Assessing total economic loss of a potential tsunami thread in Chabahar Bay

Introduction
Tsunami is a series of water waves caused by the displacement of a large amount of water which is generated by underwater earthquake, volcano, landslide or other disturbances below water. The Makran Subduction Zone (MSZ) is one of the regions that have potential to generate tsunami which also has been occurred in 1985 and is capable of another one. In MSZ, the coasts of Chabahar Bay are at risk of tsunami. This bay is an important region from economical aspect for Iran and there are two important ports there which make it strategic for economy and international trade. According to their location in bay, in case of tsunami, there will be huge loss because of delay in ships schedule for import and export and to the ports facilities. So in this study, the aim is to estimate total economic loss from Makran zone tsunami for local economy.
According to a numerical simulation of tsunami based on a probable earthquake, all coastal zones areas in Chabahar bay with inundation map are considered in three assumed scenarios (weak, moderate and strong) which is shown in Figure 1.
 
Figure 1- Inundation tsunami area in Chabahar Bay in worst scenario
To have a better view of total economic loss, we estimate TEL for two scenarios. In worst scenario with earthquake magnitude of about 9.1 Richter and maximum inundation all sectors will be affected by tsunami but in best scenario with earthquake magnitude of about 8.1 Richter only human life lost and two damaged trade ports will be the significant items. Although we have tried to consider as much as possible items, but because of lack of data, the Total Economic Loss (TEL) is minimum loss to Chabahar bay.
Marine hazard costs are categorized in three groups include direct costs, indirect costs and hidden costs. In this study we have applied Probable Maximum Loss (PML) to estimate total costs. The damage of tsunami could consider in four sectors include: social sectors, infrastructure, productive sectors and cress-sector.
Material and Methods
Among all mentioned sectors, buildings are more vulnerable to tsunami which PTVA model is used for that. This model was developed to provide first order assessment of building vulnerability and by calculating Relative Vulnerability Index (RVI) for each coastal zone building, the probable loss in residential zones in Chabahar Bay is estimated.
RVI for each building has estimated as follow:
RVI = 2/3 (SV) + 1/3 (WV)
Where SV is the standardized score for the structural vulnerability and WV is the standardized score for the vulnerability to water intrusion. For other sectors we have applied appropriate economic methods include damage cost and replacement cost approach and for those that there were no data and accurate documents, benefit transfer method have been used.
Each coastal region is divided to sub areas and in accordance with inundation map, via google map and other official documents, numbers of buildings and their characteristics are provided. Then with economic methods and PTVA model, economic loss for all sectors has been calculated.
Discussion of Results & Conclusions
The purpose of this study is to estimate the total economic loss of probable tsunami in Makran zone and especially in Chabahar bay in Iran. As this bay is very strategic for international trade and fishery in south of Iran, the costs of marine hazards like tsunami is economically important. For doing that affected sectors is categorized to four items includes: social sector, infrastructure, productive sector and cross-sectoral. In social sector, housing is the most vulnerable and important item which needs additional consideration. So the special model for buildings are provided by Papathoma et al. in 2003 and by considering each building characteristics, the vulnerability index and the total loss could be estimate. The second important item is human life loss that is one of the most costs in all marine hazards especially tsunami. In 2011 tsunami in Japan, about 15,000 people were lost or died which is a huge loss. Infrastructures and constructions in coastal areas are more fragile in tsunami and by stop their services, additional costs will occur after tsunami.
In Chabahar bay only in Chabahar province and Konarak province there is population and production firms and because of that only the inundation map for these two regions are considered. Inside bay, only one desalination plant is working and there are no residential places. These maps are shown in figure 2.
 




 
 




Figure 2- Inundation map of tsunami in residential regions in Chabahar Bay
 
The total estimate of damages and losses from probable tsunami in MSZ in Chabahar Bay in two scenarios (worst scenario and best scenario) is summarized in table 1. As shown in table 1, in worst scenario human life lost and ports is the first and second item of economic costs. In this scenario the total impact is about US$ 1.4 billion that could accrue if suitable management risk don’t establish in this area. In best scenario total loss is equal to US$ 828 million and ports are the first target for damages of tsunami waves.
Table 1- Summary of damage and losses from probable tsunami in Chabahar bay





Sectors for damage


Total Impact (Damage and Losses) ($ 2014)
In worst case


Total Impact (Damage and Losses) ($ 2014)
In best case






Social sector


 


 




Housing


16,455,660


-




Health


18,000


18,000




Human life


500,000,000


250,000,000




Education


5,468,750


-




Culture and religion


16,900


-




Infrastructure


 


 




Transports


1,321,370


-




Ports (50% damage)


450,000,000


450,000,000




Energy


622,525


-




Communication


1,414,430


-




Water and sanitation


3,859,957


1,278,985




Breakwater


6,338,683


4,282,218




Productive sector


 


 




Fisheries and lobsters


121,090,836


121,090,836




Enterprises


308,456,107


-




Corss-sectoral


 


 




Governance


201,000


-




Environment


1,305,057


1,305,057




Total Impact


1,416,568,295


827,975,096





 
The total impact in best scenario is about US$ 827 million which is still considerable. The second stage impacts is make low GDP growth and reciprocate of that needs much time an effort. Although it is not possible to omit all damages and losses but by put some rules for building construction, provide appropriate guide and evacuation map to resident and give informational brochures to resident and tourists, we could diminish economic costs of tsunami in Chabahar Bay.