Estimation and simulation of carbon emissions in Great Xi’an based on grid and patch-generated land-use simulation models

Land use change leads to substantial changes in regional carbon emissions, and estimating changes in carbon emissions caused by land use change provides an important practical reference for promoting the regional realization of “dual carbon” goals. This study aimed to investigate the spatial and temporal evolution patterns of land use types and their carbon emission effects in the Great Xi’an area from 1990 to 2020 and to predict its future carbon emission characteristics. Therefore, in this study, carbon emissions and carbon intensity involving the study area were estimated based on the emission factor method on two scales, administrative units and grids, and carbon emission characteristics of the study area in 2025 and 2030 were simulated using a patch-generated land-use simulation model. The results showed that: 1) from 1990 to 2020, the area of cultivated land continued to decrease, with an average annual decrease of 21.86 km²; the fluctuation of forest land, grassland, and water areas decreased, with an average annual decrease of 0.28 km², 1.69 km² and 0.08 km², respectively; and construction land area continued to expand, with an average annual expansion area of 23.88 km². The area of unused land fluctuated and increased by 1.14 km². 2) From 1990 to 2020, carbon emissions in Great Xi’an increased from 280.00 t∙a⁻¹ to 2342.27 t∙a⁻¹, with an average annual growth of 68.74 t. From 2005 to 2010, it had the fastest growth rate of carbon emissions with an average annual growth of 125.86 t, whereas from 1990 to 2000, these grew at the slowest rate, averaging only 10.06 t per year. Whereas spatial distribution patterns were generally high in the south and low in the north, carbon emissions of Chang’an District in the south of the study area were much higher than those of Yanliang District in the north. 3) From 1990 to 2020, the maximum carbon emission intensity in Great Xi’an increased from 7461.94 t(C)∙km⁻²∙a⁻¹ to 45 400.90 t(C)∙km⁻²∙a⁻¹, an increase of nearly five-fold. In terms of space, the carbon emission intensity in the region always exhibited a distribution pattern of high in the north and low in the south, the carbon emission intensity of the main city of Great Xi’an was much higher than that of other regions. 4) Between 2025 and 2030, cropland and forest land will continue to be the primary land-use types in the Great Xi’an area, with the sum of their areas accounting for 63.53% and 62.45% of the total study area, respectively. From 2020 to 2030, the areas of cropland, forest land, water, and unused land in the region will continue to decrease, whereas the areas of grassland and construction land will increase. The total carbon emission increased by 2.96×10⁷ t(C)∙a⁻¹, and the carbon emission intensity revealed a distribution pattern of high in the east and low in the west. Carbon emissions and their intensity in the Great Xi’an region have increased rapidly over the past 30 years.