| Lanzhou City is the capital city of Gansu Province and seat in the "seat four even" an important position in the northwest region.It is the link from East China,North China to the western region,the strategic platform to the west for China,and also the important node city under new era "development of the Belt and the Road " strategic background.Since ancient times,Lanzhou always has a special and important strategic position in the military,transportation and economic of China.After the reform and opening up,in the western development background,the urbanization of Lanzhou City was accelerating speed.Different from the plain city,Lanzhou City expansion was restricted because of basin basin terrain.To study the spatial and temporal characteristics of urban expansion under different terrain conditions can quantify the occupation of different terrain conditions by the city,and use the urban terrain conditions scientifically.In this paper,we select the valley basin and the part of the mountainous area around the basin as the research area.First,we combine the multi-source and high-definition images to extract the information of the entity area and the urban land and land use chang,and use the high-precision digital line data to obtain the DEM and get the terrain composite index and the urban geomorphology unit.Then,we analyst the temporal and spatial characteristics of the built-up area in the past 60 years;the landscape ecological changes and Land use expansion patch type under different terrain composite index;the terrain complexity of each geomorphology unit and the relationship between the single terrain factor;the terrain composite index and t city expansion.The conclusions are as follows:(1)We divide study area into different landform types,and then analyst terrain complexity of each landform type.We obtain 25 types of geomorphology in the study area by combining elevation and slope.The most extensive landform is flat land area of 49.31km~2,accounting for 22.5% of the total area.Steep slope beach area is the smallest,only 0.33km~2.The total area of flat platform,sloping platform,gentle slope beach,gentle slope secondary terrace,slow slope platform,medium slope beach,middle slope second terrace,middle slope platform,steep slope secondary terrace,steep slope platform etc is less than 11% of the study area.By calculating the terrain complexity in different geomorphic units,It is found that the complex area of terrain conditions increases from flat beach to steep slope platform with increasing elevation and slope.The total area of flat terraces,flat second terraces,flat third terraces,slightly inclined beach and slightly inclined second terrace area with excellent area of more than 95% of the total area,which is the ideal area is more than 96% of the fine area,which is the ideal area for urban construction.(2)We analyze the characteristics of land use change over the past 60 years.The analysis of urban land use change shows that the "three wasteland" and cultivated land are the main sources of urban land use,and the total amount of the two is 73.8km~2,and the contribution rate to urbanization is more than 75%.after urbanzition,residential land and industrial land accounted for 48.94% and 17.25% of the urban area,reach 47.53km~2 and 16.76km~2 respectively.(3)We analyze the temporal and spatial characteristics of landscape pattern under different terrain conditions.From the analysis of the landscape pattern,it is seen that the overall shape of the built area has not changed much from 1961 to 2015,and the degree of aggregation and connectivity increased and the fragmentation decreased.From the different terrain conditions,the terrain conditions are superior(elevation,slope and fluctuation are low)to complex areas(elevation,slope and elevation are higher)aggregation and connectivity index gradually decreased,the fragmentation index gradually increased The integral dimension of the circumference is gradually increased,which indicates that the shape is more and more complicated,and the landscape shape index is close to 1.5 in the complex area of terrain,and the landscape shape is the most unstable.(4)We analyze the temporal and spatial characteristics of land use expansion patches under different terrain conditions.Expansion of the patch type to the external extension of the main patch,followed by internal filling type patches,newborn patches at least from 1961 to 2015.external extension area is more than others in each terrain condition.The internal filling patches have only 0.2km~2 in the complex area of terrain,less than 2% of the total area,and are susceptible to terrain.The newborn patches have 3.54km~2 area in the terrain conditions are more complex and complex area of,accounting for 60% of the total area.(5)We analyze the temporal and spatial characteristics of urban expansion in different elevation,slope and relief amplitude.From the perspective of the impact of elevation on urban expansion,the area has reached 130.45 km~2 in the first-class terraces,accounting for more than 70% of the total land area.After 2000 a,the built-up area in the four and five terraces show a rapid development,the average annual expansion rate from 0.12km~2/a increased to 0.42km~2/a.From the slope of the impact of urban expansion,the built area is 97.84km~2,15.75km~2 and 15.73km~2 in flat,slightly flat and gentle slope,accounting for more than 70% of the total area of the three regions.The increasing area of mid-slope and steep slope is 3.23km~2 during 2009-2015,accounting for 30% of the total area in 54 years.From the influence of the relief amplitude on the urban expansion,the increasing area of the lower-fluctuation area is the largest,with an area of 41.55km~2.The area of the higher and high fluctuation ranges from 28.08km~2 and 18.86 km~2 respectively,which is less than 20% of the study area,not the main area of urban expansion.(6)We analyze the temporal and spatial characteristics of urban expansion under different levels of terrain composite index.From the influence of terrain comprehensive index on urban expansion,the good and the complicated terrain condition area are the main location of the built area,and the average annual expansion speed is 0.52km~2/a and 0.55km~2/a respectively.The expansion strength index and annual expansion rate in excellent terrain condition continues rising before 2000,then fluctuates.The annual average intensity in the general terrain contribution is 0.25km~2/a,which is only higher than most complicated terrain condition.The annual average intensity of the built-up area in the most complex area is 0.08km~2/a in 54 years,and the built-up area increases from 0.83km~2 to 5.37km~2. |
PDF Full Text Request