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ABSTRACT Floods are one of nature's most disturbing catastrophes, resulting in infrastructure damage, property devastation, and mortality. In Addis Ababa, flooding has significantly impacted residents and caused millions' worth of property damage in the last decade alone. It is continuously threatening and affecting city residents. This study focused on the spatial modeling of floods and the identification of areas susceptible to flood hazards in the city. Geographic information system (GIS) techniques combined with the information gain ratio (IGR) method were employed in this study. Five major flood hazard factors were identified: elevation, slope, rainfall, drainage density, and distance from drainage channels. The results show that 1.3% (7.1 km 2 ) of the area is highly susceptible to floods, 29.4% (159 km 2 ) is highly susceptible to heavy rains, 56% (302 km 2 ) of the area is moderately susceptible, 12.5% (67.3 km 2 ) of the area has low susceptibility, and less than 1% (4.2 km 2 ) has very low susceptibility. Slope is the most influential factor (42.74%), followed by drainage density (28.21%), distance from drainage channels (18.8%), rainfall (7.69%), and elevation (2.56%). The sub‐cities of Nifas Silk Lafto and Akaki Kality are the most susceptible to flood hazards; areas with steep slopes trigger high runoff during heavy rainy periods and cause flood hazards on gentle slope surfaces. It is recommended that to improve the accuracy of identifying susceptible flood‐hazard locations, flooding simulation should be performed in conjunction with other variables and rainfall data (such as rainfall duration and intensity). Nevertheless, this research provides recommendations to municipal administration decision‐makers regarding strategic management in the prioritization of flood‐hazard zones.

Abstract Climate projections contain the uncertainty due to the internal variability of the climate system, including its chaotic nature. While the uncertainty due to the internal variability can be theoretically mitigated by executing large ensemble simulations with perturbed initial conditions, only a limited number of large-ensemble experiments are available in CMIP6 future scenario dataset. Here we propose a method that increases the effective ensemble sampling size in evaluations of future projection by integrating multiple SSP-RCPs for a period corresponding to a specific increase in temperature from the preindustrial level (i.e., X°C warming). The success of the method was assessed by investigating whether the uncertainty due to small number of ensemble members could be reasonably reduced. First, we confirmed that the spatial distributions of the future flood magnitude change were similar under a 2 °C warming in all SSP-RCP scenarios. Additionally, the uncertainty due to the different SSP-RCPs (5–10%) was smaller than the differences between different warming levels such as between 2 and 3 °C (around 20–50%), suggesting differences among SSP-RCPs as to future flood discharge change are relatively small. These results suggested that integrating SSP-RCPs to increase the effective ensemble size was a reasonable approach, reducing unbiased variance among GCMs in about 70% of land grid points comparing to the result using SSP5-RCP8.5 alone.

Abstract Floods threaten human lives globally, yet the flood risk to the elderly (above 65) remains uncertain within warming climates and population aging. Hence, this study incorporated the General Circulation Model and Shared Socioeconomic Pathway projections into the hydraulic modeling framework, to analyze the flood risk to the elderly in Europe under climatic and socioeconomic changes. Results demonstrated that central Europe has experienced an increase in both surface runoff and streamflow (exceeding 50%), which have jointly contributed to intensified flooding in the major basins (Loire, Rhine, Elbe, and Danube) within the region. Among them, the Elbe basin exhibited a significant increase in 100‐year flood peak (∼107%) and elderly population (∼15%), resulting in 51,300 (CI: 45,300–60,500) of the elderly population being exposed to high‐hazard floods under a high greenhouse gas scenario (SSP5‐8.5), with at most 58% (29,800, CI: 25,100–33,700) of them being densely settled or in low‐& middle‐income groups. Among aging cities, Prague was severely affected by floods, with 40%–54% of the exposed elderly in high‐risk areas. Followed by Dresden and Hamburg, where up to 18% of the exposed elderly were threatened by high‐risk floods. This study revealed regional inequalities induced by flood exposure within the context of warming climates and population aging. The methods and findings are expected to provide additional insights into sustainable flood risk management under global change. , Plain Language Summary Floods are threatening people around the world. As the climate gets warmer and the population gets older, it's important to understand how floods might affect the elderly (older than 65). In this study, we investigated how floods could impact the elderly in Europe by 2100. We coupled climate and socioeconomic projections with numerical simulations to analyze the flood risk in different future scenarios. We found that the flood risk could spatiotemporally vary across European basins and cities. In the Elbe River basin, flood peaks could increase by more than 100%, and the elderly population could grow by 15%, resulting in a maximum of 51,300 elderly population being exposed to floods, and up to 29,800 of them are highly vulnerable because of densely settled or in low‐& middle‐income groups. In aging cities like Prague, Dresden, and Hamburg, at most 54% of the exposed elderly can be in high‐risk areas. This research revealed that the vulnerable groups (elderly, low‐income) are disproportionately threatened by high‐risk floods. Here, we advocate for incorporating social vulnerability into flood risk evaluation and management, thereby helping mitigate regional inequalities and contribute to the United Nations Sustainable Development Goals. , Key Points Flood risk to the elderly across European regions was analyzed by coupling climatic and socioeconomic projections with hydraulic modeling Flood risk spatiotemporally varied in Europe, with Elbe basin showing an increase in floods (∼107%) and elderly population (∼15%) in future Over 51,300 of the elderly were exposed to floods in Elbe basin, with 58% of them being densely settled or in low‐& middle‐income groups

Abstract. We present the results of downscaling CMIP6 global climate projections to local scales for the Mediterranean and Italian regions, aiming to produce high-resolution climate information for the assessment of climate change signals, with a focus on precipitation extreme events. We performed hindcast (i.e., ERA5-driven) and historical simulations (driven by the MPI-ESM1-2-HR model) to simulate the present (1980–2014) and future (2015–2100) climate under three different emission scenarios (SSP1-2.6, SSP2-4.5, SSP5-8.5). For each experiment, a double-nesting approach is adopted to dynamically downscale global data to the regional domain of interest, firstly over the Europe (EURO) COordinated Regional climate Downscaling Experiment (CORDEX) domain, at a spatial resolution of 15 km, and then further refined (second nesting) over Italy and the northwestern Mediterranean at a resolution of 5 km, i.e., in the so-called gray zone (5–10 km), close to the convection-permitting (CP) limit. Besides validating the experimental protocol, this work potentially questions the need for climate simulations to always resort to deep convection parameterizations when spatial refinement is increased up to the limit of the CP scale, yet convective processes are still not explicitly resolved. Analyses of air temperature and precipitation are presented, with a focus on the spatial distribution of precipitation, its probability density function, and the statistics of extreme events for both current climate and far-end scenarios. By the end of the century for all the scenarios and seasons there is a projected general warming along with an intensification of the hydrological cycle over most of continental Europe and mean precipitation reduction over the Mediterranean region accompanied, over the Italian Peninsula, by a strong increase in the intensity of extreme precipitation events, particularly relevant for the SSP5-8.5 scenario during autumn.

Abstract. When extreme hydrological events (floods and droughts) occur, there is inevitably speculation that such events are a manifestation of anthropogenic global warming. The UK is generally held to be a wet country, but recent drought events in the UK have led to growing concerns around droughts becoming more severe – for sound scientific reasons, given physical reasoning and projections for the future. In this extended review, we ask whether such claims are reasonable for hydrological droughts in the UK using a combination of literature review and extended analysis. The UK has a well-established monitoring programme and a very dense body of research to call on and, hence, provides the basis for a good international case study for addressing this question. We firstly assess the evidence for changes in the well-gauged post-1960 period before considering centennial-scale changes using published reconstructions. We then seek to provide a synthesis of the state of the art in our understanding of the drivers of change, both climatic and in terms of direct human disturbances to river catchments (e.g. changing patterns of water withdrawals, impoundments, land use changes). These latter impacts confound the identification of climate-driven changes, and yet, human influences are themselves being increasingly recognised as potential agents of changing drought regimes. We find little evidence of compelling changes towards worsening drought, apparently at odds with climate projections for the relatively near future and with widely held assumptions regarding the role of human disturbances in intensifying droughts. Scientifically, this is perhaps unsurprising (given uncertainties in future projections; the challenge of identifying signals in short, noisy records; and a lack of datasets to quantify human impacts), but it presents challenges to water managers and policymakers. We dissect some of the reasons for this apparent discrepancy and set out recommendations for guiding research and policy alike. While our focus is the UK, we envisage that the themes within this study will resonate with the international community, and we conclude with ways in which our findings are relevant more broadly, as well as how the UK can learn from the global community.