Short Time Steps Research Articles

OpenMI: Open modelling interface

Management issues in many sectors of society demand integrated analysis that can be supported by integrated modelling. Since all-inclusive modelling software is difficult to achieve, and possibly even undesirable, integrated modelling requires the linkage of individual models or model components that address specific domains. Emerging from the water sector, the OpenMI has been developed with the purpose of being the glue that can link together model components from various origins. The OpenMI provides a standardized interface to define, describe and transfer data on a time basis between software components that run simultaneously, thus supporting systems where feedback between the modelled processes is necessary in order to achieve physically sound results. The OpenMI allows the linking of models with different spatial and temporal representations: for example, linking river models and groundwater models, where the river model typically uses a one-dimensional grid and a short timestep and the groundwater model uses a two- or three-dimensional grid and a longer timestep. The OpenMI is designed to accommodate the easy migration of existing modelling systems, since their re-implementation may not be economically feasible due to the large investments that have been put into the development and testing of these systems.

Computational issues in the simulation of two-dimensional discrete dislocation mechanics

The effect of the integration time step and the introduction of a cut-off velocity for the dislocation motion was analysed in discrete dislocation dynamics (DD) simulations of a single crystal microbeam. Two loading modes, bending and uniaxial tension, were examined. It was found that a longer integration time step led to a progressive increment of the oscillations in the numerical solution, which would eventually diverge. This problem could be corrected in the simulations carried out in bending by introducing a cut-off velocity for the dislocation motion. This strategy (long integration times and a cut-off velocity for the dislocation motion) did not recover, however, the solution computed with very short time steps in uniaxial tension: the dislocation density was overestimated and the dislocation patterns modified. The different response to the same numerical algorithm was explained in terms of the nature of the dislocations generated in each case: geometrically necessary in bending and statistically stored in tension. The evolution of the dislocation density in the former was controlled by the plastic curvature of the beam and was independent of the details of the simulations. On the contrary, the steady-state dislocation density in tension was determined by the balance between nucleation of dislocations and those which are annihilated or which exit the beam. Changes in the DD imposed by the cut-off velocity altered this equilibrium and the solution. These results point to the need for detailed analyses of the accuracy and stability of the dislocation dynamic simulations to ensure that the results obtained are not fundamentally affected by the numerical strategies used to solve this complex problem.

Rainfall stochastic disaggregation models: Calibration and validation of a multiplicative cascade model

The simulation of long time series of rainfall rates at short time steps remains an important issue for various applications in hydrology. Among the various types of simulation models, random multiplicative cascade models (RMC models) appear as an appealing solution which displays the advantages to be parameter parsimonious and linked to the multifractal theory. This paper deals with the calibration and validation of RMC models. More precisely, it discusses the limits of the scaling exponent function method often used to calibrate RMC models, and presents an hydrological validation of calibrated RMC models. A 8-year time series of 1-min rainfall rates is used for the calibration and the validation of the tested models. The paper is organized in three parts. In the first part, the scaling invariance properties of the studied rainfall series is shown using various methods ( q-moments, PDMS, autocovariance structure) and a RMC model is calibrated on the basis of the rainfall data scaling exponent function. A detailed analysis of the obtained results reveals that the shape of the scaling exponent function, and hence the values of the calibrated parameters of the RMC model, are highly sensitive to sampling fluctuation and may also be biased. In the second part, the origin of the sensivity to sampling fluctuation and of the bias is studied in detail and a modified Jackknife estimator is tested to reduce the bias. Finally, two hydrological applications are proposed to validate two candidate RMC models: a canonical model based on a log-Poisson random generator, and a basic micro-canonical model based on a uniform random generator. It is tested in this third part if the models reproduce faithfully the statistical distribution of rainfall characteristics on which they have not been calibrated. The results obtained for two validation tests are relatively satisfactory but also show that the temporal structure of the measured rainfall time series at small time steps is not well reproduced by the two selected simple random cascade models.

The Evolution of Dynamical Cores for Global Atmospheric Models

The evolution of global atmospheric model dynamical cores from the first developments in the early 1960s to present day is reviewed. Numerical methods for atmospheric models are not straightforward because of the so-called pole problem. The early approaches include methods based on composite meshes, on quasi-homogeneous grids such as spherical geodesic and cubed sphere, on reduced grids, and on a latitude-longitude grid with short time steps near the pole, none of which were entirely successful. This resulted in the dominance of the spectral transform method after it was introduced. Semi-Lagrangian semi-implicit methods were developed which yielded significant computational savings and became dominant in Numerical Weather Prediction. The need for improved physical properties in climate modeling led to developments in shape preserving and conservative methods. Today the numerical methods development community is extremely active with emphasis placed on methods with desirable physical properties, especially conservation and shape preservation, while retaining the accuracy and efficiency gained in the past. Much of the development is based on quasi-uniform grids. Although the need for better physical properties is emphasized in this paper, another driving force is the need to develop schemes which are capable of running efficiently on computers with thousands of processors and distributed memory. Test cases for dynamical core evaluation are also briefly reviewed. These range from well defined deterministic tests to longer term statistical tests with both idealized forcing and complete parameterization packages but simple geometries. Finally some aspects of coupling dynamical cores to parameterization suites are discussed.

Implementation of a symplectic multiple-time-step molecular dynamics algorithm, based on the united-residue mesoscopic potential energy function

A symplectic multiple-time-step (MTS) algorithm has been developed for the united-residue (UNRES) force field. In this algorithm, the slow-varying forces (which contain most of the long-range interactions and are, therefore, expensive to compute) are integrated with a larger time step, termed the basic time step, and the fast-varying forces are integrated with a shorter time step, which is an integral fraction of the basic time step. Based on the split operator formalism, the equations of motion were derived. Separation of the fast- and slow-varying forces leads to stable molecular dynamics with longer time steps. The algorithms were tested with the Ala(10) polypeptide chain and two versions of the UNRES force field: the current one in which the energy components accounting for the energetics of side-chain rotamers (U(rot)) can lead to numerically unstable forces and a modified one in which the the present U(rot) was replaced by a numerically stable expression which, at present, is parametrized only for polyalanine chains. With the modified UNRES potential, stable trajectories were obtained even when extending the basic time step to 15 fs and, with the original UNRES potentials, the basic time step is 1 fs. An adaptive multiple-time-step (A-MTS) algorithm is proposed to handle instabilities in the forces; in this method, the number of substeps in the basic time step varies depending on the change of the magnitude of the acceleration. With this algorithm, the basic time step is 1 fs but the number of substeps and, consequently, the computational cost are reduced with respect to the MTS algorithm. The use of the UNRES mesoscopic energy function and the algorithms derived in this work enables one to increase the simulation time period by several orders of magnitude compared to conventional atomic-resolution molecular dynamics approaches and, consequently, such an approach appears applicable to simulating protein-folding pathways, protein functional dynamics in a real molecular environment, and dynamical molecular recognition processes.

Simulating cell biology

As with the experimental sciences, the cell simulation field is largely driven by the development of new techniques, and of new tools that implement those techniques. Many techniques under development are working to increase simulation accuracy while reducing the computational burden. A central challenge concerns simulation of interacting processes that occur on different time scales; the fast scale imposes a short simulation time step, but that makes the simulation too slow to observe the slow scale. This is being met with new algorithms and hybrid simulations that treat space and stochasticity only as required. Also, given the size and the possible nonlinearity and non-determinism represented by biological models, tools for analysis of models, such as those that provide parametric sensitivity analysis, and for comparing models to data for parameterization and (in)validation are both profoundly needed and in a relatively primitive state.It is easy to describe the ideal simulation tool: it should be able to simulate reactions and diffusion as accurately as needed, account for all relevant mechanical processes, help with model parameterization, validate and discriminate between models using data, and be easy to use. Many modeling tools are aiming towards this goal but it remains elusive, in part because of the extraordinary speed with which improved analysis methods and cellular measurements are being developed.

Forming of axisymmetric tubes under the influence of impulse-magnetic field and computer simulation of the process

Electro-magnetic pulse technologies use magnetic fields to move conductive material in extremely short time steps. Recent developments have demonstrated the application of these technologies to sheet metal forming, tubular space frames and drive shafts. The high velocity of the tube wall displacement under the influence of impulse-magnetic field pressure complicates the control of the deformation process. In this paper the forming process is divided into three basic stages: stage of free movement, stage of joint movement and stage of unloading. For studying the kinematics of the forming process, one of the programs of three-dimensional graphics is applied and then modeling is carried out with use of animation principles for basic stages of the process.

Grain-scale processes governing shear band initiation and evolution in sands

A variety of experimental techniques have been used to advance understanding of strain localization phenomena in sands. However, all of these methods have fallen short in characterizing the evolution of the grain-scale processes that necessarily control shear band formation and growth in sands. This paper presents results of application of the non-destructive displacement measurement technique of digital image correlation (DIC) to measure two- and three-dimensional surface displacements on plane strain and axisymmetric sand specimens over short time steps. The abundance of local displacement data, high level of accuracy, and nearly continuous (spatially and temporally) record of displacement evolution afforded by the DIC technique has finally enabled a means to quantify local displacements to particulate-scale intensity. The data have been used to evaluate the local displacement mechanisms leading to the triggering of the formation of persistent shear bands, the timing of shear band formation with regard to the achievement of peak stress, and the character of displacements within fully formed shear bands. Insights are offered regarding the relation between strain localization and global stress–strain behavior, and the ensuing interpretations of shear banding as a hardening or softening phenomenon. Comparison of behavior between plane strain and triaxial tests offer additional perspective on the influences of three-dimensional stresses and boundary conditions on shear banding. The results further shed light on the micro-deformation mechanisms (i.e. buckling columns) responsible for the observed local strain non-uniformities that characterize “steady-state” shear band evolution.

Stability-Dependent Exchange Coefficients for Air–Sea Fluxes*

Abstract This study introduces exchange coefficients for wind stress (CD), latent heat flux (CL), and sensible heat flux (CS) over the global ocean. They are obtained from the state-of-the-art Coupled Ocean–Atmosphere Response Experiment (COARE) bulk algorithm (version 3.0). Using the exchange coefficients from this bulk scheme, CD, CL, and CS are then expressed as simple polynomial functions of air–sea temperature difference (Ta − Ts)—where air temperature (Ta) is at 10 m, wind speed (Va) is at 10 m, and relative humidity (RH) is at the air–sea interface—to parameterize stability. The advantage of using polynomial-based exchange coefficients is that they do not require any iterations for stability. In addition, they agree with results from the COARE algorithm but at ≈5 times lower computation cost, an advantage that is particularly needed for ocean general circulation models (OGCMs) and climate models running at high horizontal resolution and short time steps. The effects of any water vapor flux in calculating the exchange coefficients are taken into account in the polynomial functions, a feature that is especially important at low wind speeds (e.g., Va < 5 m s−1) because air–sea mixing ratio difference can have a major effect on the stability, particularly in tropical regions. Analyses of exchange coefficients demonstrate the fact that water vapor can have substantial impact on air–sea exchange coefficients at low wind speeds. An example application of the exchange coefficients from the polynomial approach is the recalculation of climatological mean wind stress magnitude from 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) data in the North Pacific Ocean over 1979–2002. Using ECMWF 10-m winds and the authors’ methodology provides accurate surface stresses while largely eliminating the orographically induced Gibb’s waves found in the original ERA-40 surface wind stresses. These can have a large amplitude near mountainous regions and can extend far into the ocean interior. This study introduces exchange coefficients of air–sea fluxes, which are applicable to the wide range of conditions occurring over the global ocean, including the air–sea stability differences across the Gulf Stream and Kuroshio, regions which have been the subject of many climate model studies. This versatility results because CD, CL, and CS are determined for Va values of 1 to 40 m s−1, (Ta − Ts), intervals of −8° to 7°C, and RH values of 0% to 100%. Exchange coefficients presented here are called the Naval Research Laboratory (NRL) Air–Sea Exchange Coefficients (NASEC) and they are suitable for a wide range of air–sea interaction studies and model applications.

An Analysis of Spatial and Temporal Dimension of Drought Vulnerability in Turkey Using the Standardized Precipitation Index

Drought has become a recurrent phenomenon in Turkey in the last few decades. Significant drought conditions were observed during years of late 1980s and the trend continued in the late 1990s. The country’s agricultural sector and water resources have been under severe constraints from the recurrent droughts. In this study, spatial and temporal dimensions of meteorological droughts in Turkey have been investigated from vulnerability concept. The Standardized Precipitation Index (SPI) method was used to detail geographical variations in the drought vulnerability based on frequency and severity of drought events at multiple time steps. Critical (threshold) rainfall values were derived for each station at multiple-time steps in varying drought categories to determine least amount of rainfall required to avoid from drought initiation. The study found that drought vulnerability portrays a very diverse but consistent picture with varying time steps. At regional scale, south-eastern and eastern Anatolia are characterized with moderate droughts at shorter time steps, while the occurrence of severe droughts at shorter time steps is observed at non-coastal parts of the country. A similar picture was observed with very severe droughts. The critical (threshold) values exhibited rising numbers during the growing season at 3-month step in the South-eastern Anatolia, which might have significant consequences considering presence of large irrigation projects under-development in the region. In general, rainfall amounts required for non-drought conditions decrease from the coastal parts toward the interiors with increasing time steps.

Development of a New Model of Single-Speed Air Conditioners at Part-Load Conditions for Hourly Simulations

This paper deals with a new model of HVAC systems for hourly simulations. The former is derived from a short time step model that is priory described. The hourly model is appraised by comparing its predictions to those of the short time step simulations. Finally, a sensitivity analysis is carried out to understand the cause of the discrepancies between the two models when it occurs. The analysis also allows to identify the factors that mainly affect the system performance.

A Solution to the Problem of Nonequilibrium Acid/Base Gas-Particle Transfer at Long Time Step

A stable numerical solution to the unsolved problem of nonequilibrium growth/evaporation at long time step of multiple dissociating acids (e.g., nitric acid, hydrochloric acid, carbonic acid, sulfuric acid, etc.) and a base (ammonia) is discussed. The solution eliminates most oscillatory behavior observed in previous solutions at long time step. The solution is applicable across the entire relative humidity range, both in the presence and absence of solids and among multiple aerosol size bins and distributions. It involves solving growth/evaporation of semivolatile acids with a dissolutional growth scheme at high liquid water content (LWC), semivolatile acids with a condensational growth scheme at low LWC, involatile acids with a condensation scheme at all LWCs, then equilibrating ammonia and pH simultaneously between gas and solution phases at all LWCs based on updated acid contents, and finally solving internal-aerosol composition, final pH, and LWC with an operator-split equilibrium calculation. The new method at long time step (150–300 s) compares well with, and is 10–60 times faster than, a previous solution at short time step over the entire size distribution. Solutions at short and long time steps converge to equilibrium solutions when unique equilibrium solutions exist, even in the presence of calcium, magnesium, potassium, and carbonate. The new scheme is referred to as PNG-EQUISOLV II, where PNG is Predictor of Nonequilibrium Growth. Analysis with the scheme suggests that, under some conditions of high relative humidity and concentration, some coarse-mode particles (< 6 μ m diameter) may reach equilibrium on time scales < 1 h.

Optimal Rate of Convergence of the Bence--Merriman--Osher Algorithm for Motion by Mean Curvature

Bence, Merriman, and Osher proposed an algorithm for computing the motion a hypersurface by mean curvature in terms of solutions of the usual heat equation, continually reinitialized after short time steps. In this paper, applying some techniques of asymptotic analysis for the Allen--Cahn equation, we give a rate of convergence of their algorithm for the motion of a smooth and compact hypersurface by mean curvature. We also consider the special case of a circle evolving by curvature and show that our rate is optimal.

Curvy-steps approach to constraint-free extended-Lagrangian ab initio molecular dynamics, using atom-centered basis functions: Convergence toward Born–Oppenheimer trajectories

A dynamical extension of the "curvy-steps" approach to linear-scaling self-consistent field calculations is presented, which yields an extended-Lagrangian formulation of ab initio molecular dynamics. An exponential parametrization of the one-electron density matrix, expressed in terms of atom-centered Gaussian basis functions, facilitates propagation along the manifold of density matrices in a geometrically correct fashion that automatically enforces idempotency constraints. The extended Lagrangian itself is constraint free, thus neither density matrix purification nor expensive, iterative solution for Lagrange multipliers is required. Propagation is highly efficient, and time steps compare favorably to those used in Car-Parrinello molecular dynamics simulations. The behavior of the method, especially with regard to the maintenance of adiabatic decoupling of nuclei and electrons, is examined for a sequence of diatomic molecules, and comparison is made to trajectories propagated on the converged Born-Oppenheimer surface. Certain claims to the contrary notwithstanding, our results demonstrate that vibrational frequencies may depend on the value of the fictitious mass parameter, even in an atom-centered basis. Light-atom stretching frequencies can be significantly redshifted, even when the nuclear and electronic energy scales are well separated. With a sufficiently small fictitious mass and a short time step, accurate frequencies can be obtained; we characterize appropriate values of these parameters for a wide range of vibrational frequencies.

Evapotranspiration components determined by stable isotope, sap flow and eddy covariance techniques

Understanding and modeling water exchange in arid and semiarid ecosystems is complicated by the very heterogeneous distribution of vegetation and moisture inputs, and the difficulty of measuring and validating component fluxes at a common scale. We combined eddy covariance (EC), sap flow, and stable isotope techniques to investigate the responses of transpiration and soil evaporation to an irrigation event in an olive ( Olea europaea L.) orchard in Marrakech, Morocco. The primary goal was to evaluate the usefulness of stable isotope measurements of water vapor in the turbulent boundary layer for partitioning evapotranspiration under such dynamic conditions. The concentration and deuterium isotope composition ( δ 2H) of water vapor was collected from different heights within the ecosystem boundary layer of the olive canopy before and over several days following a 100 mm surface irrigation. ‘Keeling plots’ (isotope turbulent mixing relationships) were generated from these data to estimate the fractions of evaporation and transpiration contributing to the total evapotranspiration (ET) flux. Transpiration accounted for 100% of total ET prior to irrigation, but only 69–86% of ET during peak midday fluxes over the 5-day period following irrigation. The rate of soil evaporation and plant transpiration at the stand level was calculated from eddy covariance measurements and the evaporation and transpiration fractions from isotope measurements. Soil evaporation rate was positively correlated with daily atmospheric vapor pressure deficit ( D), but transpiration was not. Component fluxes estimated from the isotope technique were then compared to those obtained from scaled sap flow measurements. Sap flow in multiple-stemmed trees increased following the irrigation, but large single-stemmed trees did not. We matched the source area for eddy covariance estimates of total ET fluxes with scaled sap flow estimates developed for the different tree types. Soil evaporation was determined from the difference between total ET and the scaled sap flow. Ecosystem-level transpiration and soil evaporation estimated by the isotope approach were within 4 and 15% of those estimated by scaled sap flow, respectively, for periods of peak fluxes at midday. Our data illustrate the utility of the isotope ‘Keeling plot’ approach for partitioning ET at the ecosystem scale on short time steps and the importance of accurate spatial representation of scaled sap flow for comparison with eddy covariance measurements of ET.

Comparison of polyelectrolyte multilayers built up with polydiallyldimethylammonium chloride and poly(ethyleneimine) from salt‐free solutions by in‐situ surface plasmon resonance measurements

AbstractPolyelectrolytes offer a widespread potential for the defined modification of planar inorganic or polymer surfaces. Essential parameters for the regular adsorption of subsequent polymer layers by electrostatic interactions are the charge of polyelectrolyte and of the outermost surface region, the surface of the substrate, and the molar mass of the polyelectrolyte.To study such effects in mono‐ and multilayers we used poly(diallyldimethylammonium chloride (PD) with a molar mass from 5000 to 400000 g/mol as a strong polycation and poly(ethyleneimine) (PEI) with 75000 g/mol as a weak polycation and poly(sodium styrenesulfonate) (PSS) from 70000 to 1Mio g/mol in the diluted and semi‐diluted region.The characterization of the layers was performed by streaming potential, in‐situ SPR and UV‐Vis spectroscopy. Thereby the layer built up at the solid/liquid‐interface could be followed and quantified at the molecular level. SPR revealed that the thicknesses of the multilayer depends strongly on pK values of the polyelectrolyte (strong or weak) and the molar masses. We observed a linear growth if both polyelectrolytes are strong and an exponential growth if one polyelectrolyte is weak. The thickness increased with higher molar masses of the polyelectrolytes. The process was followed in‐situ in short time steps.

Influence of the Vertical Profile of Reflectivity on Radar-Estimated Rain Rates at Short Time Steps

Abstract The present study aims to demonstrate the major influence of the vertical heterogeneity of rainfall on radar–rain gauge assessment. For this purpose, an experimental setup was deployed during the HYDROMET Integrated Radar Experiment (HIRE-98) based on a conventional S-band weather radar operating at long range (90 km), an X-band vertically pointing radar, and a network of 25 tipping-bucket rain gauges. After calibration and attenuation corrections, the X-band radar data enables the estimation of the vertical profile of reflectivity (VPR) time series. Screening and VPR correction factors are derived for the distant S-band radar measurements. The raw and corrected S-band radar estimates are compared to rain gauge measurements for various integration time steps (6–30 min). Considering about 12 h of intense Mediterranean precipitation, the VPR influence at the X-band radar site is clear for all the time steps considered. For instance, a continuous increase in the Nash efficiency for the corrected rad...

Asymptotic Description of Vertically Fractured Wells Within the Boundary Element Method

Abstract The typical parameter that is used when describing fractured wells (the ratio of width to length) has been employed for some time. The high conductivity of fractures has allowed the use of a steady-state solution for the infinitely conductive fractures; however, the transient flow modelling problem for fractures of finite conductivity has to be solved numerically. Still, the high permeability within the fracture (as compared to that of the surrounding matrix) offers additional possibilities for simplifying the transient solution for modelling the flow in the fractures. This opportunity is based on asymptotic analysis using different time scales for the flow within the fracture and in the lower permeability surrounding rock matrix. Another difficulty related to describing fractured well behaviour arises when there is interaction with other adjacent wells or the reservoir drainage boundaries. For a finite reservoir, the fluxes on the fracture faces (panels) must be included in the solution of the problem as a whole. This can lead to very short time steps and make the numerical solution of the problem very computationally intensive. However, asymptotic analysis, based on the proximity of fractures to other objects in the reservoir, makes it possible to effectively de-couple the solution for the fracture from the solution of the reservoir as a whole, which increases computational efficiency substantially. This paper presents the conceptual grounds and mathematical details of asymptotic analysis and gives examples of calculations based on this approach. These results are compared to known numerical results employing detailed (non-asymptotic) solutions for the problem. This work illustrates how this approach may be of significant practical use to the industry as a means of conducting faster and more accurate analysis of completion methods, well placement and spacing patterns, and other reservoir development decisions. Introduction Progress in applying the Boundary Element Method (BEM) to reservoir engineering problems has substantially enhanced our understanding of reservoir performance. Great attention has been paid in the past, in particular, to modelling flow in vertically fractured wells(1–9). Stationary solutions for infinitely conducting fractures were historically the first ones used in reservoir engineering(10). Transient solutions for infinitely conducting fractures constituted the next stage in theory development(1), and a number of publications(1–3) have detailed research on finite conductivity fractures. Most of this research was performed using the BEM. This is understandable because the BEM provides a stable method for handling singular sources, which is not true for other conventional numerical solution methods (such as finite difference and finite element). Cinco-Ley et al.(2, 3) made improvements in the accuracy of the numerical solution generated using BEM methods. This was achieved through higher order approximations on the fracture(4) and by applying different kinds of analytical approaches(5, 7). In developing a practical application for reservoir engineering(11), the objective of this model was to obtain a high level of computational speed for problems with the fractures within arbitrarily-shaped reservoirs. This was accomplished through the use of different parameters to define in the flow modelling problem.

A Generalized Local Time-Step Scheme for Efficient FVTD Simulations in Strongly Inhomogeneous Meshes

A new generalized local time-step scheme is introduced to improve the computational efficiency of the finite-volume time-domain (FVTD) method. The flexibility of unstructured FVTD meshes is fully exploited by avoiding the disadvantage of a single short time step in the entire mesh. The great potential of this scheme is fully revealed in the FVTD simulation of electromagnetic (EM) problems with both large and fine structures in close proximity. The scheme is based on an automatic partition of the computational domain in subdomains where local time steps of the type 2/sup /spl lscr/-1//spl Delta/t(/spl lscr/=1,2,3,...) can be applied without violating the stability condition. Interfaces between subdomains are reduced to a generic two-level system which requires a very limited number of time interpolations during the FVTD iteration, therefore resulting in a very simple and robust technique. The application of local time stepping to three-dimensional EM problems demonstrates a significant speed-up of the computation without compromising the accuracy of the results.

Prévision hydrologique distribuée pour la gestion des barrages publics du Québec

The development of a flow forecasting system for public dam management in southern Quebec is presented. The system is based on distributed hydrological models using 3-h time steps to correctly perform short-term forecasts on small watersheds, located upstream of these dams, with quick hydrological responses. The contribution of models in the complete process of forecast evaluation is also studied. A numerical application, using the flood of the Chaudière river in July 2001, illustrated that distributed models with short time steps are needed despite the added complexity in the installation, calibration, and operation of the forecasting system. Also, the analysis of flow forecasted for the Spring 2003 flood shows that interpretation of model runs can lead the operational forecaster to better forecasting of results and can be improved by the use of distributed models.Key words: hydrology, flow forecast, distributed hydrological model, flood.