The Spatial-temporal Variations Of NDVI And Coupling Analysis With Climate Change Based On GIS And RS In Northwest China

It is very important and practical significance for the ecological environment and economic development to study the theory of surficial process under the background of global warming .Comparing with the changes of global temperature ,it is more remarkable about the law of spatial and temporal characteristics of regional climate ,so that we could be more easy to understand the surficial process .It is efficient and with the all-weather and multi-temporal using the RS with the data sources ,integrating the spatial analysis technical of GIS to analyst the temporal and spatial characteristics of NDVI in northewest of China to understand the basic facts and the features of the variation of NDVI ,while the coupling anlysis with NDVI and regional climate is to take a step forward to explore under the background of the climate change in the northwest of China .For these ,the article mainly study the NDVI and temperature,precipitation in the northewest ,including Shanxi ,Gansu ,Ningxia ,Qinghai ,Xingjiang and the west of Inner Mongolia ,analyzing the temporal and spatial characteristics of NDVI and the coupling features from 1982 to 2006 years based on GIS and RS .Tool platform : Arcgis 9 ,ENVI 4 , ORIGIN 8 .Several conclusions were drawn in this paper as follows :(1)The trend of variation of NDVI showed a slight upward and it was divided two phases ,the first was 1982-1994 years and with a rate was 0.01%/10a ,the other was 1995-2006 years and the rate was 0.03%/10a in the recent 25 years .It was increased until to the mid 90's in the 20th in spring .The trend of NDVI in summer as same as autumn .The cover of vegeatation was the best in August and the trend of NDVI increased obviously with a rate was 0.21%/10a .(2)The NDVI increased significanly and was up to 0.6 from 1998 to 2006 years ,the NDVI decreased from 1993 to 1998 years ;It was increased ,while the rate was different in 1982-1994 years and 1994-2006 years in summer ;The variation of NDVI was remarkable when it was increasing of decreasing in the Yangtze and Yellow River of Qinghai-Tibet Plateau ;There were a overall decreasing trend from 1993-1998 years about of the annual NDVI and it was particularly prominent in the Yangtze and Yellow Rivers and the Altai region .(3) It was periodic of changing of NDVI in Longdong-Guanzhong ,Hanzhong rain-fed agricultural areas and the desert meadow of the west of the Inner Mongolia .After 90's in the 20th century ,the NDVI increased more remarkable in Xinjiang and Hexi oasis .The alpine meadow and deciduous coniferous forests of natural vegetation are obvious increasing and the linear rate was 0.2%/10a ,it was relatively obvious in the irrigated agriculture areas ; The NDVI of autumn was increasing attribute to the end of growing period delayed ,and the rate was 0.27%/10a .(4) The air temperature rised significantly ,after 1998 years the precipitation started to increase ;The increasing trend of air temperature was clear in spring in Qinghai-Tibet Plateau and the Tianshan Mountains and in autumn in the Beijiang and Hanzhong ;The precipitation of spring rised in Hanzhong and Beijiang ,but the it was not inYangtze and Yellow Rivers areas ;The precipitation of Guanzhong and Qilian Mountain was more apparently .The variation of precipitation was not remarkable in autumn in the northwest of China .(5)Attributing to the rise of air temperature of spring and autumn ,the start time of greenness period was a headed and with a time was 14 days , end time pushed back 10 days ;It was positive correlation between NDVI and air temperature ,the max was in the high latitudes and high-altitude area,such as Qinghai-Tibet Plateau and the Qilian mountains ,the correlation coefficient reached 0.65.It was negatively correlated between NDVI and temperature in Hetao,Ningxia irrigation and Guanzhong ;It was high correlation between NDVI and precipitation in Hexi-Alxa and Nanjiang .The effects of temperature and precipitation on the effects of changes in vegetation are positive ,the role was different in different seasons . (6)The threshold of air temperature was 15℃,below that NDVI rised slowly ,above the value ,the NDVI would increasd sharply ,but it was linear with the precipitation increased .The NDVI would increased before the air temperature arrived at the optimum temperature of vegetation ,but after it showed a clear downward in the growth stage .The NDVI increased rapidly and reached saturation point with the increasing of precipitation .The NDVI as temperature and precipitation changes are present hysteresis in the growing seasons in north of China.