Jinning XIE，Jianhua GUO ，Kaiguo YUAN，Bin QUAN

1.School of Architecture and Urban Planning，Hunan University of Science and technology，Xiangtan 411201，China；2.Department of Economics and Management，Shaoyang University，Shaoyang 422000，China

1 Introduction

Land use structure determines the functionality and efficiency of land use，and the adjustment and optimization of land use structure is the fundamental way to solve the sustainable use problem of land resources，and also the core of overall planning of land use［1］.Limited land resources and spatial differences in land use as well as the contradiction between limited land resources and unlimited growth of socio-economic development needs，have required that the review of land use structure should be long and dynamic［2］.From the optimal allocation model of land use［3－8］，land use structure and dynamic land use［9－11］，experts and scholars have conducted a large number of studies.The evaluation of land use structure rationality is the basis of land use structure adjustment and optimization，and there are some experts and scholars having made useful discussion on the evaluation of land use structure rationality from a static point of view［12－15］.From a dynamic perspective，this paper uses dynamic TOPSPS method［16］to carry out fuzzy evaluation of rationality level of land use structure in the Changsha-Zhuzhou-Xiangtan area，to provide a reference for the optimization and adjustment of land use structure in the Changsha-Zhuzhou-Xiangtan area，establishment and revising of overall land use plan，and sustainable use of land resources.

2 Overview of the study area and data sources

The Changsha-Zhuzhou-Xiangtan area（111°53′E—114°15′E，26°03′N— 28°5′N）refers to the area administered by Changsha City，Zhuzhou City and Xiangtan City，and it is the core growth pole of economic development in Hunan Province，with complex land use structure.It has a total area of2.8240 km2，and features a typical subtropical humid continental climate with distinct four seasons.It has changeable warm springs，and clear summers and falls inmost of time.The severe winter is short while the hot summer is long.The average annual temperature is 17.5℃ and the frost-free period is over 286 d.The rainfall is abundant，and the light and heat are adequate.The average annual rainfall is about 1378 mm，and the annual average number of hours of light is1665 h.Changsha-Zhuzhou-Xiangtan's terrain is mostly mountainous and hilly，with an average elevation of 400 m or more.In the study area，red soil and paddy soil are dominant，accounting for 70%and 25%of total area of soil，respectively.There is 1342097.7 ha of woodland，the forest coverage rate reaches 54.7%.The main tree species include pine，fir and bamboo，etc.Land use data are from the land use change survey data in Hunan Province，and the land use type uses the new land use classification standard proposed in August2007.In order to avoid overly simplified or complicated classification of types，commercial use land，mining warehouse land，residential land，public administration and public service land and special land are merged into land for cities，towns and villages and land for mining and industry.A total of eight first-level types are selected for calculation and analysis.

3 Rationality evaluation of land use structure in the Changsha-Zhuzhou-Xiangtan area

The Technique for Order of Preference by Similarity to Ideal Solu-tion（TOPSIS）is a multi-criteria decision analysis method，which was originally developed by Hwang and Yoon in 1981 with further developments by Yoon in 1987，and Hwang，Laiand Liu in 1993.TOPSIS is based on the concept that the chosen alternative should have the shortest geometric distance from the positive ideal solution and the longest geometric distance from the negative ideal solution.It is first used for studying multi-attribute decision making problems［17］.At present，it has been widely used in social，economic，and military areas to solve the multi-objective mixed decision-making problems［18－19］.Compared with the static TOPSIS method，the dynamic TOPSIS method not only has index weight vector，but also has time weight vector.It can also give the final dynamic evaluation results，and the evaluation results at each time point［16］.This study takes the annual land use structure as evaluation object，and land use type as evaluation indicator.The original index data are used to measure the proportional structure of each land use type，and establish the matrix after the normalization of various time points.According to the characteristics of land use structure change，combined with the actual situation of the Changsha-Zhuzhou-Xiangtan area，the time dimension value takes 0.1，and takes0.5.The calculation results of dynamic degree of land use structure rationality in the Changsha-Zhuzhou-Xiangtan area during 2008－2010 can be shown in Table 1.

Table 1 The dynamic evaluation results of land use structure rationality in the Changsha-Zhuzhou-Xiangtan area during 2008－2011

4 Result analysis

4.1 Analysis of land use structure rationality in the Changsha-Zhuzhou-Xiangtan areaThe larger the value of Ci（tk），the better the cross-section evaluation object.As can be seen from Fig.1，the land use structure rationality has been gradually increased in the Changsha-Zhuzhou-Xiangtan area in recent years，Ci（tk）value increased from 0.4850 in 2008 to 0.6722 in 2011，and especially from 2010 to 2011，Ci（tk）value increased significantly.The trend of land use structure rationality in various regions of Changsha-Zhuzhou-Xiangtan tends to be the same as the overall trend of land use structure rationality in the Changsha-Zhuzhou-Xiangtan area，the gap between the regions is small，and this gap continues to narrow.In terms of Ci（tk）value，the difference between Xiangtan with the greatest Ci（tk）value and Zhuzhou with the smallest Ci（tk）value was 0.062 in 2008，while the difference between Changsha-Zhuzhou-Xiangtan with the greatest Ci（tk）value and Zhuzhou with the smallest Ci（tk）value was reduced to0.049.In terms of the final dynamic value hi，it is found that the current overall land use structure rationality is high in the Changsha-Zhuzhou-Xiangtan area，and rationality reaches 0.8186；the region with the highest rationality（0.8245）is Xiangtan；the region with the lowest rationality（0.7821）is Zhuzhou；the difference between the highest hi value and the lowesthi value is only 0.0424，indicating that there is a small difference in the land use structure rationality between regions in Changsha-Zhuzhou-Xiangtan.

4.2 Dynamic degree of land useThe change in land use type is directly related to the change in land use structure rationality，and this paper calculates the dynamic degree of use of8main land types in the Changsha-Zhuzhou-Xiangtan area during2008－2011.The dynamic degree of land use is calculated as follows：

where D is the dynamic degree of one land use type in the study period；S1and S2are the amount of one land use type at the early and late stages of study，respectively；T is the length of study period.

By putting the land data during 2008－2011 into the above formula，we get Table 2.Through the analysis on dynamic degree of land use in this region，it is found that within the study period，in the Changsha-Zhuzhou-Xiangtan area，there is a decline in the area of arable land，garden plot，woodland，grassland，water area，water conservancy facility land，and other land，and the woodland is reduced most，reaching 15928.68 ha；there is an increase in the area of land for cities，towns and villages，land for mining and industry and transportation land，and land for cities，towns and villages and land for mining and industry increase most，reaching15690.60 ha；except the increase of water area and water conservancy facility land in Zhuzhou，the trends in various regions are basically the same as the overall trends in the Changsha-Zhuzhou-Xiangtan area.In terms of the rate of change of single land type，it is highest for transportation land，an average increase of 5.57%annually，and it is highest for Changsha，followed by Zhuzhou and Xiangtan；the second is land for cities，towns and villages and land for mining and industry，an average increase of 1.84%annually，and it is also highest for Changsha，followed by Zhuzhou and Xiangtan；it is slowest for water area and water conservancy facility land，with an average annual reduction of 0.094%；it is slowest for arable land in various regions，with an average annual decrease of 0.40%，0.013%and 0.13%in Changsha，Zhuzhou and Xiangtan，respectively.The regional land use change rate is proportionate to regional economic development rate，and Changsha＞Xiangtan＞Zhuzhou.

Table 2 Dynamic degree of land use

4.3 Grey relational analysis of Ci（tk）value change of land use structure and land use typeThe land use structure rationality and its change are determined by land use type and its change.Table 3 shows the grey relational analysis results of Ci（tk）value and land use type.As can be seen from Table 3，the degree of correlation between Ci（tk）value and land use type is as follows：Changsha（X6＞X5＞X3＞X1＞X7＞X2＞X4＞X8）；Zhuzhou（X6＞X5＞X7＞X1＞X3＞X8＞X4＞X2）；Xiangtan（X6＞X5＞X1＞X3＞X7＞X8＞X4＞X2）；Changsha-Zhuzhou-Xiangtan（X6＞X5＞X1＞X7＞X3＞X4＞X8＞X2）.The Changsha-Zhuzhou-Xiangtan area is the pilot area of＂two-oriented society＂and economic growth pole of Hunan.Through rapid economic development in recent years，the transportation land and construction land are rapidly expanded，with the greatest dynamic change，so transportation land，the land for cities，towns and villages and the land for mining and industry are correlated with land use structure rationality to the highest degree.The dynamic change of arable land is minimal，but arable land is the most valuable resource，and the arable land protection is fundamental to stability of the state，so arable land has also an important impact on land use structure rationality.The dynamic change of woodland，water area and water conservancy facility land is also large，having an important impact on the land use structure rationality.Therefore，reasonably controlling excessive growth of transportation land，the land for cities，towns and villages and the land for mining and industry，protecting arable land，woodland，water area and water conservancy facility land，and moderately increasing garden plot，is a feasible measure to constantly improve the land use structure rationality in the Changsha-Zhuzhou-Xiangtan area.

Table 3 Grey relational analysis of Ci（tk）value change of land use structure and land use type

5 Conclusions and discussions

Using dynamic TOPSIS method，this paper constructs a model concerning land use structure rationality for comprehensive evaluation of the land use structure rationality in the Changsha-Zhuzhou-Xiangtan area.Ci（tk）can quantitatively analyze the use structure rationality of different land types in the study area from different time sections，and the dynamic value hi can conduct overall evaluation of land use rationality in the study area from a dynamic perspective.According to the grey relational analysis of land use types and Ci（tk）value of land use structure，combined with the dynamic degree of land use，we can analyze the influence of land use type change on land use structure rationality，and put forward corresponding policies.Therefore，the evaluation results of existing land use structure rationality using dynamic TOPSIS method are of theoretical and practical significance to land use structure adjustment.From the evaluation results of land use structure rationality in the Changsha-Zhuzhou-Xiangtan area，it is found that there are significant fluctuations in land use structure rationality during the evaluation period.In the future，it is necessary to fully consider the land suitability in various regions affected by topography，climate，hydrology，soil and other natural factors，as well as positioning of regional development and industrial structure adjustment；rationally developing land use plan，and timely adjusting land use structure；focus on the protection of good quality arable land，and protect and restore forest land；increase intensive level of construction land，and reasonably control transportation land size；promote the relocation and consolidation of rural settlements，and actively accelerate the urbanization process.

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