The Study On The Spatio-Temparal Evolution Of Rural Settlements In Hexi Area In Recent 32 Years

The Hexi area of Gansu Province is located in the arid regions of northwest China.The ecological environment is fragile,the degree of desertification is serious,and the proportion of population is small.With the promotion of immigration policies and urbanization construction,the newly planned rural settlements are characterized by neatly arranged and border rules.However,the early unplanned and disorderly settlements have seriously affected the land use integrity of the area.As the agricultural population decreases,the size of rural settlements was still growing,resulting in an imbalance between the proportion of people and land and the hollowing out of villages.The study of the spatial and temporal pattern of rural settlements can explore the law of the development and evolution of rural settlements in this area,and is of great significance for coordinating the balance of rural people and the ecological environment.This paper refers to the definition of rural settlements by the predecessors,combines with the land use status and economic development level of Hexi area,defines the rural settlements in Hexi area as “the rural settlements below the town”,and the vector data of rural settlements in Hexi area are extracted by visual observation based on the remote sensing image with 1986-2018 every 5 years.And then,use the dynamic degree model,regional difference model,nuclear density and landscape pattern index to reflect different characteristics in the time and space of rural settlements in the recent 32 years,and use buffer analysis method to quantitatively analyze the impact of roads,water system,township station on the spatial distribution of rural settlements,and qualitatively analyze of the impact of social and human factors on the scale and shape evolution of rural settlements.The results show:(1)The scale of rural settlements had been in different degrees of expansion,and the intensity of conversion between increased and reduced two-way had weakened.The change of area showed a trend of increasing slowly,and the change of quantity showed a process of “increase slowly(1986-2005)? tend to stabilize(2005-2018)”.Among them,the conversion between increased and reduced two-way in 2010-2015 was very frequent,and the net change in the area after offsetting was not very large.(2)The Change of rural settlements had significant regional differences.In the three major river basins,the Shule River Basin had changed the most,followed by the Shiyang River Basin and the Heihe River Basin.Among the five prefecture-level cities,Jiuquan City had changed the most,followed by Wuwei City,Jinchang City,Zhangye City and Jiayuguan City.Among the 20 counties(districts),the changes of Guazhou County,Gulang County,Yumen City,Jinchuan District were more severe,while Tianzhu County and Minle County were more stable.Generally speaking,the scale of rural settlements was characterized by the distribution of more in the east and less in the west: Shiyang River Basin > Heihe River Basin > Shule River Basin.The rural settlements of agricultural areas(Wuwei City and Zhangye City)were larger than the pastoral areas(Tianzhu County and Sunan County)and industrial areas(Jinchang City and Jiayuguan City).Ecological immigrant areas(Guazhou County,Gulang County,Yumen City,Jinchuan District and Sunan County)rural settlements had changed dramatically.(3)Rural settlements showed significant spatial low-value clustering characteristics.“Hot spots” and “cold spots” showed the distribution of east and west cold and heat bounded by Suzhou and Gaotai counties.After 2000,the “hot spot” area developed to the western region,and new hot spots such as Huahai Town of Yumen City,Shuangta Township of Guazhou,Lianghu Township and Guangzhi Township gradually appeared,and the “hot spot” area gradually became dense.According to the density,the rural settlements were divided into dense areas,lower dense areas,lower sparse areas,sparse areas,extremely sparse area.The changes in the dense areas were the most severe,and the space mainly appeared in the western areas of Ganzhou District,Minle County,Liangzhou District,Gulang County and Minqin County.In the past 32 years,the overall spatial distribution pattern had changed little,and the geographical distribution showed the distribution characteristics of “intensive in the east,dense in the central parts,and sparse in the west”.(4)Rural settlements can be divided into five modes: stable and invariant,external expansion,adjacent expansion,conversion upgrade and small atrophy.Among the change models,the scale of external expansion was the largest,which was the main direction of rural settlements change.It had experienced “stable expansion(1986-2005)? deceleration expansion(2005-2010)? accelerated expansion(2010-2015)?The process of low-speed expansion(2015-2018),the space was mostly new rural construction and ecological resettlement area,with concentrated distribution,boundary rules and compact structure.(5)In recent years,the average plaque area and plaque size standard deviation gradually increased,the new plaque area deviated farther from the average level,and the size plaque area showed a polarization state.The plaque density decreased,and the cohesion index increased,resulting in reduced landscape fragmentation,increased connectivity.Shape index slowly increased,the value of perimeter area fractal dimension was close to 1,the regularity of plaque shape was higher,the regularity of the plaque shape was strong,and the plaque structure was simpler.In general,the rural settlements in the Hexi area had generally developed towards intensification,and the structure of the plaques had become more compact and the boundaries had become more regular.(6)Rural settlements was concentrated in the range of 1km from the county road,the rural road and other roads,and 0.5km away from the ditch,which not only satisfied the convenience of transportation,dependence on water resources,but also avoid being too close to the river.In addition,the distribution of rural settlements areas was attracted by administrative stations,and about 83% of the settlements were concentrated in the range of 8km from the administrative station.Affected by urbanization,the area of settlements areas within 1km showed a decreasing trend.The social and cultural influence factors of the scale and shape evolution of rural settlements can be summarized as: policy-driven population growth and expansion of the living environment supported by social and economic development and policy.