Backward induction-based multi-layer approach for watershed flood management in arid regions.

Managing floods in interconnected nonurban and urban areas of arid regions prone to flash floods requires a more dynamic and integrated approach than traditional linear methods. In this regard, this study proposes a novel multi-stage decision-making framework which reshapes the traditional cascade approach to flood management by addressing the interdependencies between upstream and downstream regions. The proposed cyclic decision-making process involves five main steps: First, the Hydraulic and Hydrological (H/H) conditions in urban and nonurban areas were modeled using the SWMM. Then, a multi-stage optimization framework was constructed, in the first step of which the detention dams' location and dimensions were optimized in the nonurban area. Next, to link the first and second stages of the optimization, COPRAS method was employed for selecting the critical upstream management strategies. These strategies were determined as the input for the flood network optimization in the second stage. Finally, the Backward Induction Game Theory (BIGT) method was employed to find the best management strategy, under which not only the upstream conditions were considered in downstream flood protection but also stakeholders' conflicts were totally resolved by choosing the Nash Equilibrium. Our findings revealed that the implementation of the selected scenario could reduce flood peaks at the entrance of urban areas by 60.7 % and enhance shock absorption by 81.8 %. In fact, we guarantee that it is possible to propose a scenario encompassing drainage and detention dams' characteristics that, in addition to resolving stakeholders' conflicts of interest, can reduce the risk of flooding in complex watersheds. Moreover, the framework transforms the sequential, one-way cascade decision-making process into a continuous cycle, where upstream and downstream's H/H conditions and stakeholders' preferences are evaluated in coordination to achieve an agreement. Also, this framework helps decision-makers access the most sustainable solutions considering hydrological and socio-economic points of view.