Analysis of the area changes of different land types in Xinjiang

Research using CLCD dataset (https://doi.org/10.5281/zenodo.4417809) of xinjiang in 2000, 2004, 2008, 2012, 2026, 2022, the land use status data for the raw data, The area changes of cropland, forest, grassland, impervious and barren in Xinjiang from 2000 to 2022 were fabricated by reclassifying land use types using ArcGIS10.8 software (Fig. 2; Table 3).

Based on the land area data presented in Table 3, the overall trend shows a continuous increase in cropland, forest, water, and impervious, with a decrease trend in grassland. The area of barren also exhibits a downward trend, but its area increased after 2020. Table 3 shows the dynamic changes in LU area in Xinjiang from 2000 to 2022. The expansion of impervious areas was the most significant. Between 2000 and 2022, their area increased by 4145.468 km, with an average annual growth of 188.430 km. Cropland expanded continuously from 2000 to 2016, increasing by a total of 25,782.98 km. However, it decreased between 2016 and 2020 before increasing again by 2022. Water first increased and then decreased. It grew by 7483.10 km from 2000 to 2016, but declined by 5078.73 km from 2016 to 2022. Cropland expanded continuously from 2000 to 2016, increasing by a total of 25,782.98 km. However, it decreased between 2016 and 2020 before increasing again by 2022. Water first increased and then decreased. It grew by 7483.10 km from 2000 to 2016, but declined by 5078.73 km from 2016 to 2022. Barren first decreased and then increased. It decreased by 27,005.373 km² from 2000 to 2016. Subsequently, its area started to increase, adding 10,892.911 km² from 2016 to 2022. However, overall from 2000 to 2022, there was a net decrease of 16,112.409 km². Analyze the reasons, from the perspective of natural factors, the Xinjiang region is ecologically fragile, characterized by sparse vegetation and diverse types of soil erosion with complex interactions. The interplay of water, wind, and frost actions exacerbates the issue of soil erosion. Additionally, the region's climate, marked by frequent winds and scarce rainfall, intensifies the wind erosion. Regarding human factors, the pastoral industry in Xinjiang is well-developed, yet some herding practices employed by pastoralists over the long term have led to excessive depletion of grassland vegetation and severe soil erosion. This has resulted in overgrazing and significant degradation of grasslands, leading to a sharp reduction in grassland area and an escalating conflict between grazing animals and vegetation. Population growth and the inappropriate development and utilization of water and soil resources have also been significant contributors to the destruction of surface vegetation and the intensification of soil erosion.

The shift matrix for LU changes in Xinjiang from 2000 to 2022 is presented in Table 4. With respect to the changes in grassland, a total of 114,555 km of grassland was converted to other land types. The main transformations were into forest, cropland, and barren, with 67,705 km of grassland converting to barren. This shift may be attributed to the well-developed livestock industry in Xinjiang, where overgrazing could lead to the degradation of pastures. According to Xinjiang's livestock statistics (in 2022, the inventory of pigs, cattle, and sheep reached 59.8565 million, an increase of 6.5% from the previous year), livestock numbers have been continuously increasing. This has led to the increasingly prominent issue of livestock carrying capacity exceeding the standard. This undeniably accelerates the process of grassland desertification and severely damages the grassland ecosystem.

In terms of forest changes, 8286 km of forest has been converted to other land types, with more than 85% being transformed into cropland. This reflects the increasing demand for agricultural products as Xinjiang's population grows and living standards rise. To meet this demand, some forests have been converted into cropland. This expansion of agricultural land aims to increase food production. However, the reduction in forests may also lead to issues such as soil erosion and climate change.

With respect to the changes in cropland, a total of 18,110 km of cropland has been converted to other land uses. Of this, nearly 75% was transformed into grassland. This data fully demonstrates the significant success of the cropland conversion to grassland policy in Xinjiang. After 2002, Xinjiang officially launched large-scale implementation of this policy, gradually converting cropland in ecologically fragile areas into grassland. The implementation of this policy helps restore grassland ecosystems, improve the regional ecological environment, and also promotes the sustainable development of animal husbandry, achieving a positive interaction between ecological protection and economic development.

Regarding the changes in water, a total of 15,140 km of water has been converted to other land uses, with more than 75% transformed into barren. This indicates a significant degradation of water in Xinjiang. On one hand, this may be influenced by Xinjiang's natural environmental factors, such as arid climate and high evaporation. On the other hand, human activities like excessive groundwater extraction and irrational water resource allocation have accelerated the shrinkage and degradation of water. This adversely affects aquatic ecosystems, as well as the ecological environment and economic development in surrounding areas.

In terms of the changes in barren, a total of 84,216 km of barren has been converted to other land uses. This mainly includes grassland, cropland, and impervious. This indicates that over the past two decades, Xinjiang has experienced rapid economic development and urbanization. Specifically, 68,581 km of barren has been transformed into grassland. This indicates that Xinjiang has taken proactive and effective measures in ecological governance and restoration. For example, large-scale afforestation, grass planting, and desertification control projects have been implemented. These efforts transformed vast barren into ecologically functional grassland, thereby improving the regional ecological environment and enhancing the land's ecological value. Simultaneously, economic growth requires more land for agricultural expansion to ensure food security and agricultural product supply. Urbanization also demands extensive impervious for infrastructure, housing, and industrial development. These factors drive the conversion of barren into cropland and impervious, contributing to Xinjiang's socio-economic development.

The carbon emissions from cropland, forest, grassland, water, and barren in Xinjiang from 2000 to 2022 are obtained through LU data. Subsequently, the indirect carbon emissions from impervious in Xinjiang are calculated based on energy consumption data. This results in the total carbon emissions from LU in Xinjiang from 2000 to 2022 (as shown in Fig. 3). Temporally, the net carbon emissions from LU in Xinjiang increased from 15,886.954 thousand tons in 2000 to 162,302.518 thousand tons in 2022, with an annual growth rate exceeding 10%, demonstrating a strong growth trend. In contrast, the total carbon absorption in Xinjiang grew slowly from - 3317.309 thousand tons in 2000 to - 3607.063 thousand tons in 2022. Compared with other studies, Zhang Ruqian et al. found that the net carbon emissions from LU in Xinjiang increased to 1.269 × 10 tons from 2000 to 2018, which is relatively close to the data in this study.

Table 5 presents the total carbon emissions (absorption) from various types of land in Xinjiang from 2000 to 2022. Viewing the total carbon emissions (absorption) by land type, the emissions from cropland and impervious in Xinjiang have been continuously increasing, with the growth rate of carbon emissions from impervious being particularly rapid. This, to some extent, reflects the rapid economic development and significant urbanization in Xinjiang from 2000 to 2022. The rapid economic development has led to increased industrial, commercial, and residential energy demands. As urbanization accelerates, urban construction and infrastructure continue to improve, expanding the scale of impervious, which has resulted in the rapid growth of carbon emissions from this land type. The carbon absorption of forest, grassland, and water has remained relatively stable during the study period, with forest and water showing a slow growth trend in carbon absorption, while grassland carbon absorption has shown a declining trend.

Figure 4 illustrates the evolutionary trend of carbon emissions across 14 cities in Xinjiang from 2000 to 2022. Spatially, the main concentration of LU carbon emissions is in the eastern and western regions, with Urumqi at the center. The distribution of carbon emissions in these cities generally corresponds to their economic output, suggesting a strong correlation between economic development and carbon emissions. From 2000 to 2008, Urumqi and Karamay were the primary contributors to LU carbon emissions. As urbanization intensified around Urumqi, LU carbon emissions rose sharply. By 2022, the number of major cities with significant LU carbon emissions in Xinjiang increased from 2 to 6, predominantly in the eastern and western parts of the region. This shift indicates a changing pattern of LU carbon emissions, expanding beyond traditional economic centers to more cities.

In terms of the growth rate of LU carbon emissions, both Yili and Hami have experienced a remarkable surge, ascending from the third tier in 2000 to the first tier in 2022, demonstrating a strong growth trend. Geographically, Yili is a pivotal corridor connecting Xinjiang with Central Asia, West Asia, and Europe, offering unique location advantages and serving as an important platform for foreign trade and border cooperation. Hami, situated in the eastern part of Xinjiang, is a key node city on the Silk Road Economic Belt. Its strategic location and convenient transportation make it a pivotal city for Xinjiang to enhance connectivity with inland regions and neighboring countries. With the advancement of the national "Belt and Road" initiative and the rapid development of Xinjiang, both Yili and Hami are set to have broader development prospects.

To further analyze the spatial changes in LU carbon emission in Xinjiang, ArcGIS 10.8 software was used to create standard deviation ellipses and shifts in the center of gravity for LU carbon emission from 2000 to 2022 (as shown in Fig. 5). The spatial distribution of LU carbon emission in Xinjiang exhibits a significant east-west trend. From 2000 to 2022, the standard deviation ellipses of LU carbon emission in Xinjiang primarily encompass cities such as Urumqi, Changji, and Karamay, which are important economic centers in the region and likely have relatively high levels of LU carbon emission.

As indicated in Fig. 5, the center of gravity of LU carbon emission in Xinjiang shows an overall migration trend from the central-northern part of the region towards the southeast from 2000 to 2022. The regional differences in economic development across Xinjiang are pronounced, with the central-northern areas mainly engaged in traditional agriculture, animal husbandry, and tourism, which consume less energy. In contrast, the southeastern areas are dominated by industry, services, and other sectors with higher energy demands. This difference in industrial structure may lead to changes in LU patterns and carbon emission intensity, thereby influencing the migration of the carbon emission center of gravity in Xinjiang.

Figure 6 presents the locational map of carbon balance in Xinjiang from 2000 to 2022. From 2000 to 2012, regions in Xinjiang that achieved carbon balance were primarily those with weaker economic development, such as Hetian. These areas, characterized by lower population densities and slower expansion of impervious and cropland, had a relatively low energy demand. This resulted in the carbon emission from impervious and cropland being less than the carbon sequestration by forests and grasslands.

After 2012, all 14 regions in Xinjiang entered the non-carbon balance zone, indicating an accelerated pace of urban construction in Xinjiang. On one hand, the increase in population density led to the expansion of impervious and an increased demand for energy, thereby raising carbon emissions from impervious and cropland. On the other hand, due to the expansion of population and economic activities, there was a reduction in forested and grassland, leading to a decline in carbon sequestration capacity and disrupting the original state of carbon balance.

Therefore, while amidst the process of rapid urban expansion, Xinjiang should comprehensively consider how to balance economic development with environmental protection. On one hand, it is imperative to augment efforts in ecological protection and restoration to rehabilitate and augment the carbon sequestration capabilities of natural ecosystems. On the other hand, the development of a low-carbon economy and circular economy should be considered to improve energy efficiency and reduce carbon emissions.

Using formulas (3) and (4), the ECE and ECS values for Xinjiang's 14 regions were calculated. Based on these coefficients, the regions were categorized into carbon sink functional areas, low-carbon economic areas, carbon intensity control areas, and high-carbon optimization areas (Fig. 7), and the criteria for the functional area classification are outlined in Table 6. This zoning serves as a reference for future carbon emission reduction policies and development strategies in various regions across Xinjiang.

For Xinjiang's main functional zone planning, the study divides the areas based on development content into optimized development zones, key development zones, major agricultural product production zones, and key ecological function zones, as shown in Fig. 5.

Spatial and temporal evolution of land use carbon emission and carbon balance zoning: evidence from Xinjiang China - Scientific Reports