Silvio Davolio

HYMEX , a 10-year Multidisciplinary Program on the mediterranean water cycle.

The Mediterranean countries are experiencing important challenges related to the water cycle, including water shortages and floods, extreme winds, and ice/snow storms, that impact critically the socioeconomic vitality in the area (causing damage to property, threatening lives, affecting the energy and transportation sectors, etc.). There are gaps in our understanding of the Mediterranean water cycle and its dynamics that include the variability of the Mediterranean Sea water budget and its feedback on the variability of the continental precipitation through air–sea interactions, the impact of precipitation variability on aquifer recharge, river discharge, and soil water content and vegetation characteristics specific to the Mediterranean basin and the mechanisms that control the location and intensity of heavy precipitating systems that often produce floods. The Hydrological Cycle in Mediterranean Experiment (HyMeX) program is a 10-yr concerted experimental effort at the international level that aims to advance the scientific knowledge of the water cycle variability in all compartments (land, sea, and atmosphere) and at various time and spatial scales. It also aims to improve the processes-based models needed for forecasting hydrometeorological extremes and the models of the regional climate system for predicting regional climate variability and evolution. Finally, it aims to assess the social and economic vulnerability to hydrometeorological natural hazards in the Mediterranean and the adaptation capacity of the territories and populations therein to provide support to policy makers to cope with water-related problems under the influence of climate change, by linking scientific outcomes with related policy requirements.

HyMeX-SOP1: The Field Campaign Dedicated to Heavy Precipitation and Flash Flooding in the Northwestern Mediterranean

The Mediterranean region is frequently affected by heavy precipitation events associated with flash floods, landslides, and mudslides that cause hundreds of millions of euros in damages per year and often, casualties. A major field campaign was devoted to heavy precipitation and flash floods from 5 September to 6 November 2012 within the framework of the 10-year international HyMeX (Hydrological cycle in the Mediterranean Experiment) dedicated to the hydrological cycle and related high-impact events. The 2- month field campaign took place over the Northwestern Mediterranean Sea and its surrounding coastal regions in France, Italy, and Spain. The observation strategy of the field experiment was devised to improve our knowledge on the following key components leading to heavy precipitation and flash flooding in the region: i) the marine atmospheric flows that transport moist and conditionally unstable air towards the coasts; ii) the Mediterranean Sea acting as a moisture and energy source; iii) the dynamics and microphysics of the convective systems producing heavy precipitation; iv) the hydrological processes during flash floods. This article provides the rationale for developing this first HyMeX field experiment and an overview of its design and execution. Highlights of some Intense Observation Periods illustrate the potential of the unique datasets collected for process understanding, model improvement and data assimilation.

MAP D-PHASE: Real-Time Demonstration of Weather Forecast Quality in the Alpine Region

Demonstration of probabilistic hydrological and atmospheric simulation of flood events in the Alpine region (D-PHASE) is made by the Forecast Demonstration Project in connection with the Mesoscale Alpine Programme (MAP). Its focus lies in the end-to-end flood forecasting in a mountainous region such as the Alps and surrounding lower ranges. Its scope ranges from radar observations and atmospheric and hydrological modeling to the decision making by the civil protection agents. More than 30 atmospheric high-resolution deterministic and probabilistic models coupled to some seven hydrological models in various combinations provided real-time online information. This information was available for many different catchments across the Alps over a demonstration period of 6 months in summer/ fall 2007. The Web-based exchange platform additionally contained nowcasting information from various operational services and feedback channels for the forecasters and end users. D-PHASE applications include objective model verification and intercomparison, the assessment of (subjective) end user feedback, and evaluation of the overall gain from the coupling of the various components in the end-to-end forecasting system.

Orographic influence on deep convection : case study and sensitivity experiments

The non hydrostatic convection resolving model MOLOCH is employed in order to evaluate its capability to realistically simulate the evolution of the mesoscale convective system responsible for an episode of extremely heavy rainfall and flood over southeastern France (Gard event, 2002). Numerical experiments indicate large sensitivity of modelled precipitation amounts and distribution, due to different cell organization and propagation, to the specification of the initial conditions. Among different experimented initialization times (00, 06 and 12 UTC, September 8) the run starting at 06 UTC is able to predict the development and the almost stationary behaviour of the convective system, at least in the early stage of the event. Additional experiments, aimed at studying the role played by the orography in triggering the convection and controlling its evolution, have been performed in order to characterize sensitivity to ambient wind and orography. Simulations demonstrate that the presence of the orographic barrier is crucial for both triggering and maintaining the mesoscale convective system. Moreover, the location and intensity of precipitation turns out to be sensitive to variations of the mountain height and of the mean meridional wind component. A partial explanation of this behaviour in terms of the Froude number is suggested.

Effects of Increasing Horizontal Resolution in a Convection-Permitting Model on Flood Forecasting: The 2011 Dramatic Events in Liguria, Italy

AbstractCoupling meteorological and hydrological models is a common and standard practice in the field of flood forecasting. In this study, a numerical weather prediction (NWP) chain based on the BOLogna Limited Area Model (BOLAM) and the MOdello LOCale in Hybrid coordinates (MOLOCH) was coupled with the operational hydrological forecasting chain of the Ligurian Hydro-Meteorological Functional Centre to simulate two major floods that occurred during autumn 2011 in northern Italy. Different atmospheric simulations were performed by varying the grid spacing (between 1.0 and 3.0 km) of the high-resolution meteorological model and the set of initial/boundary conditions driving the NWP chain. The aim was to investigate the impact of these parameters not only from a meteorological perspective, but also in terms of discharge predictions for the two flood events. The operational flood forecasting system was thus used as a tool to validate in a more pragmatic sense the quantitative precipitation forecast obtained ...

The impact of resolution and of MAP reanalysis on the simulations of heavy precipitation during MAP cases

Two meteorological models, operating at different horizontal resolutions up to 2.2 km, are employed in order to verify quantitative precipitation forecasts during three MAP Intensive Observing Periods, characterized by relatively high amounts of precipitation in the region south of the Alps. The recent availability of the MAP reanalysis using ECMWF 4D-Var data assimilation system allows for an assessment of its impact on high resolution forecasts in comparison with the operational ECMWF analysis (as in 1999). The evaluation is made using statistical scores generally applied to precipitation fields, introducing a smoothing criterion based on model derived probability estimates. Results indicate a generally better performance of the non-hydrostatic, high resolution, convective-resolving model in comparison with the hydrostatic, moderate resolution model with parameterized convection. The impact of the MAP reanalysis is less evident, although in one case clear improvements in precipitation forecasts are noted.

Intercomparison of satellite‐based and model‐based rainfall analyses

Four satellite rain estimations based on microwave (MW), infrared (IR) or combined MW-IR techniques are compared with the BOlogna Limited Area Model (BOLAM) rain forecast for a severe weather event (8–13 November 2001) over the western Mediterranean Sea. Two of the investigated multi-channel MW rainfall algorithms use data from the Tropical Rainfall Measuring Mission (TRMM). The Frequency Difference Algorithm relies on data from the TRMM Microwave Imager (TMI) and the other one combines data from the Precipitation Radar (PR) with those from the nine-channel radiometer TMI, called PR Adjusted TMI Estimations of Rainfall (PATER) algorithm. The pure IR Rain Estimator uses geostationary IR METEOSAT data and the combined Naval Research Laboratory algorithm uses both MW data from low orbiting satellites and IR data from the geostationary orbit. Validation results, computed over a common grid, which is independent of the different field of view sizes of the applied data sets, indicate that there is generally a better performance for heavy rain (> 6m m h −1 ) than for light rain (< 1m m h −1 ). Both MW algorithms perform rather similarly, although PATER shows some rain detection problems due to thick aerosol loads originating from the desert. The BOLAM model presents a good agreement with the MW and only a minor location error of a heavy rain area was detected. Both IR-based algorithms have problems in identifying the correct rainy areas compared to MW. Overall, the results suggest that there are advantages in combining both techniques – the well-known rain physics of the MW channels with the high temporal resolution of IR algorithms – to retrieve precipitation from satellite data.

Heavy Rain Forecasting by Model Initialization With LAPS: A Case Study

Results of the assimilation of high-density data to initialize the high-resolution meteorological model MOLOCH (CNR-ISAC) are described. The local analysis and prediction system (LAPS), a mesoscale data assimilation system developed at NOAA, is applied to modeling a case study of heavy precipitation that occurred over Liguria, north-western Italy, on November 4, 2011, causing severe flood in the city of Genoa. This case is representative of some episodes that affected the region in the last few years, where the coastal orography, besides enhancing the convective uplift, contributed to the formation of convergence lines over the sea, responsible for the onset of convective cells. The present work aims at the implementation of a model-based operational short-range prediction system, with particular focus on quantitative precipitation forecasting in a time range up to 12-24 h. The use of LAPS analysis as initial condition for the MOLOCH model shows a positive impact on the intensity and distribution of the simulated precipitation with respect to the simulations where only large-scale analyses are employed as initial conditions. Effects on the models simulations are due to the assimilation of surface network data, radio-sounding profiles, radar and satellite (SEVIRI/MSG) data.

Impact of Rainfall Assimilation on High-Resolution Hydrometeorological Forecasts over Liguria, Italy

AbstractThe autumn of 2014 was characterized by a number of severe weather episodes over Liguria (northern Italy) associated with floods and remarkable damage. This period is selected as a test bed to evaluate the performance of a rainfall assimilation scheme based on the nudging of humidity profiles and applied to a convection-permitting meteorological model at high resolution. The impact of the scheme is assessed in terms of quantitative precipitation forecast (QPF) applying an object-oriented verification methodology that evaluates the structure, amplitude, and location (SAL) of the precipitation field, but also in terms of hydrological discharge prediction. To attain this aim, the meteorological model is coupled with the operational hydrological forecasting chain of the Ligurian Hydrometeorological Functional Centre, and the whole system is implemented taking operational requirements into account. The impact of rainfall data assimilation is large during the assimilation period and still relevant in th...

Rainfall Assimilation into Limited Area Models

A physical assimilation technique based on humidity nudging has been developed for application to satellite-derived rainfall fields, in the framework of the European project “EURAINSAT”. The aim of the forcing procedure is to improve the short-range precipitation forecasts with particular attention to specific meteorological phenomena, such as heavy orographic precipitation and small-scale “hurricane-like” cyclones in the Mediterranean area. The nudging scheme forces the model humidity profile in order to get model precipitation closer to the observed precipitation. The forcing is a function of the difference between the rain rates, observed and forecasted, and of precipitation type, convective, or stratiform. In addition, a modelling tool to reproduce the idealised development of midlatitude baroclinic unstable modes, including humidity in the atomsphere and a full water cycle, has been developed with the purpose of investigating the effects and capabilities of assimilation of precipitation in an idealised frame. More realistic experiments have been also performed by implementing a lagged forecast procedure, in order to evaluate, with an observing mance in terms of improvements of short-range precipitation forecasts and impact on the dynamics of the meteorological evolution. Finally, satellite rain estimates, based on combined microwave (MW) and infrared (IR) techniques, have been assimilated into the limited area meteorological model trying to improve the short-range precipitation forecasts.