ABSTRACT A state-space approach to rainfall forecasting is presented. It is based upon a simple, ... more ABSTRACT A state-space approach to rainfall forecasting is presented. It is based upon a simple, operational stochastic model featuring some analogies with the hierarchical structure of pulses introduced by many stochastic models for the point precipitation process. The suggested procedure makes use of the state-space methodology, and consists of two stages. At the first stage, we define a Dynamic Generalized Linear Model in order to estimate, in a dynamic fashion, the time varying probability of rainfall occurence over a given interval of time, the Reference Time Window (RTW). The non-linear filtering problem is solved through a Bayesian recursive algorithm. The algorithm requires the specification of a likelihood function and a prior distribution for the pre- dictions. The posterior distribution is then evaluated recursively from the data as new observations become available. A measure of uncertainty is generated via the estima- tion of posterior distributions for predictions. At the second stage, using the estimated probabilities and, more precisely, their sampling distributions in different RTWs, a dynamic model for the distribution of the total rainfall depth over an assigned RTW is defined. The whole procedure has been conceived to make use of information com- ing from different sources. At both stages, non stochastic covariates, like information coming from different measurement stations or remotely sensed data, can be easily included in the model. The covariates may also act as trigger for the forecasting sys- tem. An application to rainfall data recorded in a dense rain-gauge network is pre- sented. Particular attention will be paid to the analysis of very extreme events, typical of mediterranean regions.
ABSTRACT We investigate some properties of the rainfall and runoff processes at the daily scale l... more ABSTRACT We investigate some properties of the rainfall and runoff processes at the daily scale looking at their combination related to the flood generation mechanisms and we show how these relationships can improve the prediction of flood risk. In alpine regions, the effects on floods of snow accumulation and melting can be recognised by comparison of rainfall and runoff peaks at a seasonal basis. Similarly, evaluation of the timing and magnitude of rainfall and runoff events can provide information about the homogeneity of flood regimes both at a site and within morphologically homogeneous regions. In this paper we evaluate the within-year distribution of daily precipitation and runoff considered as peaks over threshold (POT), which provides meaningful additional information to traditional annual maximum series finalised to flood frequency analysis (FFA). Application to some 30 time series in Piemonte (Italy) shows the characters of different regimes of flood generation (snow-ice dominated and/or rainfall dominated), where joint action of both the climatic dominant factors produce non-homogeneous flood processes. Climatic implications in the selection of homogenous regions in FFA are discussed.
Abstract. Natural hydrometeorological disasters in the Mediterranean region have occurred in the ... more Abstract. Natural hydrometeorological disasters in the Mediterranean region have occurred in the past essentially by outlying storm events characterized by considerable rainfall intensity and rare frequency. The characterization of this type of event is a crucial point in risk ...
It has long been recognized that soil moisture has a key role in controlling evapo- transpiration... more It has long been recognized that soil moisture has a key role in controlling evapo- transpiration during dryer periods, as well as runoff processes, particularly saturation excess runoff. The temporal and spatial variability of moisture can be an important influence on the temporal and spatial characteristics of these processes. More recently, the role of soil moisture in controlling lateral flow processes has re- ceived close attention, with switching between persistent dry and wet states leading to switches between controls on spatial patterns of soil moisture and consequent changes in runoff behaviour. In this paper we will review results on the spatial and temporal variability of soil moisture at the small catchment scale, concentrating in particular on dominant controls and temporal changes in dominant controls. We will discuss the climatic and catchment characteristics under which switching between dominant controls is likely. We will also present results relating spatial soil...
ABSTRACT Nella recente letteratura scientifica, a causa della grande attenzione posta dalla comun... more ABSTRACT Nella recente letteratura scientifica, a causa della grande attenzione posta dalla comunità scientifica sui cambiamenti climatici, numerose sono le analisi proposte, volte alla ricerca e alla quantificazione di trend dei volumi di precipitazione. Meno investigato è il fenomeno di variazione del regime climatico, anche questo potenzialmente imputato ai cambiamenti climatici, che, cosi come per gli afflussi totali, riveste notevole importanza strategica nella gestione della risorsa idrica per usi diversi. In questa memoria, si espongono i risultati di una analisi, basata sull’introduzione di indici, relativa ad una ampia porzione della penisola italiana, volta proprio alla valutazione della variabilità spaziale e temporale del regime climatico, su un lungo orizzonte temporale.
Daily streamflow does show particular features unrecognizable in streamflow aggregated at a diffe... more Daily streamflow does show particular features unrecognizable in streamflow aggregated at a different time scale (monthly and annual), which does not enable the use of ARMA type models (Box and Jenkins, 1976), successfully applied to monthly and annual timeseries. In 1970 Bernier first and Weiss (1977) later, proposed a shot noise (SN) model for daily streamflow simulation and a few
The runoff coefficient, estimated as the ratio between quick flow and rainfall volume, on an even... more The runoff coefficient, estimated as the ratio between quick flow and rainfall volume, on an event basis, has been analyzed in an empirical framework, as a function of the initial catchment state conditions prior to an event, such as pre-event soil moisture and pre-event base flow. The resulting relationships have been tested for their utility in runoff prediction, focusing on
ABSTRACT A state-space approach to rainfall forecasting is presented. It is based upon a simple, ... more ABSTRACT A state-space approach to rainfall forecasting is presented. It is based upon a simple, operational stochastic model featuring some analogies with the hierarchical structure of pulses introduced by many stochastic models for the point precipitation process. The suggested procedure makes use of the state-space methodology, and consists of two stages. At the first stage, we define a Dynamic Generalized Linear Model in order to estimate, in a dynamic fashion, the time varying probability of rainfall occurence over a given interval of time, the Reference Time Window (RTW). The non-linear filtering problem is solved through a Bayesian recursive algorithm. The algorithm requires the specification of a likelihood function and a prior distribution for the pre- dictions. The posterior distribution is then evaluated recursively from the data as new observations become available. A measure of uncertainty is generated via the estima- tion of posterior distributions for predictions. At the second stage, using the estimated probabilities and, more precisely, their sampling distributions in different RTWs, a dynamic model for the distribution of the total rainfall depth over an assigned RTW is defined. The whole procedure has been conceived to make use of information com- ing from different sources. At both stages, non stochastic covariates, like information coming from different measurement stations or remotely sensed data, can be easily included in the model. The covariates may also act as trigger for the forecasting sys- tem. An application to rainfall data recorded in a dense rain-gauge network is pre- sented. Particular attention will be paid to the analysis of very extreme events, typical of mediterranean regions.
ABSTRACT We investigate some properties of the rainfall and runoff processes at the daily scale l... more ABSTRACT We investigate some properties of the rainfall and runoff processes at the daily scale looking at their combination related to the flood generation mechanisms and we show how these relationships can improve the prediction of flood risk. In alpine regions, the effects on floods of snow accumulation and melting can be recognised by comparison of rainfall and runoff peaks at a seasonal basis. Similarly, evaluation of the timing and magnitude of rainfall and runoff events can provide information about the homogeneity of flood regimes both at a site and within morphologically homogeneous regions. In this paper we evaluate the within-year distribution of daily precipitation and runoff considered as peaks over threshold (POT), which provides meaningful additional information to traditional annual maximum series finalised to flood frequency analysis (FFA). Application to some 30 time series in Piemonte (Italy) shows the characters of different regimes of flood generation (snow-ice dominated and/or rainfall dominated), where joint action of both the climatic dominant factors produce non-homogeneous flood processes. Climatic implications in the selection of homogenous regions in FFA are discussed.
Abstract. Natural hydrometeorological disasters in the Mediterranean region have occurred in the ... more Abstract. Natural hydrometeorological disasters in the Mediterranean region have occurred in the past essentially by outlying storm events characterized by considerable rainfall intensity and rare frequency. The characterization of this type of event is a crucial point in risk ...
It has long been recognized that soil moisture has a key role in controlling evapo- transpiration... more It has long been recognized that soil moisture has a key role in controlling evapo- transpiration during dryer periods, as well as runoff processes, particularly saturation excess runoff. The temporal and spatial variability of moisture can be an important influence on the temporal and spatial characteristics of these processes. More recently, the role of soil moisture in controlling lateral flow processes has re- ceived close attention, with switching between persistent dry and wet states leading to switches between controls on spatial patterns of soil moisture and consequent changes in runoff behaviour. In this paper we will review results on the spatial and temporal variability of soil moisture at the small catchment scale, concentrating in particular on dominant controls and temporal changes in dominant controls. We will discuss the climatic and catchment characteristics under which switching between dominant controls is likely. We will also present results relating spatial soil...
ABSTRACT Nella recente letteratura scientifica, a causa della grande attenzione posta dalla comun... more ABSTRACT Nella recente letteratura scientifica, a causa della grande attenzione posta dalla comunità scientifica sui cambiamenti climatici, numerose sono le analisi proposte, volte alla ricerca e alla quantificazione di trend dei volumi di precipitazione. Meno investigato è il fenomeno di variazione del regime climatico, anche questo potenzialmente imputato ai cambiamenti climatici, che, cosi come per gli afflussi totali, riveste notevole importanza strategica nella gestione della risorsa idrica per usi diversi. In questa memoria, si espongono i risultati di una analisi, basata sull’introduzione di indici, relativa ad una ampia porzione della penisola italiana, volta proprio alla valutazione della variabilità spaziale e temporale del regime climatico, su un lungo orizzonte temporale.
Daily streamflow does show particular features unrecognizable in streamflow aggregated at a diffe... more Daily streamflow does show particular features unrecognizable in streamflow aggregated at a different time scale (monthly and annual), which does not enable the use of ARMA type models (Box and Jenkins, 1976), successfully applied to monthly and annual timeseries. In 1970 Bernier first and Weiss (1977) later, proposed a shot noise (SN) model for daily streamflow simulation and a few
The runoff coefficient, estimated as the ratio between quick flow and rainfall volume, on an even... more The runoff coefficient, estimated as the ratio between quick flow and rainfall volume, on an event basis, has been analyzed in an empirical framework, as a function of the initial catchment state conditions prior to an event, such as pre-event soil moisture and pre-event base flow. The resulting relationships have been tested for their utility in runoff prediction, focusing on
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Papers by P. Villani