Characteristics of the 14 April 1999 Sydney hailstorm based on ground observations, weather radar, insurance data and emergency calls

International audienceHailstorms occur frequently in metropolitan Sydney, in the eastern Australian State of New South Wales, which is especially vulnerable due to its building exposure and geographical location. Hailstorms challenge disaster response agencies and pose a great risk for insurance companies. This study focuses on the Sydney hailstorm of 14 April 1999 ? Australia's most expensive insured natural disaster, with supporting information from two other storms. Comparisons are drawn between observed hailstone sizes, radar-derived reflectivity and damage data in the form of insurance claims and emergency calls. The "emergency response intensity" (defined by the number of emergency calls as a proportion of the total number of dwellings in a Census Collection District) is a useful new measure of the storm intensity or severity experienced. The area defined by a radar reflectivity ?55 dBZ appears to be a good approximation of the damage swath on ground. A preferred area for hail damage is located to the left side of storm paths and corresponds well with larger hailstone sizes. Merging hail cells appear to cause a substantially higher emergency response intensity, which also corresponds well to maximum hailstone sizes. A damage threshold could be identified for hailstone sizes around 2.5 cm (1 cm), based on the emergency response intensity (insurance claims). Emergency response intensity and claims costs both correlate positively with hailstone sizes. Higher claim costs also occurred in areas that experienced higher emergency response intensities

Mapping temporally-variable exposure to flooding in small Mediterranean basins using land-use indicators

This article deals with mapping exposure (or external vulnerability) to flood risk in two typical Mediterranean ephemeral streams: the Barranco de Carraixet and the Rambla de Poyo. The floodplains of both streams are within the metropolitan area of the city of Valencia (Spain"s third largest city). Following the Mediterranean model, they are very fertile areas (with intense periurban and highly productive agriculture) which have recently absorbed the great urban expansion of the metropolis. Hydrologically these basins remain dry for most of the year, but become particularly dangerous during flash-flood events. They generate a risk pattern highly dependent on exposure since, in general, the hazard factor is very difficult to map, given the unpredictable nature of flash-floods. This work constitutes a proof of concept based on simple estimators obtained from land uses. External vulnerability or exposure is evaluated as a function of economic land value and human exposure to hazard. Land value is directly taken from the cadastre whilst human exposure is indirectly estimated from the location of population in relation to timeeactivity profiles. The temporal dimension is introduced and three exposure scenarios have been mapped, related to different time periods: working days, nights, weekends and holidays. The results show different patterns of exposure for each plain. In Carraixet floodplain exposure is greater at night and on weekends and holidays than during working hours, on account of the dominant agricultural and residential land uses. In the Poyo plain there are no major contrasts in absolute terms between day and night time, although spatial patterns of exposure vary from day to night: during the day, exposure is higher in industrial and commercial areas (around communication routes) whilst at night residential areas show more exposure

Flood risk assessment and mapping in peri-urban Mediterranean environments using hydrogeomorphology. Application to ephemeral streams in the Valencia region (eastern Spain)

This paper proposes a methodology for mapping flood risk in ephemeral streams, based on assessing flood hazards and global exposure. The method has been applied to the peri-urban area of Valencia, extended over the floodplains of the Barranco del Carraixet and Rambla de Poyo catchments. Hazard was assessed using hydrogeomorphological methods. Global exposure was estimated as a combination between the economic value of land use and human exposure, following a previous study carried out by Camarasa, A.M., López, M.J. and Soriano, J., 2011. Mapping temporally variable exposure to flooding in small Mediterranean basins using land-use indicators, Applied Geography 31 (19), 136¿145. Synthesis mapping was elaborated to spatially rank flood risks, in terms of their hazard and exposure components. The method is simple, effective and easily comparable. The results reveal diverse risk configurations for each floodplain, even though both are in the vicinity of Valencia city (metropolitan area). This flood risk mapping method is very useful for land use planning because it enables swift diagnosis of the nature of risks and can supports decision making by risk managers and urban planners

Event trees and epistemic uncertainty in long‐term volcanic hazard assessment of Rift Volcanoes: the example of Aluto (Central Ethiopia)

Aluto is a peralkaline rhyolitic caldera located in a highly populated area in central Ethiopia. Its postcaldera eruptive activity has mainly consisted of self‐similar, pumice‐cone‐building eruptions of varying size and vent location. These eruptions are explosive, generating hazardous phenomena that could impact proximal to distal areas from the vent. Volcanic hazard assessments in Ethiopia and the East African Rift are still limited in number. In this study, we develop an event tree model for Aluto volcano. The event tree is doubly useful: It facilitates the design of a conceptual model for the volcano and provides a framework to quantify volcanic hazard. We combine volcanological data from past and recent research at Aluto, and from a tool to objectively derive analog volcanoes (VOLCANS), to parameterize the event tree, including estimates of the substantial epistemic uncertainty. Results indicate that the probability of a silicic eruption in the next 50 years is highly uncertain, ranging from 2% to 35%. This epistemic uncertainty has a critical influence on event‐tree estimates for other volcanic events, like the probability of occurrence of pyroclastic density currents (PDCs) in the next 50 years. The 90% credible interval for the latter is 5–16%, considering only the epistemic uncertainty in conditional eruption size and PDC occurrence, but 2–23% when adding the epistemic uncertainty in the probability of eruption in 50 years. Despite some anticipated challenges, we envisage that our event tree could be translated to other rift volcanoes, making it an important tool to quantify volcanic hazard in Ethiopia and elsewhere

Communicating Information on Eruptions and Their Impacts from the Earliest Times Until the Late Twentieth Century

Volcanoes hold a fascination for human beings and, before they were recorded by literate observers, eruptions were portrayed in art, were recalled in legends and became incorporated into religious practices: being viewed as agents of punishment, bounty or intimidation depending upon their state of activity and the culture involved. In the Middle East the earliest depiction of an eruption is a wall painting dating from the Neolithic at Çatal Hüyük and the earliest record dates from the third millennium BCE. Knowledge of volcanoes increased over time. In some parts of the world knowledge of eruptions was passed down by oral transmission, but as far as written records were concerned, in the first century CE only 9 volcanoes in the Mediterranean region were recognised, together with Mount Cameroon in West Africa. In the next 1000 years the list grew by 17, some 14 of these volcanoes being in Japan. The first recorded eruptions in Indonesia occurred in 1000 and 1006, and volcanoes in newly settled Iceland increased the number to just 48 in 1380 CE. After this the list continued to increase, with important regions such as New Zealand and Hawaii only being added in the past 200 years. Only from 1900 did the rate of growth decline significantly (Simkin et al. 1981: 23; Simkin, 1993 Siebert et al. 2011; Simkin, 1993), but it is sobering to recall that in the twentieth century major eruptions have occurred from volcanoes that were considered inactive or extinct examples including: Mount Lamington - Papua New Guinea, 1951; Mount Arenal - Costa Rica, 1968 and Nyos - Cameroon, 1986. Although there are instances where the human impact of historical eruptions have been compiled - with examples including the 1883 eruption of Krakatau (Simkin and Fiske (1983) and 1943 -1952 eruption of Parícutin (Luhr and Simkin, 1993) - these are exceptions and there remains a significant gap in knowledge about both the short and long-term effects on societies of major eruptions which occurred before the 1980s. Following a broad review the chapter provides a discussion of the ways in which information has been collected, compiled and disseminated from the earliest times until the 1980s in two case study areas: the Azores Islands (Portugal) and southern Italy. In Italy information on eruptions stretches back to prehistoric times and has become progressively better known over more than 2,000 years of written history, yet even here there remain significant gaps in the record even for events that took place between 1900 and 1990. In contrast, located in the middle of the Atlantic, the Azores have been isolated for much of their history and illustrate the difficulties involved in using indigenous sources to compile, not only assessments of impact, but also at a more basic level a complete list of historical events with accurate dates