Natural disaster is inevitable phenomenon. Awareness on frequency, scale of loss (casualty and property) and nature of any disaster event are important for preparedness to cope with the consequences of such disaster before and after its occurrence. In this context, capability of recent development on webGIS and Spatial Data Infrastructure (SDI) system can provide a good platform for disseminating statistics and status of historical disaster events and their assessment. Based on these events, preliminary risk assessment on vulnerability, hazard and risk can be assessed dynamically and disseminate instantly. This paper presents on the design and development of the interactive web based distributed webGIS and SDI system within open source Geographic Information System (GIS). The system covers to provide national, district and vdc level information on historical disaster events, their interacting mapping on distribution of economic and physical loss. The system is equipped with criteria based dynamic risk assessment for a given weight to each of the risk parameter, which can be used for future disaster preparedness, planning, spatial decision making and disaster risk reduction processes.