Risk management has reduced vulnerability to floods and droughts globally1,2, yet their impacts are still increasing3. An improved understanding of the causes of changing impacts is therefore needed, but has been hampered by a lack of empirical data4,5. On the basis of a global dataset of 45 pairs of events that occurred within the same area, we show that risk management generally reduces the impacts of floods and droughts but faces difficulties in reducing the impacts of unprecedented events of a magnitude not previously experienced. If the second event was much more hazardous than the first, its impact was almost always higher. This is because management was not designed to deal with such extreme events: for example, they exceeded the design levels of levees and reservoirs. In two success stories, the impact of the second, more hazardous, event was lower, as a result of improved risk management governance and high investment in integrated management. The observed difficulty of managing unprecedented events is alarming, given that more extreme hydrological events are projected owing to climate change3.

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The need to consider disaster risk reduction at the time of recovery is well-recognized. Viable disaster risk reduction measures should resolve the root causes of predisaster vulnerabilities. Accordingly, we investigated the recovery from the impact of Cyclone Aila in Koyra Upazila, Bangladesh, which was severely damaged by this 2009 cyclone. Our research focused on understanding pre-Aila vulnerabilities to cyclone impact and examined the degree of inclusion of vulnerability reduction measures within the recovery process. A composite methodology that included an institutional survey, key informant interviews, collection of the judgment of experts, focus group discussions, and a score-based quantification technique was adopted. Through a process of understanding pre-Aila vulnerabilities, recognition of the root causes of these inherent weaknesses, and identification of appropriate measures for pre-Aila vulnerability reduction, a set of 23 indicators were selected to represent the most desirable vulnerability reduction measures to implement during recovery. A score-based technique was applied to measure the degree of inclusion of vulnerability reduction within the recovery with respect to the indicators. The scoring result shows that the degree of inclusion of vulnerability reduction within the recovery was poor. The result specifies that among the 23 indicators of potential vulnerability reduction measures, 10 are completely missing and the rest are only partially included. The overall findings imply that the Koyra community continues to live with a vulnerability similar to that of the pre-Aila period.

The Ganges-Brahmaputra (GB) delta is one of the most disaster-prone areas in the world due to a combination of high population density and exposure to tropical cyclones, floods, salinity intrusion and other hazards. Due to the complexity of natural deltaic processes and human influence on these processes, structural solutions like embankments are inadequate on their own for effective hazard mitigation. This article examines nature-based solutions (NbSs) as a complementary or alternative approach to managing hazards in the GB delta. We investigate the potential of NbS as a complementary and sustainable method for mitigating the impacts of coastal disaster risks, mainly cyclones and flooding. Using the emerging framework of NbS principles, we evaluate three existing approaches: tidal river management, mangrove afforestation, and oyster reef cultivation, all of which are actively being used to help reduce the impacts of coastal hazards. We also identify major challenges (socioeconomic, biophysical, governance and policy) that need to be overcome to allow broader application of the existing approaches by incorporating the NbS principles. In addition to addressing GB delta-specific challenges, our findings provide more widely applicable insights into the challenges of implementing NbS in deltaic environments globally.

Abstract. As the adverse impacts of hydrological extremes increase in many regions of the world, a better understanding of the drivers of changes in risk and impacts is essential for effective flood and drought risk management and climate adaptation. However, there is currently a lack of comprehensive, empirical data about the processes, interactions, and feedbacks in complex human–water systems leading to flood and drought impacts. Here we present a benchmark dataset containing socio-hydrological data of paired events, i.e. two floods or two droughts that occurred in the same area. The 45 paired events occurred in 42 different study areas and cover a wide range of socio-economic and hydro-climatic conditions. The dataset is unique in covering both floods and droughts, in the number of cases assessed and in the quantity of socio-hydrological data. The benchmark dataset comprises (1) detailed review-style reports about the events and key processes between the two events of a pair; (2) the key data table containing variables that assess the indicators which characterize management shortcomings, hazard, exposure, vulnerability, and impacts of all events; and (3) a table of the indicators of change that indicate the differences between the first and second event of a pair. The advantages of the dataset are that it enables comparative analyses across all the paired events based on the indicators of change and allows for detailed context- and location-specific assessments based on the extensive data and reports of the individual study areas. The dataset can be used by the scientific community for exploratory data analyses, e.g. focused on causal links between risk management; changes in hazard, exposure and vulnerability; and flood or drought impacts. The data can also be used for the development, calibration, and validation of socio-hydrological models. The dataset is available to the public through the GFZ Data Services (Kreibich et al., 2023, https://doi.org/10.5880/GFZ.4.4.2023.001).

Exploring whether society is sufficiently equipped and motivated to adopt planned interventions is vital for modern plan development trajectories. The Motivation and Ability (MOTA) framework offers a tool to assess the societal adoptability of plans by exploring stakeholders' motivations and abilities. It was originally developed to assess plan implementation feasibility for structural measures of flood management in the Mekong Delta. Further development is necessary before applying the tool in other contexts and for other types of planning interventions. Institutional measures like participatory water management (PWM) have long been recognized as essential elements for water management, but have so far also remained out of the reach of conventional planning assessment tools such as cost–benefit or cost-effectiveness analyses. This research, therefore, aims at extending the MOTA tool in the context of PWM reforms in Bangladesh. It does this by, first, further detailing the MOTA components and identifying indicators for quantification and, second, an expert validation and application of this framework for coastal communities in Bangladesh. Our results suggest that the MOTA framework is capable of informing policymakers and implementing agencies about how to enhance the stakeholders' motivation and ability to ensure an enduring implementation of PWM reforms. HIGHLIGHTS The Motivation and Ability (MOTA) framework appeared recently to capture the societal and institutional dimensions in assessing the implementation feasibility of structural measures. This research further extends the MOTA framework and tests whether this can be applicable in case of assessing the implementation feasibility of soft measures like participatory water management.

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