A strategy for high‐resolution ensemble prediction. II: Limited‐area experiments in four Alpine flood events

Marsigli, Chiara; Montani, A.; Nerozzi, F.; Paccagnella, Tiziana; Tibaldi, S.; Molteni, Franco; Buizza, Roberto

doi:10.1002/qj.49712757613

Cited by 89 publications

(79 citation statements)

References 21 publications

(9 reference statements)

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“…The ensemble is generated as a downscaling of the global ECMWF EPS Marsigli et al, 2001), aiming at linking the forecast capabilities of a high-resolution non-hydrostatic limited-area model to the ensemble approach. In the COSMO-LEPS system, the perturbations are ingested mainly through the initial and boundary conditions, which are provided by some selected members of the operational ECMWF EPS, denoted as 'representative members' (RMs).…”

Section: Introductionmentioning

confidence: 99%

A spatial verification method applied to the evaluation of high‐resolution ensemble forecasts

Marsigli

Montani

Paccangnella

2008

Meteorological Applications

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ABSTRACT:The verification of ensemble systems is being operationally carried out in several meteorological centres. However, the main operational ensemble systems have a coarser spatial resolution with respect to the deterministic runs. Only recently, high-resolution limited-area ensembles have started to be run on a regular basis. Their verification requires combining the usual probabilistic evaluation with the statistical verification techniques which are being developed for high-resolution model forecasts (1-10 km). These techniques permit to evaluate a deterministic forecast in a probabilistic manner, by taking into account the spatio-temporal distribution of the forecast at different scales.In this work, a spatial verification technique, called 'distributional method', is used to verify the Consortium for Smallscale MOdeling Limited-area Ensemble Prediction System (COSMO-LEPS) ensemble system, a mesoscale ensemble with 10 km horizontal resolution. The system is mainly designed to give probabilistic assistance in the forecast of severe weather, in particular of intense precipitation possibly leading to floods, hence verification is focused on the ability of the system in forecasting precipitation at high spatial resolution. The methodology is based on a comparison of forecasts and observations in terms of some parameters of their distributions, evaluated after the values are aggregated over boxes of selected size. In particular, performances in terms of average, a few percentiles and maximum forecast value in a box are considered.The system is compared against European Centre for Medium-Range Weather Forecasts Ensemble Prediction System (ECMWF EPS), addressing the issues of an intercomparison between a higher-resolution smaller-size ensemble and a lower-resolution larger-size one. Results show that when the forecast of the average amount of precipitation over an area is concerned, COSMO-LEPS is more skilful than the Ensemble Prediction System (EPS) only from the resolution point of view. Therefore, although not properly calibrated, it is more capable of distinguishing between events and non-events, especially for moderate and high precipitation. Furthermore, COSMO-LEPS has skill in forecasting the occurrence of precipitation peaks over an area, irrespective of the exact location.The analysis of the score behaviour as a function of the distribution parameter shows that EPS has the maximum skill in reproducing the central part of the observed precipitation distribution over an area of about 10 000 km 2 , while COSMO-LEPS is more skilful in reproducing the tail of the observed precipitation distribution.The problem of the predictability of precipitation at different spatial scales is also investigated, showing the role of different system resolutions.

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Section: Introductionmentioning

confidence: 99%

A spatial verification method applied to the evaluation of high‐resolution ensemble forecasts

Marsigli

Montani

Paccangnella

2008

Meteorological Applications

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“…Each RM provides initial and boundary conditions for the integrations with LM, which is run 5 times for 120 h, always starting at 12:00 UTC of day N −1 and ending at 12:00 UTC of day N +4. For a discussion on the motivations that led to this set up of the system, the reader is referred to Molteni et al (2001), Marsigli et al (2001), Montani et al (2001), Montani et al (2003a) and Montani et al (2003b). The LM has a horizontal resolution x 10 km, 33 vertical levels and the time-step used for the integrations is 60 s. Probability maps based on LM runs are generated by assigning to each LM integration a weight proportional to the population of the cluster from which the RM (providing initial and boundary conditions) was selected.…”

Section: The Cosmo-leps Operational Systemmentioning

confidence: 99%

“…It has been shown Marsigli et al, 2001;Montani et al, 2001Montani et al, , 2003a, over a number of test cases and for several forecast ranges (48-120 h), that LEPS performs better than EPS concerning the quantitative forecast of intense precipitation, as well as the geographical localisation of the regions most likely to be affected by the flood events.…”

Section: Introductionmentioning

confidence: 99%

“…Nevertheless, global ensemble systems are usually run at a relatively low horizontal resolution (80 km Correspondence to: C. Marsigli (cmarsigli@smr.arpa.emr.it) at most), this limiting their usefulness when the forecast of severe and localised weather events is concerned. As regards the use of limited-area models within ensemble systems, ARPA-SIM (Agenzia Regionale Prevenzione e Ambiente -Servizio Idrometeorologico, that is the Regional Hydrometeorological Service of Emilia-Romagna) developed LEPS Marsigli et al, 2001;Montani et al, 2001Montani et al, , 2003a, the Limited-area Ensemble Prediction System. The LEPS methodology allows to combine the benefits of the probabilistic approach (a set of different evolution scenarios is provided to the forecaster) with the highresolution detail of the LAM integrations, with a limited computational investment.…”

Section: Introductionmentioning

confidence: 99%

“…LEPS methodology is based on the idea of ensemble size reduction Marsigli et al, 2001): first, the global-ensemble members are grouped into clusters and, then, a representative member (RM) is chosen within each cluster. Finally, each RM, which is representative of a possible evolution scenario, provides both initial and boundary conditions for the integrations with the high-resolution LAM, whose runs generate LEPS.…”

Section: Introductionmentioning

confidence: 99%

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Probabilistic high-resolution forecast of heavy precipitation over Central Europe

Marsigli

Montani

Nerozzi

et al. 2004

Nat. Hazards Earth Syst. Sci.

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Abstract. The limited-area ensemble prediction system COSMO-LEPS has been running operationally at ECMWF since November 2002. Five runs of the non-hydrostatic limited-area model Lokal Modell (LM) are available every day, nested on five selected members of three consecutive 12-h lagged ECMWF global ensembles. The limited-area ensemble forecasts range up to 120 h and LM-based probabilistic products are disseminated to several national weather services. COSMO-LEPS has been constructed in order to have a probabilistic system with high resolution, focussing the attention on extreme events in regions with complex orography. In this paper, the performance of COSMO-LEPS for a heavy precipitation event that affected Central Europe in August 2002 has been examined. At the 4-day forecast range, the probability maps indicate the possibility of the overcoming of high precipitation thresholds (up to 150 mm/24 h) over the region actually affected by the flood. Furthermore, one out of the five ensemble members predicts 4 days ahead a precipitation structure very similar to the observed one.

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Sensitivity of hydrological ensemble forecasts to different sources and temporal resolutions of probabilistic quantitative precipitation forecasts: flash flood case studies in the Cévennes‐Vivarais region (Southern France)

Marty

Zin

Obled

2012

Hydrological Processes

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This article analyses the performance of an integrated hydrological ensemble prediction system adapted to small to mid-sized catchments (100-600 km 2 ) situated in the Cévennes-Vivarais region (Southern France) and characterized by short lag times (3-12 h). In this framework, flood forecasts need hourly Probabilistic Quantitative Precipitation Forecasts (PQPF) so as to provide early warning with 24-72 h of anticipation. Here, two sources of PQPF at daily and subdaily (6 h) meteorological time steps are considered: Ensemble Prediction Systems from the European Centre for Medium-range Weather Forecast (ECMWF) and analogy-based PQPF provided in real-time at the Laboratoire d'étude des Transferts en Hydrologie et Environnement. The two PQPF are firstly disaggregated to respect the required hydrological hourly time step, through either the use of a stochastic rainfall generator or the application of a multimodel approach. Then, disaggregated PQPF are used as input to a hydrological model, which is called TOPSIMPL, to provide hourly ensemble discharge forecasts up to 48 h ahead. Illustration and evaluation of ensemble discharge forecasts issued in near real-time conditions are given for some recently observed flash flood events. It is shown that hourly discharge forecasts are first-order conditioned by the accuracy of PQPF at daily or subdaily time step. Six-hour ensemble prediction systems correctly reproduce the rainfall temporal dynamics, whereas daily analogy-based PQPF are less underdispersive in terms of rainfall amounts. As a result, the merging of the two sources of PQPF substantially increases the performance of discharge forecasts, the contribution of a more sophisticated hourly rainfall generator becoming marginal. Figure 3. Ratio of RMSE to spread as a function of spread (1/10 mm/h) related to hourly precipitation distributions issued during the 2007 flood event. The horizontal black line corresponds to RMSE equal to spread 38 R. MARTY, I. ZIN AND CH. OBLED

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A strategy for high‐resolution ensemble prediction. II: Limited‐area experiments in four Alpine flood events

Cited by 89 publications

References 21 publications

A spatial verification method applied to the evaluation of high‐resolution ensemble forecasts

A spatial verification method applied to the evaluation of high‐resolution ensemble forecasts

Probabilistic high-resolution forecast of heavy precipitation over Central Europe

Sensitivity of hydrological ensemble forecasts to different sources and temporal resolutions of probabilistic quantitative precipitation forecasts: flash flood case studies in the Cévennes‐Vivarais region (Southern France)

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