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The Mediterranean basin is traditionally a hotspot where copious amounts of water vapor at low- and mid-tropospheric levels often favor atmospheric instability and the deepening of storms, leading to intense rainfall events with consequent flash floods. Moreover, this region includes sharp land–sea transitions, narrow maritime areas, and mountain chains which enhance convective precipitation. In this study, radar precipitation data were used to investigate the spatial distribution of rainfall swaths for seven severe cyclones originating over the Mediterranean Sea which produced intense flash inundation events along the western coast of Italy in the last decade (2011–2020). Based on 5 min precipitation amounts gridded at a 1 km spatial resolution, the temporal evolution of these storms displays a curvilinear path moving from sea to inland. Results show that more than half of the total precipitation for the analyzed events occurred on sea, and the total amount of storm rainfall over the marine surface exceeded that over land in four events out of the seven. Since the coastline strongly affects the rainfall pattern, we analyzed the land–sea discontinuity, which is a key factor controlling the spatial distribution of storm rates through their trajectory, where a small shift in precipitation target might smooth ground effects and mitigate flood impacts. [ABSTRACT FROM AUTHOR]

Recently, vast tracts of land have been acquired by foreign and domestic–foreign partnerships to satisfy an increasing demand for agricultural products, often resulting in the conversion of forested landscapes into agricultural fields. Those conversions often occur in areas characterized by high slope angles with the potential to cause mass wasting and shallow landslides. An interesting case‐study is the Licungo basin in Mozambique, where from 2000 nearly 160,000 ha of forest were converted, 17% of which occurred in areas acquired through large‐scale land acquisitions (LSLAs). This study analyses the relationship between deforestation occurring within LSLA areas and the likelihood of landslide occurrence. To this end, we use a spatially distributed physically based model that couples the assessment of slope stability with hillslope‐scale hydrological processes and evaluates the change in slope stability associated with remotely sensed forest loss. Relative to conditions where no human modification of land cover has occurred, we find that LSLAs have the potential to increase the extent of areas susceptible to slope failure by as much as 15,000 ha. We also quantified potential direct and indirect implications of such events for the food supply of local populations, estimating that 4,000 people could lose approximately 700 kcal cap−1 d−1 if all LSLAs are put under production. This study demonstrates the linkages between LSLAs, slope instability, and knock‐on environmental and societal impacts. Governments should therefore take such impacts into account (in addition to those related to habitat destruction and carbon emissions) when issuing permits and concessions within forested lands. [ABSTRACT FROM AUTHOR]

The transient effect of forest fires on runoff, erosion and yield of woody biomass has been investigated by combining the experimental approach with mathematical models of hydrological processes. The case study is the Branega creek in Liguria, Italy, where a forest fire in August 2003 caused substantial changes to soil and vegetation, and left a considerable amount of woody debris on the ground. Immediately after the fire, rainfall simulator experiments in adjacent burned and unburned plots showed the extent to which fire had increased runoff and erosion rates. A distributed hydrological model using the tube-flux approach, calibrated on experimental measurements, has been used to investigate hill slope and channel erosion in a small sub-catchment, 1.5 ha in area, nested in the Branega basin. Simulation runs show that the model accommodates the observed variability of runoff and erosion under disturbed and undisturbed conditions. A model component describing the delivery of wood from hill slopes to the channel in post-fire conditions, validated against local survey data, showed that the removal and transport of woody biomass can be reproduced using an integrated hydrological approach. Hence, transient complexity after wildfires can be addressed by such an approach with empirically determined physically-based parameters. [ABSTRACT FROM AUTHOR]

Focuses on potential climate changes that produces substantial effects on the hydrological cycle. How major changes in runoff and rainfall-driven processes could occur; Analysis of such climate changes focusing on the Arno River basin of central Italy; Effects of transient scenarios that explicitly describes the processes involved in the rainfall-runoff transformation; Discussion of the changes in the most significant components of the water balance with respect to seasonality, distributional properties and extremes; Potential implications on water resources.

Discusses long-term simulations of temporal rainfall and temperature under transient global climate conditions of atmospheric inputs at the basin scale in the Arno River in central Italy. Discussion of a global circulation model (GCM), simulating climate changes due to an increase in the greenhouse effect; How one can infer future changes in storm duration and depth from GCM trend variables; Data suggesting that this approach provides local precipitation that, together with temperature scenarios, can be used for hydrological simulation of basin water fluxes in the Arno River.

We present a method of modeling the areal reduction factor (ARF) of storm rainfall. The ARF is widely used in reducing point rainfall to obtain areal average values for the same duration, probability of exceedance, and specified area. The concepts of scaling and multiscaling, developed in recent years, provide a powerful framework for studying spatial and temporal variability of hydrological processes. It is our view that ARF must reflect the scaling properties of rainfall in space and time. We develop a simple statistical approach to the ARF of extreme storm rainfall based on the scaling properties of the underlying process in space and time. We derive the scaling relations of mean rainfall intensity over an area A and for a duration T using the concepts of dynamic scaling and statistical self-affinity. A new physically based formula for the ARF is then obtained. Applications are made to observations from the metropolitan area of Milan, Italy, and to data in the United Kingdom, as given in the Natural Environmental Research Council Flood Studies Report. These studies indicate that storm rates in space and time are scaling for extreme events, and hence this concept is shown to provide a useful practical approach to the evaluation of design storms for specified areas. [ABSTRACT FROM AUTHOR]

This study integrates a large eddy simulation (LES) model and volume of fluid (VOF) method to simulate the free-surface flows over inflexible circular-crested dams of different shapes. The simulated water depths and pressures on the dam surface are validated by the results of laboratory experiments. Then the numerical model examines the effects of the water depths and the Reynolds number on the hydrodynamic force and the discharge coefficient. The simulation results reveal that the time-averaged drag coefficient decreases as the downstream water depth H2 increases, while the influence of water depth H2 on the lift coefficients is less significant. Furthermore, the discharge coefficients of circular and elliptical dams, computed from the simulated velocity profiles over the crest of the dam, agree with the formulae suggested by previous studies when the downstream depth H2/H1 < 0.90. In contrast, the discharge coefficient of a tear-shape dam is slightly larger than those of circular dams. [ABSTRACT FROM AUTHOR]

Since Hurst [1951] detected the presence of long-term persistence in hydrologic data, new estimation methods and long-memory models have been developed. The lack of flexibility in representing the combined effect of short and long memory has been the major limitation of stochastic models used to analyze hydrologic time series. In the present paper a fractionally differenced autoregressive integrated moving average (FARIMA) model is considered. In contrast to using traditional ARIMA models, this approach allows the modeling of both short- and long-term persistence in a time series. A framework for identification and estimation is presented. The data do not have to be Gaussian. The resulting model, which replicates the sample probability density of the data, can be used for the generation of long synthetic series. An application to the monthly and daily inflows of Lake Maggiore, Italy, is presented. [ABSTRACT FROM AUTHOR]

The response of a conceptual soil water balance model to storm events is compared to a detailed finite element solution of the one-dimensional Richards equation in order to test the capabilities of the former in calculating the local contributions to infiltration excess runoff in a distributed catchment scale model. Local infiltration excess runoff is computed from ground level precipitation using the time compression approximation and a Philip infiltration capacity curve with Brooks-Corey constitutive equations. The validity of applying the conceptual model for local runoff and soil water balance calculations is investigated by performing numerical experiments over a range of soil types, control volume depths, and initial soil moisture conditions. We find that a good agreement between the conceptual and detailed models is obtained when the gravitational infiltration rate in Philip's formula is set to the saturated hydraulic conductivity, and when percolation from the control volume is updated as a function of the soil moisture content in a stepwise fashion. The comparison between these two models suggests that the simpler (and much less computer-intensive) conceptual water balance technique could be incorporated into distributed models for large scale complex terrains as an efficient means of retaining consideration of spatial variability effects in catchment scale hydrologie simulations. This is illustrated in an application to the Rio Missiaga catchment in the eastern Italian Alps, where the local contributions to surface and subsurface runoff are routed onto a digital elevation model-based conceptual transport network via a simple numerical scheme based on the Muskingum-Cunge method. [ABSTRACT FROM AUTHOR]

The adaptive use of a conceptual model for real-time flow forecasting is investigated. Maximum likelihood and ordinary least squares estimation criteria are considered, and the performance of maximum likelihood techniques for autocorrelated (AMLE) and heteroscedastic (HMLE) errors is analyzed jointly with that provided by the commonly used ordinary least squares estimation (OLSE) technique. Streamflow forecasts are compared for three rivers in central Italy, obtained by AMLE, HMLE, and OLSE adaptive calibration of a simple conceptual model describing the rainfall-runoff transformation by accounting for Hortonian infiltration and linear basin response to rainfall excess. Although model residuals display both autocorrelation and heteroscedasticity, OLSE is found to provide a rather satisfactory performance. Because the OLSE technique also requires less computational effort compared to that for AMLE and HMLE, one could consider OLSE as a suitable option for real-time model operation. [ABSTRACT FROM AUTHOR]

Mandelbrot's (1982) hypothesis that river length is fractal has been recently substantiated by Hjelmfelt (1988) using eight rivers in Missouri. The fractal dimension of river length, d, is derived here from the Horton's laws of network composition. This results in a simple function of stream length and stream area ratios, that is, d = max (1, 2 log RL/log RA). Three case studies are reported showing this estimate to be coherent with measurements of d obtained from map analysis. The scaling properties of the network as a whole are also investigated, showing the fractal dimension of river network, D, to depend upon bifurcation and stream area ratios according to D = min (2, 2 log RB/log RA). These results provide a linkage between quantitative analysis of drainage network composition and scaling properties of river networks. [ABSTRACT FROM AUTHOR]

The geometric pattern of the stream network of a drainage basin can be viewed as a 'fractal' with a fractional dimension (Mandelbrot, 1982). For an ordered drainage system, the authors first proposed to derive the fractal dimension from Horton's laws of stream number and stream lengths (La Barbera and Rosso, 1987). This results in a simple function of bifurcation and stream length ratios of the drainage system, the analytical derivation of which is presented. Accordingly, the fractal dimension could generally vary from 1 to 2, the latter value descending from the modal values of Horton's order ratios for topological randomness. However, the analysis of a large sample of field data shows the typical fractal dimension of river networks to lie between 1.5 and 2, with an average of 1.6÷1.7. Fractality can be used to investigate the scaling properties of the attributes and parameters describing drainage basin form and process. [ABSTRACT FROM AUTHOR]

The erosional development of drainage networks is analyzed by modeling two-dimensional flow of water and sediment over a bare slope. Deterministic equations of mass and momentum conservation are coupled with random fluctuations of sediment pickup and transportation processes acting at the hydrodynamic scale. These fluctuations are then shown to be able to provide an active source of channelization at the hillslope scale. Controlled experiments are also carried out by simulation runs aimed at investigating model performance (1) to describe formation of natural drainage patterns, (2) to account for different factors (i.e., soil characteristics, hillslope geometry, and rainfall intensity) which control network formation and development, and (3) to reproduce differentiation of drainage patterns due to above factors. [ABSTRACT FROM AUTHOR]

A diffusion wave model of distributed catchment dynamics is presented. The effects of catchment topography and river network structure on storm-flow response are incorporated by routing surface runoff in cascade throughout a digital elevation model (DEM) based conceptual transport network, where the Muskingum-Cunge scheme with variable parameters is used to describe surface runoff dynamics. Dynamic scaling of hydraulic geometry is also incorporated in the model by using the “at-a-station” and “downstream” relationships by Leopold and Maddock. Numerical experiments indicate that the model is more than 98% mass conservative for possible slope and roughness configurations, which may occur for hillslopes in a natural catchment. Fluctuations in the simulated discharge may occur in response to discontinuities in rainfall excess representation if Courant number Cu during the simulation exceeds a threshold of about 3. Catchment scale simulations with different temporal resolution show that the model response is independent of structural parameters (model consistency). Also, the overall accuracy is preserved for computationally inexpensive space-time discretizations (for which Cu > 3) because fluctuations that may occur at the local scale are dampened when propagating downstream. Comparison of model results with observed outlet hydrographs of the Rio Missiaga experimental catchment (Eastern Italian Alps) show this approach to be capable of describing both overland and channel phases of surface runoff in mountainous catchments. [ABSTRACT FROM AUTHOR]

This work illustrates the contribution of flood risk assessment and adaptation to set up a conservation management plan for a masterpiece of 20th-century architecture. Case study is the iconic complex, internationally known as the National Art Schools of Cuba. It consists of five buildings built in the early 1960s within a park of Habana next to the Caribbean Sea. The path of the river (Rio Quibù) crossing the estate was modified to fit the landscape design. The complex has then been exposed to the risk of flooding. The School of Ballet, located in a narrow meander of the river, slightly upstream of a bridge and partially obstructing the flow, is particularly subject to frequent flash floods from the Rio Quibù, and it needs urgent restoration. Keeping ISA Modern is a project aimed at preserving the Schools complex. Based upon in situ surveys on the Rio Quibù and local area measurements during 2019, numerical modelling, and previous work by the Cuban National Institute of Hydraulic Resources, we pursued a flood risk analysis for the area, and a preliminary analysis of available risk reduction strategies. Using HEC-RAS 2D software for hydraulic modelling, we evaluated the flooded area and the hydraulic conditions (flow depth, velocity) for floods with given return periods. Our results show that SB is a building most subject to flooding, with high levels of risk. Defense strategies as designed by Cuban authorities may include a (new) wall around the School of Ballet and widening of the river channel, with high impact and cost, although not definitive. Temporary, light, permanent, and low cost/impact flood proofing structures may be used with similar effectiveness. We demonstrate that relatively little expensive hydraulic investigation may aid flood modelling and risk assessment in support of conservation projects for historically valuable sites. This may support brainstorming and the selection of (low to high cost) adaptation and risk reduction measures in the coastal areas of Cuba in response to ever increasing extreme storms and sea level rise controlling flood dynamics under transient climate change. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article "Bivariate Flood Frequency Analysis Using the Copula Method," by L. Zhang and V. P. Singh in the 2006 issue.