An integrated methodology for post-processing ensemble prediction systems to produce more representative extreme water level forecasts: the case of the Río de la Plata estuary

The effects of weather extreme events can pose a threat to life and property, which is why proper prediction systems take on superlative importance. Despite the significant scientific advances in the field during the last decades, due to the intrinsic imperfections of prediction systems there will always be unavoidable uncertainties. To deal with them, deterministic prediction systems have been extended to “ensemble prediction systems” (EPS), defined as a composition of several simulations under different forcings, boundary conditions, parameters, models, etc., designed to represent the uncertainties. The mean of the EPS is often used for deterministic guidance to report the prediction but, in the presence of large differences among ensemble members, the average generates skewness that might underestimate the magnitude of the forecasts. In this paper, two techniques are revisited and readapted to improve the EPS forecasts. Firstly, it is proposed to partition ensemble forecasts into sub-ensemble forecasts, using cluster analysis to produce more representative predictions; this technique seeks to eliminate from the ensemble members which occurrence is considered unlikely. Secondly, it is suggested to associate to the ensemble forecast a complementary phase-aware ensemble (PAE) forecast, which computes the ensemble mean and spread separating the signal into carrier and modulated waves using the Hilbert transform. This integrated post-processing methodology was assessed with extreme storm surges that took place at the Río de la Plata estuary (Argentina) during this century with amplitudes exceeding ± 2 m (being the tidal range of about 0.75 m), for which the EPS presents large dispersion. Results show that, in the analyzed cases, the post-processing filters out the unlikely dynamical states, adjusts the mean ensemble to the observations and significantly reduces the uncertainty; the spread is reduced from 3 m to less than 1 m. The probability was also improved; for the analyzed cases, calibrated forecasts could anticipate peak events 4 days in advance with a relatively small uncertainty in both time and amplitude (one standard deviation). Additionally, the technique does not harm the forecast in cases when the dispersion between members of the ensemble is low. These results, together with the low computational cost of applying the technique, support incorporating our post-processing methodology as part of the EPS for storm surges, in which uncertainty is paramount for issuing warnings to face the effects of extreme weather events.Fil: Dinapoli, Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Instituto Franco-Argentino sobre Estudios del Clima y sus Impactos; ArgentinaFil: Simionato, Claudia Gloria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Instituto Franco-Argentino sobre Estudios del Clima y sus Impactos; Argentin

Development and validation of a storm surge forecasting/hindcasting modelling system for the extensive Río de la Plata Estuary and its adjacent Continental Shelf

The Río de la Plata (RdP) Estuary is affected by significant surges several times per year. This phenomenon has historically caused catastrophic water-level enlargements of up to 4.44 m, threatening and claiming human lives and producing major economic and material damages. The negative surges are less frequent, but when they do occur, inhibit the access to the principal harbors and waterways and disable the drinking water intakes of the Metropolitan Area of Buenos Aires (the Capital City of Argentina) with a population of more and 16 million people. Recent works suggest that the number and strength of the surge events have been increasing with time. Nevertheless, a state-of-the-art system for the forecast of those events is not available yet. In this work, the implementation of a numerical modelling system for the forecast/hindcast of storm surges and the associated currents in the RdP and the adjacent continental shelf are presented and validated. This pre-operational system is based on an adaptation of the CROCO community ocean model to solve the dynamics associated with the surge. The model was implemented using a set of routines written in open-source programming language (Linux and Python) to be cheap and efficient and to ensure an easy future transfer to the services responsible for the alerts. For a better representation of the regional atmospheric dynamics, wind speed and sea-level pressure used to force the simulations were corrected using direct observations collected at an oceanographic buoy anchored at the estuary. The model system performance in hindcast mode was quantified by comparison with observations from tidal gauges and current meters at several locations of the estuary and the adjacent shelf. Percent errors for water level over the whole estuary and currents in the intermediate and exterior estuary drove to average results of 8 and 13%, respectively. The skill scores resulted, on average, of 0.90 and 0.80, respectively. The model performance in both hindcast and forecast modes was evaluated during historical extreme storm surges. Results support the good performance of the model to simulate even extreme events with average skill scores of 0.97 and 0.92, respectively. Results are encouraging, particularly taking into account the limitations in the atmospheric forcing for the region, where only a relatively small number of direct observations are assimilated by the reanalysis and forecast models.Fil: Dinapoli, Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; ArgentinaFil: Simionato, Claudia Gloria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; ArgentinaFil: Moreira, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; Argentin

Nonlinear Interaction Between the Tide and the Storm Surge with the Current due to the River Flow in the Río de la Plata

The Río de la Plata estuary (RdP) is characterized by the large flow of its tributary rivers (Q), with an average of 22,000 m3 s− 1 and an interannual variability range from 8000 to 90,000 m3 s− 1. In this work, the hypothesis that the current due to that flow (CDR) interacts nonlinearly with both the tides and storm surges is evaluated utilizing water level observations and numerical simulations. Two tide gauge time series gathered at the freshwater tidal zone (FTZ) of the RdP are analyzed with the novel surrogate analysis. The analysis is applied for periods of high, medium and low Q. Results show that both interactions occur at the upper half of the FTZ and increase with Q. Harmonic analyses support the surrogate analysis’ conclusions and show that tide-CDR interaction redistributes the energy among tidal harmonics, increasing asymmetry. Numerical simulations confirm that (i) both interactions maximize at the upper half of the FTZ and decrease downstream; and (ii) they are modulated by Q; a rise of about 14,000 m3 s− 1 (interquartile range) can produce an intensification of 50% and 100% of the amplitudes of the tide-CDR and surge-CDR interactions, respectively; and (iii) both interactions introduce asymmetries in the water level, with faster rises and slower falls; (iv) the quadratic bottom friction is the main source of both interactions; (v) tide-CDR interaction represents 12% of the water level associated with the tide, whereas surge-CDR interaction accounts for 5% of the surge peak; and (vi) the interactions are significant in the upper FTZ because there, the magnitude of the currents associated with the tide and the surge are comparable to CDR; downstream, the channel widens and CDR decreases.Fil: Dinapoli, Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; ArgentinaFil: Simionato, Claudia Gloria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; ArgentinaFil: Moreira, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; Argentin

Model Sensitivity during Extreme Positive and Negative Surges in the Río de la Plata Estuary: Highlighting the Need for an Appropriate Hindcast/Forecast System

The large and fast-flowing Río de la Plata (RdP) estuary is affected by extreme storm surges (above ±2 m with respect to tidal datum), which have large impacts on the millions of inhabitants and for navigation. In this work the Coastal and Regional Ocean Community Model (CROCO) numerical model was modified and implemented as a set of regional one-way nested 2D applications for the hindcast/forecast of water level in the RdP. A sensitivity analysis (SA) was carried out to determine the impact on the numerical solutions of the uncertainties in the different modeling parameter forcings and to highlight the need for the construction of a modeling system that provides meaningful information to the potential users. The SA included the friction coefficients, the wind speed and di-rection, the atmospheric surface pressure, and the continental discharge. Water level is most sensitive to uncertainties in the wind forcing; even small changes in this input can create large errors in the water level forecast/hindcast. Forcing with different analyses’ wind products yielded differences of up to 50% in the peak water levels. Results also showed that the modeling system requires a reasonable adjustment of the bottom friction parameters; that it is important to include the atmospheric surface pressure forcing; and that, from the point of view of water level forecast, it is not necessary to couple a hydrological model in spite of the enormous runoff of this estuary. Given the strong sensitivity to errors in the wind forcing, we believe it is important to provide estimates of uncertainty together with hindcast/forecast water level for these predictions to be of greatest quality and practical applicability.Fil: Dinapoli, Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Simionato, Claudia Gloria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Moreira, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentin

Study of the tidal dynamics in the Southwestern Atlantic Continental Shelf based on data assimilation

The Southwestern Atlantic Continental Shelf (SWACS) is a large oceanic region with remarkably barotropic dynamics. Several scientific studies have described how processes, such as tide or surface winds, affect the variability of the sea surface height and currents. However the tidal dynamics has not received attention for at least the last 15 years, in spite of their importance for both local and global dynamics. Since the last works, the amount of available observations and numerical models (physics, resolution, numerics, etc.) have all greatly improved. In this context, data assimilation (DA) becomes an relevant tool to merge both the observations and the model solutions, producing a better representation of the regional processes. Particularly, DA provides, in addition, an objective methodology to calibrate model parameters. Thus, the aim of this work is to perform, for the first time for this outstanding region, the calibration of the numerical model bottom friction coefficient (cD) by means of DA; then, the opportunity of a better simulation is seized to update the description of tidal dynamics. The spatial variability of the cD derived is 2.00x10^-2 consistent with the bathymetry, with a mean value of 2.00x10^-3 along the coast and nearby the shelf-break. Results show that the incorporation of a spatially varying improves the representation of the tidal amplitude and phase compared to the case when it is considered homogeneous, and drives in a single model to results of a better quality than previous nested models with much larger resolution. The optimal representation of the regional tide with a single model allowed us to provide a deeper, improved and novel description of the tidal dynamics. It was found that the energy enters the domain not only from the south but also from the north, being the flux to the north two orders of magnitude larger; those two fluxes produce an cyclonic circulation consistent with the behaviour of the SWACS as a semidiurnal tidal resonant canal theoretically proposed by Webb (1976). This explains why the energy flux is, by far, domained by the potential energy and the large amplitudes of the tide. Finally, a remaining and weaker branch exits along the coast; it enters the Río de la Plata Estuary from its southwesternmost tip and travels upstream along the Argentinean coast, reaching the upper estuary strongly attenuated.Fil: Dinapoli, Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Simionato, Claudia Gloria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentin

Development and evaluation of an ensemble forecast/hindcast system for storm surges in the Río de la Plata Estuary

The development and evaluation of ensemble hindcasting and forecasting systems (EHS and EFS, respectively) for storm surges in the Río de la Plata Estuary (RdP) is presented. The models were forced by atmospheric sea level pressure and 10 m winds. The ensemble forcing for the EHS was generated by temporal-spatial shifting of the operational global control ERA5 reanalysis provided by the European Centre of Medium-Range Weather Forecast (ECMWF), because the ERA5 associated ensemble shows too little dispersion in this area. EFS was instead based on a lead time of 4 days and forced with the 50-member high-resolution ensemble prediction system of the ECMWF. EHS was evaluated over a long period (the 2000–2010 decade), whereas EFS was evaluated for the ten most extreme surges that occurred during that period: five positive (which caused coastal flooding) and five negative (which affected navigation and drinking water supply) events. Based on traditional statistics (area under the ROC curve and Brier scores), both systems were assessed from a probabilistic point of view. Results show that both EHS and EFS can incorporate more than 90% of the observations in the uncertainty range. They also showed good skill in hindcasting and forecasting surges, particularly extreme events, EHS being about 20% better than the control model and EFS up to 55% better, in agreement with state-of-the-art models developed for other parts of the world. Results also showed that EFS can predict most of the surge peaks with 95% confidence, with a range of uncertainty of about ±0.90 m and ±9 hr. Therefore, results encourage the implementation of EHS and EFS as useful and robust tools for future climate studies, decision makers and the general public, to improve the quality of risk management decisions by quantifying forecast uncertainty.Fil: Dinapoli, Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Simionato, Claudia Gloria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Moreira, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentin

Nonlinear tide-surge interactions in the Río de la Plata Estuary

The nonlinear tide-surge interaction (NTSI) can significantly affect the levels associated with storm surges that threaten coastal areas. In this work, water level observations and numerical simulations are used to investigate those interactions in the large, mighty and socio-economically important Río de la Plata (RdP) estuary. We introduce a novel objective approach to seek evidence of nonlinear interactions in hourly water level records from six tide gauges collected along the coast. Results indicate that NTSI occurs in the RdP and suggest that it becomes more important upstream and along the southern coast of the estuary. CROCO ocean numerical model is used to quantify the interactions, to determine the areas where they are stronger, and to identify their sources. The amplitude of the interaction accounts for 16% of the total water level at the upper RdP, being comparable to tidal amplitude. The quadratic bottom friction is the principal cause of NTSI, and is modulated by the tidal current; therefore the nonlinearity is present all the time and is independent of the wind speed and direction. This is a particularity of this estuary and occurs because, as a consequence of its large width, surge currents are weak in spite of the big volume of water mobilized by the storms. Due to its nature, the interaction attenuates and smoothes the level anomalies due to the surge. Results highlight the need of utilizing a complete NTSI model for the forecast of the surge in the RdP; otherwise, the estuarine dynamic would be misrepresented generating significant forecasts errors (10%–20% at the upper RdP).Fil: Dinapoli, Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; ArgentinaFil: Simionato, Claudia Gloria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; ArgentinaFil: Moreira, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; Argentin

Improving the short-range forecast of storm surges in the southwestern Atlantic continental shelf using 4DEnSRF data assimilation

In this study, the assimilation of tide gauge and altimetry data into a two-dimensional barotropic numerical model for the southwestern Atlantic continental shelf (SWACS) was developed. To do this, the preoperative 4-day storm surges ensemble prediction system developed by Dinápoli et al. (2021, Journal of the Royal Meteorological Society 147: 557–572) was implemented for the SWACS. This new configuration, called “Model for Storm Surge Simulations” (M3S), considers a curvilinear grid that covers the SWACS with higher resolution along the shoreline (from 2 to 10 km). M3S was forced with an ensemble of 60 members conformed by the combination of perturbations of the eight principal tidal constituents and of the atmospheric products derived from the Global Ensemble Forecast System. Tidal gauge and altimetry data were assimilated in an asynchronous mode using the four-dimensional-ensemble square-root filter (4DEnSRF). The system was developed and validated forecasting two strong positive storm surges. Results show that 4DEnSRF's innovations produce a positive impact upon the forecast skill up to 2 days. Hence, the 4-day forecast can be divided into two parts: the first 2 days with a stronger dependence on the initial conditions and the other 2 days purely driven by external forcing. It was found that a symmetric assimilation window of 12 hr length produces the best initial condition. Under this configuration, 4DEnSRF removes biases and improves the timing of the M3S forecasted solutions. The largest improvements were observed at the northern SWACS, where more chaotic processes, such as the atmospheric circulation, explain a large part of the sea-surface height variability. No significant improvements were found at the southern SWACS, which can be attributed to the strong tidal dynamics that characterise the zone. Our results show that the incorporation of 4DEnSRF into M3S can significantly improve the forecast in the SWACS and also the accuracy of the short-range detection of storm surges.Fil: Dinapoli, Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Ruiz, Juan Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Simionato, Claudia Gloria. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Berden, Giuliana. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Micrometer-resolution imaging using MÖNCH: towards G2-less grating interferometry

MÖNCH is a 25 µm-pitch charge-integrating detector aimed at exploring the limits of current hybrid silicon detector technology. The small pixel size makes it ideal for high-resolution imaging. With an electronic noise of about 110 eV r.m.s., it opens new perspectives for many synchrotron applications where currently the detector is the limiting factor, e.g. inelastic X-ray scattering, Laue diffraction and soft X-ray or high-resolution color imaging. Due to the small pixel pitch, the charge cloud generated by absorbed X-rays is shared between neighboring pixels for most of the photons. Therefore, at low photon fluxes, interpolation algorithms can be applied to determine the absorption position of each photon with a resolution of the order of 1 µm. In this work, the characterization results of one of the MÖNCH prototypes are presented under low-flux conditions. A custom interpolation algorithm is described and applied to the data to obtain high-resolution images. Images obtained in grating interferometry experiments without the use of the absorption grating G(2) are shown and discussed. Perspectives for the future developments of the MÖNCH detector are also presented