Itzï (version 17.1):an open-source, distributed GIS model for dynamic flood simulation

Worldwide, floods are acknowledged as one of the most destructive hazards. In human-dominated environments, their negative impacts are ascribed not only to the increase in frequency and intensity of floods but also to a strong feedback between the hydrological cycle and anthropogenic development. In order to advance a more comprehensive understanding of this complex interaction, this paper presents the development of a new open-source tool named <q>Itzï</q> that enables the 2-D numerical modelling of rainfall–runoff processes and surface flows integrated with the open-source geographic information system (GIS) software known as GRASS. Therefore, it takes advantage of the ability given by GIS environments to handle datasets with variations in both temporal and spatial resolutions. Furthermore, the presented numerical tool can handle datasets from different sources with varied spatial resolutions, facilitating the preparation and management of input and forcing data. This ability reduces the preprocessing time usually required by other models. Itzï uses a simplified form of the shallow water equations, the damped partial inertia equation, for the resolution of surface flows, and the Green–Ampt model for the infiltration. The source code is now publicly available online, along with complete documentation. The numerical model is verified against three different tests cases: firstly, a comparison with an analytic solution of the shallow water equations is introduced; secondly, a hypothetical flooding event in an urban area is implemented, where results are compared to those from an established model using a similar approach; and lastly, the reproduction of a real inundation event that occurred in the city of Kingston upon Hull, UK, in June 2007, is presented. The numerical approach proved its ability at reproducing the analytic and synthetic test cases. Moreover, simulation results of the real flood event showed its suitability at identifying areas affected by flooding, which were verified against those recorded after the event by local authorities

Numerical modelling of the sorting and transport of non-uniform sediments in the swash zone

The sorting and transport of different sediment fractions and the resulting beachface evolution over the swash zone of a beach, is numerically investigated within the framework of the shallow water theory and the active layer theory. The shallow water and Exner equations, along with the volume fraction (sorting) equation given by the active layer theory compose the system which is numerically solved using an uncoupled approach, i.e., the model assumes that changes in bed level (and volume fraction) do not have an effect on the flow. Two different numerical methods are applied to solve the system depending on the type of flow tested (constant current or swash flow); a classic Finite Differences Method and a hybrid Finite Difference-Method of Characteristics (FD-MOC) are then used respectively. The numerical model is first tested for the case of a sand dune composed of two different sediment fractions subjected to a constant current. Comparison between simulations from the model and results given by Hudson (2001) solution (which only considers one sediment fraction) showed that the composition of the bed is crucial for the subsequent bed evolution. This case served to verify that the equations were solved correctly and some interesting features of the kinematics of the system were observed. The model is then applied to the case in which a single Shen and Meyer (1963b) swash event acts over a plane sloping beach composed of two different sediment fractions in the same proportion. Different values of the A (sediment mobility parameter) are investigated taking as a base point the value calculated by Kelly (2009). The results show that the behaviour in time of Pfa (fine volume fraction in the active layer) directly depends on the difference between sediment mobility parameters (Af and Ac) for the fine and coarse fractions; and this in turn results in an effect on the beachface evolution. The finer the mixture of sediments involved the bigger the bed change. Similar behaviour is obtained when the model is tested for the case in which a non-breaking wave swash is acting over the beach profile, although some interesting differences are noted mainly due to the different driving hydrodynamics.Finally, realistic A parameters for the fine and coarse fraction are defined linking grain diameters that can be found on real beaches to the sediment parameters used in the model.Numerical tests for both type of swash flows (breaking and non-breaking wave) are implemented, in which different initial Pfa distributions are considered. The results from these simulations confirmed the crucial role played by the initial distribution of sediments on the beach evolution; it was observed that a kink in the bed (a sort of swash bar/trough) formed around the middle part of the swash zone for the cases in which the initial distribution of sediments showed a maximum or minimum in that area. Comparing the results given by the model when two sediment fractions are considered, with those when a mean value (A¯ = (Af+Ac) / 2 )which is a common practice in coastal engineering models) showed that the inclusion of the two sediment fractions is crucial in order to get better predictions

Itzï (version 17.1):an open-source, distributed GIS model for dynamic flood simulation

Worldwide, floods are acknowledged as one of the most destructive hazards. In human-dominated environments, their negative impacts are ascribed not only to the increase in frequency and intensity of floods but also to a strong feedback between the hydrological cycle and anthropogenic development. In order to advance a more comprehensive understanding of this complex interaction, this paper presents the development of a new open-source tool named <q>Itzï</q> that enables the 2-D numerical modelling of rainfall–runoff processes and surface flows integrated with the open-source geographic information system (GIS) software known as GRASS. Therefore, it takes advantage of the ability given by GIS environments to handle datasets with variations in both temporal and spatial resolutions. Furthermore, the presented numerical tool can handle datasets from different sources with varied spatial resolutions, facilitating the preparation and management of input and forcing data. This ability reduces the preprocessing time usually required by other models. Itzï uses a simplified form of the shallow water equations, the damped partial inertia equation, for the resolution of surface flows, and the Green–Ampt model for the infiltration. The source code is now publicly available online, along with complete documentation. The numerical model is verified against three different tests cases: firstly, a comparison with an analytic solution of the shallow water equations is introduced; secondly, a hypothetical flooding event in an urban area is implemented, where results are compared to those from an established model using a similar approach; and lastly, the reproduction of a real inundation event that occurred in the city of Kingston upon Hull, UK, in June 2007, is presented. The numerical approach proved its ability at reproducing the analytic and synthetic test cases. Moreover, simulation results of the real flood event showed its suitability at identifying areas affected by flooding, which were verified against those recorded after the event by local authorities

Remote Sensing Of Total Water Storage Variability During Extreme Heat Waves

Droughts and heat waves are a major hazard for food & water security, economic development, and human & ecosystem health, among others. Over the last decade, short-term but exceptional heat waves have been observed across different regions of the world, with several locations experiencing all-time maximum temperature records. While many studies have suggested that the extreme intensity of such recent events can be attributed to a changing climate, little attention has been given to the impacts on the terrestrial water balance. This work analyzes the sensitivity of total water storage to extreme heat waves since 2003 in Europe (2003), Russia, Sahel and Middle East (2010), UK (2011), USA (2012), Australia (2013). The main objectives are to: (1) explore the relationships between temperature, precipitation and total water storage variability (2) infer the response time of extreme dry spells to total water storage decline. The methodology used in this study was based on remote sensing tools such as the GRACE mission and data assimilation from land surface models. The analysis shows recurrent annual hysteresis loops in the monthly time series of climate and water storage, which imply a time lag between the occurrence of heat waves and the depletion of soil moisture and aquifer storage. Finally, the results offer the potential to provide first-order estimates of total water storage variations for large river basins and aquifers due to climate extremes

Numerical modelling of the sorting and transport of non-uniform sediments in the swash zone

The sorting and transport of different sediment fractions and the resulting beachface evolution over the swash zone of a beach, is numerically investigated within the framework of the shallow water theory and the active layer theory. The shallow water and Exner equations, along with the volume fraction (sorting) equation given by the active layer theory compose the system which is numerically solved using an uncoupled approach, i.e., the model assumes that changes in bed level (and volume fraction) do not have an effect on the flow. Two different numerical methods are applied to solve the system depending on the type of flow tested (constant current or swash flow); a classic Finite Differences Method and a hybrid Finite Difference-Method of Characteristics (FD-MOC) are then used respectively. The numerical model is first tested for the case of a sand dune composed of two different sediment fractions subjected to a constant current. Comparison between simulations from the model and results given by Hudson (2001) solution (which only considers one sediment fraction) showed that the composition of the bed is crucial for the subsequent bed evolution. This case served to verify that the equations were solved correctly and some interesting features of the kinematics of the system were observed. The model is then applied to the case in which a single Shen and Meyer (1963b) swash event acts over a plane sloping beach composed of two different sediment fractions in the same proportion. Different values of the A (sediment mobility parameter) are investigated taking as a base point the value calculated by Kelly (2009). The results show that the behaviour in time of Pfa (fine volume fraction in the active layer) directly depends on the difference between sediment mobility parameters (Af and Ac) for the fine and coarse fractions; and this in turn results in an effect on the beachface evolution. The finer the mixture of sediments involved the bigger the bed change. Similar behaviour is obtained when the model is tested for the case in which a non-breaking wave swash is acting over the beach profile, although some interesting differences are noted mainly due to the different driving hydrodynamics.Finally, realistic A parameters for the fine and coarse fraction are defined linking grain diameters that can be found on real beaches to the sediment parameters used in the model.Numerical tests for both type of swash flows (breaking and non-breaking wave) are implemented, in which different initial Pfa distributions are considered. The results from these simulations confirmed the crucial role played by the initial distribution of sediments on the beach evolution; it was observed that a kink in the bed (a sort of swash bar/trough) formed around the middle part of the swash zone for the cases in which the initial distribution of sediments showed a maximum or minimum in that area. Comparing the results given by the model when two sediment fractions are considered, with those when a mean value (A¯ = (Af+Ac) / 2 )which is a common practice in coastal engineering models) showed that the inclusion of the two sediment fractions is crucial in order to get better predictions

Evaluation of open-access global digital elevation models (AW3D30, SRTM and ASTER) for flood modelling purposes

Elevation data in the form of Digital Elevation Models (DEMs) has been recognised as a basic piece of information for the accurate representation of topographic controls exerted in hydrologic and hydraulic models. Yet many practitioners rely on open-access global datasets usually obtained from space-borne survey due to the cost and sparse coverage of sources of higher resolution. In may 2016 the Japanese Aerospace eXploration Agency (JAXA) publicly released an open-access global DEM at an horizontal resolution of 30 m, the ALOS World 3D-30m (AW3D30). So far no published study assessed the flood modelling capabilities of this new product. The purpose of this investigation is twofold. Firstly, to present an assessment of the capacity of the AW3D30 DEM for flood modelling purposes and secondly, to compare its performance with regards to computed water levels and flood extent maps calculated using other freely available 30 m DEMs for model setup (e.g. SRTM and ASTER GDEM). For this comparison, the reference to reality is given by the water levels and flood extent maps computed with the same numerical model but using a LiDAR based DEM (5 m of spatial resolution re-sampled to 30 m). The numerical model employed in this investigation is based on a damped partial inertia approximation of the Saint-Venant equations on a regular raster grid, which is forced with a simple and synthetic rainfall storm event. Numerical results using different elevation data in model setup are compared for two regions with contrasting topographic gradients (steep and smooth). Results with regards to water depth and flood extent show that AW3D30 DEM performs better than the SRTM DEM. Notably, in the case of mountainous regions results derived with the AW3D30 DEM are comparable in skill to those obtained with a LiDAR derived DSM, suggesting its suitability in the numerical reproduction of flood events. This encouraging performance paves the way to more accurate modelling for both data-scarce regions and global flood models

The Significance of the Spatial Variability of Rainfall on the Numerical Simulation of Urban Floods

The growth of urban population, combined with an increase of extreme events due to climate change call for a better understanding and representation of urban floods. The uncertainty in rainfall distribution is one of the most important factors that affects the watershed response to a given precipitation event. However, most of the investigations on this topic have considered theoretical scenarios, with little reference to case studies in the real world. This paper incorporates the use of spatially-variable precipitation data from a long-range radar in the simulation of the severe floods that impacted the city of Hull, U.K., in June 2007. This radar-based rainfall field is merged with rain gauge data using a Kriging with External Drift interpolation technique. The utility of this spatially-variable information is investigated through the comparison of computed flooded areas (uniform and radar) against those registered by public authorities. Both results show similar skills at reproducing the real event, but differences in the total precipitated volumes, water depths and flooded areas are illustrated. It is envisaged that in urban areas and with the advent of higher resolution radars, these differences will be more important and call for further investigation

Uncertainty Propagation In A Hydro-Meteorological Approach: From The Cloud To The Flood Map.

Globally, it is widely known that floods remain the most frequent and devastating natural hazards. Likewise, there is recent evidence showing an increase in the number of extreme flood events observed around the world. Therefore, it is imperative to develop an integrated flood assessment framework that enables a better understanding of both, the generation of these events and the interaction of key variables within the hydro-meteorological system. The aim of this investigation is to study the propagation of meteorological uncertainty to a numerically estimated flood map. For such purpose, we utilise a cascade modelling approach comprised by a Numerical Weather Prediction Model (NWP), a rainfall-runoff model and a standard 2D hydrodynamic model. Uncertainty is considered in the meteorological model (Weather Research and Forecasting model) using a multi-physics ensemble technique considering twenty four parameterization schemes. The resulting precipitation fields are used as input in a distributed hydrological model to generate spaghetti plots, which are then employed as forcing in a 2D hydrodynamic model. The approach is utilised for the reproduction of an extreme flood event in southern Mexico, for which field data (rain gauges) and satellite imagery are available. Although there are more uncertainties involved in the determination of a flooded area, the methodology represents a robust approach to acknowledge the propagation from the meteorological model to the flood map. Thus, it favours preventive action in the generation of better flood management strategies

Deserción en la Universidad del Magdalena en la modalidad de pregrado presencial

Este trabajo analiza el problema de la deserción en la Universidad del Magdalena en la modalidad de pregrado presencial, para ello el estudio calcula los índices e indicadores deserción y establece los factores asociados a este fenómeno mediante la estimación de un modelo econométrico. Para el análisis de los resultados arrojados en los índices e indicadores de deserción se tiene en cuenta la metodología de selección utilizada en los procesos de admisión de la universidad. La estimación del modelo se realizó por las técnicas de Efectos Fijos (EF) y Efectos Aleatorios (EA), pero el análisis de las variables se realizó con base a los resultados obtenidos por el método de (EA), debido a que este era más pertinente para estimar el modelo

Wave-induced extreme water levels in the Puerto Morelos fringing reef lagoon

Wave-induced extreme water levels in the Puerto Morelos fringing reef lagoon are investigated by means of a phase-resolving non-hydrostatic wave model (SWASH). This model solves the nonlinear shallow water equations including non-hydrostatic pressure. The one-dimensional version of the model is implemented in order to investigate wave transformation in fringing reefs. Firstly, the numerical model is validated with (i) laboratory experiments conducted on a physical model (Demirbilek et al., 2007)and (ii) field observations (Coronado et al., 2007). Numerical results show good agreement with both experimental and field data. The comparison against the physical model results, for energetic wave conditions, indicates that high- and low-frequency wave transformation is well reproduced. Moreover, extreme water-level conditions measured during the passage of Hurricane Ivan in Puerto Morelos are also estimated by the numerical tool. Subsequently, the model is implemented at different along-reef locations in Puerto Morelos. Extreme water levels, wave-induced setup, and infragravity wave energy are estimated inside the reef lagoon for different storm wave conditions (&lt;i&gt;H&lt;/i&gt;&lt;sub&gt;s&lt;/sub&gt; &gt;2 m). The numerical results revealed a strong correlation between the offshore sea-swell wave energy and the setup. In contrast, infragravity waves are shown to be the result of a more complex pattern which heavily relies on the reef geometry. Indeed, the southern end of the reef lagoon provides evidence of resonance excitation, suggesting that the reef barrier may act as either a natural flood protection morphological feature, or as an inundation hazard enhancer depending on the incident wave conditions