Analysis Of Land Use Change And Land Ecological Risk Assessment In Yan'an City

Land is the material carrier of human survival and development.with the further development of urbanization and industrialization,the mode of land-use changes with the social economic activities and human activities have a more significant impact on land.The end result is that a series of land problems followed and the situation of land ecology are facing great challenges.This study takes Yan'an city of Shaan xi province as the research object,its special geographical environment,landform type,urban distribution and so on determine the diversity and complexity of the inner land ecological problems in Yan'an city.The assessment and analysis of land ecological risk in Yan'an will contribute to understand the local land ecological problems and provide an effective reference for the formulation of social and economic development strategies in Yan'an.Based the research and analysis of land-use types,land ecological risk assessment is carried out in this paper.According to the land-use data in 2000,2010 and 2015,the land-use status of Yan'an is analyzed by the relevant land index.The land ecological risk assessment index system is constructed from four aspects of vegetation growth,land-use degree,climate stability and soil erosion.The vegetation coverage index,risk index of land-use structure,precipitation anomaly percentage and soil hydraulic erosion amount,these four ecological indexes is selected to establish a comprehensive assessment model of land ecological risk.The land ecological status of each district and county in Yan 'an city is evaluated and its dynamic change law is analyzed.The main conclusions are as follows:(1)In the 2000-2015,the area of woodland,grassland,water,construction land and unused land were increased,and the area of cultivated land decreased greatly in Yan'an.During the past 15 years,woodland,water and construction land increased by 42612.75hm~2,645.21hm~2 and 10785.15hm~2 respectively;the grassland area increased firstly and then decreased,the total amount increased by 189538.59 hm~2;the unused land area increased by a total of 524.23 hm~2 after decreasing;The cultivated area decreased by 244105.93hm~2.(2)In the 2000-2015,land-use dynamic index in Yan'an shows that the largest for construction land and the smallest for woodland.The Construction Land(4.8708),unused land(2.8332),grassland(0.9245),water(0.5592),Woodland(0.1916)and arable land(-1.9881)are from large to small.The degree of comprehensive land-use in 2010-2015 was higher than that in 2000-2010,indicating that the development rate in the latter 5 years was higher than that in the former 10 years.The transfer matrix of land-use shows that the conversion among forest land,grassland,cultivated land and unused land was intense.(3)The spatial difference of land-use structure is large.Huanglong county,Huangling county,Fu county,Yichuan county,Ganquan county,Baota district(shrubbery),the structure type of these 6 districts and counties are based on woodland and supplemented by grassland and cultivated land;Yanchang county,Ansai district,Zhidan county,Wuqi county,Yanchuan county and Zichang county,these counties are based on grassland and supplemented by woodland and cultivated land,Luo chuan county is based on arable land and supplemented by other types in 2000,it is converted into grassland and supplemented by cultivated land in 2010.In 2000-2015,the comprehensive land-use dynamic ranking of counties changed more sharply.As of 2015,Yanchang county,Zhidan county,Baota district,the land-use dynamics of these 3 counties ranked in the top three,Huanglong county,Fu country,Huangling county are the smallest.The comprehensive index of land-use degree ranged from 266.47 to 291.3,the comprehensive index of Huangling county,Fu country and Huanglong county are relatively high,and the comprehensive land-use degree is higher;the comprehensive index of Yanchang county,Zhidan county,Luochuan county and Yanchuan county are low,and the comprehensive land-use degree is relatively low,the land resource is in the development stage.(4)The spatial difference of land ecological risk factors is large:? The vegetation coverage index decreased nonlinearly from south to north in Yan 'an city.the vegetation growth in the south region is good,and the vegetation in the southeast and southwest regions is the most flourishing;The north is relatively poor,the northern part of Wuqi country,Ansai city and Zichang country is in poor vegetation growth.?Luochuan county has the highest ecological risk index of land-use structure,followed by Yanchuan county,Baota district,Huanglong county and Fuxian county,Huangling county is relatively small,the land ecological risk situation of the other districts and counties is close.? The study of precipitation anomaly percentage shows that the precipitation in South Yan'an is more stable than that in the north;The year of 2000,2010 and 2015 are drought years,and the precipitation is less than the historical average of the same period;The precipitation anomaly percentage index decreases from south to north,indicating that the precipitation in the south is relatively higher than that in the north in dry years;@ The three periods of soil hydraulic erosion in Yan'an city are relatively light in the south,while the northern region is relatively serious;Soil water erosion is decreasing continuously and land ecological condition is improving;In Huanglong county,Huangling county,Fu county and Ganquan county,the soil hydraulic erosion is weak,Wuqi county,Zichang county,Ansai district and Yanchuan county have the strong erosion.(5)The comprehensive index of land ecological risk in Yan 'an city is low in the south and high in the north.Land ecological risk index decreased continuously;Land ecological situation of Yan 'an is improving.From 2000 to 2015,the land ecological risk of Huanglong county has been the lowest,followed by Huangling county,Fuxian and Ganquan county.Yanchuan county,Wuqi county,Zichang county,and Ansai district,these 4 counties are relatively high.By 2015,Huanglong county,Huangling county,Fu county,Yichuan county and Ganquan county,the risk of these 5 counties is level I and land ecological situation is relatively safe.Baota District(0.4379)is level III and the land ecological risk is relatively small.Yanchang County,Zhidan County and Luochuan County reaches to level IV and the risk is higher.Wuqi County,Ansai District and Zichang County reaches to the level V and the risk of land ecological is higher.The land ecological risk index of each district and county is decreasing continuously,and there is no land ecological deterioration phenomenon.The gap of land ecological risk in different counties is narrowing,and the land ecological situation in Yan 'an is improving.(6)Since the implementation of grain for green policy in 1999,the ecological situation of Yan 'an city has been improving,the green landscape has been advancing to the north and further promoting the strategy of" red Yan 'an,green development".However,as of 2015,the unused land area continued to increase and soil hydraulic erosion is serious in some areas,the ecological risk is larger.The grain for green policy,natural forest protection and construction of protective forest need to be implemented,while strengthening the conservation of water and soil,and implementing the policy of ecological red line protection.(7)The characteristics and innovation of this study are as follows:l.The land ecological risk assessment index system is constructed from four aspects of vegetation growth,land-use degree,climate stability and soil erosion.The vegetation coverage index,risk index of land-use structure,precipitation anomaly percentage and soil hydraulic erosion amount,these four ecological indexes is selected to establish a comprehensive assessment model of land ecological risk,and carry out exploratory land ecological risk assessment.2.Based on the ecological theory and mathematical method,the domain of coverage management factor C estimation model is modified to make its mathematical logic more rigorous.