The relationship of human activities and rainfall-induced landslide and debris flow hazards in Central China

Human activities have been recognized as one of the significant influencing factors on natural hazard, yet studies of quantitative relationship between human activities and natural hazard have been limited. The relations of human activities and hazards (landslide and debris flow) induced by heavy rainfall are quantitatively analyzed in this study and suggestions are provided for the integrated hazard mitigation management in the study area of Central China. The results show that human activities index (HAI) is an effective indicator to characterize spatiotemporal changes of human activities. The relations of rainfall-induced landslide, debris flow hazards and human activities are significant as shown in spatial distribution. The probability of rainfall-induced landslide, debris flow hazards is highly correlated with the intensity of human activities and the changes of HAI. However, in terms of temporal relations, human activities have more direct impact on rainfall-induced landslide hazard than on rainfall-induced debris flow hazard, as the frequency of landslide hazard shows  a 2-year delay with HAI changing, in general, according to the cross-wavelet transform analysis. In comparison, no significant correlating period is shown between the changing human activities and the frequency of rainfall-induced debris flow hazard. Specifically, there are three types of time relationship between the changing human activities and rainfall-induced landslide, debris flow hazards in the affected counties: (1) concurrent changing, accounting for 30% of landslide and 18% of debris flow; (2) lagging relationship, accounting for 54% of landslide and 30% of debris flow; (3) no direct relationship, accounting for 16% of landslide and 52% of debris flow. The results in this study suggest that HAI is a simple and effective index for the local governments to manage human impacts on rainfall-induced landslide and debris flow hazards, and integrated prevention measures are suggested to be executed when HAI reaches 0.072. In addition, the types of human activities also impact landslide, as the ratio of Economy factor to Land use factor (E/L) is significantly (P < 0.05) higher in counties with concurrent relationship of changing human activities and frequency of rainfall-induced landslide hazard. The results should assist the policy-making for integrated mitigation of rainfall-induced landslide and debris flow hazards at local/regional level, while balancing economic development and natural hazard.