## 4 Discussion
### Impacts of Human Activities on the LDD Processes  
According to the residual analysis, human factors mainly contribute to the LDD changes in coastal China compared to climate factors. Human activities, such as economic development, ecological restoration plans, and urbanization, usually significantly impact the LDD process. As shown in Figure 7, over the past 35 years, the study area has witnessed varying expansions in impervious, water, and forest areas (\(p<0.01\)). The impervious area expanded from 5.26 million ha in 1985 to 11.99 million ha in 2015, an increase of 127.93%, far exceeding that of other land types. Water and forest areas also experienced 30.76% and 3.53% growth, respectively. In contrast to the rapid expansion of impervious areas, wetland, shrub, grassland, barren, and cropland trends showed significant decreases (\(p<0.01\)). For example, croplands have decreased by 13.2% (7.81 million ha) since 1985, while barren areas decreased by 64.34% (0.13 million ha), wetland areas decreased by 95.08% (444.42 ha), grassland areas decreased by 21.28% (1.22 million ha), and shrub areas decreased by 46.54% (0.49 million ha). Figure 6: Variation trend of extreme climate indices. (**a**–**n**) Represent extreme temperature, and (**o**–**x**) represents extreme precipitation indices; The scatter plot displays the extreme climatic index value for each year, while the blue line represents the fitted trend line; the \(p\)-value indicates the significance level of the changing trend, with smaller values indicating higher significance. Rapid urbanization, particularly in eastern China, has had various direct or indirect impacts on land development in recent decades, with the most prominent issue being the loss of substantial amounts of fertile farmland due to conversion for construction purposes [27]. Among all LULC types, cropland, forest, and impervious surfaces account for 63.21% of the total area in the study area (Figure 8). Figure 8 shows that among all LULC types, the cropland, forest, and impervious land development areas account for 63.21% of the total study area. Additionally, except for barren, water, and wetland, the land development areas of all other LULC types occupy more than 50% of their respective areas, indicating that land development plays a dominant role in the LDD process for most LULC types (Figure S3). Since the reform and opening policy in 1978, China has made significant progress in industrialization and urbanization [69]. According to the China National Bureau of Statistics, the urbanization rate rose from 17.9% in 1978 to 59.6% in 2018, with an average annual increase of 1% [70]. In this context, the LULC has encountered intense pressure and challenges, leading to an imbalanced structure and increased competition among its types [71]. During this period, China has implemented a large number of sustainability programs, such as the \"Soil and Water Conservation Program\", \"Converting Cropland to Forest Project\", \"National Land Consolidation Program\", and \"Natural Forest Conservation Program\" (Table S6). In particular, since the early 20 th century, the Chinese government has invested heavily in implementing numerous nationwide sustainability programs, which have greatly changed land use patterns and improved vegetation coverage, ultimately contributing to land development [72; 73; 74]. In the study, the LDDI\({}_{\text{HA}}\) trends have continued to rise, especially after 2008, and this change is closely related to the widespread sustainability programs implemented in China since 2000. Figure 7: Temporal changes in the area of different LULC types in Coastal China from 1985 to 2015. Coastal urbanization has resulted in the conversion of vast areas of farmland and natural spaces, causing land degradation of cropland, forest, grassland, and water bodies [36; 75; 76; 77]. Among all land use and land cover (LULC) types, cropland, impervious, and forest have undergone the most significant transfer changes in each subregion.