Effects Of Climate And Land Use Change On Vegetation NDVI In The Three North Region

The Three North region is the most severe desertification area in China.In order to improve the ecological environment in this area,China started the construction project of three-north shelter forest in 1987.This paper mainly used NDVI,temperature and precipitation data,combined with mean method,trend analysis,thin plate smoothing spline,Mann-Kendall nonparametric detection method,Hurst index analysis,correlation analysis and multiple linear regression analysis.The temporal and spatial variations of vegetation NDVI,temperature and precipitation were studied in three-north shelterbelt project area from 1982 to 2015,and the influence of temperature,precipitation and LULC change on NDVI were further analyzed.The main conclusions are as follows:(1)The overall spatial distribution of vegetation cover in the study area is higher in the northeast and north China plain agricultural areas,NDVI in the northwest desert area is low,the hilly and gully area on the Loess Plateau gradually decreases from south to north,and NDVI in the sandstorm area gradually increases from west to east.From 1982 to 2015,the average annual maximum NDVI was 0.37 in the study area.The annual maximum NDVI showed an upward trend and 79.87% of the NDVI trend in the study area has no obvious change.The variation trend of NDVI showed obvious strong continuity.NDVI showed a fluctuating upward trend in the growing season,with an average of 0.32 in many years.The trend of NDVI was basically unchanged in most regions during the growing season.The seasonal NDVI from large to small is summer,autumn and spring,and NDVI has an upward trend.The spatial distribution of NDVI was similar to that of annual maximum NDVI and growth season average NDVI.NDVI has strong seasonal variation during the year.(2)The spatial distribution of annual precipitation showed that the annual precipitation in the desert areas of Northwest China is generally less than 200 mm except Tianshan Mountains,Kunlun Mountains,Qilian Mountains and Altai Mountains.The precipitation in the other three zones decreased gradually from southeast to northwest.The annual average precipitation is 299.8mm,and the precipitation have decreasing trend,and precipitation had a reduced mutation in 1987.The spatial distribution law of precipitation in the growing season is basically consistent with the annual precipitation.The average annual precipitation was 245.6 mm,and the precipitation in the growing season in 1992 produced a reduction in the mutation.The spatial distribution of annual average temperature gradually reduced from south to the north in the agricultural area of the North China Plain and the hilly and gully area of the Loess Plateau.The temperature in the sandstorm area decreased gradually from southeast to northwest.The temperature in the northwest desert area was higher in the Tarim basin,Kumutag desert and Badain Jilin desert and other areas,while the temperature was lower in the Kunlun mountains,Tianshan mountains and Qilian mountains.The average annual temperature is 4.7 ° C.Temperature around 1993 produced increased mutation,and the increased rate of temperature is 0.04?/a.The spatial distribution of growing season temperature was consistent with that of annual temperature and the average temperature is 16.8°C.Around 1994,there was a sudden rise in temperature.(3)The annual average NDVI in the study area is positively correlated with precipitation as a whole.Positive correlation regions are mainly distributed in most areas of Inner Mongolia,northern Hebei,Beijing,Tianjin,northwest Shanxi,northern Shaanxi,Ningxia,Gansu,central and northern Qinghai and northern Xinjiang.The negatively correlated regions are mainly distributed in the central and southern Xinjiang,Qinghai,central Shaanxi,Liaoning,Jilin and Heilongjiang provinces.The annual average NDVI was positively correlated with temperature.Positively correlated regions are mainly located in the southern part of North China Plain,southeastern part of sandstorm area,most of the hilly and gully area of Loess Plateau and the eastern and southern part of desert area in northwest China.While the negatively correlated regions are mainly located in Xinjiang,Inner Mongolia and northwest Heilongjiang.In general,the effect of temperature on NDVI in the study area is greater than the effect of precipitation on NDVI.NDVI is positively correlated with temperature in spring,summer and autumn.NDVI was positively correlated with precipitation in summer,but negatively correlated with precipitation in spring and autumn.There was a one-month lag between vegetation NDVI and precipitation in the previous month in May,June and July.The correlation between vegetation NDVI in May,June,August and September and the temperature in the previous month was stronger than that in the same month.The natural conditions of the north China plain agricultural area in northeast China,the greater Hinggan mountains,most areas of the loess plateau,and the Tianshan mountains,the Altai mountains and the southern Qilian mountains in the northwest desert area are more suitable for vegetation growth.The climatic conditions in southwest Xinjiang,northwest Inner Mongolia,west Qinghai,Gansu and most parts of Ningxia are not conducive to vegetation growth.Overall,human activities have significantly improved the vegetation coverage in the three northern regions.(4)The proportion of land cover and land use types in the three northern regions from large to small is unused land,grassland,cultivated land,forest land,water area and construction land.From 1995 to 2010,the main reason for the decrease of NDVI in the three northern regions was that a large amount of grassland was converted to farmland and the increase in NDVI is associated with the conversion of large amounts of unused land to arable land.In 2010-2015,the decrease of NDVI was mainly related to the large-scale development of construction land,the increase in NDVI is associated with the conversion of large amounts of grassland to woodland.From 1995 to 2015,the decrease of NDVI was mainly due to the conversion of large amount of cultivated land to construction land,while the main reason for the increase of NDVI is that a large amount of construction land was converted to cultivated land in the study area.