Analysis of the Risk of Windstorm (angin puting beliung) in Indonesia

Windstorm is “angin puting beliung” in Indonesian, which corresponds to local wind event over spatial range of 5 to 10 km during a short period of time, typically for 3 to 5 minutes. Out of all the natural disasters in Indonesia from 1815-2014, the windstorm is responsible for about 21%. Windstorm in Indonesia causes damages in various forms, among which damages on houses frequently result in injury or casualty due to windborne debris. It is postulated that the geographical differences in the occurrences of the windstorm are caused by the characteristics of the regions, topography, climate and urbanization. Since the windstorm occurs randomly in space and time, prediction or observation is very difficult and so is preparation; hence, the risk assessment of the potential windstorm is even important as preemptive measure for the mitigation of windstorm disaster. In this study, we analyzed the degree of risk through a wind speed of regional statistics and the affected areas of windstorm damage in Indonesia from August 2011 to June 2015, which contained information in terms of frequency of occurrence and its distribution, also damage to property and housing (minor to heavy damage). In order to determine the specific wind region for windstorm, and frequency distribution of the windstorm damages, the calculation of wind speed for wind hazard assessment was performed through surface roughness and terrain model, by classifying the case of windstorm in high-occurrence areas in the three provinces in Java Island; Banten, Yogyakarta, and Jakarta areas. The results show that the urban area over flat terrain results experiences the reduction of the wind speed, while the area near to coast or with large slope results in the increase of the wind speed up to 25%.