On July 20, 2024, a rainfall-induced, group-occurring debris flow event occurred in the Malie Valley, southwestern China. This study systematically investigated the damage and rainfall-triggering conditions of the debris flow event using remote sensing data, field surveys, and satellite-based rainfall measurements. Debris flows were commonly initiated by mobilizing widespread shallow landslides on steep slopes. Among them, the Lannisanwan (LNSW) debris flow was the most extensive and destructive, and its impact was amplified due to several factors, such as steep terrain gradient, high channel sinuosity index, and significant accumulation of loose material. The LNSW debris flow reached a velocity of 5.29 m/s and a peak discharge of 2,304.30 m3/s at the catchment outlet. Furthermore, the convergence of debris flows from tributaries exacerbated the hazards alongside the main valley channel. Though the event was triggered by the short-duration night rainfall, with a peak intensity of 25.44 mm/h, antecedent rainfall played a critical role. Rainfall analysis revealed that the 3-day antecedent effective rainfall total was as high as 108.75 mm, 4 to 20 times greater than those of past heavy rainfall events in the area. This study emphasizes the importance of antecedent rainfall preceding intense rainfall on landslide-type debris flows and highlights the aggravating effects of group-occurring and night-occurring on the magnitude and consequences of debris flows.

Southwest China was affected by two extreme droughts in the autumn to spring of 2012-2013 and the winter to summer of 2020-2021. These droughts caused water depletion, crop damage, and socio-economic disruption. However, little is known about the accurate representation of the two drought events and the responses of vegetation to the droughts. We used multiple vegetation indices and multi-source climate data to quantify the spatiotemporal variations of the two events. We assessed the different responses of vegetation greenness in Southwest China to the two drought events to determine the underlying mechanisms. Vegetation greenness in Southwest China showed different responses to the two events due to differences in the early hydrothermal conditions. The 2012-2013 autumn-spring drought suppressed vegetation growth in Southwest China, with a total decrease of 0.17 (31.7 %) in the normalized difference vegetation index relative to the baseline conditions in the early stage of the drought. The decrease in precipitation and soil water depletion in late summer 2012 aggravated the decrease in vegetation greenness from winter 2012 to spring 2013. By contrast, during the winter-summer drought in 2020-2021, there was an increase of 0.22 (52.3 %) in the normalized difference vegetation index in January-March 2021 relative to the baseline conditions. Adequate precipitation and soil water in the late summer to autumn of 2020 compensated for water loss due to the extreme drought, and, concurrently, more downward solar radiation and warmer conditions linked to less cloudiness contributed to vegetation greening in spring 2021. These results show that early hydrothermal conditions have a vital role in the different responses of vegetation greenness to extreme drought events. These results will help in water management and ecosystem protection in the current background of more frequent extreme weather and climate events resulting from the global climate crisis.

In the early 21st century, Southwest China (SWC) frequently experienced extreme droughts and severe haze pollution events. Although the meteorological causes of these extreme droughts have been widely investigated, previous studies have yet to understand the causes of haze pollution events over SWC. Moreover, the associations between winter atmospheric teleconnections during drought and haze pollution event across SWC has received negligible attention and therefore warrants investigation. This study examines the associations between the atmospheric teleconnections with respect to winter droughts and winter haze pollution over SWC. Our main conclusions are as follows. (1) Winter precipitation and winter haze days (WHD) over SWC had three major fluctuations from 1959 to 2016. (2) The atmospheric circulation pattern over the Eurasian (EU) continent associated with WHD over SWC resembled that of winter droughts over SWC, where both can be characterized by an EU teleconnection pattern. The Arctic Oscillation (AO) mainly induced the atmospheric circulation pattern over the EU continent that is associated with WHD over SWC. (3) The sea surface temperature (SST) and low circulation anomalies in the Pacific and north Atlantic associated with WHD were similar to those associated with winter droughts over SWC. La Nina events and negative phases of the North Atlantic Oscillation (NAO) may induce winter drought and increase the WHD over SWC. (4) Compared with winter drought over SWC, the variation in the WHD was more complex and the factors affecting WHD were more diverse, and winter drought and its related atmospheric circulations were important factors that induced haze pollution over SWC. Overall, this study not only fills a gap in the literature with respect to the associations between the atmospheric teleconnections of winter drought and winter haze pollution over SWC, but also provides an important scientific basis for the development of potential predictions of local monthly haze pollution, which improves the forecast accuracy of local short-term haze pollution and enriches the theoretical understanding of the meteorological causes of local haze pollution. (C) 2020 Elsevier B.V. All rights reserved.