## 1 Introduction  
The China Loess Plateau (CLP) has been a pivotal region for the Chinese government in implementing strategies for environmental protection and sustainable development [1, 2, 3, 4]. It spans over 640,000 km\({}^{2}\) and has a population of nearly 100 million. The surface of CLP is characterized by thick loess, complex geomorphology, aridity, and low rainfall, resulting in a fragile natural ecological environment (EE). Moreover, its urbanization process lags behind the east and central regions of China, and its land resources are relatively poor and unevenly distributed, despite its abundant underground coal and other mineral resources. Since the beginning of the 21 st century, the CLP has been a primary region for the implementation of China Western Development [5, 6]. The region is characterized by mountains, plateaus, hills, guillies, and river valley plains. China Western Development was initiated by the Chinese government in 2000 to promote sustainable and balanced economic and social development. Its major programs include the Grain for Green Project (GGP) [7, 8, 9, 10], coal mining [11], and urbanization [2, 12, 13], among others. The GGP includes two aspects: Firstly, planting trees and forests instead of cultivating sloped ground in the loess hilly-guilly regions, and secondly, hill-closing and afforestation of mountainous areas to restore forest vegetation. Since 2002, CLP has invested more than 50 billion RMB in the GGP and reforested an area of 52,000 km\({}^{2}\), with one-third of the reforestation on arable land and the rest on barren hills and wastelands, as well as hill-closing and afforestation [14]. The growth rate of vegetation cover in CLP from 2000 to the present is much higher than the national average, resulting in significantly less sediment entering the Yellow River and reduced soil erosion, making CLP a leader in China's greening efforts. The utilization of coal resources is the pillar industry of economic development in the CLP. Since 2000, several coal production bases have been built in the region, and annual coal production now exceeds 2 billion tons, accounting for about 1/4 of global coal production, making CLP the major coal production base in China and the world [15]. The rapid development of four provincial capitals in the CLP's river valley plain has been supported by the Chinese government for the past 20 years, and a large number of rural and suburban areas have been transformed into urban areas, significantly increasing the region's development. After nearly three decades of resource development and EE construction, the CLP has become a key center for China's chemical and energy industry, as well as an ecological barrier for the entire northern region. Due to the complex geomorphology and frequent human projects in CLP, it is currently poorly understood how the EE of CLP has changed over the last 20 years. GGP promotes the growth of vegetation cover and EE improvement in CLP, while coal mining damages the overlying strata, resulting in surface subsidence, collapse, and cracks, which cause EE deterioration [16]. Urbanization has caused arable or forest land to be turned into building land, resulting in serious ecological impacts [17; 18]. Due to the significant temporal and spatial divergence of these three human projects in the last 20 years, the EE characteristics of CLP have become complex and unknown. Previous studies on the EE of CLP have mainly focused on the impacts of geographical and meteorological factors on the EE of a certain region, while scientific and quantitative studies on the impact of human projects on the EE of CLP are still lacking [19; 20]. Remote sensing provides new tools for evaluating EE, especially those of ecosystems that include mining areas, forests, grasslands, and urban areas [21; 22; 23; 24; 25]. In the early stages of EE modeling, only single indicators were used [26; 27; 28]. However, due to the complexity of EE, it is insufficient to describe them using only one index. To overcome this, [PERSON] et al.