ABSTRACT The Soil Conservation Service-curve number (SCS-CN) method is widely used in hydrologic ... more ABSTRACT The Soil Conservation Service-curve number (SCS-CN) method is widely used in hydrologic practice, but its application often goes beyond the purpose of its original use. Common practice makes the method dependent on the antecedent precipitation index, a simple indicator derived from rainfall depth, which can be used to estimate the antecedent moisture condition (AMC) of soil. By taking data from an unspecified location in the United States, the SCS defined the appropriate AMC level based on the total five-day antecedent rainfall for dormant and growing seasons. These values, originally defined as an example practice at the plot scale, were subsequently adopted for general use without full awareness of scale effects and regional differences. We propose a revision to the amount of antecedent rainfall for the definition of AMC of soil, based on the minimization of the errors between an estimated and an observed runoff volume of 347 rainfall-runoff events in large mountain basins in Italy and Switzerland. A significant correlation between the new thresholds and the topographic index is shown, thus permitting extension of the method to basins not included in this study. DOI: 10.1061/(ASCE)HE.1943-5584.0000307. (C) 2011 American Society of Civil Engineers.
Hydrology and Earth System Sciences Discussions, 2007
The snow accumulation and melt processes are well known to play an important role on the river fl... more The 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.
In recent years, the interest in the prediction and prevention of natural hazards related to hydr... more In recent years, the interest in the prediction 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 (QPFs) for hydrological purposes. The development and implementation of a real-time flood forecasting system with a hydro-meteorological operational alert procedure during the MAP-D-PHASE Project is described in this paper. D-PHASE stands for Demonstration of Probabilistic Hydrological and Atmospheric Simulation of flood Events in the Alpine region and is a Forecast Demonstration Project (FDP) of the WWRP (World Weather Research Programme of WMO). It aims at demonstrating some of the many achievements of the Mesoscale Alpine Programme (MAP). The MAP FDP has addressed the entire forecasting chain, ranging from limited-area ensemble forecasting, high-resolution atmospheric modelling (km-scale), hydrological modelling and nowcasting to decision making by the end users, i.e., it is foreseen to set up an end-to-end forecasting system. The D-PHASE Operations Period (DOP) was from 1 June to 30 November 2007. In this study the hydro-meteorological chain includes both probabilistic forecasting based on ensemble prediction systems with lead time of a few days and short-range forecasts based on high resolution deterministic atmospheric models. D-PHASE hydrological ensemble forecasts are based on the 16 meteorological members, provided by COSMO-LEPS model (by ARPA Emilia-Romagna) with 5 day lead-time and a horizontal resolution of 10 km. Deterministic hydrological D-PHASE forecasts are provided by MOLOCH weather model (by ISAC-CNR) with a horizontal resolution of 2.2 km, nested into BOLAM, based on GFS initial and boundary conditions with 48 h lead-time. The hydrological model used to generate the runoff simulations is the rainfall-runoff distributed FEST-WB model, developed at Politecnico di Milano. The observed data to run the control simulations were supplied by ARPA-Piemonte. The analysis is focused on Maggiore Lake basin, an alpine basin between North-West of Italy and Southern Switzerland. The aim of this work is to evaluate how the uncertainty of the QPF affects the reliability of the whole hydro-meteorological alert system for a mountain catchment. Two significant events are analysed in order to compare the behaviour of the model driven by different weather scenarios: one convective in June that has yielded a high peak flow and one light stratiform in November that has been studied for the snow melt temperature which has affected the liquid precipitation and therefore the forecasted runoff.
This paper examines four models for estimating canopy resistance rc, since it is not a purely phy... more This paper examines four models for estimating canopy resistance rc, since it is not a purely physiological term, but it depends also on the prevailing climatic conditions get established over the canopy, in order to calculate the actual evapotranspiration on hourly and daily scales, for maize crop grown in North Italy. A comparison between Measured and estimated eddy covariance data was carried out by analysing in details the four models 1) Monteith, 2) Jarvis, 3) Katerji-Perrier, 4) Todorovic. They are either semi-empirical (1, 2 and 3) or mechanistic (4). Furthermore, the FAO approach was also evaluated and compared with the others techniques. In synthesis, rc has not been considered as constant but modelled in function of leaf area index through the approach of Monteith and influenced by the photo synthetically active radiation, the vapour pressure deficit, ambient temperature and the soil moisture through the approach of Jarvis. Moreover, rc has been modelled as a function of the climatic variables and water status condition through the approach of Katerji-Perrier which needs a calibration and finally as a function of only the climatic condition through the approach of Todorovic which does not need any calibration. The results confirmed the good accuracy of Katerji-Perrier method at both hourly and daily scale, while the approach of Monteith, Jarvis and Todorovic provided an overestimation respectively 12%, 27% and 30%. However, the evaluation of FAO method gave an overestimation and showed that both ET0 and Kc could be sources of errors. Key words: Canopy resistance, eddy covariance, Monteith, Jarvis, Katerji-Perrier, Todorovic, FAO
Definition of flood risk maps in dense urban area is a task to which modern surface hydrology add... more Definition of flood risk maps in dense urban area is a task to which modern surface hydrology addresses a substantial research effort. New methods for the definition of flood prone area, based on investigation of water depth and flow velocity, have been recently proposed. Two main issues are here investigated: first, the definition of design hydrograph, and second, the choice of the hydraulic model to simulate the 2D inundation process. A new approach for the definition of the design hydrographs is investigated. In fact, if the objective of the analysis is to assess the maximum extent of flooded area, one possible strategy is to assume the design hydrograph that maximizes the inundation volume, respect to the classical design hydrograph that maximizes the peak discharge. Two modelling approaches are compared, one based on truly 2D finite difference explicit scheme, and another one based on channel network scheme that makes use of a network of connected channels and storages to simulate flow, respectively, on the streets and into the building blocks.
In recent years, the interest in the prediction and prevention of natural hazards related to hydr... more In recent years, the interest in the prediction 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 (QPFs) for hydrological purposes. The development and implementation of a real-time flood forecasting system with a hydro-meteorological operational alert procedure during the MAP-D-PHASE Project is described in this paper. D-PHASE stands for Demonstration of Probabilistic Hydrological and Atmospheric Simulation of flood Events in the Alpine region and is a Forecast Demonstration Project (FDP) of the WWRP (World Weather Research Programme of WMO). It aims at demonstrating some of the many achievements of the Mesoscale Alpine Programme (MAP). The MAP FDP has addressed the entire forecasting chain, ranging from limited-area ensemble forecasting, high-resolution atmospheric modelling (km-scale), hydrological modelling and nowcasting to decision making by the end users, i.e., it is foreseen to set up an end-to-end forecasting system. The D-PHASE Operations Period (DOP) was from 1 June to 30 November 2007. In this study the hydro-meteorological chain includes both probabilistic forecasting based on ensemble prediction systems with lead time of a few days and short-range forecasts based on high resolution deterministic atmospheric models. D-PHASE hydrological ensemble forecasts are based on the 16 meteorological members, provided by COSMO-LEPS model (by ARPA Emilia-Romagna) with 5 day lead-time and a horizontal resolution of 10 km. Deterministic hydrological D-PHASE forecasts are provided by MOLOCH weather model (by ISAC-CNR) with a horizontal resolution of 2.2 km, nested into BOLAM, based on GFS initial and boundary conditions with 48 h lead-time. The hydrological model used to generate the runoff simulations is the rainfall-runoff distributed FEST-WB model, developed at Politecnico di Milano. The observed data to run the control simulations were supplied by ARPA-Piemonte. The study is focused on Maggiore Lake basin, an alpine basin between North-West of Italy and Southern Switzerland; results and statistical testing of the re-analyses shown in this presentation, are subdivided for each of three smaller sub-basins: Toce, Ticino and Maggia, in order to demonstrate the research progress on coupling meteorological and hydrological models in particular orographic features. It is presented how the meteorological forecasts are efficient into hydrological forecasting system, how the ensemble predictions are powerful to evaluate the uncertainty of the QPF which affects the QDF and the whole hydro-meteorological alert system for a mountain catchment. Further, in order to control the quality of the hydrological predictions in the short and medium term, statistical methods are used to calculate how the skill scores can be applied for hydrological applications and how the ensemble forecasts can help the users for decision making in management situations. Two significant events are analysed in order to compare the behaviour of the model driven by different weather scenarios: one convective in June that has yielded a high peak flow and one light stratiform in November that has been studied for the snow melt temperature which has affected the liquid precipitation and therefore the forecasted runoff. It is shown how the entire rainfall, the liquid precipitation and the runoff change in function of an areal the sub-basin scale, in order to understand where the errors are more frequently encountered.
ABSTRACT Definition of flood risk maps is a task to which modern surface hydrology devotes substa... more ABSTRACT Definition of flood risk maps is a task to which modern surface hydrology devotes substantial research effort. Their impact on the management of flood-prone, dense, urban areas has increased the need for better investigation of inundation dynamics. The problems associated with the aforementioned topics range from the definition of the design hydrograph and the identification of the surface boundary conditions for the flood routing over the inundation plan, to the choice of the hydrodynamic model to simulate urban flooding. Most of academic and commercial mathematical models, solving the De Saint Venant equations, fail on complex topography. Frequently encountered difficulties concern steep slopes, geometric discontinuities, mixed flow regimes, and initially dry areas. In the present paper, flood routing modelling approaches in urban areas and principles for the definition of the design flood events are outlined. The paper shows how urban flooding can be simulated by a quasi-2D hydrodynamic model that makes use of a network of connected channels and storages to simulate flow, respectively, on the streets and into the building blocks. Furthermore, the paper shows that, when flood hazard is assessed by considering flood extent, water depth and flow velocity, an in-depth analysis of the use of design hydrographs that maximise peak flow or inundation volume is needed.
The pluviometric flood forecasting thresholds are an easy method that helps river flood emergency... more The pluviometric flood forecasting thresholds are an easy method that helps river flood emergency management collecting data from limited area meteorologic model or telemetric raingauges. The thresholds represent the cumulated rainfall depth which generate critic discharge for a particular section. The thresholds were calculated for different sections of Arno river and for different antecedent moisture condition using the flood event distributed hydrologic model FEST. The model inputs were syntethic hietographs with different shape and duration. The system realibility has been verified by generating 500 year syntethic rainfall for 3 important subwatersheds of the studied area. A new technique to consider spatial variability of rainfall and soil properties effects on hydrograph has been investigated. The "Geomorphologic Weights" were so calculated. The alarm system has been implemented in a dedicated software (MIMI) that gets measured and forecast rainfall data from Autorità di Bacino and defines the state of the alert of the river sections.
Event-based hydrologic models need the antecedent soil moisture condition, as critical boundary i... more Event-based hydrologic models need the antecedent soil moisture condition, as critical boundary initial condition for flood simulation. Land-surface models (LSMs) have been developed to simulate mass and energy transfers, and to update the soil moisture condition through time from the solution of water and energy balance equations. They are recently used in distributed hydrologic modeling for flood prediction systems. Recent developments have made LSMs more complex by inclusion of more processes and controlling variables, increasing parameter number and uncertainty of their estimates. This also led to increasing of computational burden and parameterization of the distributed hydrologic models. In this study we investigate: 1) the role of soil moisture initial conditions in the modeling of Alpine basin floods; 2) the adequate complexity level of LSMs for the distributed hydrologic modeling of Alpine basin floods. The Toce basin is the case study; it is located in the North Piedmont (Italian Alps), and it has a total drainage area of 1534 km2 at Candoglia section. Three distributed hydrologic models of different level of complexity are developed and compared: two (TDLSM and SDLSM) are continuous models, one (FEST02) is an event model based on the simplified SCS-CN method for rainfall abstractions. In the TDLSM model a two-layer LSM computes both saturation and infiltration excess runoff, and simulates the evolution of the water table spatial distribution using the topographic index; in the SDLSM model a simplified one-layer distributed LSM only computes hortonian runoff, and doesn’t simulate the water table dynamic. All the three hydrologic models simulate the surface runoff propagation through the Muskingum-Cunge method. TDLSM and SDLSM models have been applied for the two-year (1996 and 1997) simulation period, during which two major floods occurred in the November 1996 and in the June 1997. The models have been calibrated and tested comparing simulated and observed hydrographs at Candoglia. Sensitivity analysis of the models to significant LSM parameters were also performed. The performances of the three models in the simulation of the two major floods are compared. Interestingly, the results indicate that the SDLSM model is able to sufficiently well predict the major floods of this Alpine basin; indeed, this model is a good compromise between the over-parameterized and too complex TDLSM model and the over-simplified FEST02 model.
In recent years, the interest in the prediction and prevention of natural hazards related to hydr... more In recent years, the interest in the prediction 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 (QPFs) for hydrological purposes. In mountain river basins, where snow dynamics can affect both precipitation (snow accumulation) and runoff (snow melting), uncertainty of air temperature has to be deeply investigated too. After the encouraging results obtained in the MAP-D-PHASE Project and considering that orographic precipitation has often led to disastrous flooding events over the Alps, it was decided to devote further analyses to show recent improvements in the operational use of hydro-meteorological chain, consisting of atmospheric models, hydrological prediction systems and warnings for end users, but above all to investigate better the key role played by temperature during snowy precipitation. In this study we present a hindcast for some precipitation events, occurred between 2007 and 2009 in Piemonte region and in the Maggiore Lake basin (between Italy and Switzerland). The goal is to evaluate how the uncertainty of meteorological forecasts (precipitations and temperatures) influences the performance of hydrological predictions in terms of Quantitative Discharge Forecast (QDF) at different spatial scales. A non-hydrostatic meteorological limited area model is used to force the rainfall-runoff distributed hydrological model (FEST-WB), developed at Politecnico di Milano to generate the runoff simulations; COSMO-LEPS model is based on the 16 meteorological members, provided by ARPA Emilia-Romagna, with 5 day lead-time and a horizontal resolution of 10 km. The observed hydro-weather data to run the control simulations were supplied by ARPA-Piemonte, which uses the same model every day for nowcasting monitoring and as a civil protection tool.
A groundwater model representing two-dimensional flow in unconfined aquifers is presented. The mo... more A groundwater model representing two-dimensional flow in unconfined aquifers is presented. The model is based on the paradigm of the macroscopic cellular automata, that represents dynamical systems which are discrete in space and time, operate on a uniform, regular lattice and are characterised by local interactions. Physically based equations are implemented to simulate the flow of water between adjacent cells. The model was validated against solutions of simple problems both in steady and transient condition including analytical solution and simulation performed with MODFLOW-2000 model. The developed code is simple enough to facilitate its integration into other models such as land surface models.. The good performance without detriment to accuracy makes the model adequate to perform long simulation time analysis.
This work presents a simplified numerical model of snow dynamic implemented into a continuous dis... more This work presents a simplified numerical model of snow dynamic implemented into a continuous distributed hydrological model for hydrograph simulations at basin scale. This snow model is based on air temperature thresholds that rule the snow melt and accumulation processes. A procedure to calibrate these temperature thresholds from NOAA satellite snow cover maps is discussed. We show that, for an accurate model calibration from satellite images, it is necessary to consider the presence of areas with complex topography such as mountain slopes. Snow model performance is tested both at local and basin scale on Alpine catchment. At local scale a good agreement between modelled snow dynamic and observed snow height data at snow gauge stations in the river Anza basin (Italy) is shown; at basin scale agreement between observed and simulated hydrographs at the river Toce outlet (Italy) is reported.
In recent years, the rising demand for water has led to water scarcity condition also in those ar... more In recent years, the rising demand for water has led to water scarcity condition also in those areas traditionally rich of water such as the river Po valley in Italy. On the other hand, the frequency of intense rainfall events has increased during the last years in mid and high latitudes due to the impact of climate change, causing destruction or much damage. These negative effects on human activities were also due to the lack of knowledge of the hydrological processes of the water balance at the river basin scale in an integrated perspective as requested by European Water Framework Directive. With the aim to improve the understanding of water balance related hydrological processes, sophisticated continuous hydrologic models have been developed for the simulation of soil water dynamic and river discharge also for mountain basins with complex topography. However, some uncertainties still remain. Some of the main uncertainties lie in the understanding of how the water balance of the upper river catchment can affect water resources and floods of the downstream lowland and in the importance of the interactions between the shallow groundwater and surface waters for water balance processes of alluvial plans. For this purpose a raster based distributed model was developed that allow the simulation of the processes regulating the water fluxes between soil, vegetation and atmosphere, the spatial patterns and temporal dynamics of groundwater-surface water interactions, and river discharge. The model was applied to the river Serio basin, in northern Italy.
ABSTRACT The Soil Conservation Service-curve number (SCS-CN) method is widely used in hydrologic ... more ABSTRACT The Soil Conservation Service-curve number (SCS-CN) method is widely used in hydrologic practice, but its application often goes beyond the purpose of its original use. Common practice makes the method dependent on the antecedent precipitation index, a simple indicator derived from rainfall depth, which can be used to estimate the antecedent moisture condition (AMC) of soil. By taking data from an unspecified location in the United States, the SCS defined the appropriate AMC level based on the total five-day antecedent rainfall for dormant and growing seasons. These values, originally defined as an example practice at the plot scale, were subsequently adopted for general use without full awareness of scale effects and regional differences. We propose a revision to the amount of antecedent rainfall for the definition of AMC of soil, based on the minimization of the errors between an estimated and an observed runoff volume of 347 rainfall-runoff events in large mountain basins in Italy and Switzerland. A significant correlation between the new thresholds and the topographic index is shown, thus permitting extension of the method to basins not included in this study. DOI: 10.1061/(ASCE)HE.1943-5584.0000307. (C) 2011 American Society of Civil Engineers.
Hydrology and Earth System Sciences Discussions, 2007
The snow accumulation and melt processes are well known to play an important role on the river fl... more The 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.
In recent years, the interest in the prediction and prevention of natural hazards related to hydr... more In recent years, the interest in the prediction 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 (QPFs) for hydrological purposes. The development and implementation of a real-time flood forecasting system with a hydro-meteorological operational alert procedure during the MAP-D-PHASE Project is described in this paper. D-PHASE stands for Demonstration of Probabilistic Hydrological and Atmospheric Simulation of flood Events in the Alpine region and is a Forecast Demonstration Project (FDP) of the WWRP (World Weather Research Programme of WMO). It aims at demonstrating some of the many achievements of the Mesoscale Alpine Programme (MAP). The MAP FDP has addressed the entire forecasting chain, ranging from limited-area ensemble forecasting, high-resolution atmospheric modelling (km-scale), hydrological modelling and nowcasting to decision making by the end users, i.e., it is foreseen to set up an end-to-end forecasting system. The D-PHASE Operations Period (DOP) was from 1 June to 30 November 2007. In this study the hydro-meteorological chain includes both probabilistic forecasting based on ensemble prediction systems with lead time of a few days and short-range forecasts based on high resolution deterministic atmospheric models. D-PHASE hydrological ensemble forecasts are based on the 16 meteorological members, provided by COSMO-LEPS model (by ARPA Emilia-Romagna) with 5 day lead-time and a horizontal resolution of 10 km. Deterministic hydrological D-PHASE forecasts are provided by MOLOCH weather model (by ISAC-CNR) with a horizontal resolution of 2.2 km, nested into BOLAM, based on GFS initial and boundary conditions with 48 h lead-time. The hydrological model used to generate the runoff simulations is the rainfall-runoff distributed FEST-WB model, developed at Politecnico di Milano. The observed data to run the control simulations were supplied by ARPA-Piemonte. The analysis is focused on Maggiore Lake basin, an alpine basin between North-West of Italy and Southern Switzerland. The aim of this work is to evaluate how the uncertainty of the QPF affects the reliability of the whole hydro-meteorological alert system for a mountain catchment. Two significant events are analysed in order to compare the behaviour of the model driven by different weather scenarios: one convective in June that has yielded a high peak flow and one light stratiform in November that has been studied for the snow melt temperature which has affected the liquid precipitation and therefore the forecasted runoff.
This paper examines four models for estimating canopy resistance rc, since it is not a purely phy... more This paper examines four models for estimating canopy resistance rc, since it is not a purely physiological term, but it depends also on the prevailing climatic conditions get established over the canopy, in order to calculate the actual evapotranspiration on hourly and daily scales, for maize crop grown in North Italy. A comparison between Measured and estimated eddy covariance data was carried out by analysing in details the four models 1) Monteith, 2) Jarvis, 3) Katerji-Perrier, 4) Todorovic. They are either semi-empirical (1, 2 and 3) or mechanistic (4). Furthermore, the FAO approach was also evaluated and compared with the others techniques. In synthesis, rc has not been considered as constant but modelled in function of leaf area index through the approach of Monteith and influenced by the photo synthetically active radiation, the vapour pressure deficit, ambient temperature and the soil moisture through the approach of Jarvis. Moreover, rc has been modelled as a function of the climatic variables and water status condition through the approach of Katerji-Perrier which needs a calibration and finally as a function of only the climatic condition through the approach of Todorovic which does not need any calibration. The results confirmed the good accuracy of Katerji-Perrier method at both hourly and daily scale, while the approach of Monteith, Jarvis and Todorovic provided an overestimation respectively 12%, 27% and 30%. However, the evaluation of FAO method gave an overestimation and showed that both ET0 and Kc could be sources of errors. Key words: Canopy resistance, eddy covariance, Monteith, Jarvis, Katerji-Perrier, Todorovic, FAO
Definition of flood risk maps in dense urban area is a task to which modern surface hydrology add... more Definition of flood risk maps in dense urban area is a task to which modern surface hydrology addresses a substantial research effort. New methods for the definition of flood prone area, based on investigation of water depth and flow velocity, have been recently proposed. Two main issues are here investigated: first, the definition of design hydrograph, and second, the choice of the hydraulic model to simulate the 2D inundation process. A new approach for the definition of the design hydrographs is investigated. In fact, if the objective of the analysis is to assess the maximum extent of flooded area, one possible strategy is to assume the design hydrograph that maximizes the inundation volume, respect to the classical design hydrograph that maximizes the peak discharge. Two modelling approaches are compared, one based on truly 2D finite difference explicit scheme, and another one based on channel network scheme that makes use of a network of connected channels and storages to simulate flow, respectively, on the streets and into the building blocks.
In recent years, the interest in the prediction and prevention of natural hazards related to hydr... more In recent years, the interest in the prediction 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 (QPFs) for hydrological purposes. The development and implementation of a real-time flood forecasting system with a hydro-meteorological operational alert procedure during the MAP-D-PHASE Project is described in this paper. D-PHASE stands for Demonstration of Probabilistic Hydrological and Atmospheric Simulation of flood Events in the Alpine region and is a Forecast Demonstration Project (FDP) of the WWRP (World Weather Research Programme of WMO). It aims at demonstrating some of the many achievements of the Mesoscale Alpine Programme (MAP). The MAP FDP has addressed the entire forecasting chain, ranging from limited-area ensemble forecasting, high-resolution atmospheric modelling (km-scale), hydrological modelling and nowcasting to decision making by the end users, i.e., it is foreseen to set up an end-to-end forecasting system. The D-PHASE Operations Period (DOP) was from 1 June to 30 November 2007. In this study the hydro-meteorological chain includes both probabilistic forecasting based on ensemble prediction systems with lead time of a few days and short-range forecasts based on high resolution deterministic atmospheric models. D-PHASE hydrological ensemble forecasts are based on the 16 meteorological members, provided by COSMO-LEPS model (by ARPA Emilia-Romagna) with 5 day lead-time and a horizontal resolution of 10 km. Deterministic hydrological D-PHASE forecasts are provided by MOLOCH weather model (by ISAC-CNR) with a horizontal resolution of 2.2 km, nested into BOLAM, based on GFS initial and boundary conditions with 48 h lead-time. The hydrological model used to generate the runoff simulations is the rainfall-runoff distributed FEST-WB model, developed at Politecnico di Milano. The observed data to run the control simulations were supplied by ARPA-Piemonte. The study is focused on Maggiore Lake basin, an alpine basin between North-West of Italy and Southern Switzerland; results and statistical testing of the re-analyses shown in this presentation, are subdivided for each of three smaller sub-basins: Toce, Ticino and Maggia, in order to demonstrate the research progress on coupling meteorological and hydrological models in particular orographic features. It is presented how the meteorological forecasts are efficient into hydrological forecasting system, how the ensemble predictions are powerful to evaluate the uncertainty of the QPF which affects the QDF and the whole hydro-meteorological alert system for a mountain catchment. Further, in order to control the quality of the hydrological predictions in the short and medium term, statistical methods are used to calculate how the skill scores can be applied for hydrological applications and how the ensemble forecasts can help the users for decision making in management situations. Two significant events are analysed in order to compare the behaviour of the model driven by different weather scenarios: one convective in June that has yielded a high peak flow and one light stratiform in November that has been studied for the snow melt temperature which has affected the liquid precipitation and therefore the forecasted runoff. It is shown how the entire rainfall, the liquid precipitation and the runoff change in function of an areal the sub-basin scale, in order to understand where the errors are more frequently encountered.
ABSTRACT Definition of flood risk maps is a task to which modern surface hydrology devotes substa... more ABSTRACT Definition of flood risk maps is a task to which modern surface hydrology devotes substantial research effort. Their impact on the management of flood-prone, dense, urban areas has increased the need for better investigation of inundation dynamics. The problems associated with the aforementioned topics range from the definition of the design hydrograph and the identification of the surface boundary conditions for the flood routing over the inundation plan, to the choice of the hydrodynamic model to simulate urban flooding. Most of academic and commercial mathematical models, solving the De Saint Venant equations, fail on complex topography. Frequently encountered difficulties concern steep slopes, geometric discontinuities, mixed flow regimes, and initially dry areas. In the present paper, flood routing modelling approaches in urban areas and principles for the definition of the design flood events are outlined. The paper shows how urban flooding can be simulated by a quasi-2D hydrodynamic model that makes use of a network of connected channels and storages to simulate flow, respectively, on the streets and into the building blocks. Furthermore, the paper shows that, when flood hazard is assessed by considering flood extent, water depth and flow velocity, an in-depth analysis of the use of design hydrographs that maximise peak flow or inundation volume is needed.
The pluviometric flood forecasting thresholds are an easy method that helps river flood emergency... more The pluviometric flood forecasting thresholds are an easy method that helps river flood emergency management collecting data from limited area meteorologic model or telemetric raingauges. The thresholds represent the cumulated rainfall depth which generate critic discharge for a particular section. The thresholds were calculated for different sections of Arno river and for different antecedent moisture condition using the flood event distributed hydrologic model FEST. The model inputs were syntethic hietographs with different shape and duration. The system realibility has been verified by generating 500 year syntethic rainfall for 3 important subwatersheds of the studied area. A new technique to consider spatial variability of rainfall and soil properties effects on hydrograph has been investigated. The "Geomorphologic Weights" were so calculated. The alarm system has been implemented in a dedicated software (MIMI) that gets measured and forecast rainfall data from Autorità di Bacino and defines the state of the alert of the river sections.
Event-based hydrologic models need the antecedent soil moisture condition, as critical boundary i... more Event-based hydrologic models need the antecedent soil moisture condition, as critical boundary initial condition for flood simulation. Land-surface models (LSMs) have been developed to simulate mass and energy transfers, and to update the soil moisture condition through time from the solution of water and energy balance equations. They are recently used in distributed hydrologic modeling for flood prediction systems. Recent developments have made LSMs more complex by inclusion of more processes and controlling variables, increasing parameter number and uncertainty of their estimates. This also led to increasing of computational burden and parameterization of the distributed hydrologic models. In this study we investigate: 1) the role of soil moisture initial conditions in the modeling of Alpine basin floods; 2) the adequate complexity level of LSMs for the distributed hydrologic modeling of Alpine basin floods. The Toce basin is the case study; it is located in the North Piedmont (Italian Alps), and it has a total drainage area of 1534 km2 at Candoglia section. Three distributed hydrologic models of different level of complexity are developed and compared: two (TDLSM and SDLSM) are continuous models, one (FEST02) is an event model based on the simplified SCS-CN method for rainfall abstractions. In the TDLSM model a two-layer LSM computes both saturation and infiltration excess runoff, and simulates the evolution of the water table spatial distribution using the topographic index; in the SDLSM model a simplified one-layer distributed LSM only computes hortonian runoff, and doesn’t simulate the water table dynamic. All the three hydrologic models simulate the surface runoff propagation through the Muskingum-Cunge method. TDLSM and SDLSM models have been applied for the two-year (1996 and 1997) simulation period, during which two major floods occurred in the November 1996 and in the June 1997. The models have been calibrated and tested comparing simulated and observed hydrographs at Candoglia. Sensitivity analysis of the models to significant LSM parameters were also performed. The performances of the three models in the simulation of the two major floods are compared. Interestingly, the results indicate that the SDLSM model is able to sufficiently well predict the major floods of this Alpine basin; indeed, this model is a good compromise between the over-parameterized and too complex TDLSM model and the over-simplified FEST02 model.
In recent years, the interest in the prediction and prevention of natural hazards related to hydr... more In recent years, the interest in the prediction 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 (QPFs) for hydrological purposes. In mountain river basins, where snow dynamics can affect both precipitation (snow accumulation) and runoff (snow melting), uncertainty of air temperature has to be deeply investigated too. After the encouraging results obtained in the MAP-D-PHASE Project and considering that orographic precipitation has often led to disastrous flooding events over the Alps, it was decided to devote further analyses to show recent improvements in the operational use of hydro-meteorological chain, consisting of atmospheric models, hydrological prediction systems and warnings for end users, but above all to investigate better the key role played by temperature during snowy precipitation. In this study we present a hindcast for some precipitation events, occurred between 2007 and 2009 in Piemonte region and in the Maggiore Lake basin (between Italy and Switzerland). The goal is to evaluate how the uncertainty of meteorological forecasts (precipitations and temperatures) influences the performance of hydrological predictions in terms of Quantitative Discharge Forecast (QDF) at different spatial scales. A non-hydrostatic meteorological limited area model is used to force the rainfall-runoff distributed hydrological model (FEST-WB), developed at Politecnico di Milano to generate the runoff simulations; COSMO-LEPS model is based on the 16 meteorological members, provided by ARPA Emilia-Romagna, with 5 day lead-time and a horizontal resolution of 10 km. The observed hydro-weather data to run the control simulations were supplied by ARPA-Piemonte, which uses the same model every day for nowcasting monitoring and as a civil protection tool.
A groundwater model representing two-dimensional flow in unconfined aquifers is presented. The mo... more A groundwater model representing two-dimensional flow in unconfined aquifers is presented. The model is based on the paradigm of the macroscopic cellular automata, that represents dynamical systems which are discrete in space and time, operate on a uniform, regular lattice and are characterised by local interactions. Physically based equations are implemented to simulate the flow of water between adjacent cells. The model was validated against solutions of simple problems both in steady and transient condition including analytical solution and simulation performed with MODFLOW-2000 model. The developed code is simple enough to facilitate its integration into other models such as land surface models.. The good performance without detriment to accuracy makes the model adequate to perform long simulation time analysis.
This work presents a simplified numerical model of snow dynamic implemented into a continuous dis... more This work presents a simplified numerical model of snow dynamic implemented into a continuous distributed hydrological model for hydrograph simulations at basin scale. This snow model is based on air temperature thresholds that rule the snow melt and accumulation processes. A procedure to calibrate these temperature thresholds from NOAA satellite snow cover maps is discussed. We show that, for an accurate model calibration from satellite images, it is necessary to consider the presence of areas with complex topography such as mountain slopes. Snow model performance is tested both at local and basin scale on Alpine catchment. At local scale a good agreement between modelled snow dynamic and observed snow height data at snow gauge stations in the river Anza basin (Italy) is shown; at basin scale agreement between observed and simulated hydrographs at the river Toce outlet (Italy) is reported.
In recent years, the rising demand for water has led to water scarcity condition also in those ar... more In recent years, the rising demand for water has led to water scarcity condition also in those areas traditionally rich of water such as the river Po valley in Italy. On the other hand, the frequency of intense rainfall events has increased during the last years in mid and high latitudes due to the impact of climate change, causing destruction or much damage. These negative effects on human activities were also due to the lack of knowledge of the hydrological processes of the water balance at the river basin scale in an integrated perspective as requested by European Water Framework Directive. With the aim to improve the understanding of water balance related hydrological processes, sophisticated continuous hydrologic models have been developed for the simulation of soil water dynamic and river discharge also for mountain basins with complex topography. However, some uncertainties still remain. Some of the main uncertainties lie in the understanding of how the water balance of the upper river catchment can affect water resources and floods of the downstream lowland and in the importance of the interactions between the shallow groundwater and surface waters for water balance processes of alluvial plans. For this purpose a raster based distributed model was developed that allow the simulation of the processes regulating the water fluxes between soil, vegetation and atmosphere, the spatial patterns and temporal dynamics of groundwater-surface water interactions, and river discharge. The model was applied to the river Serio basin, in northern Italy.
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