Debris flows, which can be ferocious in mountainous regions, have been increasingly rampant in arid areas, threatening nearby residents and properties. Inadequate high-quality data, labor-intensive image interpretation, inefficient field surveys, and traditional singular-variable analyses underscore the necessity for an integrative and efficient approach to evaluate debris flow scales and activities. Thus, an integrative debris flow scale-activity assessment methodology is developed, composed of parameters commonly studied and those feasible for extraction from accessible sources, leveraging dynamic avulsion of fans with distinct morphometry and boulder visibility in images. Resultantly, channel number, fan size, maximum critical shear stress, and debris flow event frequency are acquired as potential index parameters via geomorphometric analysis and image segmentation. The composite index generation, established based on these parameters and principal component analysis, is highly effective and accurate, benefiting from program efficiency, interpretation-based error control, parameter validation, and data preservation. Comprehensively, three types of debris flow processes were identified in the study region, distinguished by water content and sediment composition. Parameter and index results reveal considerable spatial-temporal disparities, complex relationships, and clustering patterns (Moran's I = 0.08) across debris flow and aridity types owing to environmental variances. The index (degree) exhibits an increasing-decreasing transition from low-index hyper-concentrated flows to high-index debris floods and debris flows and declines to less impactful debris floods as aridity decreases due to different sediment and water discharge and source. Generally, high indices tend to concentrate in the southern and glacierized northern valleys, exhibiting medium impact ranges, high maximum critical shear stress, and dynamic channel activities regarding channel quantities and event frequencies. Hence, the results correlate with debris flow formation criteria and mechanisms, suggesting a reliable composite indicator for debris flow assessment and providing guidance for debris-flow risk mitigation.