Development of Water Resources Risk Index Using the Fault Tree Analysis (Case Study: Urmia Lake Basin)

The negative consequences of losing water resources on human life and other biological diversity has led to requirement of the study on the reliability of basins in supplying water. Therefore, in the present research, for the first time, a risk analysis method was used to identify the vulnerability points of water resources, and provide a comprehensive index in the basin scale. Thus, the undesirable event of the basin was determined using risk analysis method called Fault Tree (FTA). Then, the factors that led to fault occurrence including natural hazards and human threats were identified through causal relationships and with the help of logical gates. The proposed model was applied to a case study in the Urmia Basin which is facing water crisis in recent years. The main risk of Lake Urmia Basin was considered as a top event in the structure of the fault tree due to the occurrence of the factors such as water quantity, water quality, ecological, social and economic failure events. Failure likelihood of the top event was calculated about 58% based on the aggregating the probabilities obtained from experts. Due to this high failure likelihood, in order to increase the confidence of the basin, the Birnbaum Index was used to determine the importance measure of the basic events. According to the results, three events of "Improper governance", "the low level of awareness of people", and ''non-release of environmental rights" had the highest contribution in the occurrence of the top event. According to result of this study, comprehensive index can be proposed as a general benchmark for the study water resources risk in other basins of Iran.