Analysis and Prediction of Geological Disasters Caused by Typhoon Rainstorm

Typhoon is one of the main rainstorm systems in China. Heavy rainstorm caused by typhoon during landfall may lead to geological disasters, such as landslides and mudslides. This study aims to analyze the temporal and spatial characteristics of geological disasters (landslide and mudslide) and the corresponding typhoon heavy precipitation. A procedure of separating and identifying the occurance and risk of typhoon-affected geological disasters is developed. A 26-year (1990-2015) geological disaster inventory for China mainland, with information such as disaster type, intensity and location etc., was compiled from the Ministry of Land and Resources (MLR) online databases and media reports for this study. The geological hazard database includes 29,597 cases of geological disasters, among which 935 cases were caused by typhoon precipitation. The observations show a large geological typhoon-disaster-prone area in eastern China from South (Yunnan Province) to North (Liaoning Province), with a concentration in the coastal areas of Zhejiang, Fujian and Guangdong. The most frequent type of geologic hazard is the landslide, and mainly occurred in summer (June, July, August and September). 64% (i.e., 594) of the total of the typhoon-caused geological disasters occurred in August.

The rainfall thresholds for determining the probability of geological disaster occurrence are derived as a function of rainfall Intensity-Duration (ID) based on the regression analysis, and the threshold equation is . Compared to non-typhoon caused geological disasters, typhoon-caused geological disasters tend to occur because of the rainfall on the same day with higher rainfall intensity and shorter duration. The critical rainfall and the cumulative rainfall are both greater than 24mm, or the cumulative rainfall exceeds 33mm, is a prequisite for typhoon precipitation to induce geological disasters.

The geological disaster susceptibility index was calculated using the frequency ratio method based on elevation, land cover, slope and aspect. The areas with the highest value of the susceptibility index are consistent with the spatial distribution of the heaviest typhoon precipitation during the past 26 years (1990-2015), e.g., eastern Fujian Province, northeastern Zhejiang Province, and the central part of Jiangxi Province. More than 90% of the typhoon-caused geological disasters have the susceptibility index greater than three, which might be used in issuing the warning in an operational geologic hazard warning system.

Key words: Typhoon Precipitation, Landslide, Mudslide, Extreme Rainfall, disaster susceptibility