## 1 Introduction
### Four Generations of Flood Management  
The first human response to floods or any natural hazard was to adapt. Human lifestyle and activities were adjusted to ensure minimum interference to waterways [6]. This indigenous era of flood adaptations started in the 19 th century and included growing flood-resistant crops, relocating dwellings, and early embankments.  
Growing urbanization and greater economic exposure in floodplains heralded the second generation of flood management, which was mainly characterized by structural measures to control and defend against floods. Flood control remained the dominant approach for the late 19 th century and most of the 20 th century. Initially, flood protection measures were designed to ensure that structures or measures must follow a minimum standard; this design approach was known as the element-design approach. For example, flood protection structures were designed in light of historical flood experiences [21; 22]. Despite involving analyses of previous floods, they were not optimized in terms of a cost-to-benefit ratio. This approach is still taken in situations where high accuracy is not required [23]. However, the realization dawned that structures should be designed where there is a known probability of occurrence. As a result, probability-based safety standards were developed and implemented by prioritizing safety in the field of hazard and disaster management while controlling the return period of the flood [18]. A probability-based standard can be applied only when the risk falls below an arbitrary level, and these methods lack the ability to combat severe floods [4].  
Although second-generation flood control was primarily an engineering approach, it produced more societal confidence in flood management. Nevertheless, there was a range of drawbacks, including growing exposure in a floodplain, detrimental environmental effects, and catastrophes once the flow exceeds the design flood. Initially, nonstructural measures were introduced to support the structural measures, but later on, the nonstructural possibilities were also presented as an alternative to conventional engineering solutions in the third generation of flood management. The main focus was on reducing the susceptibility to flooding or the exposure in the floodplain. Floodproofing, early warning systems, evacuation plans, public awareness, and flood zoning were introduced.  
Substantial analyses of the strengths and failures of nonstructural approaches and the recurrence of severe and extremely devastating floods have culminated in a variety of strategies (rather than a single strategy) based on a more holistic approach (fourth generation) to address floods and the root causes of flooding [24]. The approach emphasizes the inclusion of all possible measures and adaptations at the catchment, river, and floodplain levels. Flood insurance and resilience capacities are recognized as flood management options. The involvement of multiple options at different stages of flood generation and flooding need criteria that would be capable of expressing the efficiencies of spending and the benefits thus obtained. Probability-based design standards failed to support the holistic approach. Risk-based assessment gained popularity due to its ability to assess and design measures under diverse situations and options. Risk-based criteria are also helpful when choosing the appropriate flood management strategy [25].