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PAPER • OPEN ACCESS Analysis on the Characteristics of Cultivated Land Change in DianChi Lake Basin based on remote sensing image processing technonlogy in the past 20 years

To cite this article: Min Gao et al 2021 IOP Conf. Ser.: Earth Environ. Sci. 658 012006

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3rd International Forum on Geoscience and Geodesy IOP Publishing IOP Conf. Series: Earth and Environmental Science 658 (2021) 012006 doi:10.1088/1755-1315/658/1/012006

Analysis on the Characteristics of Cultivated Land Change in DianChi Lake Basin based on remote sensing image processing technonlogy in the past 20 years

Min Gao1,4, Yi Luo3,4, Lina Shi1, and Chunxue Shang2,4* 1 School of Information Science and Technology, Normal University, Yunnan, 650500, 2 Dean’s Office, Yunnan Normal University, Yunnan, 650500, China 3 Faculty of Geography, Yunnan Normal University, Yunnan, 650500, China 4 GIS Technology Research of Resource and Environment in Western China, Ministry of Education, Yunnan Normal University, Yunnan, 650500, China *Corresponding author’s e-mail: [email protected]

Abstract. Cultivated land is the fundamental guarantee of agricultural production, accurate acquisition of information such as the area and distribution of cultivated land and the change characteristics of cultivated land is of great significance for agricultural resource monitoring and production. The development of remote sensing technology provides a new technical scheme for rapid and efficient extraction of cultivated land information. This article takes Dianchi Lake Basin as the research object to study the characteristics of cultivated land changes in Dianchi Lake Basin in the past 20 years. In the past 20 years, the distribution of cultivated land in the dianchi lake basin gradually changed from species concentration to decentralization, and showed a trend of gradually moving away from dianchi lake. Through the analysis of the dynamic attitude of land use, it is found that the cultivated land area in the dianchi basin has significantly changed between the land use in the past 20 years. From the perspective of the change trend and state index of single land use in the dianchi lake basin, the bidirectional transition of all land use in the region is frequent and extremely unbalanced. The area converted from cultivated land to non- cultivated land is larger than the area converted from non-cultivated land to this type. It develops towards the direction of scale reduction and is in the state of "falling trend".

1. Introduction Cultivated land is the foundation of agriculture and the entire national economy. The use of cultivated land is one of the key issues affecting the sustainable development of the region[1]. By analyzing the change law of cultivated land and its influencing factors, it can provide a theoretical basis for the dynamic balance and regulation of cultivated land in the region, help realize the sustainable use of cultivated land in the region, and has important significance for the study of the relationship between cultivated land protection and economic development.The relationship is important[2-4]. And the change of cultivated land also affects the change of impervious area in this area[5]. International research on land use changes officially began with the "Agenda 21" formulated by the United Nations in 1992. The "Agenda 21" formulated by the United Nations in 1992 marked the official beginning of international land use change research[6].

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3rd International Forum on Geoscience and Geodesy IOP Publishing IOP Conf. Series: Earth and Environmental Science 658 (2021) 012006 doi:10.1088/1755-1315/658/1/012006

Kunming's current rapid economic development and rapid population growth are the key reasons for the reduction of cultivated land in the Dianchi Lake Basin. Analyzing the change trend of cultivated land and the impact of urbanization development on cultivated land change can provide a reference for policy formulation. This study mainly uses satellite data of the Dianchi Lake Basin in the past 20 years to extract the cultivated land in the Dianchi Lake Basin, uses ENVI and ArcGIS software to analyze the temporal and spatial characteristics of the cultivated land changes in the Dianchi Lake Basin in the past 20 years, and provides a scientific basis for the formulation of government planning and development decision-making plans.

2. Study area and method

2.1. Study area The Dianchi Lake Basin is located in the middle of the Yunnan Plateau, in the three watershed areas of the Yangtze River, the Pearl River and the Red River. The drainage area is 2920 km2. The basin covers the and Wuhua in City, and most of the , and . The center of the basin is 1895 meters above sea level. It has a low- latitude plateau mountain monsoon climate. There is no severe cold in winter and no heat in summer. The annual average temperature is 15.1℃, the average annual rainfall is 1,075 mm, the average annual sunshine is 2,200 hours, and the frost-free period is more than 240 days. It is suitable for farming. The topography of the basin is generally high in the north and low in the south, with a long and narrow basin shape from north to south. For a long time, under the control of the address structure and other factors, an asymmetric stepped landform pattern with Dianchi as the center, wide on the south, north and east, and narrow on the west has been formed.

2.2. Data source and processing In the research process of this paper, Landsat series satellite images are used as the data basis. The Landsat series of remote sensing satellite data are downloaded from the official website of the United States Geological Survey (USGS). The Dianchi Lake Basin covers two sceneries. The strip numbers are 129/042 and 129/043 respectively. Due to the influence of natural factors such as climate, summer is selected as the remote sensing satellite image research season. In order to maximize the extraction accuracy, the image should be summer and cloudless remote sensing images. Choose a date when the cloud cover is less than 5%, and the image has no cloud cover, which is convenient for identifying and extracting cultivated land. The image acquisition dates are as shown in table 1: Table.1 Cloud-free image acquisition time. Year Statellite and sensor types Date Stripe

1999 Landsat-5 TM 1.24 129/(42、43)

2001 Landsat-7 ETM+ 6.14 129/(42、43)

2004 Landsat-5 TM 3.10 129/(42、43)

2008 Landsat-5 TM 4.6 129/(42、43)

2010 Landsat-5 TM 2.7 129/(42、43)

2013 Landsat-8 OLI/TIRS 4.20 129/(42、43) In this paper, the commonly used FLAASH model is used for radiometric correction of remote sensing images. This module has been integrated into the ENVI 5.3 and can be used directly. This method has high accuracy.Since the Dianchi Lake Basin in the study area is in the strip number 129/042, 129/043, the images need to be cropped and spliced, and the histogram matching method is used to splice the two images of each year.

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3rd International Forum on Geoscience and Geodesy IOP Publishing IOP Conf. Series: Earth and Environmental Science 658 (2021) 012006 doi:10.1088/1755-1315/658/1/012006

2.3. Research methods

2.3.1. Cultivated land extraction There are traditionally two methods for classification of mainstream remote sensing images: visual interpretation classification and computer automatic classification. This research uses computer automatic classification. Computer automatic classification is usually divided into two forms: unsupervised classification and supervised classification. In the image accuracy evaluation, it is mainly used to compare the classification result with the actual measured value, and the accuracy of the classification result can be displayed in a confusion matrix. The confusion matrix is calculated by comparing the position and classification of each measured pixel with the corresponding position and classification in the classified image.

2.3.2. Dynamic analysis method of cultivated land conversion According to the interpretation results of remote sensing images, the land use/cover Conversion Matrix model is used to analyze the direction and scale of land use/cover change transfer. The dynamics of land use/cover change are commonly expressed by three mathematical models: △𝑈 △ 𝑈 1 𝑅 100% (1) 𝑈 𝑇 Where: ∆U_out is the sum of the areas of a land use/cover type converted to other types during the study period T, ∆U_in is the sum of the areas converted from other types to this type, and U_a is a certain land use/ The area of the cover type, T is the study period, when T is set to year, RS is the average annual rate of change of a certain land use/cover type. △𝑈 △ 𝑈 1 𝑅 100% (2) 𝑈 𝑇 Where: △𝑈, △𝑈, 𝑈 and T are the same as above, and Rss is the degree of spatial change of a certain land use/cover type. △𝑈 △ 𝑈 𝑃 1 𝑃 1 (3) △𝑈 △ 𝑈 Where: △𝑈 and △𝑈 are the same as above, and Ps is the change trend and state index of a certain land use/cover type.

3. Results and analysis

3.1. Inspection of extraction accuracy The overall accuracy of supervised classification and unsupervised classification are 93.8% and 80.8%, respectively, and the kappa coefficients are 0.845 and 0.552, respectively. The results of supervised classification are better than unsupervised classification. Therefore, the analysis of cultivated land dynamics in this study uses this result.

3.2. Analysis of spatial characteristics of cultivated land changes In order to more accurately analyze the spatial change process of cultivated land in the Dianchi Lake Basin, the extracted cultivated land information is subjected to pixel-based focus statistics, and the sum value is calculated in units of 10*10 pixels and divided into 5 classes by equal distance. That is, very low cultivated land coverage (0% ＜ Coverage≤20%), low cultivated land coverage (20% ＜ Coverage≤40%), medium cultivated land coverage (40%＜Coverage≤60%), medium to high cultivated land coverage (60% %＜Coverage≤80%), high cultivated land coverage (80%＜Coverage≤100%), using ArcGis software to obtain the spatial change characteristics of cultivated land from 1999 to 2017 through the overlay analysis of the classification result map. Since 1999, the land has been concentrated around the Dianchi Lake Basin and distributed to the north of Dianchi Lake and the southeast of Dianchi Lake. Except for the surrounding areas of Dianchi

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3rd International Forum on Geoscience and Geodesy IOP Publishing IOP Conf. Series: Earth and Environmental Science 658 (2021) 012006 doi:10.1088/1755-1315/658/1/012006

Lake, the land distribution in other places is relatively dense. The Songhuaba Reservoir area to the north of Dianchi Lake is densely distributed. From 1999 to 2004, the arable land around the Dianchi Lake Basin became sparse. From 2004 to 2008, the area to the north of the Dianchi Lake Basin saw a significant decrease in arable land, and the area to the north has become increasingly sparser arable land. From 2008 to 2010, the decrease was most obvious. The cultivated land in the north and east of the Dianchi Lake Basin decreased significantly, and some areas directly decreased to nothing. From 2010 to 2013, the southeast area around the Dianchi Lake Basin decreased significantly. From 2013 to 2017, only the southeast area around the Dianchi Lake Basin retained relatively dense cultivated land, and the rest of the area was relatively sparse, with a small increase in cultivated land in the Songhuaba Reservoir area.

3.3. Change rate and dynamics of cultivated land in Dianchi Lake Basin The Markov conversion matrix was used to simulate the change of cultivated land in the Dianchi Lake Basin from 1999 to 2017. The conversion matrix is shown in the table 3 and table 4: Table.2 Conversion of cultivated land area from 1999 to 2008. 1999

2008 arable land Non-arable land total（km2） （km2） （km2）

arable land

（km2） 178.546 125.244 303.79 Non-arable land

（km2） 173.929 2361.448 2535.377 total（km2） 352.475 2486.692 2839.167 Table.3 Conversion of cultivated land area from 2008 to 2017. 2010

2017 arable land Non-arable land total（km2） （km2） （km2）

arable land

（km2） 71.435 121.9192 193.3542 Non-arable land

（km2） 232.355 2413.458 2645.813

total（km2） 303.79 2535.377 2839.167 Looking at the two 10 years, it is found that the amount of cultivated land has decreased significantly. This is because Kunming has gradually accelerated its economic development and urban construction during these ten years, because urban construction will inevitably occupy cultivated land, and Dianchi Lake is located in the center of Kunming and has a relatively relatively large terrain It is gentle and suitable for urban construction. Based on the above analysis, land use is not only affected by natural factors, but also by social, economic, historical and other human factors. It is highly comprehensive and regional[7]. Generally speaking, natural factors control the status and changes of land use in the general environment. Before human activities, the driving mechanism of land use change is mainly the change of the natural

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3rd International Forum on Geoscience and Geodesy IOP Publishing IOP Conf. Series: Earth and Environmental Science 658 (2021) 012006 doi:10.1088/1755-1315/658/1/012006

environment. Since then, with the emergence of human beings, human activities have become another important driving force for land use changes[8]. In this study, 2008 is the intermediate year, and the transfer dynamics for each of the nine years before and after are calculated, as shown in the table: Table.4 Transfer dynamics from 2008 to 2017. 1999~2008 2008~2017

𝑅 -3.03% -17.18%

𝑅 18.62% 55.10%

𝑃 -0.16273 -0.31172 It can be seen from the table that the RS values of the two 10-year periods from 1999 to 2008 and 2008 to 2017 are both negative, and the RS values from 2008 to 2017 are even greater. This shows that the area has decreased at a faster rate during this decade than in the previous decade.Reflect the dynamic degree model RSS of a certain land use/cover type in a certain period of time. From 1999 to 2008 and 2008 to 2017, the dynamics of spatial changes in the two decades have increased significantly, indicating that the cultivated land has also changed more and more spatially during these two decades, and the area of change has continued to increase.Reflect the change trend and state index model PS of a certain land use/cover type. It can be seen from the table that the value of PS is between -1 and 0, and PS is getting closer and closer to -1. The PS in the table is getting closer and closer to -1, indicating that the conversion direction of land types is mainly the conversion of cultivated land to non-cultivated land, presenting an extremely unbalanced state, causing the cultivated land area to gradually shrink.

4. Conclusion According to the data obtained from the research, it can be clearly seen that the cultivated land near the Dianchi Lake Basin has been decreasing year by year in the past 20 years. The analysis of comprehensive economic and cultural factors shows that the annual reduction and the spatial scope are not consistent. Through the computer automatic classification results and spatiotemporal characteristics analysis of the land use impact of the Dianchi Lake Basin during the 20 years from 1999 to 2017, the following conclusions are obtained: (1)In the past 20 years, the arable land in the Dianchi Lake Basin has been mainly distributed near the Dianchi Lake Basin, and the waters outside the Dianchi Lake are relatively scattered. Affected by factors such as climate, hydrology, topography, human activities, etc., the area of cultivated land has changed greatly in the past 20 years. (2)During the ten years from 1999 to 2008, since 1999, the land was more concentrated around the Dianchi Lake Basin and distributed to the north and southeast of Dianchi Lake. Except around Dianchi Lake, the land distribution in other places is relatively dense, and the Songhuaba Reservoir area to the north of Dianchi Lake is relatively densely distributed. Since then, the cultivated land has been decreasing year by year. Based on remote sensing data, this paper analyzes the characteristics of cultivated land changes in the Dianchi Lake Basin. The research shows that population growth and rapid economic development are the main driving forces of land use changes in the Dianchi Lake Basin. With population growth and economic development, the construction land in the Dianchi Lake Basin has expanded rapidly, and cultivated land and unused land have been continuously reduced. It can be clearly seen that the continuous population growth in the Dianchi Lake Basin has gradually aggravated the contradiction between land supply and demand.

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3rd International Forum on Geoscience and Geodesy IOP Publishing IOP Conf. Series: Earth and Environmental Science 658 (2021) 012006 doi:10.1088/1755-1315/658/1/012006

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