Stylized sociohydrological models have mainly used social memory aspects such as community awareness or sensitivity to connect hydrologic change and social response. However, social memory alone does not satisfactorily capture the details of how human behavior is translated into collective action for water resources governance. Nor is it the only social mechanism by which the two‐way feedbacks of sociohydrology can be operationalized. This study contributes toward bridging of this gap by developing a sociohydrological model of a flood resilience that includes two additional components: (1) institutions for collective action, and (2) connections to an external economic system. Motivated by the case of community‐managed flood protection systems (polders) in coastal Bangladesh, we use the model to understand critical general features that affect long‐term resilience of human‐flood systems. Our findings suggest that occasional adversity can enhance long‐term resilience. Allowing some hydrological variability to enter into the polder can increase its adaptive capacity for resilience through the preservation of social norm for collective action. Further, there are potential trade‐offs associated with optimization of flood resistance through structural measures. By reducing sensitivity to floods, the system may become more fragile under the double impact of floods and economic change.

Flood inundation maps play a key role in assessment and mitigation of potential flood hazards. However, owing to high costs associated with the conventional flood mapping methods, many communities in the United States lack flood inundation maps. The objective of this study is to develop and examine an economical alternative approach to floodplain mapping using widely available soil survey geographic (SSURGO) database. In this study, floodplain maps are developed for the entire state of Indiana, and some counties in Minnesota, Wisconsin, and Washington states by identifying flood‐prone soil map units based on their attributes. For validation, the flood extents obtained from SSURGO database are compared with the extents from other floodplain maps such as the Federal Emergency Management Agency issued flood insurance rate maps (FIRMs), flood extents observed during past floods, and flood maps derived using digital elevation models. In general, SSURGO‐based floodplain maps (SFMs) are largely in agreement with other flood inundation maps. Specifically, the floodplain extents from SFMs cover 78‐95% area compared to FIRMs and observed flood extents. Thus, albeit with a slight loss in accuracy, the SSURGO approach offers an economical and fast alternative for floodplain mapping. In particular, it has potentially high utility in areas where no detailed flood studies have been conducted.

ABSTRACT. Modern social-ecological systems are often partly engineered to enhance the robustness (or reduce the variance) of human welfare to environmental fluctuations over a foreseeable time horizon. Recent studies show, however, that subtle trade-offs are usually inherent in such efforts of enhancing short-term robustness. Managing variance on short time scales is likely to be associated with the buildup of hidden fragilities on longer time scales. Using a flood-prone social-ecological system (SES) of coastal Bangladesh as an example, this paper investigates some of the ways in which such robustness-fragility trade-offs can manifest. This SES has been extensively modified in the last few decades through the construction of large-scale flood protection structures (polders) and the introduction of commercial shrimp farming to enhance the robustness of food production to hydrological variability. Our case study analysis of the long-term changes in the SES shows that, although the modifications helped with stability in short time scales, the resulting changes also induced unforeseen problems such as infrastructure maintenance issues, land degradation and sinking, and exposure to market volatility. With this paper therefore we contribute to better understanding of the notion of robustness-fragility trade-offs by illustrating an exemplary case of the phenomenon in the engineered coastal environment context.

Floodplain delineation may inform protection of wetland systems under local, state, or federal laws. Nationally available Federal Emergency Management Agency Flood Insurance Rate Maps (FIRMs, “100‐year floodplain” maps) focus on urban areas and higher‐order river systems, limiting utility at large scales. Few other national‐scale floodplain data are available. We acquired FIRMs for a large watershed and compared FIRMs to floodplain and integrated wetland area mapping methods based on (1) geospatial distance, (2) geomorphic setting, and (3) soil characteristics. We used observed flooding events (OFEs) with recurrence intervals of 25‐50 to >100 years to assess floodplain estimate accuracy. FIRMs accurately reflected floodplain areas based on OFEs and covered 32% of river length, whereas soil‐based mapping was not as accurate as FIRMs but characterized floodplain areas over approximately 65% of stream length. Geomorphic approaches included more areas than indicated by OFE, whereas geospatial approaches tended to cover less area. Overall, soil‐based methods have the highest utility in determining floodplains and their integrated wetland areas at large scales due to the use of nationally available data and flexibility for regional application. These findings will improve floodplain and integrated wetland system extent assessment for better management at local, state, and national scales.

A community capacity to cope with flood hazards, or community flood resilience, emerges from the interplay of hydrological and social processes. This interplay can be significantly influenced by the flood control strategy adopted by a society, i.e., how a society sets its desired flood protection level and strives to achieve this goal. And this interplay can be further complicated by rising land‐sea level differences, seasonal water level fluctuations, and economic change. But not much research has been done on how various forms of flood control strategies affect human‐flood interactions under these disturbances and therefore flood resilience in the long run. The current study is an effort to address these issues by developing a conceptual model of human‐flood interaction mediated by flood control strategies. Our model extends the existing model of Yu et al. (2017), who investigated the flood resilience of a community‐based flood protection system in coastal Bangladesh. The major extensions made in this study are inclusions of various forms of flood control strategies (both adaptive and nonadaptive ones), the challenge of rising land‐sea level differences, and various high tide level scenarios generated from modifying the statistical variances and averages. Our results show that adaptive forms of flood control strategies tend to outperform nonadaptive ones for maintaining the model community's flood protection system. Adaptive strategies that dynamically adjust target flood protection levels through close monitoring of flood damages and social memories of flood risk can help the model community deal with various disturbances.