基于转移函数分析的蒙东地区不同类型植被变化对干旱的响应

Response of Different Types of Vegetation Changes to Drought in Eastern Inner Mongolia Based on Transfer Function Analysis

为了量化不同类型植被与干旱的响应关系,首先采用回归模式降尺度方法获取内蒙古地区1982-2019年1 km分辨率的归一化植被指数(normalized difference vegetation index,NDVI)数据集,并计算标准化降水蒸发指数(standardized precipitation evapotranspiration index,SPEI)以表征干旱状况;然后,利用转移函数分析(transfer function analysis,TFA)频域技术进行内蒙古东部不同类型植被变化对干旱响应的存在性、强度和时滞性的研究.发现在年、6个月和3个月尺度上,草地、灌木、阔叶林和针叶林NDVI与SPEI的相干性分别为0.44、0.57、0.31,0.43、0.60、0.32,0.30、0.19、0.14和0.20、0.13、0.10;各类型植被NDVI对干旱的响应强度表现为灌木>草地>阔叶林>针叶林;草地、灌木、阔叶林和针叶林在3个时间尺度上滞后干旱的时间分别为31 d、20 d、12 d,77 d、28 d、34 d,120 d、69 d、57 d和179 d、103 d、65 d.研究结果表明:草地和灌木与干旱的相干性显著,响应强度较大,响应速度更快;而针叶林和阔叶林与干旱的相干性较低,其对干旱的抵抗力较强,对干旱的响应时间较长,受干旱影响较小.

To quantify the response relationships between different types of vegetation and drought,firstly,the dataset of normalized difference vegetation index(NDVI)with a resolution of 1 km in Inner Mongolia from 1982 to 2019 was obtained through regression model downscaling method and standardized precipitation evapotranspiration index(SPEI)was calculated for characterizing drought conditions.Then,the frequency domain technique of transfer function analysis(TFA)was used to explore the existence,intensity and time delay of the response of different types of vegetation changes to drought in eastern Inner Mongolia.It was found that the coherence between NDVI and SPEI of grassland,shrub,broad-leaved forest and coniferous forest was 0.44,0.57,0.31,0.43,0.60,0.32,0.30,0.19,0.14 and 0.20,0.13,0.10 on annual,6 months and 3 months scales,respectively.The response intensity of NDVI of various types of vegetation to drought showed that the shrub was stronger than that of grassland.The following was broad-leaved forest.The response intensity of NDVI of coniferous forest was weakest.The lag times of the NDVI of grassland,shrub,broad-leaved forest and coniferous forest on drought at three time scales for were 31,20,12 days,77,28,34 days,120,69,57 days and 179,103,65 days,respectively.The results show that grassland and shrub have significant coherence with drought,strong response intensity and faster response speed.However,coniferous forest and broad-leaved forest have low coherence with drought,strong resistance to drought,long response time to drought and less affected by drought.