Macroscopic cellular automata for groundwater modelling: A first approach

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Snow satellite images for calibration of snow dynamic in a continuous distributed hydrological model

International audienceThe snow accumulation and melt processes are well known to play an important role on the river flow regime, in particular this is enhanced for basin with complex topography where the snow dynamic is strongly affected by hillslope exposition. This paper presents a simplified numerical model for snow dynamic simulation based on air temperature thresholds that rule the snow melt and accumulation processes implemented into a continuous distributed hydrological model for hydrograph simulations at basin scale. The possibility to calibrate these temperature thresholds from snow cover maps derived from NOAA satellite images is discussed. Snow covered pixels are classified according to a procedure based on aspect and elevation of each pixel, that allows to identify snow covered pixels also in shadowed areas. Snow model performance is proved at local and basin scale. The former shows a good agreement between modelled snow dynamic and observed snow height data at the Antrona station in the Toce basin; the latter shows agreement between observed and simulated hydrographs for the three gauge stations of Toce, Ticino and Maggia rivers

Elevation based correction of snow coverage retrieved from satellite images to improve model calibration

reserved4The most widely used method for snow dynamic simulation relies on temperature index approach, that makes snow melt and accumulation processes depend on air temperature related parameters. A recently used approach to calibrate these parameters is to compare model results with snow coverage retrieved from satellite images. In area with complex topography and heterogeneous land cover, snow coverage may be affected by the presence of shaded area or dense forest that make pixels to be falsely classified as uncovered. These circumstances may have, in turn, an influence on calibration of model parameters. In this paper we propose a simple procedure to correct snow coverage retrieved from satellite images. We show that using raw snow coverage to calibrate snow model may lead to parameter values out of the range accepted by literature, so that the timing of snow dynamics measured at two ground stations is not correctly simulated. Moreover, when the snow model is implemented into a continuous distributed hydrological model, we show that calibration against corrected snow coverage reduces the error in the simulation of river flow in an Alpine catchment.C. Corbari; G. Ravazzani; J. Martinelli; M. ManciniCorbari, Chiara; Ravazzani, Giovanni; J., Martinelli; Mancini, Marc

Operational flood-forecasting in the Piemonte region – development and verification of a fully distributed physically-oriented hydrological model

Abstract. A hydrological model for real time flood forecasting to Civil Protection services requires reliability and rapidity. At present, computational capabilities overcome the rapidity needs even when a fully distributed hydrological model is adopted for a large river catchment as the Upper Po river basin closed at Ponte Becca (nearly 40 000 km2). This approach allows simulating the whole domain and obtaining the responses of large as well as of medium and little sized sub-catchments. The FEST-WB hydrological model (Mancini, 1990; Montaldo et al., 2007; Rabuffetti et al., 2008) is implemented. The calibration and verification activities are based on more than 100 flood events, occurred along the main tributaries of the Po river in the period 2000–2003. More than 300 meteorological stations are used to obtain the forcing fields, 10 cross sections with continuous and reliable discharge time series are used for calibration while verification is performed on about 40 monitored cross sections. Furthermore meteorological forecasting models are used to force the hydrological model with Quantitative Precipitation Forecasts (QPFs) for 36 h horizon in "operational setting" experiments. Particular care is devoted to understanding how QPF affects the accuracy of the Quantitative Discharge Forecasts (QDFs) and to assessing the QDF uncertainty impact on the warning system reliability. Results are presented either in terms of QDF and of warning issues highlighting the importance of an "operational based" verification approach

Integrating glaciers raster-based modelling in large catchments hydrological balance: the Rhone case study

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Effects of temperature on flood forecasting: analysis of an operative case study in Alpine basins

Abstract. In recent years the interest in the forecast and prevention of natural hazards related to hydro-meteorological events has increased the challenge for numerical weather modelling, in particular for limited area models, to improve the quantitative precipitation forecasts (QPF) for hydrological purposes. After the encouraging results obtained in the MAP D-PHASE Project, we decided to devote further analyses to show recent improvements in the operational use of hydro-meteorological chains, and above all to better investigate the key role played by temperature during snowy precipitation. In this study we present a reanalysis simulation of one meteorological event, which occurred in November 2008 in the Piedmont Region. The attention is focused on the key role of air temperature, which is a crucial feature in determining the partitioning of precipitation in solid and liquid phase, influencing the quantitative discharge forecast (QDF) into the Alpine region. This is linked to the basin ipsographic curve and therefore by the total contributing area related to the snow line of the event. In order to assess hydrological predictions affected by meteorological forcing, a sensitivity analysis of the model output was carried out to evaluate different simulation scenarios, considering the forecast effects which can radically modify the discharge forecast. Results show how in real-time systems hydrological forecasters have to consider also the temperature uncertainty in forecasts in order to better understand the snow dynamics and its effect on runoff during a meteorological warning with a crucial snow line over the basin. The hydrological ensemble forecasts are based on the 16 members of the meteorological ensemble system COSMO-LEPS (developed by ARPA-SIMC) based on the non-hydrostatic model COSMO, while the hydrological model used to generate the runoff simulations is the rainfall–runoff distributed FEST-WB model, developed at Politecnico di Milano

A comparison of ensemble strategies for flash flood forecasting: The 12 October 2007 case study in Valencia, Spain

On 12 October 2007, several flash floods affected the Valencia region, eastern Spain, with devastating impacts in terms of human, social, and economic losses. An enhanced modeling and forecasting of these extremes, which can provide a tangible basis for flood early warning procedures and mitigation measures over the Mediterranean, is one of the fundamental motivations of the international Hydrological Cycle in the Mediterranean Experiment (HyMeX) program. The predictability bounds set by multiple sources of hydrological and meteorological uncertainty require their explicit representation in hydrometeorological forecasting systems. By including local convective precipitation systems, short-range ensemble prediction systems (SREPSs) provide a state-of-the-art framework to generate quantitative discharge forecasts and to cope with different sources of external-scale (i.e., external to the hydrological system) uncertainties. The performance of three distinct hydrological ensemble prediction systems (HEPSs) for the small-sized Serpis River basin is examined as a support tool for early warning and mitigation strategies. To this end, the Flash-Flood Event-Based Spatially Distributed Rainfall-RunoffTransformation-Water Balance (FEST-WB) model is driven by ground stations to examine the hydrological response of this semiarid and karstic catchment to heavy rains. The use of a multisite and novel calibration approach for the FEST-WB parameters is necessary to cope with the high nonlinearities emerging from the rainfall-runofftransformation and heterogeneities in the basin response. After calibration, FEST-WB reproduces with remarkable accuracy the hydrological response to intense precipitation and, in particular, the 12 October 2007 flash flood. Next, the flood predictability challenge is focused on quantitative precipitation forecasts (QPFs). In this regard, three SREPS generation strategies using the WRF Model are analyzed. On the one side, two SREPSs accounting for 1) uncertainties in the initial conditions (ICs) and lateral boundary conditions (LBCs) and 2) physical parameterizations are evaluated. An ensemble Kalman filter (EnKF) is also designed to test the ability of ensemble data assimilation methods to represent key mesoscale uncertainties from both IC and subscale processes. Results indicate that accounting for diversity in the physical parameterization schemes provides the best probabilistic high-resolution QPFs for this particular flash flood event. For low to moderate precipitation rates, EnKF and pure multiple physics approaches render undistinguishable accuracy for the test situation at larger scales. However, only the multiple physics QPFs properly drive the HEPS to render the most accurate flood warning signals. That is, extreme precipitation values produced by these convective-scale precipitation systems anchored by complex orography are better forecast when accounting just for uncertainties in the physical parameterizations. These findings contribute to the identification of ensemble strategies better targeted to the most relevant sources of uncertainty before flash flood situations over small catchments

HERASE: monitorare l’erosione del suolo nelle Alpi con tecniche Geomatiche

In Italia ci sono circa 4 milioni di ettari di terreno agricolo e forestale a rischio di erosione o frana e recenti stime del Ministero dell’Ambiente (2013) indicano che sarebbero necessari 40 miliardi di Euro per ridurre il rischio dovuto alla perdita di suolo sul territorio nazionale. Il progetto Hydrogeological modeling for Erosion Risk Assessment from SpacE (HERASE), finanziato da Fondazione Cariplo (Grant Nr.2016-0768), affronta questo tema nel bacino camuno del fiume Oglio, un’area alpina dell’Italia settentrionale. Scopo di HERASE è mettere a punto una metodologia di analisi basato sul Revised Universal Soil Loss Equation (RUSLE), reso dinamico dall’uso di mappe di copertura del suolo multi-temporali, per evidenziare le zone potenzialmente soggette a fenomeni erosivi e le dinamiche dei cambiamenti del territorio capaci di influenzarne l’entità. Misure in situ di erosione realizzate con un simulatore di pioggia permetteranno la caratterizzazione idrologica di zone rappresentative e la taratura del modello. Infine, le previsioni restituite dai modelli climatici saranno utilizzate per delineare possibili scenari di rischio futuro, in un contesto che vede il territorio montano, e quello alpino in particolare, soggetto a sempre più evidenti cambiamenti climatici. Il presente lavoro riporta alcuni risultati preliminari del progetto HERASE ottenuti sul sotto-bacino del torrente Arcanello (circa 21 km2), dove la stima preliminare dell’erosione è pari a 7,61 [t ha-1 a-1]. Tale risultato è concorde con il valore medio annuo a livello nazionale