指数(SPEI)存在显著的负相关关系,相关系数分别为−0.624(p=0.002)、−0.531(p=0.013),说明旱情越严重的年份GPP、NPP越高,而旱情较轻或无旱的年份GPP、NPP较低。干旱对GPP最明显的影响主要发生在干旱当月,累积/滞后效应时间较短;干旱事件对GPP的影响是“先增-后缓-再减”,干旱发生初期GPP呈增加趋势,而随着干旱的持续发展,GPP的增加幅度明显减弱,甚至出现负效果。

Global warming has intensified drought occurrences,but their impacts on ecosystem carbon cycle remain unclear.This study analyzes the spatio-temporal variations of Gross Primary Productivity(GPP)and Net Primary Productivity(NPP)in Fujian Province from 2001 to 2021 using MODIS data.We employed Sen’s trend analysis,the Mann-Kendall test,Pearson’s correlation analysis and other methods to assess drought’s influence on vegetation productivity anomalies.Additionally,we explored cumulative and lagged effects of drought events.The results showed that:1)Annual average GPP and NPP exhibited a“high southeast,low northwest”pattern,with regional differences of 37.4%and 65.1%,respectively.Nearly 80.8%of the region showed an increasing GPP trend,concentrated in southern and southeastern agricultural lands and fruit plantations.Conversely,NPP showed a downward trend in over 59.7%of areas,mainly in central and inland mountainous evergreen broad-leaved forests and savannas.2)Vegetation GPP exhibited significant year-to-year fluctuations with a weak overall upward trend(4.86 g∙m^(−2)∙a^(−2)[in terms of carbon,the same below],p=0.130).However,pronounced annual increases exceeding 15 g∙m^(−2)∙a^(−2)occurred in 6.7%of the regions.NPP showed a weak declining trend(−1.05 g∙m^(−2)∙a^(−2),p=0.396),with annual decreases exceeding 6 g∙m^(−2)∙a^(−2)in 4.9%of the regions.3)Moderate drought(52.5%)was the dominant type during the study period,followed by light drought(34.0%).A significant negative correlation existed between the standardized anomaly indices of GPP and NPP and the drought index(SPEI),with the correlation coefficients(r)−0.624(p=0.002)and−0.531(p=0.013),respectively.This implies higher GPP and NPP during severe droughts and lower values during light drought years or no drought years.The most pronounced GPP response to drought occurred in the drought month with a short cumulative/lagging effect.The initial drought stage exhibited an increasing GPP trend,but this growth weakened and even reversed with prolonged drought.