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Abstract: As crises happen more frequently and in bigger magnitudes in urban communities, disaster prevention and disaster mitigation become increasingly more important. One useful preventive measure is for community members to report relevant risk information before an actual crisis occurs. This paper presents a Public Participation GIS (PPGIS) system called Collaborative Risk Map System (CRMS), which is community based and through which local residents can report risk information of crisis events and share the information in disaster mitigation. Although the Internet and mobile phones are the preferred methods for public participation due to their convenience and ease of use, the feedback information needs to be filtered before usage, so we designed a credibility model to filter out the mendacious information. A risk model of crisis events is also proposed which transformed the static pre-planning to dynamic and timely risk map as a result of public participation. The risk state of the community and reliable risk feedback is displayed on the map using Oracle Spatial technology so that public can see the risk information visually. Through the analysis of risk information, the community can directly access reliable risk information easily and can prepare for it immediately. Most importantly, decision-makers can get the most up-to-date risk information and do more accurate risk analysis so as to make better informed decisions. We demonstrate the prototype system by selecting 20 places to be a community in Chengguan district in Lanzhou, the capital city in Gansu Province, China and selecting fire risk to evaluate its effectiveness and efficiency. [Copyright &y& Elsevier]

• Ill-considered urban planning around Niwan gully may multiply the human and economic losses caused by debris flows. • A depth-integrated model was adopted to determine the hazard zones of debris flows with different recurrence intervals. • The debris flow inundation and evolutionary trajectory are shown to be reasonably comparable with historical debris flows. • This study established a relatively complete system to implement hazard and risk assessment in the study area. The highly geologically active, structurally complex Bailongjiang river basin, Longnan City, Gansu Province hosts many debris-flow gullies. The recent Wenchuan and Jiuzhaigou earthquakes have increased the amount of source material available in these debris flow gullies, and the disturbed nature of the slopes makes them prone to failure under high rainfall, increasing the risk of large-scale debris flows. Moreover, poor urban planning in the region may multiply the human and economic losses caused by debris flows. Therefore, it is necessary to determine the potential hazard zones associated with such debris flows and to implement debris flow hazard and risk assessment. In this paper, Niwan gully is chosen as the study object, as it is characterized by repeated debris flow outbreaks and an ill-considered urban planning at the outlet of the gully. A depth-integrated continuum method is adopted to determine the potential hazard zones of debris flows with different recurrence intervals. The debris flow inundation and evolutionary trajectory are shown to be reasonably comparable with historical debris flows. A two-factor model that couples maximum flow depth with momentum is used to better classify the hazard zones. This study also provides a complete and efficient means to determine the values of debris flow parameters and to implement a hazard and risk assessment based on the solid material reserve method and a probabilistic method. This proposed approach efficiently generated a debris flow risk distribution map that can be used for effective disaster prevention in the Bailongjiang River basin. [ABSTRACT FROM AUTHOR]