Temporal and spatial variation study of vegetation coverage in the Yellow River Basin based on GEE cloud platform

Vegetation coverage is an important indicator for land ecological status.The Yellow River Basin,rich in coal resources and as the important economic development zone,spans China’s topography from the west to the east and across nine provinces.In order to reveal the land ecological status of both Yellow River Basin and its State Planned Coal-mining Areas (SPCA),the authors obtained the vegetation cover data of 34 years based on the platform of Google Earth Engine (GEE) by processing 40525 Landsat TM/ETM+/OLI remote sensing images of the Yellow River Basin from 1987 to 2020 with procedures including batch cloud removal,fusion and NDVI cloud computing.The spatial and temporal variation characteristics of vegetation coverage in both Yellow River Basin and its SPCA are quantitatively analyzed using the methods of maximum synthesis,pixel dichotomy model,trend analysis of linear regression and F-test,etc.Then the topographic factors and climatic factors are identified one by one in terms of the impact on vegetation cover in the Yellow River basin and its SPCA.The study results show as follows:firstly,during the 34 years period,the average vegetation coverage of the Yellow River Basin presents a fluctuating upward trend from 0.457 4 in 1986 to 0.581 7 in 2020,and the average vegetation coverage within its SPCA increased from 0.355 6 to 0.536 1,where they show a consistent increase fluctuation trend.Secondly,the improved area of vegetation coverage,about 33.19%,is much larger than the degraded area,about 3.55% of Yellow River Basin,by the transformation analysis of vegetation coverage change tendency categories in the study area.Though the proportion of improved area of vegetation coverage in the SPCA is higher than that in the Yellow River Basin,but its vegetation coverage in the SPCA is still significantly lower than the average level of the Yellow River Basin.Thirdly,there are significant spatial differences in the mean FVC over the years.Except for Ningxia Plain,Hetao Plain,et al.,the FVC is comparatively higher in the south and lower in the north,and is decreased from southeast to northwest.Fourthly,those terrain factors’influence on vegetation coverage shows in rank as "elevation > slope > aspect" in both Yellow River Basin and its SPCA.The effect of temperature on vegetation coverage is bigger than that of precipitation.The change of land use type promotes the multidirectional trend of vegetation cover change in the study area.Fifthly,among those 44 SPCA,the improvement of vegetation coverage in Binchang mining area and Xiangning mining area is comparatively more significant,and the degradation of vegetation coverage is comparatively evident in Shitanjing mining area and Baotou mining area.At last,the conclusion is drawn that the application of long sequence,multi-source data can reveal the differences and similarities of temporal and spatial change characteristics on vegetation coverage between the Yellow River basin and its SPCA,which is the basis for the scientific understanding,evaluation of their ecological conditions and providing the data support for policy-making on ecological protection and restoration,while the formation mechanism of the temporal and spatial differences of vegetation coverage remains for further in-depth analysis in the future research.