1,721,074 research outputs found
Exploring the use of multi-gene genetic programming in regional models for the simulation of monthly river runoff series
No full textThe use of new data-driven approaches based on the so-called expert systems to simulate runoff generation processes is a promising frontier that may allow for overcoming some modeling difficulties related to more complex traditional approaches. The present study highlights the potential of expert systems in creating regional hydrological models, for which they can benefit from the availability of large database. Different soft computing models for the reconstruction of the monthly natural runoff in river basins are explored, focusing on a new class of heuristic models, which is the Multi-Gene Genetic Programming (MGGP). The region under study is Sicily (Italy), where a regression based rainfall-runoff model, here used as benchmark model, was previously built starting from the analysis of a regional database relative to several gauged watersheds across the region. In the present study, different models are created using the same dataset, including: six MGGPs generated considering different modeling set-up; a Multi-Layer Perceptron Artificial Neural Network (ANN); two new hybrid models (ANN-MGGP), combining a Classifier ANN and two MGGPs that simulate separately low and high runoff. Results show how all the soft computing models perform similarly and outperform the benchmark model, demonstrating that MGGP can be considered as a valid alternative to the much more consolidated ANN technique. The new introduced hybrid ANN-MGGP is the only model showing at least satisfactory performance (i.e. Nash-Sutcliffe Efficiency above 0.5) over the full range of 38 watersheds explored, representing a useful regional tool for reconstructing monthly runoff series also at ungauged sites
Exploring the linkage between dew point temperature and precipitation extremes: A multi-time-scale analysis on a semi-arid Mediterranean region
Full text linkUnderstanding warming climate implications on precipitation is of crucial importance, especially for areas particularly subjected to climate changes and land use/cover modifications, which could be extremely vulnerable to phenomena typically caused by rainfall extremes, such as floods and landslides. Past decade has been witnessing an increasing interest on simple modeling approaches based on the observation of commonly available meteorological variables and their physical linkages. In particular, based on the well-known thermodynamic Clausius-Clapeyron (CC) equation, it was widely investigated the scaling relation between rainfall extremes and variables representative of the near surface humidity, typically the surface air temperature, through the use of general regression models. In some cases, conventional approaches have shown some evident limitations related to the use of surface temperature as covariate, limited size of the analyzed datasets and some climatic peculiarities of the investigated areas, especially for tropical, arid and semi-arid environments. The use of quantile regression instead of general regression and dew point temperature instead of surface temperatures have recently revealed promising potentialities for overcoming some of the above limitations for wet areas, while it has been scarcely tested in arid and semi-arid regions. The purpose of this study is to analyze the suitability of a quantile regression-based approach in a semi-arid Mediterranean region and to explore the impact of different modeling choices on the estimation of the scaling rate. More specifically, the sensitivity of extreme precipitation to dew point temperature is investigated through a multi-time-scale analysis, performed on a wide regional dataset of Sicily (Italy) including high temporal resolution climatic data from 86 gauges. The role of the considered rainfall accumulation period, conditional quantile and time-lag between precipitation-dew point temperature paired data is investigated considering different spatial and temporal data aggregation. The results reveal scaling rate values always below the theoretical CC-rate. Hourly and sub-hourly rainfall extremes are more sensitive to changes in dew point temperature than longer precipitation. The analysis of the driest and hottest season shows a dew point temperature dependence of extreme rainfall more complex than for the other seasons. Compared to the use of general regression, the scaling relationship observed with the quantile regression approach, here used, is more regular across different gauges and sub-regions, rainfall accumulation periods and seasons, with similar scaling rates, confirming promising potentialities areas also for semi-arid regions
Budyko’s Based Method for Annual Runoff Characterization across Different Climatic Areas: an Application to United States
No full textRunoff data knowledge is of fundamental importance for a wide range of hydrological, ecological, and socioeconomic applications. The reconstruction of annual runoff is a fundamental task for several activities related to water resources management, especially for ungauged basins. At catchment scales, the Budyko's framework provides an extremely useful and, in some cases, accurate estimation of the long-term partitioning of precipitation into evapotranspiration and runoff as a function of the prevailing climatic conditions. Recently the same long-term partitioning rules have been successfully used to describe water partitioning also at the annual scale and calculate the annual runoff distribution within a simple analytic framework in arid and semi-arid basins. One of the main advantages of the latter method is that only annual precipitation and potential evapotranspiration statistics, and the Fu's equation parameter omega are required to obtain the annual runoff probability distribution. The aim of this study is to test the limit and potentialities of the aforementioned method under different climatic conditions. To this aim, the model is applied to more than four hundred basins located in the United States. Catchments were grouped into five different samples, following the subdivision of the continental region in five homogeneous climatic zones according to Koppen-Geiger classification. The theoretical probability distribution of annual runoff at each basin has been compared with that derived from historical observations. The results confirm the capability of the tested technique to reproduce the empirical annual runoff distributions with similar and satisfactory performances across different areas, revealing a good option also in cases characterized by climate and hydrological conditions very different from those hypothesized during the original analytical model design, thus extending the geographical and conceptual limits of applicability of the framework
Ecohydrological modelling of flow duration curve in Mediterranean river basins
No full textFlow duration curve provides an important synthesis of the relevant hydrological processes occurring at the basin scale, and, although it is typically obtained from field observations, different theoretical approaches finalized to its indirect reconstruction have been developed in recent years. In this study a recent ecohydrological model for the probabilistic characterization of base flows is tested through its application to a study catchment located in southern Italy, where long historical series of daily streamflow are available. The model, coupling soil moisture balance with a simplified scheme of the hydrological response of the basin, provides the daily flow duration curve. The original model is here modified in order to account for rainfall reduction due to canopy interception and stress its potential applicability to most of the ephemeral Mediterranean basins, where measurements of air temperature and rainfall often represent the only meteorological data available. The model shows a high sensitivity to two parameters related to the transport and evapotranspiration processes. Two different operational approaches for the identification of such parameters are explored and compared: by the first approach, these parameters are considered as time invariant quantities, while, in the second approach, empirical relationships between such parameters and the underlying climatic forcings are first derived and then adopted in the parameters calibration procedure. The model ability in reproducing the empirical flow duration curves and the model sensitivity to climate forcings, here referred as elasticity of the model, are investigated and it is shown how the adoption of the second approach leads to a general improvement of the model elasticity
Generation of natural runoff monthly series at ungauged sites using a regional regressive model
No full textMany hydrologic applications require reliable estimates of runoff in river basins to face the widespread lack of data, both in time and in space. A regional method for the reconstruction of monthly runoff series is here developed and applied to Sicily (Italy). A simple modeling structure is adopted, consisting of a regression-based rainfall-runoff model with four model parameters, calibrated through a two-step procedure. Monthly runoff estimates are based on precipitation, temperature, and exploiting the autocorrelation with runoff at the previous month. Model parameters are assessed by specific regional equations as a function of easily measurable physical and climate basin descriptors. The first calibration step is aimed at the identification of a set of parameters optimizing model performances at the level of single basin. Such "optimal" sets are used at the second step, part of a regional regression analysis, to establish the regional equations for model parameters assessment as a function of basin attributes. All the gauged watersheds across the region have been analyzed, selecting 53 basins for model calibration and using the other six basins exclusively for validation. Performances, quantitatively evaluated by different statistical indexes, demonstrate relevant model ability in reproducing the observed hydrological time-series at both the monthly and coarser time resolutions. The methodology, which is easily transferable to other arid and semi-arid areas, provides a reliable tool for filling/reconstructing runoff time series at any gauged or ungauged basin of a region
Climate changes' effects on vegetation water stress in Mediterranena areas
No full textMany recent studies have demonstrated that CO(2) increase is driving the climate in Mediterranean areas towards important changes, mainly represented by a temperature increase and a contemporaneous rainfall reduction. Starting from this premise, the primary aim of the present study is to investigate the effects of potential climatic changes on vegetational stress in Mediterranean ecosystems. Particular attention is here focussed only on the plants' water stress in water controlled ecosystems, mainly related to soil water balance. The interactions among climate, soil and vegetation are evaluated numerically by means of an ecohydrological model. In this work, different future climatic scenarios and their effects on woody and grassy vegetation are analysed, and the results show an increase in water stress for woody and grass vegetations: trees could suffer more because of the higher evapotranspiration rates and the decrease of the winter recharge. Results are strictly dependent on the future rainfall seasonal distribution and the possible modification in rainfall frequency and intensity
Performance di impianti per la microirrigazione mediante misure di uniformità ed efficienza di distribuzione.
No full textIl lavoro si propone di valutare, attraverso una indagine di campo, la performance di tre diverse tipologie di impianto per la microirrigazione utilizzate su parcelle coltivate a vigneto. Nelle prime due tipologie di impianto l’erogazione avviene mediante gocciolatori e spruzzatori posizionati al disopra del piano di campagna, mentre nella terza le linee erogatrici sono state poste a circa 40 cm al disotto del piano di campagna, in prossimità dell’apparato radicale delle piante
EHSM: a conceptual ecohydrological model for daily streamflow simulation
No full textA parsimonious conceptual lumped model is here presented with the aim of simulating daily streamflow in semi-arid areas. The model, processing daily rainfall and reference evapotranspiration at basin scale, reproduces surface and subsurface runoff, soil moisture dynamics, and actual evapotranspiration fluxes. The key elements of this numerical model are the soil bucket, where rainfall, evapotranspiration, and leakage drive soil moisture dynamics, and two linear reservoirs working in parallel with different characteristic response times. The surface reservoir, able to simulate the fast response of the basin, is fed by rain falling on impervious area and by runoff generated with excess of saturation mechanism, whereas the deep reservoir, which simulates the slow response, is fed by instantaneous leakage pulses coming from the soil bucket. Seven model parameters, which summarize soil, vegetation, and hydrological catchment properties, are assessed on a Sicilian basin, first using simple basic ecohydrological knowledge and then Monte Carlo simulations as well.
The proposed model provides reliable estimate of daily runoff, accurate reproduction of flow duration curve, and physically consistent traces of soil moisture and evapotranspiration fluxes. Model performances are comparable in the two cases of calibrated and ecohydrologically driven parameters, emphasizing how basic descriptors are able to provide runoff estimatio
- …
