Quantifying surface cracks in alpine meadows is a prerequisite and a key aspect in the study of grassland crack development. Crack characterization indices are crucial for the quantitative characterization of complex cracks, serving as vital factors in assessing the degree of cracking and the development morphology. So far, research on evaluating the degree of grassland degradation through crack characterization indices is rare, especially the quantitative analysis of the development of surface cracks in alpine meadows is relatively scarce. Therefore, based on the phenomenon of surface cracking during the degradation of alpine meadows in some regions of the Qinghai-Tibet Plateau, we selected the alpine meadow in the Huangcheng Mongolian Township, Menyuan Hui Autonomous County, Qinghai Province, China as the study area, used unmanned aerial vehicle (UAV) sensing technology to acquire low-altitude images of alpine meadow surface cracks at different degrees of degradation (light, medium, and heavy degradation), and analyzed the representative metrics characterizing the degree of crack development by interpreting the crack length, length density, branch angle, and burrow (rat hole) distribution density and combining them with in situ crack width and depth measurements. Finally, the correlations between the crack characterization indices and the soil and root parameters of sample plots at different degrees of degradation in the study area were analyzed using the grey relation analysis. The results revealed that with the increase of degradation, the physical and chemical properties of soil and the mechanical properties of root-soil composite changed significantly, the vegetation coverage reduced, and the root system aggregated in the surface layer of alpine meadow. As the degree of degradation increased, the fracture morphology developed from linear to dendritic, and eventually to a complex and irregular polygonal pattern. The crack length, width, depth, and length density were identified as the crack characterization indices via analysis of variance. The results of grey relation analysis also revealed that the crack length, width, depth, and length density were all highly correlated with root length density, and as the degradation of alpine meadows intensified, the underground biomass increased dramatically, forming a dense layer of grass felt, which has a significant impact on the formation and expansion of cracks.

Cracking phenomena are prevalent within clayey soils, substantially augmenting the evaporation process and exerting notable influences on soil thermo-hydro-mechanical properties. In this study, a new numerical method is developed to study the evaporation process of cracked soil, coupling moisture migration and heat transfer within both soil and air domains. The interconnection between these domains is established through boundary conditions based on soil-atmosphere interaction. This new model enables precise spatio-temporal tracking of evaporation rates and corresponding water redistribution. It is of significance for assessing the stability of soil slopes with cracks under changing climate. Three sets of numerical tests are performed to investigate the effects of different environmental conditions on the evaporation process: various groundwater tables, atmospheric conditions and crack morphologies. Results revealed that alterations in groundwater levels modify water recharge pathways, leading water content reduces firstly at soils where away from the water table. Atmospheric conditions, represented by Datm, affect the migration of water vapor. When Datm is low, it leads to the accumulation of vapor at the soil-atmosphere interface, consequently decreasing the rate of evaporation. Furthermore, crack morphology plays a significant role in evaporation process at crack surface, notably expediting water loss between cracks, particularly in closer proximities.