Mountainous areas in China face complex problems due to conflicts between natural eco-environmental protection and socio-economic development. Mountain water resources have evolved in the context of climate change and human activities, which further affects their coordination and matching with regional climate resources, land resources and socio-economy. Hence, it is of fundamental significance for mountain development to study these issues to identify key weakness and provide solutions. The paper focuses on three typical mountainous areas under different natural geographic conditions and at socio-economic development levels in China, namely, Taihang Mountains Area (TMA), Hengduan Mountains Region (HMR) and Guizhou-Guangxi Karst Area (GKA), and studies the spatio-temporal variations of precipitation and runoff from 1956 to 2015 by Mann-Kendall test based on national water resources assessment results and statistical data of land use and socio-economy. The characteristics of natural and socio-economic factors are analyzed by matching distance and imbalance index. In this process, four groups of parameters are selected, including water (precipitation and runoff), heat (accumulated temperature and radiation), land (total area and farmland area) and socio-economy (population and GDP). The results indicate that, the water resources endowment of TMA is the worst, and significant reduction of runoff since 2000 makes it even worse, while the precipitation and runoff of HMR and GKA are abundant and there is no obvious change trend. According to the analysis of regional water-heat-human-land matching characteristics, TMA mainly suffers from water shortage, land and heat resources have great disadvantages in most parts of HMR with uneven distribution of water and heat, and land resources are relatively deficient in all counties of GKA. In general, mismatching degree of water and other factors is the highest, and the allocation and coordination of water are the key issue for sustainable development of mountainous areas, especially in TMA.

Land change science has become an interdisciplinary research direction for understanding human-natural coupling systems. As a process-oriented modelling approach, Agent based model (ABM) plays an important role in revealing the driving forces of land change and understanding the process of land change. This paper starts from three aspects: the theory, application and modeling framework of ABM. First, we summarize the theoretical basis of ABM and introduce some related concepts. Then we expound the application and development of ABM in both urban land systems and agricultural land systems, and further introduce the case study of an model on Grain to Green Program in the Hengduan Mountains region, Southwest China. On the basis of combing the ABM modeling protocol, we propose the land system ABM modeling framework and process from the perspective of agents. In terms of urban land use, ABM research initially focused on the study of urban expansion based on landscape, then expanded to issues like urban residential separation, planning and zoning, ecological functions, etc. In terms of agricultural land use, ABM application presents more diverse and individualized features. Research topics include farmers' behavior, farmers' decision-making, planting systems, agricultural policy. Compared to traditional models, ABM is more complex and difficult to generalize beyond specific context since it relies on local knowledge and data. However, due to its unique bottom-up model structure, ABM has an indispensable role in exploring the driving forces of land change as well as the impact of human behavior on the environment.

Water and land resources are the foundation for human wellbeing. The coupling of water-land elements in mountainous areas is closely related to the functionality of production-living-ecology space, whose coupling process and features are closely related to ecosystem services and sustainable socio-economic development in mountainous areas. Through constructing a more scientific coupling index of water-land elements (CIWL), the present study conducted a large-scale and long-term analysis of the coupling characteristics of the Taihang Mountains, Hengduan Mountains and Guizhou-Guangxi karst mountains. The influencing factors of the coupling index in each period were analyzed by employing geodetector method. The results show that: (1) The three mountainous areas are significantly different in spatial differences of coupling index of water-land elements. The Taihang Mountains are dominated by water deficiency, while the Hengduan Mountains are by the balanced area. The Guizhou-Guangxi mountainous areas are dominated by water deficiency and the abundant areas. (2) In terms of the vertical differentiation, the coupling of water-land elements of the three major mountainous areas varies at 1300 m, 1800-3400 m and 500-1500 m, respectively, with the coupling index of water-land elements in ecological functional sub-regions indicating that the forest ecological sub-region > forest grass ecological sub-region > agro-ecological sub-region. (3) Natural factors and human factors are responsible for spatial differentiation of coupling index, among which, the climate is a dominant driving factor, the topography and land use type are secondary, and the human factors are superimposed on the natural factors, jointly causing the complexity and variation of the coupling of water-land elements. The coupling index of water and land elements established in this paper has deepened the study of spatial-temporal processes of water and land interaction in mountainous areas, thereby providing a decision-making reference for coping with the sustainable development of mountainous areas in a changing environment.

Environmental factors determine the spatial and temporal distribution of debris flows. Understanding the relationship between debris flows and their effective factors is important for debris flows risk assessment at regional scale. In this paper, geographic detectors and gray correlation analysis are used to explore the relationship between 11 influencing factors, including precipitation, climate, landforms, geology, land cover type, soil thickness and topographic wetness, and the spatial distribution of debris flows-prone catchments, as well as the spatial and temporal correlation between precipitation and debris flows disasters in the Hengduan Mountains region. The results show that the topographic wetness index is the most dominant factor controlling the spatial distribution of the catchments, followed by topographic relief and soil thickness. Temporal correlation between debris flows disasters and precipitation characteristics has large regional heterogeneity. The rainfall characteristics of debris flows disaster events in different regions exhibit significant difference. The frequency of debris flows with rainfall, topographic wetness, topographic relief and soil thickness in the Hengduan Mountains region varies significantly in different zones, which indicates that not only the rainfall but also the other factors controlling the spatial pattern of debris flows should be reflected in debris flows early warning model in the region.