Estimation of human damage and economic loss of buildings related to tsunami inundation in the city of Augusta, Italy

We propose a methodology to assess tsunami risk in terms of human damage (HD: the quantification of people affected/killed by the tsunami) and economic loss (EL: the loss of the economic value of constructions damaged/destroyed by the tsunami). The methodology makes a combined use of detailed information on buildings, demography and reasonable tsunami inundation heights (IH). First, after defining the tsunami inundation area, we estimate the level of damage to each building within this area, which depends on the building vulnerability and on the flow depth (FD) affecting the building. To estimate the HD, by making use of census data, we infer the number of people present in each residential building of the inundated area. Then, based on FD and building damage, we evaluate the level of people exposure. Finally, we provide an estimate of fatalities. The EL is computed for two types of constructions (residential and trade/industrial) by using data on inundation and data from the real estate market. The methodology is applied to the town of Augusta (eastern Sicily coast, Italy), which, according to historical accounts, was affected by several tsunamis in the course of its history. The results are discussed in terms of the level of damage to buildings, the number of fatalities and the loss of economic value of the building stock for different tsunami sizes. This latter is prescribed through a simple bathtub approach: that is, by assuming uniform IHs with the maximum IH chosen to be consistent with historical data. Partial collapse occurs only above 6 m for residential buildings and above 8 m for trade/industrial buildings. Approximately 47% of the people living in Augusta are potentially affected by the tsunami inundation. For the highest selected IH (10 m), 70% of the people in the inundated area are effectively exposed and the fatalities are estimated at about 47%. The number of people involved increases linearly with the IH, while the number of fatalities increases following a quasi-quadratic law. Finally, the EL is also found to vary linearly with the IH, and the estimated loss in the case of the worst IH (10 m) is around 11% of the gross domestic product (GDP) of the entire province of Siracusa, to which Augusta belongs.