Evaluation of rainfall thresholds triggering debris flows in western China with gauged- and satellite-based precipitation measurement

Abstract

In recent years, global satellite precipitation accuracy has improved considerably, and their application have increased widely. However, research on rainfall thresholds of debris flows (DF), particularly in China, is insufficient. In this study, rainfall thresholds triggering DF were evaluated in the western region of China (WRC) using four high-resolution satellite-based precipitation datasets, combined with gauge measurements and a DF inventory containing over 523 events for 2000–2021. The results showed that the ability of satellite products to capture rainfall-triggering DF (Rtrig) was generally higher than that of gauge observations. Global Precipitation Measurement (GPM) showed the best overall performance throughout the WRC, with a 98.9 % probability of detection (POD) for heavy rainfall. However, it exhibited a relatively poor ability to capture Rtrig in the western region of the WRC. The four satellite products exhibit complementary advantages in terms of their spatial distribution. The combined ability of all four satellite products perfectly captured Rtrig, with a POD of 100 % over the WRC. The critical daily Rtrig estimated from GPM was the highest, which exhibited an overall decreasing trend from the east (>100 mm) to the west (<50 mm) in the WRC. The critical rainfall duration estimated from satellite products was generally less than three days in the WRC, particularly in western Sichuan. The antecedent effective rainfall of the first 6, 10, and 14 days was critical for triggering DF in the WRC. The critical rainfall event-duration (E-D) curves of the WRC at low and medium early warning levels were consistent with the global E-D curves estimated from other studies. The mean early warning rainfall of the WRC at 3 h, estimated from the four products, was 16.5, 20.9, and 37 mm at the low, medium, and high levels, respectively. The corresponding warning rainfall values at 24 h were 64.2, 91.4, and 152.6 mm, for low, medium, and high levels, respectively. The critical rainfall intensity-duration curve fitted in each subregion showed a higher reliability than the curve of the WRC, with a fitted R2 higher than 0.80. The short-term (<9h) rainfall intensity in each region was higher than that of the entire WRC at all early warning levels. A combination of multi-source satellite precipitation products is recommended to further improve the accuracy of satellite-based measurements at the local scale.