Multi-Scenario Land Use/Cover Change and Its Impact on Carbon Storage Based on the Coupled GMOP-PLUS-InVEST Model in the Hexi Corridor, China

Abstract

Understanding the relationship between land use and carbon storage is vital for achieving sustainable development goals. However, our understanding of how carbon storage develops under land policy planning is still incomplete. In this study, a comprehensive framework that integrates Gray Multi-objective Optimization Programming (GMOP), the Patch-generating Land Use Simulation (PLUS) model, and the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) models is introduced to evaluate land use dynamics and ecosystem services. Two scenarios have been established to estimate Land Use and Land Cover Change (LUCC) patterns in the Hexi Corridor by 2035: the business-as-usual (BAU) scenario, developed based on historical trends, and the ecological conservation scenario (ECS), optimized with multiple policy objectives. The results show the following: (1) From 2000 to 2020, the predominant land use type in the Hexi Corridor was unutilized land, with LUCC mainly involving the transformation of unutilized land to grass land. (2) Carbon storage in the Hexi Corridor increased by approximately 9.05 × 10⁶ t from 2000 to 2020 due to LUCC, characterized by higher levels in the south and lower levels in the north. (3) The areas of grass land and arable land are expected to continue increasing until 2035, while the extent of unutilized land is projected to decrease. The ECS is poised to create a balance between ecological protection and economic development. (4) By 2035, both the BAU scenario and ECS estimate an increase in the carbon storage of the Hexi Corridor, with the ECS expected to result in the most significant gains. These research findings provide valuable insights for administrators and researchers, guiding more rational land use planning and ecological restoration policies to achieve carbon peaking and neutrality.

1. Introduction

Greenhouse gas emissions, particularly those of carbon dioxide, are exacerbating the effects of global warming, presenting a critical climate issue with extensive effects on global ecosystems [1,2]. Elevating carbon storage is an effective measure to decrease CO₂ emissions, serving as a vital approach to alleviate global climate change [3]. Additionally, as the main basis of human livelihoods and well-being, land plays a salient role in the global climate system; in particular, land use/cover change (LUCC) can ultimately affect the regional carbon cycle process by directly affecting vegetation biomass and soil carbon sequestration capacity [4]. On the other hand, with the development of human economy and society, the increasing intensity of land development has also led to a large amount of terrestrial carbon loss. Therefore, the impact of LUCC on carbon storage has received extensive attention in the field of climate change [5,6,7].

Consequently, numerous countries have set targets to achieve net-zero carbon emissions [8], aiming for a balance between carbon emissions and natural absorption. As the world’s largest developing country and carbon emitter, China has actively responded to climate change challenges. This commitment includes reducing anthropogenic carbon emissions, enhancing ecosystem carbon storage, attaining the carbon peak by 2030, and achieving carbon neutrality by 2060, collectively known as the dual carbon target [9]. However, rapid urbanization, while fostering economic growth, has also led to the inevitable encroachment of ecological land, adversely affecting the overall carbon storage of terrestrial ecosystems. Therefore, studying the past and projected impacts of Land Use and Land Cover Change (LUCC) on carbon storage in China’s terrestrial ecosystems is crucial for regional sustainable development.

Land use significantly influences carbon storage in terrestrial ecosystems [10]. Numerous studies have examined how various land use types affect carbon storage. Li et al. employed the InVEST model to show that ecological engineering on the Loess Plateau from 2000 to 2016 increased the area of ecological land, resulting in enhanced regional carbon storage [11]. Similarly, Ouyang et al. conducted a hotspot analysis and spatial autocorrelation modeling to determine that urbanization in China’s urban agglomerations from 1995 to 2018 led to a reduction in carbon storage [12]. However, these studies do not reflect the future spatiotemporal dynamics of land use and carbon storage. Consequently, optimizing carbon storage via strategic LUCC scenario planning is garnering heightened interest [13,14,15]. Simulation methods for LUCC are mainly classified into two types: bottom-up and top-down approaches. [16]. Presently, predominant bottom-up models comprise cellular automata–Markov [17], CLUE-S [18], FLUS [19], and PLUS [20]. These methods allocate land use types to suitable locations, and they depend on specific conversion rules. However, these methods are limited in their capacity to quantitatively optimize land use structures and do not adequately address the synergistic optimization of multiple objectives, including economic, social, and ecological benefits [21]. While the top-down approach effectively optimizes LUCC structures, it does not adequately reveal the spatial distribution of LUCC [22]. Thus, combining LUCC planning policies with multi-objective optimization algorithms in simulation leads to outcomes that more accurately reflect real-world scenarios and offer greater reference significance.

Sample land inventories [23], carbon density assessments [24], and biogeochemical models (e.g., Biome-BGG [25], Century [26], and CEVSA) are principal methods for estimating carbon storage. Sample land inventories offer precise data for small-scale, budget-limited studies; however, their cost-effectiveness diminishes with large-scale applications [27]. The complexity of biogeochemical models can compromise their accuracy in regional carbon storage assessments due to the numerous field parameters tied to specific landscape features [28,29]. Compared to other models, the InVEST model, as a leading tool for carbon density assessment, boasts advantages including minimal data requirements, rapid computation, and high accuracy [30,31]. However, results of the model heavily depend on the precision of carbon density inputs. Consequently, it is essential to adjust carbon density values for different carbon pools in line with regional and local conditions, enhancing the precision of carbon storage assessments.

Besides carbon density, the precision of the InVEST model in estimating carbon stocks is significantly influenced by LUCC. Although the InVEST and PLUS models have been integrated to estimate the spatial and temporal patterns of LUCC, there has been limited research on the synergistic optimization of the quantity, spatial arrangement, and benefits of LUCC within the framework of future development scenarios and policy objectives. As a crucial tool in land use optimization research, the GMOP approach addresses multiple conflicting objectives, suggesting development pathways that enhance the overall utility of land use. The combined “GMOP-PLUS-InVEST” model augments the reliability of future scenario projections, thereby enhancing the simulation accuracy of LUCC and carbon storage.

The Hexi Corridor is crucial for realizing the dual carbon goal, as it serves as both a major industrial hub and a significant energy user in Gansu province. The Carbon Peak Implementation Plan [32], promulgated in 2023, highlighted the need to increase the carbon sink capacity in the Hexi Corridor. In the present study, using revised carbon density data, we computed regional carbon stocks, applied Gray Multi-objective Optimization Programming (GMOP) to determine land use requirements under policy directives, and integrated this with the PLUS model to examine land conversion guidelines contained in the Gansu province land use and ecological restoration master plan. We introduced the “GMOP-PLUS-InVEST” framework to assess spatial patterns in the Hexi Corridor from 2000 to 2020 and to estimate carbon storage through to 2035. The purpose is to clarify the influence of LUCC on carbon storage in the Hexi Corridor from 2000 to 2035 and determine the optimal development path. The research objectives are as follows: (1) analyze the effects of spatiotemporal changes in LUCC on carbon storage in the Hexi Corridor during 2000–2020; (2) provide quantitative estimates and spatial simulations of LUCC in the Hexi Corridor for 2035 under business-as-usual and ecological conservation scenarios; (3) examine the spatiotemporal distribution of carbon storage in 2035 under BAU scenario and ECS. Overall, this study estimated carbon storage using revised carbon density metrics and integrated policy-based quantitative limitations into land use simulations. Compared to previous studies, our predictions more closely align with realistic planning. These findings offer a new perspective on addressing climate change and provide decision-making support for sustainable development in arid and semi-arid areas, exemplified by the Hexi Corridor.

2. Materials and Methods

2.1. Study Area

The Hexi Corridor (92°21′–104°45′ E, 37°15′–41°30′ N) lies in northwest Gansu Province, China (Figure 1a). Nestled between the Qilian Mountains and the Badian Jaran Desert, it is a key transport route on the Silk Road. Spanning five prefecture-level cities—Jiuquan, Jiayuguan, Zhangye, Jinchang, and Wuwei, with a total population of 4,071,600—the corridor occupies about 271,000 km², half of the area of Gansu Province (Figure 1b). The terrain is marked by dramatic elevation changes, with the Qilian Mountains in the south rising above 4000 m [33], providing ample meltwater for irrigation in the oasis areas. This results in a unique landscape pattern: the southern region is a critical surface-water supply area, the central area serves as the primary zone for production and habitation, and the northern region plays a key role in wind and sand control (Figure 1c). Located in the arid and semi-arid zones of northwest China, the dry climate and sparse rainfall of the region contribute to a fragile ecosystem vulnerable to climate change, and is a crucial component of China’s ecological security strategic pattern—“Three Barriers and Four Belts” [34]. As a principal area for ecological engineering in China, including projects like the Three-North Shelterbelts (in order to improve the ecological environment, the Chinese government has built large-scale artificial forestry ecological projects in northwest, north and northeast China), Grassland Desertification Control [35], and the Return Grazing Land to Grassland initiative [36], the Hexi Corridor has experienced a 3.2% increase in fractional vegetation coverage from 2000 to 2020, which also gives the Hexi Corridor a significant carbon storage capacity [37] (Figure 1d). Its role as a major industrial center in Gansu Province leads to rapid economic and urban expansion, challenging the carbon equilibrium and exacerbating land use conflicts. Therefore, selecting the Hexi Corridor to simulate land use scenarios and study carbon storage dynamics is a well-founded decision.

2.2. Data Sources and Processing

This study utilized the following data sources: (1) Land use/cover information from 2000 to 2020 was obtained from the China Land Cover Dataset (CLCD), provided by Wuhan University, with a 30 m resolution. (https://essd.copernicus.org, accessed on 14 February 2023) [38]. This dataset has an overall accuracy of 79.31%, demonstrating high interpretative accuracy. Following the LUCC system of the Chinese Academy of Sciences and adapting to the unique land use traits of Hexi Corridor, land cover was classified into six categories: arable, forest, grass, water, construction, and unutilized lands. (2) Digital Elevation Model (DEM) data with a 30 m resolution, derived from ASTER GDEM, was accessed from the Geospatial Data Cloud (http://www.gscloud.cn, accessed on 20 March 2023). The slope and aspect were derived from DEM data. (3) Average temperature and precipitation information were acquired from the National Earth System Science Data Center (http://www.geodata.cn, accessed on 10 March 2023), while data regarding nature reserves were sourced from the China Nature Reserve Specimen Resource Sharing Platform (http://www.papc.cn, accessed on 22 January 2023). (4) Information on administrative divisions, population density, GDP, NDVI, vegetation, and soil was collected from the Resource and Environmental Sciences and Data Center, Chinese Academy of Sciences (http://www.resdc.cn, accessed on 18 March 2023.). (5) Road vector data were sourced from the National Basic Geographic Database (https://www.webmap.cn, accessed on 3 April 2023), used to compute Euclidean distances.

All data underwent preprocessing to align with the WGS_1984 coordinate system, adopt a consistent resolution of 1 km, and maintain uniform row and column numbers, using the ArcGIS 10.8 software.

2.3. Methodology

This study employed a research framework comprising three main components, as illustrated in Figure 2. First, we conducted a simulation to quantify LUCC demand in 2035 under two different scenarios using the Markov and GMOP models. Second, the PLUS model helped to distribute the future LUCC amounts to appropriate locations based on spatial requirements. Ultimately, the carbon storage and sequestration module of the InVEST model was employed to assess alterations in carbon storage under both scenarios.

2.3.1. Optimization of LUCC Structure Based on GMOP

The GMOP model integrates gray linear regression with multi-objective programming to address uncertainties in goal functions and constraints related to LUCC [39]. It also resolves multiple objectives that are critical for optimizing LUCC structures [40]. The model construction involves defining decision variables, formulating objective functions, establishing gray constraints, and selecting appropriate solution techniques.

Decision Variables

In this study, we identified decision variables reflecting the land use and regional characteristics of the Hexi Corridor, specifying six categories: arable land, forest land, grass land, water areas, construction land, and unutilized land.

Decision Variables

Considering the important ecological barrier function of the Hexi Corridor, we delineated two scenarios for this study: a business-as-usual (BAU) scenario and an ecological conservation scenario (ECS).

BAU Scenario: Follow the natural evolution of LUCC without adding additional restrictions. Specifically, the projected areas for each land use category in 2035 under the business-as-usual scenario were estimated with a Markov model, employing a transition probability matrix based on data from 2000 to 2015.

ECS: Guided by the Gansu Province land use master plan and ecological restoration plan, the emphasis is on enhancing ecological benefits without compromising economic benefits. The GMOP framework is applied to develop ECSs.

$$F_1\left(x\right)=max{\displaystyle \sum }_{j=1}^n{c}_j{x}_j$$

(1)

Here, F₁(x) represents the total carbon storage, x_j represents the decision variables linked to various land use categories, and c_j indicates the carbon density per unit area for each of these variables. Specifically, x₁ through x₆ correspond to the areas of arable land, forest land, grass land, water areas, construction land, and unutilized land, respectively. We predicted the values of c_j for 2035 using the GM (1.1) model. Specifically, the c_j values (in units of CNY 10/km²) for x₁ through x₆ were 8.6911, 15.4525, 8.3087, 0.0213, 0.0177, and 1.9592, respectively.

Constraint Conditions

(1)

Total land:

The sum of the areas represented by each land use decision variable must equal the total land area of the study region.

$$x_1+x_2+x_3+x_4+x_5+x_6=\mathrm{417,652}$$

(2)

(2)

Arable land:

Given its status as a vital food-producing hub within an arid region, the Hexi Corridor necessitates a judicious increase in arable land from the 2020 baseline, ensuring that it remains within 120% of the BAU scenario, in consideration of the constrained water resources in the region.

$$\mathrm{23,195}\le x_1\le \mathrm{30,838}$$

(3)

(3)

Forest land

In alignment with the objectives set forth in the “Gansu Province Overall Territorial Space Plan (2021–2035)” [41] to bolster forest cover protection and development, imperative measures for ecological construction and the augmentation of forest coverage are required. Consequently, the area designated for forest land must surpass the extent recorded in 2020, yet not exceed 120% of the BAU scenario.

$$4448\le x_2\le 5336$$

(4)

(4)

Grass land

In accordance with the “Gansu Province Territorial Ecological Restoration Plan (2021–2035)” [42], which is dedicated to facilitating the transition from pasture to grass land and establishing artificial grasslands, there is an observed expansion in the area of grasslands. Consequently, the area allocated for grasslands should surpass the measurements recorded in 2020, yet it must not exceed 120% of the projection established in the BAU scenario.

$$\mathrm{92,793}\le x_3\le \mathrm{118,086}$$

(5)

(5)

Water area

Based on the growth trajectory from 2000 to 2020, as projected by the Markov chain analysis, the aquatic area is anticipated to reach 3073.2 km² under the BAU scenario. This expansion is largely attributable to the vigorous execution of government initiatives aimed at the ecological restoration of lakes, thereby bolstering water conservation efforts. In accordance with the “Gansu Province Territorial Ecological Restoration Plan (2021–2035)”, the proposed efforts aim to increase the protection of wetland. Given that a portion of this project has already reached completion within the study region, we believe that, under the ECS, by 2035, the lower limit of the water area of the Hexi Corridor should be higher than the current value in 2020, and the upper limit should be slightly larger than the BAU scenario (limited by the planned engineering volume).

$$2596\le x_4\le 3148$$

(6)

(6)

Construction land

In accordance with the “Gansu Province Overall Territorial Space Plan (2021–2035)”, there will be a drive towards urbanization and the intensive development of construction land. Given the average yearly growth rate of construction land at 5.43% from 2000 to 2020, the construction land area within the Hexi Corridor is projected to not surpass 166.3 km² by 2035.

$$157\le x_5\le 166$$

(7)

(7)

Unutilized land

As construction land use expands and development scales up, coupled with the initiation of several ecological restoration projects, the unutilized land area decreased significantly in the period of 2000–2020. Reflecting the observed total decrease in unutilized land area within the Hexi Corridor of 3.18% from 2005 to 2020, we have set a target total reduction rate of approximately 5% for the year 2035 in comparison to 2020.

$$x_6\ge \mathrm{271,517}$$

(8)

(8)

Model self-constraint

$$x_i\ge 0, i=1,2,3,\dots ,6$$

(9)

Solution

We will utilize Lingo 18.0 to solve the constrained functions and ascertain the land demand for the 2035 multi-objective optimization scenarios.

2.3.2. Optimization of Spatial LUCC Structure Based on PLUS

In the preceding steps, we derived the quantitative structure of land use for 2035, employing the ECS as determined by the GMOP method and the BAU scenario ascertained through the Markov chain analysis. This step involved integrating the 2035 land use quantitative structure into the PLUS model to project the spatial distribution of land use under both scenarios. Ultimately, the land use data for these scenarios, projected for 2035, were inputted into the InVEST model to calculate the spatial distribution of the expected carbon storage.

The PLUS model combines the Land Expansion Analysis Strategy (LEAS) with a cellular automata (CA) model utilizing multi-type random patch seeds (CARS) to investigate the drivers of land expansion and landscape transformation [19]. In comparison to alternative models, the PLUS model achieves greater simulation accuracy and yields landscapes that more closely resemble the observed reality.

Eleven driving factors for LUCC were identified based on the regional characteristics and data availability of the study area, encompassing three topographic (elevation, slope, aspect), two climatic (temperature, precipitation), four transportation (distance to railroads, highways, and national and provincial highways), and two socioeconomic factors (GDP, population density). Additionally, the Hexi Corridor is home to several provincial nature reserves, including the Qilian Mountain National Park, Yumen Nanshan, and Changmahe. Given their significance for ecological conservation and restoration, these areas require stringent management and transformation, necessitating the selection of nature reserves as a limiting factor.

Neighborhood factors illustrate the interplay between various types of LUCC, as well as within particular units in the adjacent area. This study established the following parameter values for neighborhood factors: arable land at 0.7627, forest land at 0.6273, grass land at 1.0, water areas at 0.5969, construction land at 0.6025, and unutilized land at 0.1. In future development scenarios, the regulatory rules for land type conversions will markedly affect the configuration and dispersion of LUCC. Table S1 displays the matrices of conditional suitability for different scenarios.

Before simulating land cover for 2030, validating the accuracy of the model was crucial. Therefore, this study first utilized the PLUS model to simulate 2020 Land Use and Land Cover Change (LUCC) in the Hexi Corridor. Comparing actual to simulated outcomes, the model demonstrated an overall accuracy of 91.6% and a Kappa coefficient of 0.819 (Figure S1). The results substantiate the exceptional simulation precision of the PLUS model in this research area, confirming its dependability and applicability.

2.3.3. Evaluation of Carbon Storage Utilizing the InVEST Model

For evaluating the carbon storage capacity in the Hexi Corridor, the InVEST model’s carbon storage and sequestration module was utilized. Our analysis incorporates carbon density assessments across different land use types, encompassing aboveground, belowground, soil, and dead organic matter [43]. A calculation of the Hexi Corridor’s carbon storage was conducted using the following formula:

$$C_i=C_{i\_above}+C_{i\_below}+C_{i\_soil}+C_{i\_dead}$$

(10)

$$C_{total}={\displaystyle \sum }_i^n{C}_i\times S_i \left(i=1,2,\dots ,6\right)$$

(11)

In the formulas presented, C_i represents the carbon density of the i-th land use category. Additionally, C_{i_above}, C_{i_below}, C_{i_soil}, and C_{i_dead} refer to the aboveground, belowground, soil, and dead organic matter carbon densities of the i-th land use category, respectively. C_total denotes the total carbon storage, while S_i indicates the area of the i-th land use category.

Significantly, this study fully investigated the literature on the use of measured methods to obtain carbon density in China from 2000 to 2020, and after sorting and analyzing, the carbon density in China was determined [44,45]. Additionally, local carbon density levels are profoundly influenced by temperature and precipitation [46]. The following formulas were derived from Giardina and Ryan [47].

The R² value in the formula is used to determine whether the model is a linear model or a power (exponential) model. The result showed that the correlation between air temperature and soil carbon density was significantly lower than that of precipitation, so only the influence of precipitation on soil carbon density was considered. We utilize the following assertions to adjust the carbon density data of the Hexi Corridor that were obtained from research in the literature:

$$C_{SP}=3.3968\times MAP+3996.1 \left(R^2=0.11\right)$$

(12)

$$C_{BP}=6.798\times e^{0.0054\times MAP} \left(R^2=0.70\right)$$

(13)

$$C_{BT}=28\times MAT+398 \left(R^2=0.477,p<0.01\right)$$

(14)

In Equations (12)–(14), MAP indicates annual precipitation (mm) and MAT denotes the annual temperature (°C). C_SP, the soil carbon density (kg·m⁻²), is derived from MAP, whereas C_BP and C_BT, the biomass carbon densities (kg·m⁻²), are calculated from MAP and MAT, respectively.

The ratio of MAT and MAP (average for 2000–2020) for both China (7.87 °C, 667.3 mm) and the Hexi Corridor (5.57 °C, 197.6 mm) serves as the carbon density correction coefficient of the Hexi Corridor.

Table 1. Carbon density of each land use type in the study area (kg/m²).

Land Use Type	Aboveground Carbon Density	Belowground Carbon Density	Soil Carbon Density	Dead Organic Carbon Density
Arable land	0.04	0.57	8.08	0.00
Forest land	0.30	0.82	14.33	0.00
Grass land	0.25	0.61	7.44	0.00
Water area	0.02	0.00	0.00	0.00
Construction land	0.02	0.00	0.00	0.00
Unutilized land	0.01	0.00	1.95	0.00

displays the results of the corrected carbon density.

$$K_{BP}=\frac{C_{BP}^{\prime }}{C_{BP}^{″}}$$

(15)

$$K_{BT}=\frac{C_{BT}^{\prime }}{C_{BT}^{″}}$$

(16)

$$K_B=K_{BP}\times K_{BT}=\frac{C_{BP}^{\prime }}{C_{BP}^{″}}\times \frac{C_{BT}^{\prime }}{C_{BT}^{″}}$$

(17)

$$K_S=\frac{C_{SP}^{\prime }}{C_{SP}^{″}}$$

(18)

In the aforementioned formulas, K_BP denotes the adjustment factor for biomass carbon density in relation to precipitation, while K_BT represents the adjustment factor for biomass carbon density concerning the temperature. K_B is the composite biomass carbon density correction factor, and K_S is the soil carbon density correction factor. C′ and C″ represent the carbon density for the Hexi Corridor and China, respectively.

3. Results

3.1. LUCC from 2000 to 2020

3.1.1. Analysis of LUCC Characteristics from 2000 to 2020

From 2000 to 2020, the Hexi Corridor primarily comprised unutilized and grass land (Figure 3a). Unutilized land constituted more than 70% of the total area, with a widespread distribution across the region. Grass land, the second most prevalent land use type, covered over 19.80% of the area, primarily scattered in the southern regions adjacent to the Qilian Mountains, including areas like Shandan County in Zhangye City. Arable land constituted more than 4.70% of the area, predominantly situated in the plain regions of the central corridor, such as the Liangzhou District of Wuwei City. Forest land, accounting for approximately 1%, was mainly scattered in the southeastern region (such as the Tianzhu Tibetan Autonomous County of Wuwei City). Water areas comprised roughly 0.5% of the total area, predominantly situated in the high-altitude regions of the southwest. The area designated for construction constituted over 0.01% and was concentrated in the central districts of each municipality.

Between 2000 and 2020, the unutilized land area witnessed a 3.45% reduction. The grassland and water areas expanded initially, followed by a decrease. As a result, the proportions of grass land and water areas increased by 2.41% and 0.13%, respectively, over the 20-year period. The areas of arable land, forest land, and construction land all experienced growth from 2000 to 2020, with the proportion notably surging from 0.01% to 0.04% for construction land (Figure 3b).

3.1.2. Analysis of Land Use Transfer from 2000 to 2020

Between 2000 and 2020, the Hexi Corridor underwent a total LUCC affecting an area of 32,155.76 km², constituting 7.7% of its total area, as shown in

Table 2. Transfer matrix of land use in Hexi Corridor during 2000–2020 (km²).

Year		2020
		Arable Land	Forest Land	Grass Land	Water Area	Construction Land	Unutilized Land	Total
2000	Arable land	17,488.24	9.38	2175.55	15.77	23.88	132.64	19,845.45
	Forest land	0.67	3890.82	166.35	0.00	0.00	0.00	4057.85
	Grass land	3303.42	555.10	73,442.28	118.81	35.29	5293.88	82,748.76
	Water area	8.74	0.11	37.37	1858.21	0.25	191.23	2095.91
	Construction land	0.02	0.00	0.09	0.45	57.05	0.01	57.61
	Unutilized land	2422.30	0.65	16,970.76	657.57	35.50	288,743.75	308,830.52
	Total	23,223.39	4456.05	92,792.39	2650.82	151.96	294,361.51	417,636.11

. The predominant land conversion observed was from unutilized land to grassland, significantly driven by continuous ecological initiatives including the Grass land Desertification Control (2001) and Return Grazing Land to Grassland (2003) projects. Generally, there is a frequent interchange of arable land, grassland, and unutilized land within the region. The arable land area increased by 3377.93 km², predominantly converted from grassland and unutilized land, which constituted 57.60% and 42.24% of the arable land conversion, respectively. The forest land area expanded by 398.20 km². This was chiefly a result of the transformation from grassland, with the grassland area expanding by 10,043.62 km², largely due to conversions from unused land and farmland.

3.2. Spatial and Temporal Variations in Carbon Storage from 2000 to 2020

3.2.1. Temporal Alterations in Carbon Storage

The findings reveal a positive trend in the total carbon storage of the Hexi Corridor over twenty time periods (Figure 4a), with a 9.05 × 10⁶ t increase and a growth rate of 5.93% from 2000 to 2020. Between 2005 and 2010, carbon storage experienced its most rapid increase at a rate of approximately 2.69%, contributing to 46.08% of the total increase. The cumulative increases in carbon storage from 2000 to 2005, 2010 to 2015, and 2015 to 2020 were 2.53 × 10⁶ t, 2.04 × 10⁶ t, and 0.38 × 10⁶ t, representing 27.96%, 22.54%, and 3.42% of the total growth, respectively.

3.2.2. Spatial Changes in Carbon Storage

The areas with high carbon storage exhibited a “West Belt–Southeast flake” distribution pattern (Figure 4b). In these areas, arable and grass land, which have high soil carbon density, predominate. Compared to other regions, the northern area stores the least carbon, mainly due to its prevalent land use type of unutilized land, which has a low carbon density value.

The data were classified into five categories—highly significant increase (p > 0.01), significant increase (p > 0.05), unchanged, significant decrease (p > 0.05), and highly significant decrease (p > 0.01)—through the SEN + MK test. This categorization better represents the spatial variability of carbon storage in the Hexi Corridor. Carbon storage in the Hexi Corridor shows a consistent spatial pattern, with 98.60% of the areas remaining stable (see Figure 4c). This accounts for 1.15% of the total area; the increase in carbon storage primarily occurred in the central plain and southeast mountain regions, including Aksai Kazak Autonomous County and Subei Mongolian Autonomous County. Carbon storage decreased in 0.25% of the area, exhibiting a sporadic and scattered distribution. Overall, the Hexi Corridor has seen a greater increase than decrease in its carbon storage area, attributable to the adoption of sustainable, eco-friendly practices and the conservation of high-carbon-density lands such as arable areas.

3.3. Response Mechanism of LUCC to Carbon Storage Changes from 2000 to 2020

In the Hexi Corridor, the area and carbon density associated with various land use types significantly affect regional carbon storage. Grass land and unutilized land are the primary and most crucial carbon pools, accounting for 46.93% and 37.2% of the total carbon storage in the region, respectively. These are followed by arable land (11.83%) and forest land (4.04%), demonstrating that the area and carbon density of different land use types collaboratively determine their contribution to carbon storage. For instance, despite its larger area, the carbon sequestration capacity of unutilized land is surpassed by grass land, making the latter the most significant carbon pool in the Hexi Corridor. While forest land possesses the highest per-unit carbon sequestration capacity, its limited area restricts its overall contribution to regional carbon storage. From 2000 to 2020, increases in the carbon storage of grass land, arable land, and forest land in the Hexi Corridor have been observed, primarily due to the ongoing implementation of ecological projects and agricultural expansion by the Chinese government.

Based on the geo-informatic atlas (

Table 3. Alterations in carbon storage resulting from transformations in land use types within the Hexi Corridor from 2000 to 2020.

Land Use Type Conversion	Change in Area/km2	Percent/%	Change in Carbon Storage/103 t
Arable land–Forest land	9.38	7.33%	6.34
Arable land–Grass land	2175.55		−84.85
Arable land–Water area	15.77		−13.68
Arable land–Construction land	23.88		−20.70
Arable land–Unutilized land	132.64		−89.27
Subtotal	2357.22		−202.15
Forest land–Arable land	0.67	0.52%	−0.46
Forest land–Grass land	166.35		−118.94
Forest land–Water area	0.00		−0.01
Forest land–Unutilized land	0.00		−0.00
Subtotal	167.03		−119.40
Grass land–Arable land	3303.42	28.94%	128.83
Grass land–Forest land	555.10		396.89
Grass land–Water area	118.81		−98.37
Grass land–Construction land	35.29		−29.22
Grass land–Unutilized land	5293.88		−3356.32
Subtotal	9306.48		−2958.18
Water area–Arable land	8.74	0.74%	7.58
Water area–Forest land	0.11		0.17
Water area–Grass land	37.37		30.94
Water area–Construction land	0.25		0.00
Water area–Unutilized land	191.23		37.10
Subtotal	237.70		75.79
Construction land–Arable land	0.02	0.00%	0.02
Construction land–Grass land	0.09		0.07
Construction land–Water area	0.45		0.00
Construction land–Unutilized land	0.01		0.00
Subtotal	0.57		0.09
Unutilized land–Arable land	2422.30	62.47%	1630.21
Unutilized land–Forest land	0.65		0.88
Unutilized land–Grass land	16,970.76		10,759.46
Unutilized land–Water area	657.57		−127.57
Unutilized land–Construction land	35.50		−6.89
Subtotal	20,086.77		12,256.09
Total	32,155.76	100%	9052.23

), this study explored the response mechanism of the spatiotemporal evolution of land use to changes in carbon storage across different periods. The most pronounced increase in carbon storage occurred in the transition from unutilized land to grassland, amounting to 1.076 × 10⁷ t, succeeded by the change from unutilized land to arable land, which accounted for 0.163 × 10⁷ t. The largest reduction in carbon storage occurred during the shift from grassland to unutilized land, amounting to 0.336 × 10⁷ t. Following closely, the change from unutilized land to water areas resulted in a decrease of 0.128 × 10⁶ t in carbon storage.

Between 2000 and 2020, arable land conversion in the Hexi Corridor led to a 2.02 × 10⁵ t decrease in carbon storage, predominantly due to its transformation to unutilized land with a lower carbon density, which constituted 44% of total carbon loss of the arable land. A 1.19 × 10⁵ t reduction in the carbon storage of the Hexi Corridor resulted from forest land conversion, with 99.60% of this area transforming into grass land. Given that forest land possesses a higher carbon density than grassland, this transition led to a decrease in carbon storage. Grass land conversion resulted in a 2.96 × 10⁶ t decrease in carbon storage. While transitions to arable and forest lands did contribute to an increase, these gains were insufficient to offset the losses, leading to an overall decline in carbon storage. Conversions to water areas and unutilized lands culminated in carbon storage increments of 0.758 × 10⁶ t and 1.23 × 10⁷ t, respectively, with transitions to grassland being the predominant factor for these enhancements. Owing to the minimal extent of construction land conversion, the associated changes in carbon storage were negligible.

3.4. Land Simulation and Carbon Storage Estimation under Different Scenarios

3.4.1. Simulation of LUCC Scenarios

We employed the GMOP-PLUS model to derive the spatial distribution of land use in the Hexi Corridor for the year 2035, considering two scenarios: BAU and the ECS (Figure 5).

Table 4. Areas of LUCC types in the study area in 2020 and predictions for 2035 under different scenarios (km²).

Year	Arable Land	Forest Land	Grass Land	Water Area	Construction Land	Unutilized Land
2020	23,223.39	4456.05	92,792.40	2650.82	151.96	294,361.52
2035 (BAU)	25,697.02	4446.83	98,401.26	3147.88	146.99	285,796.14
2035 (ECS)	30,836.83	3971.85	118,081.51	2595.90	156.99	261,993.04

displays the statistical figures for various land use categories. Compared to 2020, it is anticipated that the land use composition in the Hexi Corridor will experience a range of changes under both scenarios by 2035. In the BAU scenario, the predominant tendencies of land use alterations are characterized by “enhancing food security, expanding ecological lands, and decelerating urban development”. Specifically, the areas of forest land, construction land, and unutilized land are expected to decrease by 9.22 km², 4.97 km², and 8565.38 km², respectively. Additionally, increases in arable land, grass land, and water areas are anticipated to be 2473.63 km², 5608.86 km², and 497.06 km², respectively. Compared to the BAU scenario, the ECS is projected to result in a more substantial expansion of arable land (5139.81 km², an increase of 20.00%), a significant enlargement of grassland area (19,680.25 km², an increase of 19.99%), and a faster urbanization rate (an additional 10 km², constituting a 6.80% increase). In essence, the ECS facilitates a harmonious balance between ecological construction and urban development in the Hexi Corridor.

3.4.2. Response Simulation of Carbon Storage Change

The simulation results predict that future spatial distribution patterns of carbon storage in the Hexi Corridor will align with current patterns (Figure 6a,b). High-carbon-storage areas are expected to predominantly occupy central arable lands and elevated southern regions, whereas areas with low carbon storage values will likely extend across northern unutilized lands, demonstrating a substantial correlation with land cover types.

According to

Table 5. The temporal variation in carbon storage in the Hexi Corridor from 2020 to 2035.

	2020	2035 BAU		2035 ECS
	Carbon Storage /106 t	Carbon Storage /106 t	Percent/%	Carbon Storage/ 106 t	Percent/%
Arable land	20.18	22.33	10.66%	26.80	32.79%
Forest land	6.88	6.87	−0.20%	6.88	−0.09%
Grass land	77.02	81.68	6.05%	88.98	15.54%
Water area	0.01	0.01	18.76%	0.01	−2.07%
Construction land	0.00	0.00	−3.26%	0.00	3.32%
Unutilized land	57.69	56.02	−2.91%	53.39	−7.46%
Total	161.78	166.90	3.16%	176.06	8.82%

, under the BAU scenario, the projected carbon storage of the Hexi Corridor is estimated to be 1.67 × 10⁸ t, marking a 3.16% increase from 2020. This increase can be broken down by land type, with arable land, grass land, and water areas experiencing increments of 10.66%, 6.05%, and 18.76%, respectively. Conversely, forest land, construction land, and unutilized land are expected to decrease by 0.2%, 3.26%, and 2.91%, respectively. In the ECS, the anticipated carbon storage in the Hexi Corridor is projected to increase to 1.76 × 10⁸ t, an 8.82% hike compared to 2020. Specifically, arable land, grass land, and construction land are projected to increase by 32.79%, 15.44%, and 3.32%, respectively. In contrast, forest land, water areas, and unutilized land are expected to decrease by 0.09%, 2.07%, and 7.46%, respectively.

In contrast to the BAU scenario, the ECS is expected to further amplify the expansion of both arable land and grassland areas, which possess higher carbon densities. Concurrently, it will facilitate the proper expansion of construction land. Additionally, the carbon storage values in arable and grassland areas are projected to increase by 4.47 × 10⁶ t and 7.3 × 10⁶ t, respectively. In summary, the Hexi Corridor is expected to experience an upward trend in carbon storage under both aforementioned development scenarios in the future, with the increase being more pronounced under the ECS.

Additionally, there will be considerable differences in the spatial alterations in carbon storage within the Hexi Corridor under the two scenarios (Figure 6c,d). In the BAU scenario, regions exhibiting diminished carbon storage will span 598 km², constituting 0.14% of the total area, sporadically distributed in the southwestern part. Conversely, regions with augmented carbon storage will encompass 8114 km², making up 1.94% of the entire region, primarily concentrated in areas rich in arable land and grass land. Under the ECS, regions experiencing a decrease in carbon storage will cover 1787 km², comprising 0.43% of the total area. In fact, the spatial distribution of regions with reduced carbon storage would be akin to that observed in the BAU scenario. Regions demonstrating increased carbon storage will span 33,771 km², representing 8.09% of the total area, with a spatial distribution resembling that of the BAU scenario.

4. Discussion

The results demonstrate that LUCC significantly influences carbon storage values. Utilizing the “GMOP-PLUS-InVEST” integrated approach effectively refines the structure of LUCC, achieving optimization targets for quantity and spatial arrangement. This enhancement boosts both ecosystem value and economic returns, promoting their balanced progress. In the 2035 land use simulation for the Hexi Corridor, the estimated carbon storage under both scenarios exceeded the 2020 levels. Additionally, the ECS, facilitated by the “GMOP-PLUS-InVEST” framework, successfully maximized both ecological and economic benefits, further exemplifying the capacity of the framework to optimize land use and enhance these benefits.

4.1. Analysis of the Response of Carbon Storage to LUCC in Hexi Corridor from 2000 to 2020

Carbon storage is vital for maintaining the regional carbon cycle and is a key index of ecosystem services [48]. From 1990 to 2020, the Hexi Corridor showed a distinctive carbon storage pattern: higher levels in the southern areas and lower in the northern areas. The eastern and southern parts of the Hexi Corridor, with their dense forests and grasslands, along with the central oasis plain rich in arable land, are areas of high carbon storage. In contrast, the northern regions, mostly consisting of unutilized land, exhibit low carbon storage. This distribution is consistent with Zhu et al.’s findings in arid northwest China [23]. The spatial distribution of carbon storage in the area is clearly influenced by land use types [49]. A temporal analysis of carbon storage in the Hexi Corridor from 2000 to 2020 shows a significant increase of 9.05 × 10⁶ t over the two decades, attributable to both natural and anthropogenic factors. Ecological projects like the National Three-North Shelterbelt, efforts to prevent grassland desertification, and the reversion of farmland to grassland have increased forest and grassland areas, which have higher carbon densities. These observations align with Zhao et al.’s research in the Heihe River basin [50]. Additionally, the ongoing climate trends of warming and increasing humidity in northwest China [51], coupled with the implementation of ecological strategies like water distribution and intra-basin water transfer [52], have further enhanced the capacity of the Hexi Corridor for carbon sequestration.

Besides land use, various other factors influence carbon storage. Figure 7 and

Table 6. The optimal types and extents of influence from various driving factors on carbon storage.

Driving Factors	Suitable Zoning	Suitable Range/Type	Mean Carbon Storage/108 t
NDVI	5	0.67–0.92	1.057
Average annual precipitation	5	311–467 mm	0.868
Soil type	1	semi-eluvial soil, pedocal, xerosol	0.855
Annual average temperature	2	−3.2–1.0 °C	0.630
Slope	5	35.9–74.5°	0.695
Elevation	3	2276–3072 m	0.752
GDP	2	9.49–50.16 million yuan	0.886
Population density	2	128–693 per/km2	0.510
Vegetation type	1	Aciculiailvae, mixed coniferous broad-leaved forest, broad-leaved forest	1.125

illustrate the explanatory power and optimal intervals of the driving factors influencing carbon storage. Consequently, the NDVI, annual mean precipitation, and soil type emerge as the principal factors influencing the carbon storage of the Hexi Corridor, suggesting a predominant regulation by natural elements. This aligns with the observations made by Liu et al. [53] and Zhang et al. [54]. Moreover, the NDVI, precipitation, and slope exhibit a positive correlation with carbon storage, whereas the temperature, population density, and GDP show a negative correlation. The GDP level of a region significantly affects its construction area expansion: a higher GDP correlates with a greater scale and inclination towards urban construction area enlargement. Indeed, while urban expansion may offer immediate economic benefits, it poses a long-term threat by potentially diminishing the carbon storage capacity of regional ecosystems [55]. It is also identified as a primary contributor to the increase in carbon emissions [56]. The carbon emissions in the Hexi Corridor exhibited a significant increase, rising from 1.7 × 10⁷ t in 2000 to 4.49 × 10⁷ t in 2020 [57]. However, urban expansion is a complex process, frequently accompanied by infrastructure development, which significantly impacts the surrounding ecosystem [58].

4.2. Impact of Different Future Development Scenarios on Carbon Storage in Hexi Corridor

The Hexi Corridor serves as a crucial grain supply region in China. Given the challenges to the food security of China [59], arable land is fundamental to achieving food security strategies. Simultaneously, building an ecological civilization is a long-term endeavor, necessitating a strong adherence to the principle that “clear waters and lush mountains are invaluable assets” [60]. As a vital element of the national ecological security strategy, ecological construction in the Hexi Corridor must persist. In 2035, under various scenarios, the carbon storage of the Hexi Corridor surpasses its 2020 levels, with a notably larger increase under the ECS than under the BAU scenario, attributable mainly to substantial alterations in arable and grassland areas. The transition from unused land to grassland has escalated, while the ECS sees a restrained conversion of arable and grassland to lower-carbon-density lands, safeguarding the vegetation carbon pool and yielding pronounced ecological benefits. Nonetheless, under the BAU scenario, ecological land expansion occurs at the expense of construction land, hindering the balanced advancement of ecological conservation and high-quality socio-economic progress. The ECS enhances the carbon balance of the region through ecological restoration, mitigates carbon storage loss, and more effectively showcases the carbon sequestration capabilities of the Hexi Corridor. This aligns with the findings of other researchers, who have also observed an increase in carbon storage under the ECS [61].

4.3. Limitations, Prospects, and Policy Recommendations

This research constitutes a thorough assessment of the spatial and temporal characteristics of carbon storage in the Hexi Corridor between 2000 and 2035, examining the relationship between land use and carbon storage, and furnishing valuable insights for optimizing land use patterns and promoting sustainable ecological development in both the Hexi Corridor and the broader arid regions of northwest China. Nonetheless, it has certain limitations. Firstly, the InVEST model employed herein simplifies the carbon cycle, presupposing a linear relationship between regional carbon sequestration and time [62]. However, carbon density is subject to variations induced by human activities and environmental factors, displaying temporal and spatial fluctuations [63]. Moreover, this model considers land use change as the sole determinant of carbon storage variations. The effects of LUCC on atmospheric circulation and landmark reflectance were ignored [64]. Additionally, the soil type, photosynthetic rate, and seasonal changes to vegetation [63] all have certain effects on carbon storage, which will inevitably bring errors to the assessment results [65]. The carbon pools in this study were derived using a model parameter correction method, based on findings from previous research. While the results of this study are more precise than the national carbon density values directly cited by some researchers, they are less accurate than those obtained through field sampling and surveys. The carbon density of identical land use types can exhibit spatial heterogeneity, as influenced by factors such as forest management practices, forest types, and age [66]. Secondly, although the drivers selected for model prediction demonstrate a strong correlation across various land types, their quantification is challenging due to significant influences from socio-economic and policy factors. This challenge partially reduces the explanatory power of the regression function. Finally, the application of the “GMOP-PLUS-InVEST” model in simulating and estimating carbon storage for 2035 does not currently account for the impact of future climate change. This omission could introduce a degree of bias in the results [67].

It is important to recognize that achieving a net-zero carbon goal necessitates a combined effort to both reduce emissions and enhance carbon storage. However, a significant reduction in carbon emissions depends on the large-scale global implementation of energy transitions and carbon capture technologies, which are still in their nascent stages [68]. Additionally, there is uncertainty surrounding carbon offset projects [69]. Furthermore, climate change is a complex global challenge, and a singular focus on a net-zero carbon goal may not comprehensively address all pertinent issues [70].

The Hexi Corridor region, selected for this study, is, to some extent, representative of arid and semi-arid areas in China. Future studies could extend the “GMOP-PLUS-InVEST” framework to encompass all arid and semi-arid regions, including the Loess Plateau. For a more precise simulation of carbon storage, land use categories should be further refined and more accurate carbon density data should be employed in actual sampling. Additionally, the objective functions, constraints, and optimization scenarios within the GMOP framework can be adapted based on the specific circumstances of the study area to enhance the accuracy of simulations.

The Hexi Corridor is an important ecological security barrier in China, as well as an important dry farming production area and advanced manufacturing base in Gansu Province; in this light, this study proposes the following four policy recommendations:

(1) Grass land, being the most vital carbon pool in the Hexi Corridor from 2000 to 2035, necessitates the strict implementation of policies like the “Gansu Province Land Use Master Plan” and the “Gansu Province Land Space Ecological Restoration Plan”. These should include protecting and restoring key ecological barriers and corridors, improving nature reserve management systems (e.g., Qilian Mountain National Park), and enhancing the carbon storage of crucial ecosystems, particularly grass land. Grasses grow relatively quickly, so their carbon storage potentials are rapidly realized [71]. In the north of the corridor, ecological projects like the “Three North” should focus on planting grass seeds around critical ecological barriers for combined carbon storage and soil conservation improvements. In the south, efforts should be focused on restoring degraded forest land and grassland, tailoring to local conditions, and addressing challenges like soil erosion, local flooding, and reduced groundwater recharge.

(2) In the ECS, arable land emerges as a significant potential carbon storage type. Recognizing its dual role in food production and ecological protection, strategies should involve expanding arable land and implementing effective farmland management. This could include establishing multifunctional farmlands (e.g., farmland with interspersed trees) and employing ecological agricultural practices like straw returning to enhance carbon storage and soil water retention.

(3) The study from 2000 to 2035 indicates that although construction land contributes minimally to regional carbon storage, its uncontrolled expansion (often encroaching on arable land) could lead to significant carbon loss. Thus, promoting urban blue–green networks and optimizing urban space buildings are critical. These measures will not only increase the happiness of residents but also augment the carbon storage level in urban spaces and reduce carbon emissions.

(4) The water area of the Hexi Corridor is small, but because the Hexi Corridor is located in an arid and semi-arid region, regional water resource management is of great significance for agricultural cultivation and urban development, and the significance of the water area to the Hexi Corridor is not limited to its direct carbon storage capacity. Therefore, it is necessary to further strengthen the protection of lake and wetland water resources and carry out water quality testing to strengthen the role of water areas in maintaining regional ecological stability.

5. Conclusions

Utilizing the “GMOP-PLUS-InVEST” integrated framework, this study systematically simulates and evaluates LUCC and corresponding carbon storage responses in the Hexi Corridor for the period from 2000 to 2035. The principal findings of this study are summarized as follows:

• The Hexi Corridor exhibits a relatively simplistic land use structure, characterized by marked spatial differentiation. Predominantly, unutilized land constitutes the most significant land use category, encompassing over 70% of the total area. From 2000 to 2020, the land use of the Hexi Corridor experienced substantial alterations, predominantly characterized by the transformation of unutilized land into grassland, indicating a general trend towards ecological enhancement.
• From 2000 to 2020, carbon storage in the Hexi Corridor augmented by 9.05 × 10⁶ t, exhibiting an initial rapid growth phase followed by a slowdown, with the most pronounced increase, 4.17 × 10⁶ t, occurring from 2005 to 2010. Spatially, carbon storage distribution within the Hexi Corridor displayed a distinct gradient, being higher in the southern regions and lower in the northern areas.
• The simulation results for land use in 2035 under the BAU scenario suggest a prevailing trend towards “enhancing food security, expanding ecological land, and decelerating urban development”. In comparison, the ECS not only expands the area of arable land and significantly increases grassland but also further accelerates the urbanization process.
• By 2035, carbon storage in the Hexi Corridor is projected to increase by 1.67 × 10⁸ t and 1.76 × 10⁸ t under the BAU scenario and ECS, respectively, each exhibiting varying degrees of growth. In spatial terms, the increased area of carbon storage in the BAU scenario and ECS is similar, distributed equally in arable land and dense grass land areas. Consequently, it is crucial for the Hexi Corridor to leverage the carbon sequestration benefits of arable land, fortify its ecological security frameworks, and harness the supportive functions of ecological buffers.