基于TVDI的内蒙古草地干旱变化特征分析

Analysis of Spatial-Temporal Characteristics of Drought Variation in Grassland Area of Inner Mongolia Based on TVDI

【目的】研究内蒙古草地2000—2017年温度植被干旱指数(TVDI)的时空演变特征,并探讨其与气象因子的关系,以期为研究区的生态预警和生态修复提供理论参考。【方法】基于MODIS增强型植被指数(EVI)和陆地表面温度(LST)产品构建Ts-EVI特征空间,根据该特征空间计算TVDI,对多年TVDI均值采用Theil-Sen Median趋势分析、Mann-Kendall检验等方法来研究干旱的空间分布特征、时间变化特征及时空演变趋势。【结果】从整体上看,内蒙古草地多年平均干旱程度西南高东北低,各草地类型年均TVDI大小依次为温性荒漠类>温性草原化荒漠类>温性荒漠草原类>沼泽>温性草原类>温性草甸草原类>低地草甸>山地草甸。其中荒漠型草地(温性荒漠类、温性草原化荒漠类和温性荒漠草原类)主要为重度和轻度干旱状态,非荒漠型草地(温性草原类、温性草甸草原类、低地草甸类、山地草甸类和沼泽类)主要为轻度干旱、正常和轻度湿润状态。18年来荒漠型草地整体在缓慢变干;而非荒漠型草地除温性草原类外基本在缓慢变湿。从空间分布上,三类荒漠型草地干旱程度保持稳定以及具有变干趋势(轻微变干、变干、显著变干)的面积比之和分别为44.93%、55.01%;五类非荒漠型草地干旱程度保持稳定以及具有变湿趋势(轻微变湿、变湿、显著变湿)的面积比之和分别为72.19%、24.27%。【结论】18年来,荒漠型草地的干旱情况主要为保持稳定和持续变干状态,并且持续变干的区域较多,草地生态环境在持续恶化;非荒漠型草地干旱情况主要为保持稳定状态,少部分面积具有变湿趋势,草地生态环境在稳定好转。此外,降水稀少对非荒漠型草地的干旱程度具有显著性影响,但对荒漠型草地的影响并不显著。温度升高则仅对温性草原类以及温性草原化荒漠类的干旱程度具有显著影响。

【Objective】To study the spatio-temporal characteristics of temperature vegetation drought index(TVDI)in the grassland area of Inner Mongolia in the past 18 years and to explore the relationship between TVDI and meteorological factors,so as to provide theoretical reference for ecological warning and ecological restoration of the study area.【Method】Based on MODIS enhanced vegetation index(EVI)and land surface temperature(LST)products to build Ts-EVI characteristic space,according to the characteristic space to calculate TVDI,for normal value of accumulated year of TVDI using unary the Theil-Sen Median trend analysis and Mann-Kendall examination to study the spatial distribution,time-varying characteristics and spatiotemporal evolution trend of drought in the study area during 18 years.【Result】On the whole,the average drought degree of grassland in Inner Mongolia is high in southwest and low in northeast,and the average annual TVDI of all grassland types is in order of temperate desert type>temperate steppe-desert type>temperate desert-steppe type>marsh type>temperate steppe type>temperate meadow-steppe type>lowland meadow type>montane meadow type.Among them,the desert grasslands(temperate desert type,temperate steppe-desert type and temperate desert-steppe type)are mainly in the state of severe and mild drought,while non-desert grasslands(temperate steppe type,temperate meadow steppe type,lowland meadow type,mountain meadow type and marsh type)are mainly in the state of mild drought,normal state and mild wetness.Over the past 18 years,the desert grassland has been gradually drying out.In contrast,the non-desert grassland is basically getting wet slowly except for temperate steppe type.In terms of spatial distribution,the total area ratios of the three types of desert grasslands with stable drought degree and drying tendency(slight drying,drying and significant drying)are respectively 44.93%and 55.01%.The total area ratios of the five types of non-desert grassland with stable drought degree and wetting trend(slightly wetting,wetting and significantly wetting)were 72.19%and 24.27%,respectively.【Conclusion】Therefore,in the past 18 years,the drought situation of desert grassland is mainly stable and continuous drying,and there are more areas that keep drying,so the ecological environment of grassland continues to deteriorate.The drought situation of non-desert grassland is mainly stable,a small part of the area has a tendency of becoming wet,so the ecological environment of grassland is improving steadily.In addition,the lack of precipitation has a significant effect on the drought degree of non-desert grassland,but not on the desert grassland.The increase of temperature only has a significant effect on the drought degree of the temperate steppe type and the temperate steppe-desert type.