Low-temperature rain and snow disasters in southern China under different winter thermal backgrounds

Low-temperature rain and snow disasters (LTRSDs) are an important winter hazard in southern China, and their activity characteristics vary markedly under different winter thermal backgrounds. Using disaster records from the Encyclopedia of Meteorological Disasters in China , together with station meteorological observations and precipitation-phase data, this study developed an ExtraTrees-based identification model for LTRSDs in 10 provinces of southern China and applied it to retrospectively reconstruct historical LTRSD activity rather than to conduct operational forecasting. The results show that the spatial coverage of solid precipitation, snowfall intensity, precipitation extent, and low-temperature anomalies are key factors influencing disaster occurrence. Based on the identification results, 82 large-scale LTRSD processes were detected. Further analyses show that LTRSDs occurred more frequently in cold winters, persisted longer, and produced more cumulative disaster days, whereas disaster activity was weaker in warm winters, with normal winters showing intermediate characteristics. Disaster activity was concentrated in January and February, and Hunan, Jiangxi, Guizhou, Anhui, and Zhejiang were identified as relatively disaster-prone regions. Composite analyses indicate that the differences in LTRSDs under different winter backgrounds primarily reflect coordinated differences in precipitation-phase structure, moisture-transport pathways, and large-scale circulation background. During LTRSDs in warm winters, anomalous warm-moist transport is mainly confined to relatively lower latitudes, favoring increased rainfall in South China and coastal regions. During LTRSDs in normal and cold winters, the moisture-transport pathway extends farther northward. During LTRSDs in cold winters, its stronger overlap with the cold-anomaly region favors snow- or solid-precipitation-dominated disaster processes in Hunan, Jiangxi, Anhui, and Zhejiang. Overall, the study suggests that winter thermal background is an important factor associated with the occurrence, persistence, and spatial distribution of LTRSD activities in southern China, and provides an impact-based perspective for retrospective LTRSD event reconstruction and comparative disaster characterization in southern China.