Simulating Flash Floods Research Articles

A physically based distributed hydrological model of wadi system to simulate flash floods in arid regions

Many hydrological approaches have been developed for humid areas; however, we still have many challenges regarding flash floods simulation in arid regions. Thus, the main purpose of this study is to develop a physically based hydrological model for flash floods simulation, to understand the hydrological processes, and to overcome the water relating problems, as water scarcity, data deficiency. In this study, Hydrological River Basin Environmental Assessment Model incorporating wadi system (Hydro-BEAM-WaS) integrated with both Geographic Information System (GIS) and remote sensing data is proposed. To overcome the lack of observational data, Global Satellite Mapping of Precipitation (GSMaP) data has been compared with the Global Precipitation Climatology Center (GPCC) data. We found that the GSMaP has an overestimated or underestimated systematic seasonal bias. Wadi El-Khoud in Oman was chosen for model calibration, while the River Nile basin in Egypt was chosen for flash flood simulations. The simulation has been successfully carried out where it exhibits a reasonable fit between both the simulated and observed results, in spite of the deficiency of high quality observations. This approach can be used to evaluate and simulate the wadi runoff behaviors, such as discontinuous surface flow. It also can help in estimating the initial and transmission losses. Flash flood water has been assessed and evaluated as new water resources, which would be properly utilized to overcome the problem of water shortage in such regions. The proposed model has been proven to provide reliable simulations of flash floods referring to ungauged wadi systems.

Using High-Resolution Satellite Rainfall Products to Simulate a Major Flash Flood Event in Northern Italy

AbstractEffective flash flood warning procedures are usually hampered by observational limitations of precipitation over mountainous basins where flash floods occur. Satellite rainfall estimates are available over complex terrain regions, offering a potentially viable solution to the observational coverage problem. However, satellite estimates of heavy rainfall rates are associated with significant biases and random errors that nonlinearly propagate in hydrologic modeling, imposing severe limitations on the use of these products in flood forecasting. In this study, the use of three quasi-global and near-real-time high-resolution satellite rainfall products for simulating flash floods over complex terrain basins are investigated. The study uses a major flash flood event that occurred during 29 August 2003 on a medium size mountainous basin (623 km2) in the eastern Italian Alps. Comparison of satellite rainfall with rainfall derived from gauge-calibrated weather radar estimates showed that although satellite products suffer from large biases they could represent the temporal variability of basin-averaged precipitation. Propagation of satellite rainfall through a distributed hydrologic model revealed that systematic error in rainfall was severely magnified when transformed to error in runoff under dry initial soil conditions. Simulation hydrographs became meaningful only after recalibrating the model for each satellite rainfall input separately. However, the unrealistic values of model parameters after recalibration show that this approach is erroneous and that model recalibration using satellite rainfall data should be treated with care. Overall, this study highlights the need for improvement of satellite rainfall retrieval algorithms in order to allow a more appropriate use of satellite rainfall products for flash flood applications.

Numerical assessment of flood hazard risk to people and vehicles in flash floods

Flash flooding often leads to extremely dangerous and sometimes catastrophic conditions in rivers due to characteristics such as: short timescales, the limited opportunity for issuing warnings, and the frequent high average mortality. Many past extreme flood events have been accompanied by flash floods, and they have also been one of the main sources of serious loss of human life among the world’s worst natural disasters. Flash floods can also cause large loss of property, such as the recent floods in Pakistan and the damage to vehicles in the 2004 Boscastle flood in the UK. It is therefore desirable to be able to assess the degree of safety of people and vehicles during flash floods using numerical models. In the current study, an algorithm for assessing the flood hazard risk to people and vehicles has been integrated into an existing two-dimensional hydrodynamic model capable of simulating flash floods. In the algorithm, empirical curves relating water depths and corresponding critical velocities for children and adults, developed by previous researchers, are used to assess the degree of people safety, and a new incipient velocity formula is used to evaluate the degree of vehicle safety. The developed model was then applied to three real case studies, including: the Glasgow and Boscastle floods in the UK, and the Malpasset dam-failure flood in France. According to the analysis of model predictions, the following conclusions have been obtained: (i) simulated results for the Glasgow flood showed that children would be in danger of standing in the flooded streets in a small urban area; (ii) simulations for the Boscastle flood indicated that vehicles in the car park would be flushed away by the flow with high velocity, which indirectly testified the predictive accuracy of the incipient formula for vehicles; and (iii) simulations for the Malpasset dam-failure flood showed that the adopted method for the assessment of people safety was applicable, and some local people living below the dam would have been swept away, which corresponded well with the report of casualties. Therefore, the developed integrated model can be used to evaluate the flood hazard risk to people and vehicles in flash floods, and these predictions can be used in flood risk management.

Flood Characteristics of Upper Meghna River Basin, Bangladesh

This paper presents the outcome of a research study conducted to analyze the propagation time of the flash floods in the Upper Meghna river basin in Bangladesh and corresponding socio-economic impacts. A numerical model set-up in the general river model system named MIKE 11 was applied to simulate flash floods in the river basin and the travel time of their flood peak from the border towards India (only limited information is available from inside India) and into North East region. The results reveal that there is only little warning time from the time the flood passes the border towards India and until the flood impacts the rural people in the North East region of Bangladesh. The corresponding socio-economic impacts were quantified and found to be substantial.

Simulating Flash Flood Events: Importance of the Subgrid Representation of Convection

Abstract The Pennsylvania State University–NCAR Mesoscale Model is used to simulate six flash flood events that occurred in the central and eastern United States. Results suggest that standard model simulations of 24-h accumulated precipitation provide little indication of the potential for flash flood–producing rainfall for most events. Often the model generates convective outflow boundaries that rapidly move away from their source region and initiate new convection well removed from the original convective activity. This self-sustaining propagation mechanism prevents long-lived heavy rainfall over a particular region. Three modifications to the Kain–Fritsch convective parameterization scheme, each designed to test model sensitivity to the convective scheme formulation, are discussed. The modifications include maximizing the convective scheme precipitation efficiency and altering the scheme’s treatment of convective downdrafts. Model results using the three modifications of the convective scheme each sho...