Occurrence Of Flood Events Research Articles

Analysing the outbreaks of leptospirosis after floods in Kerala, India

A growing number of studies have linked the incidence of leptospirosis with the occurrence of flood events. Nevertheless, the interaction between flood and leptospirosis has not been extensively studied to understand the influence of flood attributes in inducing new cases. This study reviews leptospirosis cases in relation to multiple flood occurrences in Kerala, India. Leptospirosis data were obtained for three years: 2017 (non-flood year) and two years with flooding—2018 (heavy flooding) and 2019 (moderate flooding). We considered the severity of flood events using the discharge, duration and extent of each flooding event and compared them with the leptospirosis cases. The distribution of cases regarding flood discharge and duration was assessed through descriptive and spatiotemporal analyses, respectively. Furthermore, cluster analyses and spatial regression were completed to ascertain the relationship between flood extent and the postflood cases. This study found that postflood cases of leptospirosis can be associated with flood events in space and time. The total cases in both 2018 and 2019 increased in the post-flood phase, with the increase in 2018 being more evident. Unlike the 2019 flood, the flood of 2018 is a significant spatial indicator for postflood cases. Our study shows that flooding leads to an increase in leptospirosis cases, and there is stronger evidence for increased leptospirosis cases after a heavy flood event than after a moderate flooding event. Flood duration may be the most important factor in determining the increase in leptospirosis infections.

Multicriteria analysis for flood risk map development: a hierarchical method applied to Brazilian cities.

Floods have caused socio-economic and environmental damage globally and, thus, require research. Several factors influence flooding events, such as extreme rainfall, physical characteristics, and local anthropogenic factors; therefore, such factors are essential for mapping flood risk areas and enabling measures that mitigate the damage they cause. This study aimed to map and analyze regions susceptible to flood risk in three different study areas belonging to the same Atlantic Forest biome, in which flood disasters are recurrent. Due to the presence of numerous factors, a multicriteria analysis using the Analytical Hierarchical Process was conducted. First, a geospatial database was composed of layers of elevation, slope, drainage distance, soil drainage, soil hydrological group, precipitation, relief, and land use and cover. Flood risk maps for the study area were then generated, and patterns in the study areas were verified, with the greatest influence being exerted by intense precipitation on consecutive days, elevation at the edges of the channel with low altimetric variation and a flat combination, densely built areas close to the banks of the main river, and an expressive water mass in the main watercourse. The results demonstrate that these characteristics together can indicate the occurrence of flooding events.

Hydrologic and geomorphic effects on the reduction of channel discharge capacity in the Middle Yangtze River

A systematic increase in the occurrence of flood events has been noted in rivers worldwide. However, our understanding remains unclear of how the flood level is affected by the change in channel discharge capacity. Therefore, the reduction of channel discharge capacity was quantified in the Middle Yangtze River (MYR) based on extensive measured data. It is confirmed that the variation in channel discharge capacity is a superposition result of channel-morphology and channel-resistance changes, as well as the change in local base-level at the outlet. Then a series of numerical simulations were carried out to quantitatively identify the contribution of each factor to the reduction of channel discharge capacity in the MYR for the years of 2004 and 2020. Simulated results reveal that channel degradation increased the flow passage area, helping the channel to convey floods, with the effect being weakened along the reach; however, the decline in flood level under the same discharge was not observed, which was primarily attributed to the increases in channel resistance and local base-level at the outlet. These two factors accounted for 16–91 % and 9–84 % of the total impact at four hydrometric stations in the MYR. It should be noted that the dominant factor to influence the discharge capacity varied greatly at different stations, which depended on the degree of bed-material coarsening, the distance from the confluence of lakes, etc. At the stations immediately downstream of the dam, the contribution of the increased movable bed roughness usually played a more essential role; while at the stations close to the outlet with the confluence of large lakes, the increase in local base-level became the main factor that accounted for the rise of high-flood levels under the specified large discharge.

Toponyms: a neglected asset within the water framework and flood directives implementation process; the case study of Greece

Proxy data and qualitative information are important assets in water resources and floods management. In the research, the river water bodies with characteristic toponyms (hydronyms) in Greece that potentially reflect the water’s quality or the occurrence of floods are evaluated in comparison to the European Union’s (EU) Water Framework and Flood Directives implementation process outputs. For doing so, after identifying the river water bodies with characteristic toponyms which form the 10.2% of the Greek water bodies, the toponyms are cross correlated with the water bodies quality status as retrieved by the Directives’ databases to validate the existence of linkages between the names and the quality. Similarly, the significant floods, as derived from the Flood Directive, are spatially allied with the water bodies with characteristic toponyms to ground truth the connection between significant floods and water bodies whose toponyms imply flood prone areas. The research outputs indicate a high degree of correlation both in terms of water quality and floods, meaning that in almost all cases the water body toponym depicts the good or bad quality of the water body or the occurrence of flood events. Moreover, it is established that almost 90% of the water bodies with characteristic names are intermittent and ephemeral ones. The water bodies’ toponyms, hence, are proposed as an auxiliary criterion during the Directives implementation process that could foster increased water quality and flood-related knowledge, especially in intermittent and ephemeral water bodies which are generally lacking observations, and can be applied not only in all EU-Member States’ waters, but also in global scale.

Development of Regional Climate Model (RCM) for Cameron Highlands based on Representative Concentration Pathways (RCP) 4.5 and 8.5

Development of local climate is important for climate hazard assessment. Cameron Highlands was chosen as study area (longitude from 101°21’ to 101°30’ and latitude from 4°19’ to 4°37’) for climate downscaling. This paper presents the work of downscaling techniques and regional climate model (RCM) development. The second-generation Canadian Earth System Model (CanESM2) based on the representative concentration pathways (RCP) 4.5 and 8.5 was applied to develop the local climate model for the period 2020-2100. The climatic parameters chosen were temperature (maximum and minimum) and rainfall. The simulated RCMs are then analysed using statistical reliability including Pearson correlation coefficient, linear regression, root mean square error (RMSE) and probability density function (PDF). The result showed that the simulated maximum, minimum temperature, and rainfall are most likely to follow RCP 8.5 scenario. Precipitation threshold for occurrence of flood event was estimated using intensity duration frequency (IDF) relationship generated by maximum precipitation. Return period of two years and four hours rainfall duration is used for threshold estimation as the rainfall is convective. The daily rainfall threshold for flood occurrence is estimated to be 11.3 mm/hr.

FLOOD ANALYSIS AND HYDRAULIC COMPETENCE OF DRAINAGE STRUCTURES ALONG ADDIS ABABA LIGHT RAIL TRANSIT

The occurrence of flooding events and the associated risks are increasing in the urban areas of most developing countries. Flooding in any circumstance causes major stresses on affected area’s economic, social and environmental regimes. Therefore, the current study presents a flood analysis and hydraulic competence of existing drainage structures on some selected roads of Addis Ababa City, after integration with Addis Ababa Light Rail Transit (AALRT) Drainage Systems. The existing side drains and cross drainage structures located within the study area were inspected and assessed to ascertain different aspects relating to their performance. Different watersheds were delineated. Hydrological analysis was then carried out using Geospatial tools such as ARCGIS, ARCSWAT, and HEC GEOHMS to determine the different watersheds contributing to the flows. The flows were obtained from the rational method for areas less than 0.5 km2 and HEC HMS for areas greater than 0.5 km2. The hydraulic analysis was carried out using HY-8 for the culvert and the Hydraulic toolbox for side drains. It was found from field surveys and measurements that the existing side drain of 900 mm circular pipe could not convey the maximum flow. The existing box culvert, which comprised of one barrel was able to convey the design flow of 29.52 m3/s with a headwater elevation of 2300.94 m. The existing box culvert was sufficient in conveying the designed flow since its headwater elevation was lower than that of the roadway elevation. However, observations like the presence of accumulated silt, debris within most side drains, and an undersized side drain reduced its hydraulic competence. The undersized side drain was redesigned by increasing its diameter to 1200 mm. The study acts as a yardstick for drainage assessment, especially for existing structures, an indicator for identifying the most flood-prone areas along the railway track. It recommended an intermediate cross culvert before Lancha, regular desilting, and putting screens at inlets of side drains and some distance before the entrance of the culverts. Periodic maintenance of the existing drainage structures and widening of the pipe conduits for the side drains to about 1200 mm for easy maintenance is also necessary.

Going Beyond the Ensemble Mean: Assessment of Future Floods From Global Multi‐Models

AbstractFuture changes in the occurrence of flood events can be estimated using multi‐model ensembles to inform adaption and mitigation strategies. In the near future, these estimates could be used to guide the updating of exceedance probabilities for flood control design and water resources management. However, the estimate of return levels from ensemble experiments represents a challenge: model runs are affected by biases and uncertainties and by inconsistencies in simulated peak flows when compared with observed data. Moreover, extreme value distributions are generally fit to ensemble members individually and then averaged to obtain the ensemble fit with loss of information. To overcome these limitations, we propose a Bayesian hierarchical model for assessing changes in future peak flows, and the uncertainty coming from global climate, global impact models and their interaction. The model we propose allows use of all members of the ensemble at once for estimating changes in the parameters of an extreme value distribution from historical to future peak flows. The approach is applied to a set of grid‐cells in the eastern United States to the full and to a constrained version of the ensemble. We find that, while the dominant source of uncertainty in the changes varies across the domain, there is a consensus on a decrease in flood magnitudes toward the south. We conclude that projecting future flood magnitude under climate change remains elusive due to large uncertainty mostly coming from global models and from the intrinsic uncertain nature of extreme values.

Developing a Web-based decision support system for reservoir flood management

Abstract Proper management of reservoirs in flood conditions minimizes flood damage and keeps the reservoir in a stable condition. This paper presents a Web-based decision support system of reservoir flood management (WDRFM) for reservoirs with gated spillways. WDRFM is capable of estimating the current situation of the reservoir and before the flood reaches the reservoir, provides the operator with suggestions to have optimal control over gates, using multistage simulation-optimization models to minimize flood damage downstream. Investigating the possibility of changing the dam's discharge gates, carrying out dam pre-release, and announcing relevant flood control warnings can all be performed by WDRFM, while allowing the operator to determine such observations and make final decisions on a time step basis. To assess the performance of WDRFM, 15 scenarios in four groups for flood management were defined on April 14, 2016 at Dez Dam, Iran. A comparison of one scenario with similar initial conditions with the occurrence of flood event has shown that a daily peak discharge shows 997 m3/s decrease from that recorded by the operator. The ability to examine different scenarios based on the conditions at any time in the WDRFM enables the decision-makers and operators to confront various circumstances.

Copula-based multivariate flood probability construction: a review

Basin perspective hydrology and hydraulic water-related queries often demanding an accurate estimation of flood exceedance probabilities or return periods for assessing hydrologic risk. The research on the advancements of flood probability modelling contributed to reduction of flood risk, damage property and human life losses associated with the occurrence of flood events. Higher degree of uncertainty and complex flood dependence structure did not facilitate for their accurate prediction through deterministic approaches, which often demand a probability distribution framework. Unreliability of univariate frequency analysis under parametric or non-parametric framework would be an attribute for underestimation or overestimation of flood risk. Multivariate distribution framework facilitating a comprehensive understanding of flood structure for various possible occurrence combinations among the flood-related random vectors (i.e. flood peak flow, volume and duration). In this literature, copula function is recognized as a highly flexible tool for establishing multivariate joint dependency and their associated return periods in comparison with traditional multivariate functions. The incorporation of vine or pair-copula constructions (or PCC) further exaggerated the efforts of higher dimension copula construction, in terms of precision level in their estimated quantiles, under the minimum information concept. This review explored the efficacy of copula-based methodology for tackling multivariate design problems and can be used as a guideline for water practioner and hydrologist.

Evaluation of flood prediction capability of the distributed Grid‐Xinanjiang model driven by weather research and forecasting precipitation

AbstractThe lead time of operational flood forecasting is critical for the effectiveness of flood alert and flood risk reduction. It is impossible to extend the lead time of flood forecasting by solely using rain gauge observations. However, the weather research and forecasting (WRF) model has the potential to produce quantitative precipitation forecasts that can facilitate the flood risk management by increasing the flood forecasting lead time. This study investigates the flood prediction capabilities of the well‐tested Grid‐Xinanjiang model (GXM) in a flood‐prone area, located in the upper region of the Huaihe River Basin, when driven by gauge observations and WRF precipitation forecasts, respectively. The results indicate that GXM is capable of producing improved flood predictions by using the WRF precipitation forecasts. The incoming floods are difficult to be predicted in advance by using the gauge‐measured precipitation, especially when the lead time is larger than the flow concentration time. However, with the WRF forecasts, the occurrence of flood events can be predicted for longer lead times. This study also demonstrates that the temporal and spatial patterns of precipitation forecasts have an important impact on the prediction of both timing and magnitude of incoming floods.

Underlying causes and the impacts of disaster events (floods) on fertility decision in rural Bangladesh

Abstract The study attempts to uncover how people living in vulnerable areas address the relationship between the impacts of extreme weather events (floods) and fertility preference. The study selected a village, Sharat Pur from Sunamganj District, which is highly vulnerable to the adverse impacts of flooding. The study gathered information from 158 respondents by using a semi-structured questionnaire and in-depth interviews. With the small sample size the study used descriptive statistics and qualitative analysis. Findings show that there is still a preference for more sons to recover the damage caused from the impacts of floods. However, people think having a large family is a burden. They emphasize controlling family size through family planning programs and do not take into account the risk of children dying affecting their desire to have additional children. Therefore they consider having more children especially sons as a gift from God and the occurrence of flood events as the wish of God. The intention of the study is not to generalize findings but to comprehend the underlying mechanism between disaster events and fertility behavior. The study collected information from a very small sample size. Future studies might consider a large sample size and explore more deeply the mechanism between the different disaster events and fertility decisions by using a comparative analysis between regions vulnerable to different extreme weather events and not vulnerable to extreme weather events within Bangladesh, and comparing Bangladesh with other South Asian countries.

Clustering of historical floods observed on Iguaçu River, in União da Vitória, Paraná

ABSTRACT The occurrence of flood events has become more frequent, and, in Brazil, there are regions that suffer with the repetition of those events. In União da Vitória, located in Paraná State, Brazil, those phenomena are commonly recorded, generating series of consequences for each flood event, such as financial losses, environmental damages, home losses and deaths. So, since it is not possible to avoid the occurrence of floods, it is necessary to reduce its impacts, and in a scenario of repeated flood events, as observed in União da Vitória, it is justified the clustering of historical floods, aiming to improve the knowledge about the river basin hydrological behavior and to assist in the determination of hydrological models parameters. Clustering analysis aims to establish sets of events with similar characteristics, and, for this, based on fuzzy logic, the present study uses the fuzzy c-means method to cluster Iguaçu river floods, observed in União da Vitória, using a set of different flood severity indicators. The classification defined four clusters, according to different flood severity levels, so-called: low; medium; high; and, disaster or catastrophe. Therefore, by the analysis of similar features among different clusters of events, it is further possible to study the flood formation mechanisms, contributing to the reduction of its impacts, through real-time flood alert and forecasting systems, for instance.

Trends in reference evapotranspiration and associated climate variables over the last 30 years (1984–2014) in the Pampa region of Argentina

Agricultural production is sensitive to weather and thus directly affected by climate change. In Argentina, the geographic region known as the “Pampa” is at the heart of agricultural production. In this context, the objective of the present study was to evaluate the presence of long-term trends and abrupt changes in reference evapotranspiration (ETo PM) and associated climate variables in 30 weather stations of the Pampa over the 1984–2014 period. The presence of temporal trends was evaluated using Mann-Kendall’s statistical test, whereas abrupt changes were detected through Pettitt test. Significant upward trends were observed in 80 and 43% of maximum temperature (Tmax) and ETo PM time series, whereas relative humidity (RH) and wind speed (WS), in contrast, presented decreasing trends in 57 and 47% of the locations. Abrupt changes were frequently observed in the years 2000–2003 for Tmax, RH, and ETo PM time series, a period that coincides with the occurrence of flooding events in the region. Weather stations of the Pampa region could be divided into two broad categories based on their trends in ETo PM and influencing climate variables: (A) stations exhibiting a rising trend in ETo PM and a concomitant decreasing trend in RH and (B) stations presenting invariant ETo PM and a decreasing trend in WS. The spatial distribution of the two categories of stations did not exhibit any specific geographic pattern. The information provided herein on modern trends in climate and evaporative demand is essential to the development of climate models and future scenarios necessary to evaluate food security prospects both regionally and globally.

Urban floods and residential rental values nexus in Kumasi, Ghana

The supposition that the occurrence of flood event will have an inverse effect on rental values of residential housing properties is often accepted as a fact. However, the mechanism for this supposed impact has not been clearly articulated and the hypothesis is far from proven in Ghanaian housing rental market. This paper examined the impact of flood on residential rental values in Kumasi. The study adopted multiple research approaches in selecting zones with both flood and non-flood liable residential properties. The repeated sales model was then used to create local market indices to gauge flood impact on the rental values. The rental values of non-flooded residential properties were generally higher than their flooded counterparts by a margin of GHS 62.66 ±0.09 annually. While this supports existing postulations of a negative impact of flood on rental values, the results further showed that the extent of the impact varies across different residential property types. It is concluded that the wholesale assumption in literature that flood events diminish rental values should be interpreted with caution. The study recommends that the (dis)amenity effects of flood on rental values should therefore be assessed on case by case basis.Keywords: Floods, Ghana, Kumasi, Residential Rental Value, T-test

Performance of Two Real-Life California Bridges under Regional Natural Hazards

AbstractThe performance of two real-life California bridges is assessed under a possible regional multihazard condition involving floods and earthquakes. For flood events with varied frequency, expected scour depths at bridge piers are calculated and incorporated in finite-element analyses (FEAs) of the bridges under earthquakes that represent regional seismic hazards. Based on FEA results, fragility curves of bridges are developed at component and system levels. Fragility surfaces are generated to acquire comprehensive knowledge on bridge failure probability for the combined effect of earthquake and flood events of varying frequency. Quantified bridge vulnerability is applied to a risk evaluation framework that combines hazard probability with bridge failure consequences. Obtained results depict that the occurrence of flood events can increase the seismic vulnerability and risk of bridges, although the amount of increase depends on bridge attributes. Bigger (large-diameter) foundations tend to reduce the...

Modelling the interaction between flooding events and economic growth

Abstract. Socio-hydrology describes the interaction between the socio-economy and water. Recent models analyze the interplay of community risk-coping culture, flooding damage and economic growth (Di Baldassarre et al., 2013; Viglione et al., 2014). These models descriptively explain the feedbacks between socio-economic development and natural disasters like floods. Contrary to these descriptive models, our approach develops an optimization model, where the intertemporal decision of an economic agent interacts with the hydrological system. In order to build this first economic growth model describing the interaction between the consumption and investment decisions of an economic agent and the occurrence of flooding events, we transform an existing descriptive stochastic model into an optimal deterministic model. The intermediate step is to formulate and simulate a descriptive deterministic model. We develop a periodic water function to approximate the former discrete stochastic time series of rainfall events. Due to the non-autonomous exogenous periodic rainfall function the long-term path of consumption and investment will be periodic.

A study on the occurrence of flood events over Jammu and Kashmir during September 2014 using satellite remote sensing

During the first week of September 2014, the Jammu and Kashmir region witnessed devastating floods across the majority of its districts, caused by multi-day heavy rainfall events. According to data provided by the Home Ministry of India, several thousand villages across the state were hit and 390 villages completely submerged. The preliminary assessment of property damage was estimated between INR 50,000 million to INR 60,000 million. Approximately 277 people died. In this study, an effort was made to analyze the heavy rainfall events over Jammu and Kashmir using hourly data at the fine spatial scale from satellite remote sensing. Data over Jammu and Kashmir reveal strong diurnal variation in rainfall over the severely affected districts. Most of these districts experienced continuous frequent heavy rainfall rates in the range of 15–22 mm/h during the first week of September 2014. The results show that the cumulative rainfall during 2–6 September 2014 may have contributed to the flood events.

Tidal changes in a heavily modified coastal wetland

Changes in tidal regime in the heavily modified Venice Lagoon, Italy, are investigated using long-term observations and numerical modelling. The amplitudes of the major tidal constituents exhibit a significant increase over the last century. Analysis of tide gauge data in the adjacent Adriatic Sea reveals that these changes could be only partially attributed to the rise of the mean sea level. Numerical experiments confirm that natural and anthropogenic morphological changes are responsible for the alteration of tidal regime inside the lagoon. Temporal and spatial changes in tidal asymmetry highlight the complex impacts of human interventions on tidal changes and long-term morphodynamics. Our results suggest that over time the lagoon became more and more an ebb-dominant system. Moreover, in Venice the tidal modulations are significantly impacting the frequency with which high water level thresholds are exceeded. Occurrence of flooding events is therefore influenced by sea level rise and secondarily by the increase in amplitude of principal tidal waves.

Assessment of future precipitation indices in the Shikoku region using a statistical downscaling model

In this study, we used the statistical downscaling model (SDSM) to estimate mean and extreme precipitation indices under present and future climate conditions for Shikoku, Japan. Specifically, we considered the following mean and extreme precipitation indices: mean daily precipitation, R10 (number of days with precipitation >10 mm/day), R5d (annual maximum precipitation accumulated over 5 days), maximum dry-spell length (MaDSL), and maximum wet-spell length (MaWSL). Initially, we calibrated the SDSM model using the National Center for environmental prediction (NCEP) reanalysis dataset and daily time series of precipitation for ten locations in Shikoku which were acquired from the surface weather observation point dataset. Subsequently, we used the validated SDSM, using data from NCEP and outputs form general circulation models (GCM), to predict future precipitation indices. Specifically, the HadCM3 GCM was run under the special report on emissions scenarios (SRES) A2 and B2 scenarios, and the CGCM3 GCM was run under the SRES A2 and A1B scenarios. The results showed that: (1) the SDSM can reasonably be used to simulate mean and extreme precipitation indices in the Shikoku region; (2) the values of annual R10 were predicated to decrease in the future in northern Shikoku under all climate scenarios; conversely, the values of annual R10 were predicted to increase in the future in the range of 0–15 % in southern and western Shikoku. The values of annual MaDSL were predicted to increase in northern Shikoku, and the values of annual MaWSL were predicted to decrease in northeastern Shikoku; (3) the spatial variation of precipitation indices indicated the potential for an increased occurrence of drought across northeastern Shikoku and an increased occurrence of flood events in the southwestern part of Shikoku, especially under the A2 and A1B scenarios; (4) characteristics of future precipitation may differ between the northern and southern sides of the Shikoku Mountains. Regional variations in extreme precipitation indices were not notably evident in the B2 scenario compared to the other scenarios.

Reconstructing coastal flood occurrence combining sea level and media sources: a case study of the Solent, UK since 1935

Using newly digitised sea-level data for the ports of Southampton (1935–2005) and Portsmouth (1961–2005) on the south coast of the UK, this study investigates the relationship between the 100 highest sea-level events recorded at the two cities and the incidence of coastal floods in the adjoining Solent region. The main sources of flood data are the daily newspapers The Southern Daily Echo, based in Southampton and The News, based in Portsmouth, supported by a range of local publications and records. The study indicates a strong relationship between the highest measured sea levels and the incidence of coastal floods and highlights the most vulnerable areas to coastal flooding which include parts of Portsmouth, Southampton, Hayling Island, Fareham and Cowes. The most severe flood in the dataset resulted from the storm surge events of 13–17 December 1989 when eight consecutive extreme high waters occurred. The data suggest that while extreme sea-level events are becoming more common, the occurrence of flood events is not increasing. This is attributed to improved flood remediation measures combined with a reduction of storm intensity since the 1980s. However, several recent events of significance were still recorded, particularly 3 November 2005 when Eaststoke on Hayling Island (near Portsmouth) was flooded due to high sea levels combined with energetic swell waves.