荒漠-绿洲过渡带NDVI演变及影响因子相关性分析

Evolution of NDVI and analysis of its correlation with influencing factors in desert-oasis transition zone

荒漠-绿洲过渡带是绿洲与荒漠相互转化过程中表现最活跃的地区,具有防止荒漠扩张、维持绿洲生态安全等重要的生态功能。本研究以民勤县为研究区域,根据绿洲外围归一化差异植被指数(Normalized difference vegetation index,NDVI)的变化规律,确定民勤荒漠-绿洲过渡带的范围;利用2000—2020年内最大NDVI数据及降水、温度、日照时数、土壤水分影响因子,在像元尺度采用偏相关及多元相关分析方法,研究过渡带NDVI变化趋势及影响因子相关性分析。结果表明,绿洲边界外5000 m范围为民勤荒漠-绿洲过渡带范围,其中绿洲外0~300 m为过渡带核心区,300~2000 m为过渡带交错区,2000~5000 m范围为过渡带缓冲区。自2000年以来,过渡带区域NDVI整体呈增加趋势,其中,明显改善和稳定不变的面积占比较高,分别为47.8%和42.2%,其他占比较小,严重退化区域主要在靠近绿洲的过渡带核心区。降水增加对过渡带南部地带性植被的改善起主导作用,温度的上升对过渡带东部及西北部NDVI改善的促进作用更明显,日照时数的增加对过渡带西部及东南部NDVI改善的促进作用更大,土壤水分的增加对过渡带整体NDVI的改善均具有促进作用。土壤水分和降水是促进过渡带NDVI改善的主要因子。

The desert-oasis transition zone,as the ecotone between desert and oasis,is the most active area in the mutual transformation process of oasis and desert,and has important ecological functions such as preventing desert expansion and maintaining oasis ecological security.Taking Minqin Basin as the research area,the Normalized difference vegetation index(NDVI)between oasis and desert was used to determine the range of desert-oasis transition zone in Minqin.Then,using the maximum NDVI data from 2000 to 2020 and the influencing factors such as precipitation,temperature,sunshine hours and soil moisture,partial correlation and multiple correlation analysis methods were used at pixel scale to study the trend of NDVI change and correlation analysis of influencing factors.The results show that the 5000 m area outside the oasis boundary is the Minqin desert-oasis transition zone,in which the 0-300 m area outside the oasis is the core area of the transition zone,the 3000-2000 m area is the ecotone area,and the 2000-5000 m area is the buffer zone.Since 2000,NDVI in the transition zone has shown an overall increasing trend,among which the areas with obvious improvement and stability account for a relatively high proportion(47.8%and 42.2%,respectively),while the other areas account for a relatively small proportion.The severely degraded areas are mainly in the core area of the transition zone near the oasis.The increase of precipitation plays a leading role in the improvement of zonal vegetation in the southern part of the transition zone,the increase of temperature plays a more significant role in the improvement of NDVI in the eastern and northwestern parts of the transition zone,the increase of sunshine hours plays a greater role in the improvement of NDVI in the western and southeastern parts of the transition zone,and the increase of soil moisture can promote the improvement of NDVI in the transition zone.Soil moisture and precipitation are the main factors to improve NDVI in transition zone.