Aristoteles Tegos

The stochastic structures of potential evaporation and evapotranspiration (PEV and PET or ETo) are analyzed using the ERA5 hourly reanalysis data and the Penman–Monteith model applied to the well-known CIMIS network. The latter includes high-quality ground meteorological samples with long lengths and simultaneous measurements of monthly incoming shortwave radiation, temperature, relative humidity, and wind speed. It is found that both the PEV and PET processes exhibit a moderate long-range… Show more

The stochastic structures of potential evaporation and evapotranspiration (PEV and PET or ETo) are analyzed using the ERA5 hourly reanalysis data and the Penman–Monteith model applied to the well-known CIMIS network. The latter includes high-quality ground meteorological samples with long lengths and simultaneous measurements of monthly incoming shortwave radiation, temperature, relative humidity, and wind speed. It is found that both the PEV and PET processes exhibit a moderate long-range dependence structure with a Hurst parameter of 0.64 and 0.69, respectively. Additionally, it is noted that their marginal structures are found to be light-tailed when estimated through the Pareto–Burr–Feller distribution function. Both results are consistent with the global-scale hydrological-cycle path, determined by all the above variables and rainfall, in terms of the marginal and dependence structures. Finally, it is discussed how the existence of, even moderate, long-range dependence can increase the variability and uncertainty of both processes and, thus, limit their predictability. Show less

Dams design and their operation cause strong environmental alteration and therefore a long-term debate is ongoing for the scale of these projects. At the same time, the concept of Environmental Flow Assessment (EFA) is a crucial element of modified ecosystems featuring large infrastructure such as dams and reservoirs for mitigating potential environmental degradation while they operate. Nowadays, integrated scientific frameworks are required to quantify the risks caused by large infrastructure.… Show more

Dams design and their operation cause strong environmental alteration and therefore a long-term debate is ongoing for the scale of these projects. At the same time, the concept of Environmental Flow Assessment (EFA) is a crucial element of modified ecosystems featuring large infrastructure such as dams and reservoirs for mitigating potential environmental degradation while they operate. Nowadays, integrated scientific frameworks are required to quantify the risks caused by large infrastructure. Through the use of stochastic analysis, it is possible to quantify these uncertainties, and present a solution that incorporates long-term persistence and environmental sustainability into a balanced reservoir simulation model. In this work, an attempt is made to determine a benchmark reservoir size incorporating hydrological and ecological criteria though stochastic analysis. The primary goal is to ensure the best possible conditions for the ecosystem, and then secondarily to allow a steady supply of water for other uses. Using a synthetic timeseries based on historical inputs, it is possible to determine and preserve essential statistical characteristics of a river’s streamflow, and use these to detect the optimal reservoir capacity that maximizes environmental and local water demand reliability. Show less

In February 2017, a failure occurring in Oroville Dam’s main spillway risked causing severe damages downstream. A unique aspect of this incident was the fact that it happened during a flood scenario well within its design and operational procedures, prompting research into its causes and determining methods to prevent similar events from reoccurring. In this study, a hydroclimatic analysis of Oroville Dam’s catchment is conducted, along with a review of related design and operational manuals… Show more

In February 2017, a failure occurring in Oroville Dam’s main spillway risked causing severe damages downstream. A unique aspect of this incident was the fact that it happened during a flood scenario well within its design and operational procedures, prompting research into its causes and determining methods to prevent similar events from reoccurring. In this study, a hydroclimatic analysis of Oroville Dam’s catchment is conducted, along with a review of related design and operational manuals. The data available allows for the comparison of older flood-frequency analyses to new alternative methods proposed in this paper and relevant literature. Based on summary characteristics of the 2017 floods, possible causes of the incident are outlined, in order to understand which factors contributed more significantly. It turns out that the event was most likely the result of a structural problem in the dam’s main spillway and detrimental geological conditions, but analysis of surface level data also reveals operational issues that were not present during previous larger floods, promoting a discussion about flood control design methods, specifications, and dam inspection procedures, and how these can be improved to prevent a similar event from occurring in the future. Show less

Over the last decade, Environmental Flow Assessment (EFA) has focused scientific attention around heavily-modified hydrosystems, such as flow regulated releases downstream of dams. In this light, numerous approaches of varying complexity have been developed, the most holistic of which incorporate hydrological, hydraulic, biological and water quality inputs, as well as socioeconomic issues. Finding the optimal flow releases, informing policy and determining an operational framework are often the… Show more

Over the last decade, Environmental Flow Assessment (EFA) has focused scientific attention around heavily-modified hydrosystems, such as flow regulated releases downstream of dams. In this light, numerous approaches of varying complexity have been developed, the most holistic of which incorporate hydrological, hydraulic, biological and water quality inputs, as well as socioeconomic issues. Finding the optimal flow releases, informing policy and determining an operational framework are often the main focus. This work exhibits a simplification of the DRIFT framework, and is regarded as the first holistic EFA approach, consisting of three modules, namely hydrological, hydraulic and fish quality. A novel conceptual classification for fish quality is proposed, associating fish fauna requirements with hydraulic characteristics, exported by fish survey analyses. The new methodology was applied and validated successfully at three stream sites in Lesotho, where DRIFT was formerly employed. Show less

Interbasin water transfer is a primary instrument of water resources management directly related with the integrated development of the economy, society and environment. Here we assess the project of the interbasin water transfer from the river Acheloos to the river Pinios basin which has intrigued the Greek society, the politicians and scientists for decades. The set of criteria we apply originate from a previous study reviewing four interbasin water transfers and assessing whether an… Show more

Interbasin water transfer is a primary instrument of water resources management directly related with the integrated development of the economy, society and environment. Here we assess the project of the interbasin water transfer from the river Acheloos to the river Pinios basin which has intrigued the Greek society, the politicians and scientists for decades. The set of criteria we apply originate from a previous study reviewing four interbasin water transfers and assessing whether an interbasin water transfer is compatible with the concept of integrated water resources management. In this respect, we assess which of the principles of the integrated water resources management the Acheloos to Pinios interbasin water transfer project does or does not satisfy. While the project meets the criteria of real surplus and deficit, of sustainability and of sound science, i.e., the criteria mostly related to the engineering part, it fails to meet the criteria of good governance and balancing of existing rights with needs, i.e., the criteria associated with social aspects of the project. The non-fulfilment of the latter criteria is the consequence of chronic diseases of the Greek society, which become obvious in the case study. Show less

We present and validate a global parametric model of potential evapotranspiration (PET) with two parameters which are estimated through calibration, using as explanatory variables temperature and extraterrestrial radiation. The model and the parameters estimation approach were tested over the globe, using the FAO CLIMWAT database that provides monthly averaged values of meteorological inputs at 4300 locations worldwide. A preliminary analysis of these data allowed explaining the major drivers… Show more

We present and validate a global parametric model of potential evapotranspiration (PET) with two parameters which are estimated through calibration, using as explanatory variables temperature and extraterrestrial radiation. The model and the parameters estimation approach were tested over the globe, using the FAO CLIMWAT database that provides monthly averaged values of meteorological inputs at 4300 locations worldwide. A preliminary analysis of these data allowed explaining the major drivers of PET over the globe and across seasons. Next, we developed an automatic optimization software tool to calibrate the model and provide point PET estimations against the given Penman-Monteith values. We also employed extended analysis of model inputs and outputs, including the production of global maps of optimized model parameters and associated performance metrics. Also, we employed interpolated values of the optimized parameters to validate the predictive capacity of our model against monthly meteorological time series, at several stations worldwide. The results were very encouraging, since even with the use of abstract climatic information for model calibration and the use of interpolated parameters as local predictors, the model generally ensures reliable PET estimations. In few cases the model performs poorly in estimating the reference PET, due to irregular interactions between temperature and extraterrestrial radiation, as well as because the associated processes are influenced by additional drivers, e.g. relative humidity and wind speed. However, the analysis of the residuals showed that the model is consistent in terms of parameters estimation and model validation. The provided parameters maps allow the direct use of the parametric model wherever in the world, providing PET estimates in case of missing data, that can be further improved even with a short term acquisition of meteorological data. Show less

We present an R function for testing the trend significance of time series. The function calculates the trend significance using a modified Mann- Kendall test, which takes into account the well-known physical behavior of the Hurst-Kolmogorov dynamics. The function is tested in 10 stations in Greece, with approximately 50 years of PET data with the use of a recent parametric approach. A significant downward trend was detected in two stations. The R software is now suitable for extensive use in… Show more

We present an R function for testing the trend significance of time series. The function calculates the trend significance using a modified Mann- Kendall test, which takes into account the well-known physical behavior of the Hurst-Kolmogorov dynamics. The function is tested in 10 stations in Greece, with approximately 50 years of PET data with the use of a recent parametric approach. A significant downward trend was detected in two stations. The R software is now suitable for extensive use in the several fields of the scientific community, allowing a physical consistent of a trend analysis. Show less

One-dimensional and quasi-two-dimensional hydraulic freeware models (HEC-RAS, LISFLOOD-FP and FLO-2d) are widely used for flood inundation mapping. These models are tested on a benchmark test with a mixed rectangular-triangular channel cross section. Using a Monte-Carlo approach, we employ extended sensitivity analysis by simultaneously varying the input discharge, longitudinal and lateral gradients and roughness coefficients, as well as the grid cell size. Based on statistical analysis of… Show more

One-dimensional and quasi-two-dimensional hydraulic freeware models (HEC-RAS, LISFLOOD-FP and FLO-2d) are widely used for flood inundation mapping. These models are tested on a benchmark test with a mixed rectangular-triangular channel cross section. Using a Monte-Carlo approach, we employ extended sensitivity analysis by simultaneously varying the input discharge, longitudinal and lateral gradients and roughness coefficients, as well as the grid cell size. Based on statistical analysis of three output variables of interest, i.e. water depths at the inflow and outflow locations and total flood volume, we investigate the uncertainty enclosed in different model configurations and flow conditions, without the influence of errors and other assumptions on topography, channel geometry and boundary conditions. Moreover, we estimate the uncertainty associated to each input variable and we compare it to the overall one. The outcomes of the benchmark analysis are further highlighted by applying the three models to real-world flood propagation problems, in the context of two challenging case studies in Greece. Show less

Within the ongoing research project “Combined Renewable Systems for Sustainable Energy Development” (CRESSENDO), we have developed a novel stochastic simulation framework for optimal planning and management of large-scale hybrid renewable energy systems, in which hydropower plays the dominant role. The methodology and associated computer tools are tested in two major adjacent river basins in Greece (Acheloos, Peneios) extending over 15 500 km2 (12% of Greek territory). River Acheloos is… Show more

Within the ongoing research project “Combined Renewable Systems for Sustainable Energy Development” (CRESSENDO), we have developed a novel stochastic simulation framework for optimal planning and management of large-scale hybrid renewable energy systems, in which hydropower plays the dominant role. The methodology and associated computer tools are tested in two major adjacent river basins in Greece (Acheloos, Peneios) extending over 15 500 km2 (12% of Greek territory). River Acheloos is characterized by very high runoff and holds ~40% of the installed hydropower capacity of Greece. On the other hand, the Thessaly plain drained by Peneios – a key agricultural region for the national economy – usually suffers from water scarcity and systematic environmental degradation. The two basins are interconnected through diversion projects, existing and planned, thus formulating a unique large-scale hydrosystem whose future has been the subject of a great controversy. The study area is viewed as a hypothetically closed, energy-autonomous, system, in order to evaluate the perspectives for sustainable development of its water and energy resources. In this context we seek an efficient configuration of the necessary hydraulic and renewable energy projects through integrated modelling of the water and energy balance. We investigate several scenarios of energy demand for domestic, industrial and agricultural use, assuming that part of the demand is fulfilled via wind and solar energy, while the excess or deficit of energy is regulated through large hydroelectric works that are equipped with pumping storage facilities. The overall goal is to examine under which conditions a fully renewable energy system can be technically and economically viable for such large spatial scale Show less

Evapotranspiration is a key hydrometeorological process and its estimation is important in many fields of hydrological and agricultural sciences. Simplified estimation proves very useful in absence of a complete data set. In this respect, a parametric model based on simplification of the Penman-Monteith formulation is presented. The basic idea of the parametric model is the replacement of some of the variables and constants that are used in the standard Penman-Monteith model by regionally… Show more

Evapotranspiration is a key hydrometeorological process and its estimation is important in many fields of hydrological and agricultural sciences. Simplified estimation proves very useful in absence of a complete data set. In this respect, a parametric model based on simplification of the Penman-Monteith formulation is presented. The basic idea of the parametric model is the replacement of some of the variables and constants that are used in the standard Penman-Monteith model by regionally varying parameters, which are estimated through calibration. The model is implemented in various climates on monthly time step (USA, Germany, Spain) and compared on the same basis with four radiation-based methods (Jensen-Haise, McGuiness and Bordne, Hargreaves and Oudin) and two temperature-based (Thornthwaite and Blaney-Criddle). The methodology yields very good results with high efficiency indexes, outperforming the other models. Finally, a spatial analysis including the correlation of parameters with latitude and elevation together with their regionalization through three common spatial interpolation techniques along with a recent approach (Bilinear Surface Smoothing), is performed. Also, the model is validated against Penman-Monteith estimates in eleven stations of the well-known CIMIS network. The total framework which includes the development, the implementation, the comparison and the mapping of parameters illustrates a new parsimonious and high efficiency methodology in the assessment of potential evapotranspiration field. Show less

Potential evapotranspiration (PET) is key input in water resources, agricultural and environmental modelling. For many decades, numerous approaches have been proposed for the consistent estimation of PET at several time scales of interest. The most recognized is the Penman-Monteith formula, which is yet difficult to apply in data-scarce areas, since it requires simultaneous observations of four meteorological variables (temperature, sunshine duration, humidity, wind velocity). For this reason… Show more

Potential evapotranspiration (PET) is key input in water resources, agricultural and environmental modelling. For many decades, numerous approaches have been proposed for the consistent estimation of PET at several time scales of interest. The most recognized is the Penman-Monteith formula, which is yet difficult to apply in data-scarce areas, since it requires simultaneous observations of four meteorological variables (temperature, sunshine duration, humidity, wind velocity). For this reason, parsimonious models with minimum input data requirements are strongly preferred. Typically, these have been developed and tested for specific hydroclimatic conditions, but when they are applied in different regimes they provide much less reliable (and in some cases misleading) estimates. Therefore, it is essential to develop generic methods that remain parsimonious, in terms of input data and parameterization, yet they also allow for some kind of local adjustment of their parameters, through calibration. In this study we present a recent parametric formula, based on a simplified formulation of the original Penman-Monteith expression, which only requires mean daily or monthly temperature data. The method is evaluated using meteorological records from different areas worldwide, at both the daily and monthly time scales. The outcomes of this extended analysis are very encouraging, as indicated by the substantially high validation scores of the proposed approach across all examined data sets. In general, the parametric model outperforms well-established methods of the everyday practice, since it ensures optimal approximation of PET Show less

Flood engineering is typically tackled as a sequential application of formulas and models, with specific assumptions and parameter values, thus providing fully deterministic outputs. In this procedure, the unique probabilistic concept is the return period of rainfall, which is set a priori, to represent the acceptable risk of all design variables of interest (peak flows, flood hydrographs, flow depths and velocities, inundated areas, etc.). Yet, a more consistent approach would require… Show more

Flood engineering is typically tackled as a sequential application of formulas and models, with specific assumptions and parameter values, thus providing fully deterministic outputs. In this procedure, the unique probabilistic concept is the return period of rainfall, which is set a priori, to represent the acceptable risk of all design variables of interest (peak flows, flood hydrographs, flow depths and velocities, inundated areas, etc.). Yet, a more consistent approach would require estimating the risks by integrating the uncertainties of all individual variables. This option can be offered by stochastic simulation, which is the most effective and powerful technique for analysing systems of high complexity and uncertainty. This presupposes to recognize which of the modelling components represent time-varying processes and which ones represent unknown, thus uncertain, parameters. In the proposed framework both should be handled as random variables. The following computational steps are envisaged: (a) generation of synthetic time series of areal rainfall, through multivariate stochastic disaggregation models; (b) generation of random sets of initial soil moisture conditions; (c) run of hydrological and hydraulic simulation models with random sets of parameter values, picked from suitable distributions; (d) statistical analysis of the model outputs and determination of empirical pdfs; and (e) selection of the design value, which corresponds to the acceptable risk. This approach allows for estimating the full probability distribution of the output variables, instead of a unique value, as resulted by the deterministic procedure. In this context, stochastic simulation also offers the means to introduce the missing culture of uncertainty appreciation in flood engineering. Show less

Floods can simply be defined as the physical phenomena, during which an initially dry land area is covered by water. Floods are normally caused by extreme weather conditions, while their evolution depends mainly on geomorphologic factors, such as soil stability, vegetation cover, as well as the geometrical characteristics of the river basin. To prevent floods’ consequences, we have to study the hydraulic behavior of all the basins. Here, the study is focused on the upstream part of the Rafina… Show more

Floods can simply be defined as the physical phenomena, during which an initially dry land area is covered by water. Floods are normally caused by extreme weather conditions, while their evolution depends mainly on geomorphologic factors, such as soil stability, vegetation cover, as well as the geometrical characteristics of the river basin. To prevent floods’ consequences, we have to study the hydraulic behavior of all the basins. Here, the study is focused on the upstream part of the Rafina basin, located in the east of Athens (Greece). Particularly, a hydraulic simulation is accomplished via the one-dimensional HEC-RAS and the quasi-two-dimensional LISFLOOD-FP and FLO-2D models. Additionally, a sensitivity analysis is carried out to investigate the effects of the floodplain and river roughness coefficients on the flood inundation in conjunction with a modern probabilistic view. Finally, a comparison between the three models is made regarding the simulated maximum water depth and maximum flow velocity. Show less

The lower course of Acheloos River is an important hydrosystem of Greece, heavily modified by a cascade of four hydropower dams, which is now being extended by two more dams in the upper course. The design of the dams and hydropower facilities that are in operation has not considered any environmental criteria. However, in the last fifty years, numerous methodologies have been proposed to assess the negative impacts of such projects to both the abiotic and biotic environment, and to provide… Show more

The lower course of Acheloos River is an important hydrosystem of Greece, heavily modified by a cascade of four hydropower dams, which is now being extended by two more dams in the upper course. The design of the dams and hydropower facilities that are in operation has not considered any environmental criteria. However, in the last fifty years, numerous methodologies have been proposed to assess the negative impacts of such projects to both the abiotic and biotic environment, and to provide decision support towards establishing appropriate constraints on their operation, typically in terms of minimum flow requirements. In this study, seeking for a more environmental-friendly operation of the hydrosystem, we investigate the outflow policy from the most downstream dam, examining alternative environmental flow approaches. Accounting for data limitations, we recommend the Basic Flow Method, which is parsimonious and suitable for Mediterranean rivers, whose flows exhibit strong variability across seasons. We also show that the wetted perimeter – discharge method, which is an elementary hydraulic approach, provides consistent results, even without using any flow data. Finally, we examine the adaptation of the proposed flow policy (including artificial flooding) to the real-time hydropower generation schedule, and the management of the resulting conflicts. Show less

The European Union Floods Directive defines a flood as ‘a covering by water of land not normally covered by water’. Human activities, such as agriculture, urban development, industry and tourism, contribute to an increase in the likelihood and adverse impacts of flood events. The study of the hydraulic behaviour of a river is important in flood risk management. Here, we investigate the behaviour of three hydraulic models, with different theoretical frameworks, in a real case scenario. The area… Show more

The European Union Floods Directive defines a flood as ‘a covering by water of land not normally covered by water’. Human activities, such as agriculture, urban development, industry and tourism, contribute to an increase in the likelihood and adverse impacts of flood events. The study of the hydraulic behaviour of a river is important in flood risk management. Here, we investigate the behaviour of three hydraulic models, with different theoretical frameworks, in a real case scenario. The area is located in the Penios river basin, in the plain of Thessaly (Greece). The three models used are the one-dimensional HEC-RAS and the quasi two-dimensional LISFLOOD-FP and FLO-2D which are compared to each other, in terms of simulated maximum water depth as well as maximum flow velocity, and to a real flood event. Moreover, a sensitivity analysis is performed to determine how each simulation is affected by the river and floodplain roughness coefficient, in terms of flood inundation. Show less

Temperature is strongly linked to the hydrological cycle in numerous ways and mainly with the evapotranspiration. Our aim here is to examine the possible influence of spatial characteristics on the temperature temporal variability of the monthly absolute maxima/minima and the monthly means over Greece. To achieve this, the temperature records of the Hellenic National Meteorological Service station network, which date back to 1950, are analysed. The analysis involved two steps: the determination… Show more

Temperature is strongly linked to the hydrological cycle in numerous ways and mainly with the evapotranspiration. Our aim here is to examine the possible influence of spatial characteristics on the temperature temporal variability of the monthly absolute maxima/minima and the monthly means over Greece. To achieve this, the temperature records of the Hellenic National Meteorological Service station network, which date back to 1950, are analysed. The analysis involved two steps: the determination of regions with similar climatic properties and the investigation of the possible correlations of temperature in time. Thus, the time series are classified in three groups based on their location (continental, coastal and island) and four types regarding the proximity of the station to a city (at the city centre, near the city border, far away from city border) or to an airport. Each one of the time series is then examined for (a) the influence of the city heat island as Greek cities expanded in time, (b) the effect of the general atmospheric circulation (NAO phase), (c) its correlation to the global temperature record and (d) the implied change on evapotranspiration in the area. Show less

Acheloos, the river with the highest discharge among rivers of Greece, hosts three hydroelectric dams, while two more dams are under construction. In addition, there are plans for partial diversion of the river to a nearby water district, for irrigation and hydroelectric development. The Acheloos Delta is considered to be one of the most significant Mediterranean wetland habitats for its ecological importance, including fish fauna. In this case study we aim to redefine the ecological flow and… Show more

Acheloos, the river with the highest discharge among rivers of Greece, hosts three hydroelectric dams, while two more dams are under construction. In addition, there are plans for partial diversion of the river to a nearby water district, for irrigation and hydroelectric development. The Acheloos Delta is considered to be one of the most significant Mediterranean wetland habitats for its ecological importance, including fish fauna. In this case study we aim to redefine the ecological flow and propose an outflow management policy from the most downstream reservoir (Stratos), in order to preserve the ecosystem at the Acheloos Delta. A hydrological analysis is employed to reconstruct the natural discharge records along the river on a daily basis, accompanied by a detailed evaluation of alternative methodologies for the estimation of the ecological flow. Based on the results of the analyses, the corresponding water management policy is determined, taking into account the characteristics of the hydropower plan and the related hydraulic works. Show less

Technological applications aiming at the exploitation of the natural sources appear in all ancient civilizations. The unique phenomenon in the ancient Greek civilization is that technological needs triggered physical explanations of natural phenomena, thus enabling the foundation of philosophy and science. Among these, the study of hydrometeorological phenomena had a major role. This study begins with the Ionian philosophers in the seventh century BC, continues in classical Athens in the fifth… Show more

Technological applications aiming at the exploitation of the natural sources appear in all ancient civilizations. The unique phenomenon in the ancient Greek civilization is that technological needs triggered physical explanations of natural phenomena, thus enabling the foundation of philosophy and science. Among these, the study of hydrometeorological phenomena had a major role. This study begins with the Ionian philosophers in the seventh century BC, continues in classical Athens in the fifth and fourth centuries BC, and advances and expands through the entire Greek world up to the end of Hellenistic period. Many of the theories developed by ancient Greeks are erroneous according to modern views. However, many elements in Greek exegeses of hydrometeorological processes, such as evaporation and condensation of vapour, creation of clouds, hail, snow and rainfall, and evolution of hydrological cycle, are impressive even today. Show less

We develop a parametric expression which approximates the Penman-Monteith equation thus providing easy estimation of the potential evapotranspiration with minimal data requirements. Namely, the method requires as inputs the mean temperature and the extraterrestrial radiation, from which only the temperature needs to be measured. The model was applied on a monthly step in 37 meteorological stations of Greece for the periods 1968-1983 (calibration period) and 1984-1989 (validation period). The… Show more

We develop a parametric expression which approximates the Penman-Monteith equation thus providing easy estimation of the potential evapotranspiration with minimal data requirements. Namely, the method requires as inputs the mean temperature and the extraterrestrial radiation, from which only the temperature needs to be measured. The model was applied on a monthly step in 37 meteorological stations of Greece for the periods 1968-1983 (calibration period) and 1984-1989 (validation period). The results are satisfactory as the efficiency is greater than 0.97 for all stations and for both calibration and validation periods. Initially, the parametric expression involves three parameters but regional analysis indicates that reduction to one or two parameters is possible and does not increase the error substantially. Using optimization and geographic interpolation through a geographical information system, the parameter values were mapped for the entire territory of Greece, which makes the method directly applicable to any site in the country, the only requirement being that mean temperature data be available. Show less

An integrated scheme, comprising a conjunctive hydrological model and a systems oriented management model, was developed, based on a semi-distributed approach. Geographical input data include the river network, the sub-basins upstream of each river node and the aquifer dicretization in the form of groundwater cells of arbitrary geometry. Additional layers of distributed geographical information, such as geology, land cover and terrain slope, are used to define the hydrological response units… Show more

An integrated scheme, comprising a conjunctive hydrological model and a systems oriented management model, was developed, based on a semi-distributed approach. Geographical input data include the river network, the sub-basins upstream of each river node and the aquifer dicretization in the form of groundwater cells of arbitrary geometry. Additional layers of distributed geographical information, such as geology, land cover and terrain slope, are used to define the hydrological response units. Various modules are combined to represent the main processes at the water basin such as, soil moisture, groundwater, flood routing and water management models. Model outputs include river discharges, spring flows, groundwater levels and water abstractions. The model can be implemented in daily and monthly basis. A case study to the West Thessaly region performed. The discharges of five hydrometric stations and the water levels of eight boreholes were used simultaneously for model calibration. The implementation of the model to the certain region demonstrated satisfactory agreement between the observed and the simulated data. Show less

Precision irrigation constitutes a breakthrough for agricultural water management since it provides means to optimal water use. In recent years several applications of precision irrigation are implemented based on spatial data from different origins, i.e. meteorological stations networks, remote sensing data and in situ measurements. One of the factors affecting optimal irrigation system design and management is the daily potential evapotranspiration (PET). A commonly used approach is to… Show more

Precision irrigation constitutes a breakthrough for agricultural water management since it provides means to optimal water use. In recent years several applications of precision irrigation are implemented based on spatial data from different origins, i.e. meteorological stations networks, remote sensing data and in situ measurements. One of the factors affecting optimal irrigation system design and management is the daily potential evapotranspiration (PET). A commonly used approach is to estimate the daily PET for the representative day of each month during the irrigation period. In the present study, the implementation of the recently introduced non-parametric bilinear surface smoothing (BSS) methodology for spatial interpolation of daily PET is presented. The study area was the plain of Arta which is located at the Region of Epirus at the North West Greece. Daily PET was estimated according to the FAO Penman-Monteith methodology with data collected from a network of six agrometeorological stations, installed in early 2015 in selected locations throughout the study area. For exploration purposes, we produced PET maps for the Julian dates: 105, 135, 162, 199, 229 and 259, thus covering the entire irrigation period of 2015. Also, comparison and cross validation against the calculated FAO Penman-Monteith PET for each station, were performed between BSS and a commonly used interpolation method, i.e. inverse distance weighted (IDW). During the leave-one-out cross validation procedure, BSS yielded very good results, outperforming IDW. Given the simplicity of the BSS, its overall performance is satisfactory, providing maps that represent the spatial and temporal variation of daily PET. Show less