Natural Flood Research Articles

The environmental impact of dam construction in a wetland area. A case study Boukhroufa (El Taref) Algeria

This article presents an approach to the assessment of the environmental impact of a dam construction for agricultural use in the Boutheldja region. This region’s environment is rich in natural resources and forms a part of the El Kala National Park (P.N.E.K). It was designated a wetland of international importance under the Ramsar convention by UNESCO in 1983 and later declared a biosphere reserve in 1990. It is among the most significant aquatic areas in this region (contains about 40% of surface water resources). The physical characteristics of the watershed support the construction of the dam, although there could be a number of unfavorable effects: upstream – including soil erosion and reservoir sedimentation, reduced storage capacity, lower water quality and loss of productivity of flooded area; downstream – removal of silt from downstream flows, loss of fertilising functions, changes in water quality, changes in productivity, reduction in natural floods, loss of access to resources and ecological disturbance. Such processes will have an impact on an ecosystem so fragile. Although Boukhroufa dam provides significant benefits to the city, such as controlling stream regime, preventing floods, and supplying agricultural water from stored water, it also has significant negative effects on the surrounding watershed ecosystem.

Improving Flood Streamflow Estimation of Ungauged Small Reservoir Basins Using Remote Sensing and Hydrological Modeling

Small- and medium-sized reservoirs significantly alter natural flood processes, making it essential to understand their impact on runoff for effective water resource management. However, the lack of measured data for most small reservoirs poses challenges for accurately simulating their behavior. This study proposes a novel method that utilizes readily available satellite observation data, integrating hydraulic, hydrological, and mathematical formulas to derive outflow coefficients. Based on the Grid-XinAnJiang (GXAJ) model, the enhanced GXAJ-R model accounts for the storage and release effects of ungauged reservoirs and is applied to the Tunxi watershed. Results show that the original GXAJ model achieved a stable performance with an average NSE of 0.88 during calibration, while the NSE values of the GXAJ and GXAJ-R models during validation ranged from 0.78 to 0.97 and 0.85 to 0.99, respectively, with an average improvement of 0.03 in the GXAJ-R model. This enhanced model significantly improves peak flow simulation accuracy, reduces relative flood peak error by approximately 10%, and replicates the flood flow process with higher fidelity. Additionally, the area–volume model derived from classified small-scale data demonstrates high accuracy and reliability, with correlation coefficients above 0.8, making it applicable to other ungauged reservoirs. The OTSU-NDWI method, which improves the NDWI, effectively enhances the accuracy of water body extraction from remote sensing, achieving overall accuracy and kappa coefficient values exceeding 0.8 and 0.6, respectively. This study highlights the potential of integrating satellite data with hydrological models to enhance the understanding of reservoir behavior in data-scarce regions. It also suggests the possibility of broader applications in similarly ungauged basins, providing valuable tools for flood management and risk assessment.

An Assessment of Land Use and Land Cover Changes on Urban Flooding: A Case Study in Sri Jayewardenepura Kotte

This study investigates the relationship between Land Use and Land Cover (LULC) changes and urban flooding in the Sri Jayewardenepura Kotte Divisional Secretariat Division (DSD). The research objectives include analysing flooding patterns, mapping LULC changes, and assessing the correlation between these changes and flooding occurrences. Additionally, a temporal rainfall variation analysis was conducted to provide further context. The study employed Geographic Information System (GIS) technology, specifically utilising ArcGIS for LULC classification and Inverse Distance Weighting (IDW) interpolation technique for rainfall data. The analysis reveals a clear association between heightened precipitation and major flood events. In 2010, the flood inundation area was 5.762 km² during the major flood in May, despite a monthly rainfall of over 650mm. However, in 2016, with over 700 mm of rainfall in May, the flood-inundated area was reduced to 4.046 km², highlighting the role of other factors such as wetland recovery. Moreover, it identifies significant LULC changes, emphasising rapid urbanisation and wetland decline. From 2009 to 2018, built-up areas increased from 11.49 km² to 14.18 km², while wetlands decreased from 2.29 km² in 2009 to 1.19 km² in 2015, before recovering slightly to 1.58 km² by 2018. The expansion of built-up areas is found to slightly increase flood risks, while wetland recovery acts as a natural flood buffer. This research underscores the importance of targeted interventions for urban flood resilience, such as flood-resistant infrastructure and wetland management. The findings provide critical insights for evidence-based urban planning and flood management strategies, aiming to create more resilient and sustainable urban environments.

Understanding bimodal seas, shingle beach response and flood risk at Hayling Island, UK

Beach management through nourishment and annual recycling has been applied for over 37 years to manage flood and coastal erosion risk to 1700 properties at Eastoke, Hayling Island, UK. This form of natural flood risk management has proved successful in avoiding the annual flooding that blighted this area previously. However, there have been unexpected storm events that have caused beach erosion and localised flooding. Using long-term nearshore wave datasets and state-of-the-art statistical methods, new multi-variate extreme wave conditions were derived and applied to assess beach performance. Eastoke beach was found to meet its original design criteria of a 0.5% AEP standard of protection for unimodal wave conditions. However, it experiences greater rollback erosion, wave overwash and therefore flood inundation under certain (but not all) bimodal wave conditions, causing uncertainty around the future standard of protection. Communicating these inconsistencies to practitioners and a non-specialist audience is challenging as we tend to oversimplify, despite every beach and storm being unique. Better understanding of mixed beaches, both in situ and through parametric and numerical models, would reduce uncertainty to ensure communities are resilient to climate change.

Coupling dynamics of urban flood resilience in china from 2012 to 2022: A network-based approach

Urban flooding presents a significant challenge in Chinese cities, necessitating a deeper understanding of the coupling effects of China's urban flood resilience for effective resilience planning. This study introduces a four-component Environment-Institution-Infrastructure-Agent (EIFA) framework and utilizes an updated correlation network approach to analyze the temporal variation of coupling effects of urban flood resilience across 639 Chinese cities from 2012 to 2022. The findings indicate a decline in synergy and increased tradeoffs, primarily due to intensified competition within and between institutional and infrastructural sectors, marginal impacts of infrastructure investments, and socially excessive infrastructure. The study also highlights the agent component's strong internal and inter-component coupling effects, implying the effectiveness of China's people-centered resilience strategies, though risks of decoupling remain. Additionally, it notes a good match between societal urban flood resilience and natural flood risks, while natural vegetation loss due to urban expansion is noteworthy. The study further suggests that refining agent-focused deposit and insurance policies could coordinatively enhance urban flood resilience, as these elements are hubs within the network. The updated network-based framework and its findings offer insights for informing and optimizing urban flood resilience planning in China.

From community engagement to community inclusion for socially and procedurally just flood risk governance

AbstractUrban flood risk governance (FRG) approaches increasingly seek to engage local communities—and their surrounding ecosystem in natural flood management (NFM) approaches—to co‐produce socio‐ecological resilience. This systematic review investigates current approaches, barriers, and enablers of community engagement in urban FRG through a flood risk justice lens. Employing a systematic search and an adapted ‘best fit’ framework synthesis methodology, and reporting results according to the Preferred Reporting Items for Systematic Reviews and Meta‐Analyses transparent reporting system. The central theme of inclusivity emerged from the synthesis, which integrated sub‐themes of relationality, non‐universalism, power structures, and personal paradigms in a conceptual model. Results invite FRG practitioners to reframe community engagement as community inclusion in order to respond to the procedural, social, and environmental justice concerns of urban ‘flood disadvantage’ which may be reinforced by current engagement approaches. Critical discussion of evidence—informed by the conceptual model—recognised five principles for realising procedurally just community inclusion; promoting the co‐production of integrated community inclusion strategies alongside the communities themselves. The study identified a gap in the literature concerning community involvement in NFM; highlighting a priority for future research with a view to realise more inclusive FRG.

Can we adapt fairly? Systematic review of health equity implications of climate change in coastal communities in the UK

Abstract As climate change becomes more apparent, it is important to evaluate the equity implications of adaptation interventions and policy measures. Many coastal populations experience high levels of social deprivation, which can be compounded by environmental factors. Coastal hazards, such as erosion and flooding can cause short and long term impacts on physical and mental health. To systematically review the published evidence on the differential impacts of coastal change on health inequalities and review the implications of adaptation responses for health inequality. We systemically reviewed the evidence for the UK only on a) inequalities in coastal flood impact or risk, and b) effectiveness and equity implications of current measures to manage the climate risks to an acceptable level of impact. Interventions included: plans and guidance, insurance, and infrastructure, including natural flood management. We found 8 papers quantifying differentials in current and future impacts of coastal flood risk and 6 papers assessing equity implications of adaptation measures. Coastal flood risk is unevenly distributed. Those owning their own home were more likely to experience flood impacts including increased stress and displacement. There is good evidence that policies for household insurance and property level protection measures have the potential to increase inequalities; other measures (community engagement; planning; defences) may reduce health inequalities, depending on implementation and local context. Adaptation to coastal change requires a range of approaches in the short and longer term, which potentially exacerbate current inequalities. Adaptation responses that rely on individual behaviour change, such as relocation, purchasing insurance, or retrofitting dwellings, may exacerbate inequalities within coastal communities. Climate change challenges organisations to deliver national and local policy responses ensuring that adaptation is effective and equitable.

Physically-based modelling of UK river flows under climate change

This study presents the model setup and results from the first calibrated, physically-based, spatially-distributed hydrological modelling of combined land cover and climate change impacts on a large sample of UK river catchments. The SHETRAN hydrological model was automatically calibrated for 698 UK catchments then driven by the 12 regional climate model projections from UKCP18, combined with urban development and natural flood management scenarios. The automatic calibration of SHETRAN produces a median Nash-Sutcliffe efficiency value of 0.82 with 581 catchments having a value greater than 0.7. 24 summary metrics were calculated to capture changes to important aspects of the flow regime. The UKCP18 realisations in SHETRAN indicate that a warming climate will cause river flows, on average, to decrease. These decreases are simulated to be greatest in the south and east of the UK, with droughts becoming longer and more severe. While high flows also decrease on average, an increased number of extremes are exhibited, implying a greater number of extreme flood events in the future, particularly in the north and west of the UK. In the urban development scenarios, for flood events there is an increase in flow with the increased urbanization, with the 1 in 3-year peak flow event showing the greatest increase. The natural flood management scenarios consider the effect of increasing woodland and adding surface water storage ponds. The inclusion of these features produces a complex response but overall, the modelling shows a reduction in low, median, and high flows, although the more extreme the flow event the smaller the percentage change in flow. Simulated timeseries and summary metric datasets are freely available on the CEDA archive.

Disentangling the Effects of Multiple Impacts of Natural Flooding on a Riverine Floodplain Lake by Applying the Phytoplankton Functional Approach

Riverine floodplains are ecologically remarkable systems that have historically faced strong anthropogenic pressures. The aim of this study was to examine whether the phytoplankton functional approach by Reynolds is a useful tool for disentangling anthropogenic pressure from the impact of natural flooding on a riverine floodplain lake. Lake Sakadaš, part of the large conserved river–floodplain system along the Danube River (Kopački Rit, Croatia), was used as a case study. Historical data on phytoplankton dynamics from the 1970s, when the lake was exposed to direct inflows of agricultural wastewater, were compared with current data from a time when the lake was a strongly protected area. Analysis of the phytoplankton community, based on functional groups and their beta diversities, revealed clear variation between the observed periods. The heavy bloom of species from only one functional group with extremely high biomass indicated a highly impacted environment in the past. Recent data suggest that, with the cessation of direct pollution, near-natural hydrological conditions with flooding as a fundamental environmental driving factor, support algal assemblages characteristic of a naturally eutrophic lake. Assessing multiple pressures on floodplain lakes and disentangling their specific impacts on ecological statuses are crucial for defining the protection and sustainable management of these particularly sensitive and endangered freshwater systems.

Evaluating Flood Damage to Paddy Rice Fields Using PlanetScope and Sentinel-1 Data in North-Western Nigeria: Towards Potential Climate Adaptation Strategies

Floods are significant global disasters, but their impact in developing countries is greater due to the lower shock tolerance, many subsistence farmers, land fragmentation, poor adaptation strategies, and low technical capacity, which worsen food security and livelihoods. Therefore, accurate and timely monitoring of flooded crop areas is crucial for both disaster impact assessments and adaptation strategies. However, most existing methods for monitoring flooded crops using remote sensing focus solely on estimating the flood damage, neglecting the need for adaptation decisions. To address these issues, we have developed an approach to mapping flooded rice fields using Earth observation and machine learning. This approach integrates high-resolution multispectral satellite images with Sentinel-1 data. We have demonstrated the reliability and applicability of this approach by using a manually labelled dataset related to a devastating flood event in north-western Nigeria. Additionally, we have developed a land suitability model to evaluate potential areas for paddy rice cultivation. Our crop extent and land use/land cover classifications achieved an overall accuracy of between 93% and 95%, while our flood mapping achieved an overall accuracy of 99%. Our findings indicate that the flood event caused damage to almost 60% of the paddy rice fields. Based on the land suitability assessment, our results indicate that more land is suitable for cultivation during natural floods than is currently being used. We propose several recommendations as adaptation measures for stakeholders to improve livelihoods and mitigate flood disasters. This study highlights the importance of integrating multispectral and synthetic aperture radar (SAR) data for flood crop mapping using machine learning. Decision-makers will benefit from the flood crop mapping framework developed in this study in a number of spatial planning applications.

Maintenance of High Phytoplankton Diversity in the Danubian Floodplain Lake over the Past Half-Century.

Riverine floodplains are recognized as centers of biodiversity, but due to intense anthropogenic pressures, many active floodplains have disappeared during the last century. This research focuses on the long-term changes in phytoplankton diversity in the floodplain lake situated in the Kopački Rit (Croatia), one of the largest conserved floodplains in the Middle Danube. The recent dataset from 2003 to 2016 and historical data from the 1970s and 1980s indicate high phytoplankton diversity, summarising 680 taxa for nearly half a century. The variability of species richness is driven by specific in-lake variables, particularly water temperature, water depth, total nitrogen, pH, and transparency, determined by a redundancy analysis of the current data. The high phytoplankton diversity levels are sustained regardless of intense pressures on the lake environment, including exposure to strong anthropogenic pollution in the past and extreme hydrological events, both droughts and floods, which have increasingly affected this part of the Danube in the last decades. The conserved hydrological connection between various biotopes along the river-floodplain gradient seems crucial in maintaining high phytoplankton diversity. Accordingly, conserving natural flooding is mandatory to maintain high biodiversity in complex and dynamic river-floodplain systems.

Spatiotemporal Variations in Urban Wetlands in Kazakhstan: A Case of the Taldykol Lake System in Astana City

Acquiring a comprehensive understanding of the spatiotemporal dynamics of urban wetlands in Kazakhstan is crucial for their effective preservation and sustainable urban development. Our findings identify past and present Land Use Land Cover (LULC) in the capital city, providing policymakers with scientific evidence for improved management. Using remote sensing and Geographic Information System (GIS) techniques, this study examines the spatiotemporal changes in the Taldykol catchment area during the rapid development of Astana. In 1992, over 90% of the catchment area was grassland and vegetation. By 2022, 30% of the area became barren land. Urban areas increased by 127%, and water areas decreased by 24%. The most significant changes occurred in lakes Taldykol and Kishi Taldykol, whose areas shrank by 91% and 54%, respectively. The near-disappearance of the Taldykol wetlands is likely to contribute to rising land surface temperatures (LST), decreased natural flood control capacity, reduced biodiversity, and diminished recreational opportunities. The fate of Taldykol lakes underscores the urgent need to raise public awareness about the role of wetlands in Kazakhstan’s ecosystems and take action to preserve urban wetlands.

Dam regulation alters the spatio-temporal delivery of organic carbon along the Yellow River

Global river damming has significantly altered the riverine hydrodynamics and organic carbon (OC) delivery along the Land-to-Ocean Aquatic Continuum (LOAC). The Yellow River, one of the largest rivers in the world, has been under perturbation and fragmentation by dam construction. In this study, we quantified particulate OC (POC) and dissolved OC (DOC) fluxes, on daily-monthly-annual timescales, to explore the effects of dam-triggered perturbations on OC delivery in the Yellow River. We found that the “natural” seasonal delivery of OC upstream of the Xiaolangdi (XLD) reservoir had shifted to a heavily dam-regulated pattern downstream of the XLD reservoir. The dam-oriented Water-Sediment Regulation increased the periodic export of OC to the sea in June and July, as opposed to the natural flood season upstream of the XLD reservoir. The dam-modulated annual and inter-annual export of OC, from the Yellow River to the sea, is also teleconnected by El Niño/Southern Oscillation (ENSO) events. Historically known for its high POC flux, the Yellow River has seen a decline in POC/DOC ratios over the recent decades due to dam regulation. The dam-driven changes in organic carbon delivery along the Yellow River will continue to affect carbon cycling in its estuary and marginal seas.

A MAP-based approach to identify the social vulnerability to flood hazard in states adjacent to Mexican Gulf

The impact of floods can significantly differ based on the local circumstances. The severity of the impact caused by a natural flood in one area compared to another depends on the distinct vulnerability factors present within the affected community, encompassing cultural, social, and economic aspects. Understanding a society's capacity to anticipate, adapt to, endure, and recover from the effects of natural floods relies on evaluating its social vulnerability, which is closely connected with potential risks and community resilience. This study adopts a framework that can analyze the interaction between natural hazards and social factors and is flexible to be applied to different geographic locations. This framework encompasses flood hazards and social vulnerability within the scope of flood risk reduction. This paper explores how social vulnerability can be integrated into the analysis of flood risks within the states adjacent to the Mexican Gulf. Initially, social components are selected and applied to measure and map the Social Vulnerability Index (SVI). Next, a MAP-based methodology is adopted to identify the spatial variability of social vulnerability concerning flood hazards. Then, a risk matrix is developed and the classifications on SVI map are aligned with those on a flood hazard map; provided by the Federal Emergency Management Agency (FEMA). This led to the development of a qualitative social vulnerability exposure map to flood hazards, emphasizing regions marked by high levels of both flood risk and social vulnerability. The findings of this study highlight the importance of integrating social vulnerability into flood risk mitigation policies and emergency management, and planning.

Natural Flood Management Through Peatland Restoration: Catchment‐Scale Modeling of Past and Future Scenarios in Glossop, UK

AbstractField‐scale experiments have shown the Natural Flood Management (NFM) potential of peatland restoration. The likelihoods of effectiveness are yet unknown at scales and storms large enough to impact human lives. Using GMD‐TOPMODEL, we upscale a rare Before‐After‐Control‐Intervention empirical data set to a 25 km2 catchment with >600 properties at flood‐risk, and test storms of up to a 1,000‐year return period (RP). Under these scales/storms, we find that it is not necessary (nor feasible) to delay the outlet flow‐peak to meaningfully attenuate it. Enhancing catchment “kinematic” storage, for example, through restoration, can be sufficient to reduce flow magnitudes without detectable changes to peak‐flow timing. NFM benefit increases exponentially with restoration area size under smaller storms, but linearly under larger storms. At RP ≤ 100 years, longer‐lasting frontal‐type storms are more challenging to defend against via NFM, but at RP > 100 years shorter‐duration convectional‐type events become more challenging. In the order of 1,000–10 years storms: (a) revegetating the bare‐peat areas in 15% of the catchment is 31%–61% likely to reduce peak‐flows by >5%; (b) revegetating & damming the erosion gullies in ∼20% of the catchment is 42%–71% likely to reduce peak‐flows by >5%; (c) Growth of Sphagnum in the dammed gullies of ∼20% and ∼40% of the catchment increase the likelihoods of >5% peak reductions to 65%–86% and 90%–98%, respectively. The numerical evidence of significant NFM benefit due to Sphagnum re‐establishment is an important finding, because it shows that meaningful flood‐risk mitigation in headwater catchments under scales/storms relevant to communities at risk can be delivered alongside other ecosystem benefits of Sphagnum re‐establishment.

Contaminant mobilization from the vadose zone to groundwater during experimental river flooding events

Natural river flooding events can mobilize contaminants from the vadose zone and lead to increased concentrations in groundwater. Characterizing the mass and transport mechanisms of contaminants released from the vadose zone to groundwater during these recharge events is particularly challenging. Therefore, conducting highly-controlled in-situ experiments that simulate natural flooding events can help increase the knowledge of where contaminants can be stored and how they can move between hydrological compartments. This study specifically targets uranium pollution, which is accompanied by high sulfate levels in the vadose zone and groundwater. Two novel experimental river flooding events were conducted that utilized added non-reactive halides (bromide and iodide) and 2,6-difluorobenzoate tracers. In both experiments, about 8 m3 of traced water from a nearby contaminant-poor river was flooded in a 3-m diameter basin and infiltrated through the vadose zone and into a contaminant-rich unconfined aquifer for an average of 10 days. The aquifer contained 13 temporary wells that were monitored for solute concentration for up to 40 days. The groundwater analysis was conducted for changes in contaminant mass using the Theissen polygon method and for transport mechanisms using temporal moments. The results indicated an increase in uranium (21 and 24%), and sulfate (24 and 25%) contaminant mass transport to groundwater from the vadose zone during both experiments. These findings confirmed that the vadose zone can store and release substantial amounts of contaminants to groundwater during flooding events. Additionally, contaminants were detected earlier than the added tracers, along with higher concentrations. These results suggested that contaminant-rich pore water in the vadose zone was transported ahead of the traced flood waters and into groundwater. During the first flooding event, elevated concentrations of contaminants were sustained, and that chloride behaved similarly. The findings implied that contaminant- and chloride-rich evaporites in the vadose zone were dissolved during the first flooding event. For the second flooding event, the data suggested that the contaminant-rich evaporites continued to dissolve whereas chloride-rich evaporites were previously flushed. Overall, these findings indicated that contaminant-rich pore water and evaporites in the vadose zone can play a significant role in contaminant transport during flooding events.

Walking With/In Place: The Walking Turn In Socially Engaged Public Art From Aotearoa New Zealand

This article first suggests that there has been a “Walking Turn” in contemporary socially engaged public art and then considers critically how these practices might be best framed and understood in the context of Aotearoa. There has been a multitude of walking-based artworks in Aotearoa since the second half of the 2010s to the present. In the wake of the global pandemic and natural flooding and cyclone disasters in Aotearoa that soon followed, “going out for a walk” has been repeatedly problematized and reframed for most citizens. This article seeks to establish a theoretical framework that is responsive to Indigenous as well as posthumanist discourse, through which we might best consider walking art practices in Aotearoa. To do this, the concept of walking “with/in” place is employed as an entry point. Drawing on research interviews, a number of culturally informed concepts related to walking are examined alongside notions of countermapping and countermonument. The artwork analysis considers the decolonial, counterneoliberal, and regenerative principles underlining these practices. The artworks discussed engage in histories and contemporary politics of place and can be characterized by quietude, humility, and hyperlocality.

Urban development and the loss of natural streams leads to increased flooding

Developing countries with hard pressed economies and a rapidly growing population have a myriad of issues to face. Karachi is one of the largest cities of Pakistan and is rapidly growing. The city has been hit by floods in the year 2016, 2018, 2019 and 2020, recently. Since the early 1990s Karachi has seen a rapid spike in development and in the process many natural streams have been built over. This has led reduced space for rainwater runoff and has created problems for urban flood managers. To ascertain this, topographic records of 1940s and 1980s and Landsat imagery of 2000, 2008, 2015 and 2020 were used to map historical urban extent. Sentinel—1, Synthetic Aperture Radar (SAR) imagery was used to extract flooded areas during 2015, 2017, 2019 and 2020 floods. In the year 2020, 64.3 km2 of area was flooded which was the highest. There has been a growth of 286% in urban area observed between 1980 and 2000. The city was built with several natural flood water carrying streams, north and west of it. It was found that that out of 3600 km of these streams, 870 km of streams have either been blocked or removed and a 100% in core urban area. DEM of difference (DOD) prepared by subtracting 1945 DEM from SRTM DEM indicated that most of embankments along these streams were in the areas that show erosion in DOD surface, thus explaining the expansion of built areas along historical stream channels. Forcing floods to enter these built areas.

Global, regional and national trends and impacts of natural floods, 1990-2022.

To assess global, regional and national trends in the impact of floods from 1990 to 2022 and determine factors influencing flood-related deaths. We used data on flood disasters from the International Disaster Database for 1990-2022 from 168 countries. We calculated the annual percentage change to estimate trends in the rates of people affected and killed by floods by study period, World Health Organization (WHO) region, country income level and flood type. We used multivariable logistic regression analysis to assess the factors associated with death from floods. From 1990 to 2022, 4713 floods were recorded in 168 countries, which affected > 3.2 billion people, caused 218 353 deaths and were responsible for more than 1.3 trillion United States dollars of economic losses. The WHO Western Pacific Region had the most people affected by floods (> 2.0 billion), accounting for 63.19% (2 024 599 380/3 203 944 965) of all affected populations. The South-East Asia Region had the most deaths (71 713, 32.84%). The African and Eastern Mediterranean Regions had the highest number of people affected and killed by floods per 100 000 population in 2022. The odds of floods causing more than 50 deaths were significantly higher in low-income countries (adjusted odds ratio: 14.34; 95% confidence interval: 7.46 to 30.04) compared with high-income countries. Numbers of people affected and mortality due to floods declined over time. Despite the decreases in populations affected and deaths, floods still have a serious impact on people and economies globally, particularly in lower-income countries. Action is needed to improve disaster risk management and flood mitigation.

Real-time biological early-warning system based on freshwater mussels’ valvometry data

Abstract. Quantifying the effects of external climatic and anthropogenic stressors on aquatic ecosystems is an important task for scientific purposes and management progress in the field of water resources. In this study, we propose an innovative use of biotic communities as real-time indicators, which offers a promising solution to directly quantify the impact of these external stressors on the aquatic ecosystem health. Specifically, we investigated the influence of natural river floods on riverine biotic communities using freshwater mussels (FMs) as reliable biosensors. Using the valvometry technique, we monitored the valve gaping of FMs and analysed both the amplitude and frequency. The valve movement of the FMs was tracked by installing a magnet on one valve and a Hall effect sensor on the other valve. The magnetic field between the magnet and the sensor was recorded using an Arduino board, and its changes over time were normalised to give the opening percentage of the FMs (how open the mussels were). The recorded data were then analysed using continuous wavelet transform (CWT) analysis to study the time-dependent frequency of the signals. The experiments were carried out both in a laboratory flume and in the Paglia River (Italy). The laboratory experiments were conducted with FMs in two configurations: freely moving on the bed and immobilised on vertical rods. Testing of the immobilised configuration was necessary because the same configuration was used in the field in order to prevent FMs from packing against the downstream wall of the protection cage during floods or from breaking their connection wires. These experiments allowed us to verify that immobilised mussels show similar responses to abrupt changes in flow conditions as free mussels. Moreover, immobilised mussels produced more neat and interpretable signals than free-moving mussels due to the reduced number of features resulting from movement constraints. We then analysed the response of 13 immobilised mussels under real river conditions during a flood on 31 March 2022. The FMs in the field showed a rapid and significant change in valve gap frequency as the flood escalated, confirming the general behaviour observed in the laboratory in the presence of an abrupt increase in the flow. These results highlight the effectiveness of using FMs as biosensors for the timely detection of environmental stressors related to natural floods and emphasise the utility of CWT as a powerful signal-processing tool for the analysis of valvometry data. The study proposes the integration of FM valvometry and CWT for the development of operational real-time biological early-warning systems (BEWSs) with the aim of monitoring and protecting aquatic ecosystems. Future research should focus on extending the investigation of the responsiveness of FMs to specific stressors (e.g. turbidity, temperature, and chemicals) and on testing the applications of the proposed BEWSs to quantify the impact of both natural stressors (e.g. heat waves and droughts) and anthropogenic stressors (e.g. hydropeaking, reservoir flushing, and chemical contamination).