A Limited area model intercomparison on the "Montserrat-2000" flash-flood event using statistical and deterministic methods

In the scope of the European project Hydroptimet, INTERREG IIIB-MEDOCC programme, limited area model (LAM) intercomparison of intense events that produced many damages to people and territory is performed. As the comparison is limited to single case studies, the work is not meant to provide a measure of the different models' skill, but to identify the key model factors useful to give a good forecast on such a kind of meteorological phenomena. This work focuses on the Spanish flash-flood event, also known as "Montserrat-2000" event. The study is performed using forecast data from seven operational LAMs, placed at partners' disposal via the Hydroptimet ftp site, and observed data from Catalonia rain gauge network. To improve the event analysis, satellite rainfall estimates have been also considered. For statistical evaluation of quantitative precipitation forecasts (QPFs), several non-parametric skill scores based on contingency tables have been used. Furthermore, for each model run it has been possible to identify Catalonia regions affected by misses and false alarms using contingency table elements. Moreover, the standard "eyeball" analysis of forecast and observed precipitation fields has been supported by the use of a state-of-the-art diagnostic method, the contiguous rain area (CRA) analysis. This method allows to quantify the spatial shift forecast error and to identify the error sources that affected each model forecasts. High-resolution modelling and domain size seem to have a key role for providing a skillful forecast. Further work is needed to support this statement, including verification using a wider observational data set

The 8 and 9 September 2002 flash flood event in France: a model intercomparison

Within the framework of the European Interreg IIIb Medocc program, the HYDROPTIMET project aims at the optimization of the hydrometeorological forecasting tools in the context of intense precipitation within complex topography. Therefore, some meteorological forecast models and hydrological models were tested on four Mediterranean flash-flood events. One of them occured in France where the South-eastern ridge of the French “Massif Central”, the Gard region, experienced a devastating flood on 8 and 9 September 2002. 24 people were killed during this event and the economic damage was estimated at 1.2 billion euros. To built the next generation of the hydrometeorological forecasting chain that will be able to capture such localized and fast events and the resulting discharges, the forecasted rain fields might be improved to be relevant for hydrological purposes. In such context, this paper presents the results of the evaluation methodology proposed by Yates et al. (2005) that highlights the relevant hydrological scales of a simulated rain field. Simulated rain fields of 7 meteorological model runs concerning with the French event are therefore evaluated for different accumulation times. The dynamics of these models are either based on non-hydrostatic or hydrostatic equation systems. Moreover, these models were run under different configurations (resolution, initial conditions). The classical score analysis and the areal evaluation of the simulated rain fields are then performed in order to put forward the main simulation characteristics that improve the quantitative precipitation forecast. The conclusions draw some recommendations on the value of the quantitative precipitation forecasts and way to use it for quantitative discharge forecasts within mountainous areas

Effects of model domain extent and horizontal grid size on contiguous rain area (CRA) analysis: A MesoVICT study

As a contribution to the Mesoscale Verification Inter-Comparison over Complex Terrain (MesoVICT) project, the present work investigates how the variation of the model domain size and native resolution can affect the application of the contiguous rain area (CRA) analysis on quantitative precipitation forecast (QPF) verification. The investigation is based on the analysis of two of the six MesoVICT core events monitored during the forecast demonstration phase of the Mesoscale Alpine Programme (referred to as MAP D‑PHASE), and the Convective and Orographically-induced Precipitation Study (COPS), which occurred respectively on 20–22 June and 25–28 September 2007, plus one additional high impact event that took place on 22–24 November 2007 at the end of the MAP D‑PHASE Operations Period (DOP). The MesoVICT test-bed area is centred over Central Europe and it covers a complex terrain region characterized by the presence of the Alps (i.e., complex orography) and the Mediterranean Sea (i.e., lack of observations, coastlines). Specifically, the CRA analysis is applied to 24‑h QPF fields provided by four different configurations of the hydrostatic BOlogna Limited Area Model (BOLAM), with horizontal grid size ranging between 0.07° and 0.1° and model domain extending from only the Alpine area to the entire MesoVICT test-bed area, and by an ad‑hoc MesoVICT customized configuration of the convection-permitting MOLOCH model, with a horizontal grid size of 0.0225° and model domain covering the entire MesoVICT test-bed area. Rainfall measurements collected during DOP are objectively analysed on the verification grid using a two-pass Barnes scheme in order to be used for the spatial verification analysis. The results confirm that the correlation-based pattern matching criterion is a more suitable basis for the applicability of the CRA approach than the Mean Square Error (MSE) criterion. The limits of the latter criterion are also discussed. The extent of the model domain affects the CRA application in a way comparable to the effect of data-void areas in the observational analysis fields and in the QPFs. Sensitivity to the increase of the model (native) resolution is found as well, especially when a complex spatial structure characterizes the rainfall event under investigation. A quality control of the CRA outcomes is then recommended to accurately evaluate the diagnosed spatial forecast errors and to distinguish reliable results from suspicious ones. The results suggest the need for future studies that apply the CRA analysis at shorter rainfall integration times and on sub-structures of the rainfall fields

Factors affecting the quality of QPF: a multi-method verification of multi-configuration BOLAM reforecasts against MAP D-PHASE observations

This paper discusses the results of a quantitative precipitation forecast (QPF) verification study aimed at comparing different alternative new configurations of the meteorological BOlogna Limited Area Model (BOLAM) to be implemented in 2013 into the ISPRA’s Hydro-Meteo-Marine forecasting system (SIMM) in place of the currently operational version, dated 2009. Five new configurations are defined after considering several combinations of the following model settings: horizontal grid spacing, domain extension, initial and boundary conditions, nesting design and the BOLAM code version. Such testing configurations are inter-compared with the operational BOLAM version following a multi-method approach including Fourier spectral analysis, several categorical scores, quasi-relative operating characteristic diagram and visual inspection of the spatial distributions of the contingency table elements. Rain gauge measurements available between June and November 2007 within the international initiative ‘Demonstration of Probabilistic Hydrological and Atmospheric Simulation of flood Events in the Alpine region’ of the Mesoscale Alpine Programme (MAP D-PHASE) are considered as observational dataset. A 6month reforecast campaign is performed in order to produce, for each compared configuration, the corresponding forecast series. Results show that decreasing model grid spacing and simultaneously increasing model domain extension is effective in improving the QPF quality when higher-resolution initial and boundary conditions are directly applied to BOLAM, without using a coarser-resolution parent model run. Therefore, such skilful configuration has been deployed in late 2012 within the international research programme ‘HYdrological cycle in Mediterranean EXperiment’ (HyMeX). On the contrary, when keeping the low-resolution, double nesting configuration, improving input data decreases the QPF performance

Comparison of rain gauge observations with modeled precipitation over Cyprus using Contiguous Rain Area analysis

Verification of modeled rainfall with precipitation\ud observed by a rain gauge network has been performed in a\ud case study over the Cyprus Island. Cyprus has a relatively\ud dense rain gauge network. The applied verification method is\ud the Contiguous Rain Area (CRA) analysis. Some drawbacks\ud of the CRA method are pointed out when it is applied to such\ud a case study. Impact on the CRA results, when considering\ud different dimensions of the verification sub-domain and different types of indicators (correlation and mean square error) used in the comparison, are discussed. Results indicate thatcare should be taken when verification of modeled rainfall is performed over a domain smaller than the model one

QPF performance of the updated SIMM forecasting system using reforecasts

International audienc

Sensitivity of forecast rainfall verification to a radar adjustment technique

A ground-based radar (GR) has to measure rain from close to the radar to large distances from it. Consequently, the scattering volume of the GR changes significantly. As an advantage, the scattering volume of a space-borne radar is of similar size at all locations, thus allowing the compensation of the decreasing spatial resolution of the GR with range (range-adjustment). Adjustment with range is here performed by means of data observed by the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) using a ∼10 dB per decade factor. For instance, about 8 dB are added to the measured reflectivity at 100 km, while 2 dB are subtracted at 10 km from the radar site. Thus, two different radar datasets, the range-adjusted data and the original ones, can be compared with forecast precipitation. In the framework of the EU VOLTAIRE project (Fifth Framework Programme), where observations from rain gauges, GR, TRMM PR and forecast precipitation were available for the island of Cyprus, such a kind of study was performed. The chosen comparison method was contiguous rain area (CRA) analysis. Three pattern-matching criteria, involving mean square error, mean absolute error and correlation, have been used to match forecast and observed precipitation patterns. In this paper, we show that the results of the comparison in a selected case study are sensitive to the application of a range-adjustment technique. Observational analysis, obtained by merging rain gauge data with the adjusted GR data, seems to give more stable results when changing the pattern-matching criterion, and proposing it as the better field reconstruction in the comparison

Multi-Sensor Comparison and Numerical Modeling of Atmospheric Water Fields: A VOLTAIRE Case Study over Cyprus

This paper presents a study performed within the framework of the European Union's (EU) VOLTAIRE project (Fifth Framework Programme). Among other tasks, the project aimed at the integration of the Tropical Rainfall Measuring Mission (TRMM) data with ground-based observations and at the comparison between water fields (precipitation and total column water vapor) as estimated by multisensor observations and predicted by NWP models. In particular, the VOLTAIRE project had as one of its main objectives the goal of assessing the application of satellite-borne instrument measures to model verification. The island of Cyprus was chosen as the main "test bed," because it is one of the few European territories covered by the passage of the TRMM Precipitation Radar (PR) and it has a dense rain gauge network and an operational weather radar. TRMM PR provides, until now, the most reliable space-borne spatial high-resolution precipitation measurements. Attention is focused on the attempt to define a methodology, using state-of-the-art diagnostic methods, for a comprehensive evaluation of water fields as forecast by a limited area model (LAM). An event that occurred on 5 March 2003, associated with a slow cyclone moving eastward over the Mediterranean Sea, is presented as a case study. The atmospheric water fields were forecast over the eastern Mediterranean Sea using the Bologna Limited Area Model (BOLAM). Data from the Cyprus ground-based radar, the Cyprus rain gauge network, the Special Sensor Microwave Imager (SSM/I), and the TRMM PR were used in the comparison. Ground-based radar and rain gauge data were merged together in order to obtain a better representation of the rainfall event over the island. TRMM PR measurements were employed to range-adjust the groundbased radar data using a linear regression algorithm. The observed total column water vapor has been employed to assess the forecast quality of large-scale atmospheric patterns; such an assessment has been performed by means of the Hoffman diagnostic method applied to the entire total column water vapor field. Subsequently, in order to quantify the spatial forecast error at the finer BOLAM scale (0.09°), the object-oriented contiguous rain area (CRA) analysis was chosen as a comparison method for precipitation. An assessment of the main difficulties in employing CRA in an operational framework, especially over such a small verification domain, is also discussed in the pape