| The eastern part of the Qinghai-Tibet Plateau,which connects with the Loess Plateau and Sichuan Basin,is the middle zone of the transition from the Loess Plateau to the Qinghai Tibet Plateau.Its geographical location is very special.Affected by multiple factors such as high altitude and low temperature,the ecological environment of the area is extremely fragile.The area is a natural supply station for many rivers such as the Yangtze River and Yellow River,and also a green ecological barrier to ensure water safety.It is also one of the important highland pastures in China.Therefore,the health and stability of its ecological environment have an important impact on the water safety of the Yangtze River and Yellow River and the production and life of local herdsmen.This study visually interpreted the wetlands and desertified land in the Eastern of the Qinghai-Tibet Plateau,combined with the CCI-LC products released by ESA as the land cover data for the study.Then,combined with the field measured land type data and high-definition image verification points,based on the classification accuracy evaluation of the data in the Eastern of the Qinghai-Tibet Plateau,the spatio-temporal dynamic change characteristics of land cover types in the study area from 1991 to 2019 are analyzed,the driving forces of the change of natural vegetation area in this area were studied.The natural vegetation distribution in the eastern of Qinghai-Tibet Plateau was determined by using the method of intersection of land cover data in 2000,2010 and 2019,MOD13A3 was used to analyze the spatio-temporal changes and overall stability of NDVI in the study area,and the effects of meteorological and anthropogenic factors on NDVI were studied.The main results are as follows:(1)The average producer accuracy of visual interpretation for the 4 stage of wetland and sandy land is 95.25%and 80.49%,and the average user accuracy is 87.71%and 92.40%,respectively.The average overall accuracy of the 4 land cover data is 75.19%,and the average kappa coefficient is 0.75.Among the six land cover types reclassified by CCI-LC products,grassland was better identified,the average producer accuracy of 4 land cover data is 83.87%.(2)From 1991 to 2019,the grassland area first decreased and then increased,with a total decrease of 4872.15 km~2;The forest area showed a continuous increasing trend,and the total increased area was 6258.15 km~2;The forest area showed a continuous decreasing trend,with a total decrease of 1189.80 km~2;The area of sandy land continued to increase,with a total increase of 33.12 km~2 in 29 years.The land cover types mainly showed the large area mutual transformation of grassland,forest land and artificial surfaces,and the small area transformation between them and wetland and sandy land,among which the grassland was the most transferred out and the forest was transferred most.(3)The NDVI of natural vegetation in the eastern of Qinghai-Tibet Plateau is relatively high,with an average of 0.7313 from 2000 to 2019.The area with NDVI between 0.6 and 0.8is the largest,accounting for 58.21%of the total vegetation area.NDVI of all types of natural vegetation in the study area showed a fluctuating upward trend.And the area with increasing trend of NDVI(74.20%)was larger than that with decreasing trend(25.80%),of which the area with significantly increasing trend accounted for 21.65%,and the area with significantly decreasing trend accounted for 2.17%.(4)In 2000-2019,the NDVI of natural vegetation in the study area fluctuated steadily,the area with small fluctuations(Cv?0.15)accounted for 95.14%,and the area with high fluctuations(Cv>0.3)accounted for only 0.79%.The proportion of areas with high fluctuations of different types of natural vegetation in the total area of this type of vegetation in descending order is:grassland>forest>wetland>sandy land.(5)The main driving factors for changes in the area of grassland and wetland are the same,the number of livestock and evaporation,both of which are negatively correlated with changes in the area of grassland and wetland.The main factors of forest area change are population quantity and temperature.And The leading factors for the increase in the area of dandy land is the number of population and livestock.The average partial correlation coefficient of natural vegetation NDVI and temperature(0.0912)is greater than precipitation(0.0526),and the area of positive correlation(66.12%)is also greater than precipitation(60.82%).That is,the temperature increase in the eastern part of the Qinghai-Tibet Plateau has a positive effect on the increase of vegetation NDVI,and the effect of precipitation on vegetation NDVI is less than temperature. |
PDF Full Text Request