Taking Nanchang as the research area, analyzed and studied the characteristics of land use change in 2005, 2010, 2015 and 2020. The relationship between driving factors such as DEM, slope, and road distribution data was analyzed, and the above elements were selected as the driving factors of land use simulation in Nanchang to construct a CA-Markov model. Using a single land use dynamic, land use structure table, and land use transfer matrix method, coupled with land use classification and processed to predict the future development of land use in Nanchang of 2035.
Through remote sensing image extraction and land use dynamics formula calculation, the various land use areas of Nanchang City in 2005, 2010, 2015 and 2020 were classified and counted, and the land use status map of the four phases was obtained, and the land use situation was shown in Fig. 2. Agricultural land is the most widely distributed land type, dominating land use in various periods, and agricultural land has always accounted for more than 50%; followed by woodland and water areas, both accounting for about 16%; The proportion of unused land is getting smaller and smaller, the proportion of grassland and construction land is increasing, and the expansion rate of construction land is increasing. From 2010 to 2020, agricultural land continued to decrease, and the expansion rate of construction land further increased, while in the process of construction land expansion, the conversion of agricultural land and construction land was frequent, and the quality and quantity of cultivated land were greatly affected. From 2005 to 2020, the woodland continued to decrease, with a total decrease of 300.27 km2 in 15 years, which changed greatly from the quantitative point of view, and also showed that Nanchang's urban economic development should pay more attention to the coordinated development of ecology and agriculture. Unused land continued to decrease between 2005 and 2020, and unused land was developed for construction or converted into agricultural land. Base on remote sensing image extraction and land use dynamic formula calculation, various types of land use areas of Nanchang in 2005, 2010, 2015 and 2020 were classified and counted, and land use status maps of the four phases were obtained, as shown in Fig. 2.
3.1 Land use characteristics and transfer changes of Nanchang
Agricultural land is the most widely distributed type of land, and occupies a dominant position in the land utilization in all periods, with the proportion of agricultural land always above 50%. Next, woodland and water area both accounted for about 16%. The proportion of unused land decreased, the proportion of grassland and construction land increased, and the expansion speed of construction land increased rapidly. Agricultural land kept decrease from 2010 to 2020 (Table 3), and the expansion speed of construction land kept in increasing. In the process of construction land expansion, the transformation of agricultural land and construction land is frequently, which greatly affects the quality and quantity of cultivated land. From 2005 to 2020, woodland continued to decrease, with a total decrease of 300.27 km2 in 15 years. From the perspective of quantity, the change of woodland was large, which also reflected that the urban economic development of Nanchang should pay more attention to the coordinated development of ecology and agriculture to a certain extent. As for unused land, it decreased from 2005 to 2020, most of the unused land was developed into construction land or converted into agricultural land.
Table 3
Dynamic table of land use classification in Nanchang City, 2005–2020
| Area/km2 | Change/% | Area /km2 | Change /% | Area /km2 | Change /% | Area /km2 |
Time | 2005 | 2005–2010 | 2010 | 2010–2015 | 2015 | 2015–2020 | 2020 |
Agricultural land | 3901.22 | 0.79% | 3932 | -1.20% | 3884.81 | -1.35% | 3832.46 |
Woodland | 1202.07 | -1.18% | 1187.84 | -1.08% | 1175.07 | -23.18% | 902.64 |
Grassland | 92.74 | -17.93% | 76.11 | -0.05% | 76.07 | 311.46% | 313.69 |
Waters | 1159.53 | -3.44% | 1119.61 | 0.20% | 1121.9 | 14.81% | 1288.04 |
Construction land | 516.87 | 4.03% | 537.69 | 11.82% | 601.26 | 38.13% | 830.52 |
Unused land | 312.18 | 6.14% | 331.34 | -1.83% | 325.28 | -17.60% | 268.03 |
In the land transfer situation from 2005 to 2010, the changes of agricultural land and construction land were more obvious. The area of agricultural land transferred out from 2005 to 2010 was 72.05km2, the largest the part of which was converted into construction land, about 37.91km2, which shows that the expansion of construction land occupies serious agricultural land. In terms of transfers, agricultural land was the most transferred part, with 40.675km2, which was due to the conversion of woodland into agricultural land. For construction land, construction land increased by 20.825 km2 from 2005 to 2010, with agricultural land occupying the most. From the perspective of the total area of land types, the transferred area of agricultural land was greater than that of transferred out, and the total amount of agricultural land was increased. The transfer out of construction land is less than that of transfer in, and the transfer out part is mainly converted into agricultural land by the value of 21.894 km2, the total amount increases. The transfer of agricultural land in and out frequently, and the expansion speed of construction land is relatively fast. Both woodland and grassland have decreased, and unused land has increased, possibly because some water areas have increased due to water level change, resulting in an increase in unused land.
From 2010 to 2015, the more obvious land use transfer was still construction land and agricultural land. 6.158 km2 of construction land was transferred out, the value of which converted into agricultural land was 5.045 km2, and 69.711 km2 was transferred in construction land, of which mainly agricultural land and woodland were transferred. For woodland grasslands, woodlands and grasslands continued their decreasing trend. Unused land remained unchanged, and from the perspective of land use transfer matrix, the transformation of unused land and water area was still relatively frequently.
In the land use transfer from 2015 to 2020, the largest type of land transferred from agricultural land was construction with the value of 273.334 km2, and the largest transfer was woodland by 287.720 km2, for the woodland was used as farmland after land reclamation. For construction land, the largest transfer is agricultural land by 125.222 km2, because part of the construction land isreturned to farmland, and the most transferred is also agricultural land, and construction land occupies part of the agricultural land. From 2015 to 2020, agricultural land continued to decrease, woodland continued to decrease, and grassland and water areas increased, which may be caused by the abandonment of agricultural land.
According to the calculation results, the annual average change is mainly to construction land, and the dynamic change of single land use is more obvious, which is 4.03% in 2005–2010, 11.08% in 2010–2015, and 38.13% in 2015–2020, respectively. For agricultural land, due to the large base, the change is not obvious; The dynamics of single land use of woodland showed a decreasing trend year by year, which was − 1.18% in 2005–2010, -1.08% in 2010–2015, and − 23.18% in 2015–2020. The change of single land use dynamics of grassland is more obvious, of which 311.46% from 2015 to 2020, which may be due to the reduction of unused land, this paper classifies tidal flats into unused land, due to the change of water level may lead to the transformation of coastal tidal flats into grassland in some waters, grassland itself accounts for relatively small, so the land use dynamics are obvious when the change occurs, and the base of grassland area is small, and with the strengthening of urban expansion parks and community greening, the grassland area increases rapidly. As a whole, the use of land and woodland gradually decreased, while the area of water and grassland increased. The construction land expanded rapidly, and the agricultural use gradually decreased. It can be seen that urban development increased the use of land and woodland, and in the process of urban development, with the construction of parks and other landscapes, the area of water and grassland increased.
3.2 Predictive analysis of land use pattern in Nanchang
Taking 2010 land use as the base period and 2015 as the end period, the land use transfer probability matrix and land use suitability atlas were created. On this basis, 2015 is set as the base period, the land use status in 2020 is simulated, and the Kappa coefficient is used to quantitatively test according to the comparison between the simulation results and the actual 2020 land use results.
According to the simulation results, the Kappa value is 0.94, which proves that the simulation effect of the study area is good, and the land use of Nanchang in 2035 is simulated and predicted, and the error classification of the simulation results in 2020 is shown in Table 4. Through the area of land use change directly extracted and predicted in 2020, it can be seen that unused land, building land and agricultural land have quite high prediction effect, and the change is kept below 5%. Woodland, grassland, and water areas were slightly less effective, with a variation of 5-7.5%.
Table 4
Nanchang Land Simulation Error Table
Land types | Actual land use area of 2020/km2 | Projected land use area of 2020/km2 | E Error |
Agricultural land | 3832.46 | 3768.9 | -1.66% |
Woodland | 902.64 | 970.03 | 7.47% |
Grassland | 313.69 | 330.11 | 5.23% |
Waters | 1288.04 | 1192.5 | -7.42% |
Construction land | 830.52 | 801.36 | -3.51% |
Unused land | 68.03 | 68.62 | 0.86% |
Total | 7235.38 | 7131.52 | |
Use CA-Markov model to simulate land use, the accuracy of the simulation results is tested to ensure the rationality and effectiveness of the model. On the basis of passing the accuracy test, taking 2020 as the base period, the land use transfer probability matrix is entered, the land use suitability atlas is set to the prediction range of 15 years, and the land use in Nanchang City in 2035 is simulated and predicted, and the statistical analysis is obtained as shown in Table 5 and Table 6. From the perspective of land use structure changes (Figs. 2 and 3), agricultural land will not change much in 2035 and 2020, and will remain basically stable. Woodland has decreased slightly, from 12.48–11.12%, which also requires attention to environmental protection in social and economic development; The grassland and water area showed a decreasing trend, and the overall change was not obvious. For construction land, Nanchang accounted for 11.48% in 2020 and 15.83% in 2035, an increase of 306.31km2, which is also an inevitable trend of Nanchang's social and economic development; the overall change of unused land is not obvious, accounting for 0.79% in 2035 and 0.94% in 2020, respectively.
Table 5
Land use simulation structure table of Nanchang City
Land types | Actual land use area of 2020/km2 | Percentage | Projected land use area of 2035/km2 | Percentage | Land use change |
Agricultural land | 3832.46 | 52.97% | 3778.49 | 52.63% | -0.09% |
Woodland | 902.64 | 12.48% | 798.73 | 11.12% | -0.77% |
Grassland | 313.69 | 4.34% | 355.11 | 4.95% | 0.88% |
Waters | 1288.04 | 17.80% | 1054.21 | 14.68% | -1.21% |
Construction land | 830.52 | 11.48% | 1136.83 | 15.83% | 2.46% |
Unused land | 68.03 | 0.94% | 56.39 | 0.79% | -1.14% |
Total | 7235.38 | 100% | 7179.76 | 100% | |
Table 6
Land use transfer matrix from 2020 to 2035 (unit: km2)
2035/2020 | Agricultural land | Woodland | Grassland | Waters | Construction land | Unused land | Total |
Agricultural land | 3515.66 | 72.10 | 25.40 | 164.64 | 0.28 | 0.41 | 3778.49 |
Woodland | 11.67 | 729.90 | 38.91 | 18.26 | 0.00 | 0.01 | 798.73 |
Grassland | 50.77 | 51.09 | 242.67 | 10.48 | 0.01 | 0.10 | 355.11 |
Waters | 0.25 | 0.02 | 0.05 | 1037.53 | 0.00 | 16.38 | 1054.21 |
Construction land | 251.53 | 48.58 | 6.25 | 51.11 | 779.25 | 0.11 | 1136.83 |
Unused land | 1.21 | 0.00 | 0.02 | 4.37 | 0.00 | 50.79 | 56.39 |
Total | 3831.09 | 901.68 | 313.29 | 1286.39 | 779.54 | 67.79 | 3778.49 |
Transfer in | 262.83 | 68.84 | 112.45 | 16.69 | 357.58 | 5.61 | |
Transfer out | 315.42 | 171.79 | 70.62 | 248.86 | 0.29 | 17.00 | |
Change | -52.596 | -102.951 | 41.823 | -232.173 | 357.291 | -11.394 | |
From the perspective of land use simulation dynamics in Nanchang, agricultural land changed the least, and the annual land use dynamics were − 0.09%; and showed a decreasing trend, and the dynamic degree of single land use was − 0.77%. The increase in grassland may be caused by changes in topography, water and soil, and the single land use dynamic is 0.88%; In the land use simulation of Nanchang, the water area showed a trend of decrease in 2035, and the single land use dynamic degree was − 1.21%. The change of construction land is the most obvious, and the expansion of urban and rural construction land is relatively fast, mainly reflected in the junction of existing construction land and other land use types, and the dynamic degree of single land use is 2.46%; With regard to unused land, there was little change overall, with a single land-use dynamic of -1.14%, which is due to a normal decrease due to the use of land partially for use.
From the perspective of land use transfer matrix, agricultural land transfer in and out frequently, agricultural land mainly transferred out of the land category is grassland and construction land, of which construction land accounts for a relatively large amount, 251.53 km2, which to a certain extent shows that the expansion of construction land may occupy cultivated land, so in the future land use in Nanchang City, more attention should be paid to the divination balance of cultivated land and the protection of cultivated land, the transferred land types are woodland and water area, respectively, 72.10 km2 and 164.64 km2, This may be due to climatic conditions as well as hydrological changes; Some of the woodland is converted into construction land and agricultural land, and the conversion area is small; The transfer of grassland is mainly agricultural land and woodland, and some grassland suitable for agriculture and forestry is converted into agricultural land and woodland; Regarding construction land, there are almost no transfers, mainly agricultural land, land and water areas, which are 251.53 km2, 48.58 km2 and 51.11 km2 respectively, and the construction scale has expanded significantly compared with 2020. For unused land, from the simulation results, from 2020 to 2035, the area will change from 67.79 km2 to 56.39 km2, showing an overall decreasing trend, but the change is not much, from urban development to occupy part of the unused land, but most of the unused land is retained, which is related to the ease of use of this part of the unused land.
From the perspective of natural factors, agricultural land, woodland, grassland and water area are greatly affected by the elevation slope. However, construction land is greatly affected by convenient transportation, and the old construction land as the starting boundary of expansion has driven the transformation of surrounding land use, resulting in frequent land use type changes within this range. From the perspective of land use structure changes, agricultural land will not change much in 2035 and 2020, and it will remain basically stable. Woodland has decreased slightly, from 12.48–11.12%, which also requires attention to environmental protection in social and economic development; The grassland and water area showed a decreasing trend, and the overall change was not obvious. For construction land, Nanchang accounted for 11.48% in 2020 and 15.83% in 2035, an increase of 306.31km2, which is also an inevitable trend of Nanchang's social and economic development; the overall change of unused land is not obvious, accounting for 0.79% in 2035. From the perspective of land use simulation dynamics in Nanchang, agricultural land changed the least, and the annual land use dynamics were − 0.09%; Woodland showed a decreasing trend, and the dynamic degree of single land use was − 0.77%. The increase in grassland may be caused by changes in topography, water and soil, and the single land use dynamic is 0.88%; In the land use simulation of Nanchang, the water area showed a trend of decrease in 2035, and the single land use dynamic degree was − 1.21%. The change of construction land is the most obvious, and the expansion of urban and rural construction land is relatively fast, mainly reflected in the junction of existing construction land and other land use types, and the dynamic degree of single land use is 2.46%; With regard to unused land, there was little change overall, with a single land-use dynamic of -1.14 per cent, which is due to a normal decrease due to the use of land partially for use. From the perspective of land use transfer matrix, agricultural land transfer in and out frequently, agricultural land mainly transferred out of the land category is grassland and construction land, of which construction land accounts for a relatively large amount, 251.53km2, which to a certain extent shows that the expansion of construction land may occupy cultivated land, so in the future land use in Nanchang City, more attention should be paid to the divination balance of cultivated land and the protection of cultivated land, the transferred land types are woodland and water area, respectively, 72.10 km2 and 164.64 km2, This may be due to climatic conditions as well as hydrological changes; Some of the woodland is converted into construction land and agricultural land, and the conversion area is small; The transfer of grassland is mainly agricultural land and woodland, and some grassland suitable for agriculture and forestry is converted into agricultural land and woodland; Regarding construction land, there are almost no transfers, mainly agricultural land, wood land and water areas, which are 251.53 km2, 48.58 km2 and 51.11 km2 respectively, and the construction scale has expanded significantly compared with 2020. For unused land, from the simulation results, from 2020 to 2035, the area will change from 67.79 km2 to 56.39 km2, showing an overall decreasing trend, but the change is not much, from urban development to occupy part of the unused land, but most of the unused land is retained, which is related to the ease of use of this part of the unused land. From the perspective of natural factors, agricultural land, woodland, grassland and water area are greatly affected by the elevation slope. However, construction land is greatly affected by convenient transportation, and the old construction land as the starting boundary of expansion has driven the transformation of surrounding land use, resulting in frequent land use type changes within this range.