| Yellow River is the most sandy river in the world,and the Loess Plateau in its middle reaches is one of the most eroded areas in the world,and 90% of the sediment in the lower reaches of the Yellow River comes from the Loess Plateau.In order to control soil erosion and prevent ecological deterioration,the state has invested a lot of human,material and financial resources in ecological construction and environmental management in the Loess Plateau area in recent decades.In particular,since the implementation of large-scale vegetation construction,such as retuning farmland to forest(grass),closing the land for reforestation and afforestation on barren hills since 1999,the vegetation cover has increased significantly,and the erosion sediment yield and sediment inflow have decreased significantly,while the direction of land use change and the degree of land cover change determine the process of eroding sand and sediment transfer.This study takes the Beiluo River basin in the hinterland of the Loess Plateau as the study area,sharing,sorting,mining data from different periods and sources.By interpreting series of data,using remote sensing technology and spatial analysis methods,the land use data of five periods from 1980-2019 and long-term vegetation coverage data of 2001-2017 were obtained,and characteristics of temporal and spatial changes in the land use/cover and landscape pattern in the study area over the past 40 years were analyzed,and the process of underlying surface changes on the Loess Plateau was analyzed to provide basic information for the construction of ecological environment.The main conclusions are as follows:1)Using a random forest classification algorithm,the 25-view Landsat image data from five time nodes in 1980,1990,2000,2010 and 2019 was classified,and the land use data set with a resolution of 30 m was obtained for five periods in the study area.According to the same data source evaluation method and different data source expert evaluation method,the accuracy rate of land use information interpretation was 92.85% and 79.94% respectively,and kappa coefficient was 0.8965 and 0.7025 respectively,with good classification accuracy.The confusion matrix showed that cultivated land,grassland and residential land were easily confused,and the accuracy of forest land and water area classification was high.2)The average value of cultivated land,forest land,grassland,residential land and water area in five periods of Beiluo River Basin was 29.62%,47.90%,19.84%,2.41% and 0.23%.The spatial distribution of land use types in the basin was uniform.The upstream hilly and gully area was mainly cultivated land and grassland,the middle reach of gully area was mainly cultivated land and forest land,the forestland of earth-rock mountain areas was mainly forest land,and the terrace plain area was mainly cultivated land and residential land.3)In the four periods from 1980 to 2019,the comprehensive dynamic degree of land use in Beiluo River basin was 8.52%/a?12.5%/a?10.26%/a?7.18%/a,and the change rate of land use in the basin showed the trend of increasing first and then decreasing.The main transfer directions of land use types in each period were cultivated land to grassland,cultivated land to woodland grassland to forest land.The change trend of land use in hilly and gully areas and gully areas was similar to the change trend of river basin,which was mainly manifested as the decrease of large area of cultivated land,the substantial increase of forest land.And the conversion of farmland and grassland to forest land,mainly distributed in Wuqi,Zhidan,Huachi,Luochuan and other counties.4)Based on the analysis of the landscape pattern changes in the hilly and gully area of the basin,it was considered that the area of forest land and the number of patches in the hilly and gully area increased rapidly at five time nodes,and the degree of fragmentation increased at first and then decreased significantly.After 2000,the forest land showed an obvious trend of development.Grassland was the dominant landscape type in the hilly and gully area.After 2000,the area of grassland decreases gradually and the degree of fragmentation slowly increased.At the landscape level,the landscape diversity and heterogeneity of hilly and gully areas increased,the dominant advantage of a single landscape patch became less obvious,and the degree of aggregation of different patches gradually decreased.5)Based on the vegetation coverage data set retrieved by MODIS,the temporal and spatial variation characteristics of photosynthetic vegetation(PV)in the Beiluo River basin from 2001 to 2017 were analyzed.The results showed that: 1)the average annual vegetation coverage of the study area was 60.2%,63.2% and 68.5% at the beginning,middle and end of the period,respectively.In space,the vegetation coverage in the hilly and gully areas of the upper reaches was the lowest,and that in the forestland of earth-rock mountain of the middle reaches was the highest.2)From 2001 to 2017,the vegetation coverage of Beiluo River basin increased by 90.9% and 44.3% respectively.During the 17 years,the vegetation coverage of the whole basin,hilly area,gully area and forestland of earth-rock mountain area showed a significant(P < 0.05)increasing trend,and the annual variation rates were 0.65%/a,1.18%/a,0.64%/a,0.42%/a,respectively.Among the main 12 counties in the upper and middle reaches of the basin,Zhidan,Wuqi and Jingbian had the fastest increase in annual vegetation coverage,with a change range of 1.05-1.36%/a,and Huanglong,Huangling and Heshui had the slowest increase,with a range of 0.31-0.33%/a.3)Consistent with the degree and direction of land use change,the main contribution to the significant increase of vegetation coverage of the whole basin was from the hilly and gully region,with a contribution rate of 46.3%.On the county scale,it mainly came from Zhidan(23.1%)and Wuqi county(20.4%),followed by Fuxian(10.6%)and Ganquan county(10.2%). |
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