This paper is the result of geological survey engineering.

Objective The assessment of mountain hazard risk in Motuo County requires comprehensive consideration of dynamic hydrological processes such as rainfall runoff and snow/ice melt. This study aims to identify and analyze the spatiotemporal characteristics of this risk and reveal the influential mechanisms of dynamic hydrological factors (rainfall runoff and meltwater) on hazard risk evolution.

Methods Slope units were adopted as the fundamental evaluation unit, with a random forest model employed to assess disaster susceptibility. Hydrological simulations of rainfall-runoff and glacial meltwater were conducted using the soil conservation service curve number (SCS–CN) model and the degree-day model, respectively. These components were integrated through the analytic hierarchy process (AHP) to construct a comprehensive hazard assessment model. Furthermore, spatiotemporal risk dynamics were analyzed using seasonal-trend decomposition based on LOESS (STL), the Mann‒Kendall trend test (M‒K test), and Theil–Sen slope estimation. This analytical framework enabled the quantification of long-term trends, seasonal fluctuations, and abrupt change points within the mountain hazard risk (MHR) series from 2010 to 2018, thereby elucidating the spatiotemporal evolutionary patterns of regional disaster risks under the coupled effects of hydrological processes and geomorphic conditions.

Results Spatially, MHR in Motuo County exhibits significant zonal variation. High-risk areas form belts along the Yarlung Tsangpo River and its tributaries, concentrated in the central–southern region, which is characterized by active tectonics, steep terrain, and high rainfall. Low-risk areas occur at high elevations and gentle slopes. Temporally, MHR shows a bimodal pattern: a secondary spring peak driven by snow/ice melt and a dominant summer peak driven by rainfall runoff. The overall annual trend follows a “rising–stabilising–declining” pattern, with the summer peak dictating intra-annual variation. M‒K trend analysis revealed an overall increasing MHR trend from 2010 to 2018, which was particularly significant in mid-low elevation areas of the southwest and, northeast, and southern slopes of high-elevation zones. This reflects the enhanced role of hydrological processes in driving regional hazard risk under climate change.

Conclusions By incorporating dynamic hydrological processes such as rainfall runoff and snowmelt into the spatiotemporal analysis of the MHR, this study reveals its seasonal fluctuation characteristics and long-term trends. Spatially, the MHR is jointly controlled by topography, tectonics, and hydrological conditions, which is characterized by banded clustering along river valleys and tectonic belts. Temporally, the MHR exhibits a double-peak pattern: a primary peak dominated by summer rainfall runoff and a secondary peak driven by spring snowmelt. Overall, a rising trend was observed from 2010 to 2018, with pronounced phased characteristics.