Combining Geostatistics and Remote Sensing Data to Improve Spatiotemporal Analysis of Precipitation

The wide availability of satellite data from many distributors in different domains of science has provided the opportunity for the development of new and improved methodologies to aid the analysis of environmental problems and to support more reliable estimations and forecasts. Moreover, the rapid development of specialized technologies in satellite instruments provides the opportunity to obtain a wide spectrum of various measurements. The purpose of this research is to use publicly available remote sensing product data computed from geostationary, polar and near-polar satellites and radar to improve space–time modeling and prediction of precipitation on Crete island in Greece. The proposed space–time kriging method carries out the fusion of remote sensing data with data from ground stations that monitor precipitation during the hydrological period 2009/10–2017/18. Precipitation observations are useful for water resources, flood and drought management studies. However, monitoring stations are usually sparse in regions with complex terrain, are clustered in valleys, and often have missing data. Satellite precipitation data are an attractive alternative to observations. The fusion of the datasets in terms of the space–time residual kriging method exploits the auxiliary satellite information and aids in the accurate and reliable estimation of precipitation rates at ungauged locations. In addition, it represents an alternative option for the improved modeling of precipitation variations in space and time. The obtained results were compared with the outcomes of similar works in the study area

Integrated mathematical modelling of surface water - groundwater systems

The scope of the present research study was the numerical simulation and the experimental investigation of flow and pollution interaction between surface water and groundwater. A 3–D Integrated suRface watEr–grouNdwater modEl (IRENE) was developed, which consists of (a) an integrated surface water–groundwater flow model (IRENE–HYD) and (b) an integrated surface water–groundwater quality model (IRENE–QUAL). IRENE–HYD solves the continuity and momentum equations describing constant density 3–D shallow water flows and the equation for 3–D saturated groundwater flow of constant density in heterogeneous anisotropic porous media. The shallow water equations are solved using a semi–implicit finite difference scheme; while the groundwater flow equation is solved using a fully implicit finite difference scheme. The algebraic equations, which result from the discretisation of the partial differential equations describing surface water and groundwater flows, are coupled at the common surface water–groundwater interface through Darcy’s law and are solved simultaneously at each time step with the iterative Bi–CGSTAB method, in such a fashion which gives computational efficiency at low computational cost. In IRENE–QUAL, the partial differential equation describing the fate and transport of contaminants introduced in a 3–D turbulent flow field and the partial differential equation describing the fate and transport of contaminants in 3–D transient groundwater flow systems are solved using various finite difference numerical schemes. The surface water and groundwater quality equations are coupled are coupled at the common interface of the surface water and groundwater bodies through the total contaminant mass flux (advective and dispersive) normal to the surface water–groundwater interface. The coupled surface water and groundwater quality equations are solved simultaneously at each time step using either the iterative conjugate gradient method or the LANCZOS/ORTHOMIN method with Modified Incomplete Cholesky (MIC) preconditioning. The experimental part of the present research work was performed at Cardiff University. The experiments were conducted in two phases. During the first phase, flow and pollution interaction between surface water and groundwater was measured in an experimental setup simulating a rectangular channel flowing through a homogeneous and isotropic aquifer. A novel approach was used for the construction of the aquifer, which involved the use of porous permeable polyurethane foam. The experiments of the second phase were conducted in an experimental setup simulating a hypothetical hydrological basin consisting of a river and a small lake interacting through a sand embankment. In both experimental setups steady and non–steady state flow conditions were simulated. Non–steady state flow conditions were simulated using a weir to create tidal waves at the downstream river boundary. For both steady and non–steady state flow experiments the transport of Rhodamine WT, injected in the porous medium, was monitored in the surface water–groundwater system. Water levels and tracer concentrations were measured in both the river and the porous medium. The experimental data collected were used for the calibration and the verification of IRENE. Finally, IRENE was applied to the area of the hydrological basins of Acheloos river, lake Lisimachia and lake Trichonida.Αντικείμενο της παρούσας εργασίας ήταν η αριθμητική προσομοίωση και η πειραματική διερεύνηση της αλληλεπίδρασης ροής και ρύπανσης μεταξύ επιφανειακών και υπόγειων νερών. Αναπτύχθηκε τρισδιάστατο ολοκληρωμένο αριθμητικό μοντέλο επιφανειακών–υπόγειων νερών (IRENE), το οποίο αποτελείται από (α) ολοκληρωμένο υδροδυναμικό μοντέλο επιφανειακών–υπόγειων νερών (IRENE–HYD) και (β) ολοκληρωμένο μοντέλο ποιότητας επιφανειακών–υπόγειων νερών (IRENE–QUAL). Στο IRENE–HYD επιλύονται οι εξισώσεις συνέχειας και ποσότητας κίνησης για ρηχά νερά σταθερής πυκνότητας για την προσομοίωση της τρισδιάστατης υδροδυναμικής κυκλοφορίας επιφανειακών νερών και η εξίσωση που περιγράφει την τρισδιάστατη μη μόνιμη ροή υπόγειων νερών στην κορεσμένη ζώνη πορώδους μέσου. Οι εξισώσεις ρηχών νερών επιλύονται χρησιμοποιώντας ένα ημί–πεπλεγμένο σχήμα πεπερασμένων διαφορών, ενώ η εξίσωση που περιγράφει τη ροή των υπόγειων νερών επιλύεται εφαρμόζοντας ένα πλήρως πεπλεγμένο σχήμα πεπερασμένων διαφορών. Οι αλγεβρικές εξισώσεις που προκύπτουν από τη διακριτοποίηση των μερικών διαφορικών εξισώσεων που διέπουν τη ροή επιφανειακών και υπόγειων υδάτων συνδυάζονται στην κοινή διεπιφάνεια των επιφανειακών–υπόγειων νερών μέσω του νόμου του Darcy και επιλύονται ταυτόχρονα σε κάθε χρονικό βήμα με την επαναληπτική μέθοδο Bi–CGSTAB. Στο IRENE–QUAL επιλύεται η εξίσωση μεταφοράς–διάχυσης ρύπου σε τρισδιάστατο τυρβώδες πεδίο ροής επιφανειακών νερών και η εξίσωση μεταφοράς–διασποράς ρύπου σε τρισδιάστατο πεδίο ροής υπόγειων νερών χρησιμοποιώντας αριθμητικά σχήματα πεπερασμένων διαφορών. Οι εξισώσεις που περιγράφουν τη συμπεριφορά ρύπων σε επιφανειακά και υπόγεια νερά συνδυάζονται στην κοινή διεπιφάνεια των επιφανειακών–υπόγειων υδάτων υπολογίζοντας τη ροή μάζας ρύπου, εγκάρσια προς την κοινή διεπιφάνεια επιφανειακών–υπόγειων νερών, που οφείλεται στους μηχανισμούς της μεταφοράς και της διασποράς. Οι συνδυασμένες εξισώσεις ποιότητας των επιφανειακών και των υπόγειων νερών επιλύονται ταυτόχρονα σε κάθε χρονικό βήμα με τη μέθοδο συζυγών κλίσεων ή τη μέθοδο LANCZOS/ORTHOMIN. Η πειραματική διερεύνηση της αλληλεπίδρασης επιφανειακών–υπόγειων νερών πραγματοποιήθηκε στο Πανεπιστήμιο του Cardiff. Συγκεκριμένα διερευνήθηκε η αλληλεπίδραση υδατορεύματος–υπόγειου υδροφορέα σε πειραματική διάταξη η οποία περιελάμβανε ευθύγραμμο κανάλι ορθογωνικής διατομής, το οποίο διερχόταν μέσα από ομογενή και ισότροπο υδροφορέα, ο οποίος κατασκευάσθηκε από ειδικό πορώδες υλικό (polyurethane foam). Διερευνήθηκε επίσης η αλληλεπίδραση επιφανειακών–υπόγειων νερών σε πειραματική διάταξη η οποία κατασκευάσθηκε για την προσομοίωση υποθετικής υδρολογικής λεκάνης που περιλαμβάνει υδατόρευμα και μικρή λίμνη, τα οποία επικοινωνούν μέσω αμμώδους φράγματος. Και στις περιπτώσεις δημιουργήθηκαν συνθήκες μόνιμης και μη μόνιμης ροής και μετρήθηκαν (α) η στάθμη του νερού στο κανάλι και στο πορώδες μέσο και (β) οι συγκεντρώσεις συντηρητικού δείκτη, που εισήχθη στο πορώδες μέσο, στο σύστημα των επιφανειακών–υπόγειων νερών. Οι μετρήσεις χρησιμοποιήθηκαν για την επιβεβαίωση του IRENE. Τέλος, το IRENE εφαρμόστηκε στην περιοχή των υδρολογικών λεκανών Αχελώου, Λυσιμαχείας και Τριχωνίδας

Integrated mathematical modelling of surface water-groundwater systema

χ.α.Αντικείμενο της παρούσας εργασίας ήταν η αριθμητική προσομοίωση και η πειραματική διερεύνηση της αλληλεπίδρασης ροής και ρύπανσης μεταξύ επιφανειακών και υπόγειων νερών. Αναπτύχθηκε τρισδιάστατο ολοκληρωμένο αριθμητικό μοντέλο επιφανειακών–υπόγειων νερών (IRENE), το οποίο αποτελείται από (α) ολοκληρωμένο υδροδυναμικό μοντέλο επιφανειακών–υπόγειων νερών (IRENE–HYD) και (β) ολοκληρωμένο μοντέλο ποιότητας επιφανειακών–υπόγειων νερών (IRENE–QUAL). Στο IRENE–HYD επιλύονται οι εξισώσεις συνέχειας και ποσότητας κίνησης για ρηχά νερά σταθερής πυκνότητας για την προσομοίωση της τρισδιάστατης υδροδυναμικής κυκλοφορίας επιφανειακών νερών και η εξίσωση που περιγράφει την τρισδιάστατη μη μόνιμη ροή υπόγειων νερών στην κορεσμένη ζώνη πορώδους μέσου. Οι εξισώσεις ρηχών νερών επιλύονται χρησιμοποιώντας ένα ημί–πεπλεγμένο σχήμα πεπερασμένων διαφορών, ενώ η εξίσωση που περιγράφει τη ροή των υπόγειων νερών επιλύεται εφαρμόζοντας ένα πλήρως πεπλεγμένο σχήμα πεπερασμένων διαφορών. Οι αλγεβρικές εξισώσεις που προκύπτουν από τη διακριτοποίηση των μερικών διαφορικών εξισώσεων που διέπουν τη ροή επιφανειακών και υπόγειων υδάτων συνδυάζονται στην κοινή διεπιφάνεια των επιφανειακών–υπόγειων νερών μέσω του νόμου του Darcy και επιλύονται ταυτόχρονα σε κάθε χρονικό βήμα με την επαναληπτική μέθοδο Bi–CGSTAB. Στο IRENE–QUAL επιλύεται η εξίσωση μεταφοράς–διάχυσης ρύπου σε τρισδιάστατο τυρβώδες πεδίο ροής επιφανειακών νερών και η εξίσωση μεταφοράς–διασποράς ρύπου σε τρισδιάστατο πεδίο ροής υπόγειων νερών χρησιμοποιώντας αριθμητικά σχήματα πεπερασμένων διαφορών. Οι εξισώσεις που περιγράφουν τη συμπεριφορά ρύπων σε επιφανειακά και υπόγεια νερά συνδυάζονται στην κοινή διεπιφάνεια των επιφανειακών–υπόγειων υδάτων υπολογίζοντας τη ροή μάζας ρύπου, εγκάρσια προς την κοινή διεπιφάνεια επιφανειακών–υπόγειων νερών, που οφείλεται στους μηχανισμούς της μεταφοράς και της διασποράς. Οι συνδυασμένες εξισώσεις ποιότητας των επιφανειακών και των υπόγειων νερών επιλύονται ταυτόχρονα σε κάθε χρονικό βήμα με τη μέθοδο συζυγών κλίσεων ή τη μέθοδο LANCZOS/ORTHOMIN. Η πειραματική διερεύνηση της αλληλεπίδρασης επιφανειακών–υπόγειων νερών πραγματοποιήθηκε στο Πανεπιστήμιο του Cardiff. Συγκεκριμένα διερευνήθηκε η αλληλεπίδραση υδατορεύματος–υπόγειου υδροφορέα σε πειραματική διάταξη η οποία περιελάμβανε ευθύγραμμο κανάλι ορθογωνικής διατομής, το οποίο διερχόταν μέσα από ομογενή και ισότροπο υδροφορέα, ο οποίος κατασκευάσθηκε από ειδικό πορώδες υλικό (polyurethane foam). Διερευνήθηκε επίσης η αλληλεπίδραση επιφανειακών–υπόγειων νερών σε πειραματική διάταξη η οποία κατασκευάσθηκε για την προσομοίωση υποθετικής υδρολογικής λεκάνης που περιλαμβάνει υδατόρευμα και μικρή λίμνη, τα οποία επικοινωνούν μέσω αμμώδους φράγματος. Και στις περιπτώσεις δημιουργήθηκαν συνθήκες μόνιμης και μη μόνιμης ροής και μετρήθηκαν (α) η στάθμη του νερού στο κανάλι και στο πορώδες μέσο και (β) οι συγκεντρώσεις συντηρητικού δείκτη, που εισήχθη στο πορώδες μέσο, στο σύστημα των επιφανειακών–υπόγειων νερών. Οι μετρήσεις χρησιμοποιήθηκαν για την επιβεβαίωση του IRENE. Τέλος, το IRENE εφαρμόστηκε στην περιοχή των υδρολογικών λεκανών Αχελώου, Λυσιμαχείας και Τριχωνίδας.The scope of the present research study was the numerical simulation and the experimental investigation of flow and pollution interaction between surface water and groundwater. A 3–D Integrated suRface watEr–grouNdwater modEl (IRENE) was developed, which consists of (a) an integrated surface water–groundwater flow model (IRENE–HYD) and (b) an integrated surface water–groundwater quality model (IRENE–QUAL). IRENE–HYD solves the continuity and momentum equations describing constant density 3–D shallow water flows and the equation for 3–D saturated groundwater flow of constant density in heterogeneous anisotropic porous media. The shallow water equations are solved using a semi–implicit finite difference scheme; while the groundwater flow equation is solved using a fully implicit finite difference scheme. The algebraic equations, which result from the discretisation of the partial differential equations describing surface water and groundwater flows, are coupled at the common surface water–groundwater interface through Darcy’s law and are solved simultaneously at each time step with the iterative Bi–CGSTAB method, in such a fashion which gives computational efficiency at low computational cost. In IRENE–QUAL, the partial differential equation describing the fate and transport of contaminants introduced in a 3–D turbulent flow field and the partial differential equation describing the fate and transport of contaminants in 3–D transient groundwater flow systems are solved using various finite difference numerical schemes. The surface water and groundwater quality equations are coupled are coupled at the common interface of the surface water and groundwater bodies through the total contaminant mass flux (advective and dispersive) normal to the surface water–groundwater interface. The coupled surface water and groundwater quality equations are solved simultaneously at each time step using either the iterative conjugate gradient method or the LANCZOS/ORTHOMIN method with Modified Incomplete Cholesky (MIC) preconditioning. The experimental part of the present research work was performed at Cardiff University. The experiments were conducted in two phases. During the first phase, flow and pollution interaction between surface water and groundwater was measured in an experimental setup simulating a rectangular channel flowing through a homogeneous and isotropic aquifer. A novel approach was used for the construction of the aquifer, which involved the use of porous permeable polyurethane foam. The experiments of the second phase were conducted in an experimental setup simulating a hypothetical hydrological basin consisting of a river and a small lake interacting through a sand embankment. In both experimental setups steady and non–steady state flow conditions were simulated. Non–steady state flow conditions were simulated using a weir to create tidal waves at the downstream river boundary. For both steady and non–steady state flow experiments the transport of Rhodamine WT, injected in the porous medium, was monitored in the surface water–groundwater system. Water levels and tracer concentrations were measured in both the river and the porous medium. The experimental data collected were used for the calibration and the verification of IRENE. Finally, IRENE was applied to the area of the hydrological basins of Acheloos river, lake Lisimachia and lake Trichonida.Αικατερίνη Ε. Σπανουδάκ

Oil Spill Modeling: A Critical Review on Current Trends, Perspectives, and Challenges

Several oil spill simulation models exist in the literature, which are used worldwide to simulate the evolution of an oil slick created from marine traffic, petroleum production, or other sources. These models may range from simple parametric calculations to advanced, new-generation, operational, three-dimensional numerical models, coupled to meteorological, hydrodynamic, and wave models, forecasting in high-resolution and with high precision the transport and fate of oil. This study presents a review of the transport and oil weathering processes and their parameterization and critically examines eighteen state-of-the-art oil spill models in terms of their capacity (a) to simulate these processes, (b) to consider oil released from surface or submerged sources, (c) to assimilate real-time field data for model initiation and forcing, and (d) to assess uncertainty in the produced predictions. Based on our review, the most common oil weathering processes involved are spreading, advection, diffusion, evaporation, emulsification, and dispersion. The majority of existing oil spill models do not consider significant physical processes, such as oil dissolution, photo-oxidation, biodegradation, and vertical mixing. Moreover, timely response to oil spills is lacking in the new generation of oil spill models. Further improvements in oil spill modeling should emphasize more comprehensive parametrization of oil dissolution, biodegradation, entrainment, and prediction of oil particles size distribution following wave action and well blow outs

Estimation of Hydropower Potential Using Bayesian and Stochastic Approaches for Streamflow Simulation and Accounting for the Intermediate Storage Retention

Hydropower is the most widely used renewable power source worldwide. The current work presents a methodological tool to determine the hydropower potential of a reservoir based on available hydrological information. A Bayesian analysis of the river flow process and of the reservoir water volume is applied, and the estimated probability density function parameters are integrated for a stochastic analysis and long-term simulation of the river flow process, which is then used as input for the water balance in the reservoir, and thus, for the estimation of the hydropower energy potential. The stochastic approach is employed in terms of the Monte Carlo ensemble technique in order to additionally account for the effect of the intermediate storage retention due to the thresholds of the reservoir. A synthetic river flow timeseries is simulated by preserving the marginal probability distribution function properties of the observed timeseries and also by explicitly preserving the second-order dependence structure of the river flow in the scale domain. The synthetic ensemble is used for the simulation of the reservoir water balance, and the estimation of the hydropower potential is used for covering residential energy needs. For the second-order dependence structure of the river flow, the climacogram metric is used. The proposed methodology has been implemented to assess different reservoir volume scenarios offering the associated hydropower potential for a case study at the island of Crete in Greece. The tool also provides information on the probability of occurrence of the specific volumes based on available hydrological data. Therefore, it constitutes a useful and integrated framework for evaluating the hydropower potential of any given reservoir. The effects of the intermediate storage retention of the reservoir, the marginal and dependence structures of the parent distribution of inflow and the final energy output are also discussed

Estimation of Hydropower Potential Using Bayesian and Stochastic Approaches for Streamflow Simulation and Accounting for the Intermediate Storage Retention

Hydropower is the most widely used renewable power source worldwide. The current work presents a methodological tool to determine the hydropower potential of a reservoir based on available hydrological information. A Bayesian analysis of the river flow process and of the reservoir water volume is applied, and the estimated probability density function parameters are integrated for a stochastic analysis and long-term simulation of the river flow process, which is then used as input for the water balance in the reservoir, and thus, for the estimation of the hydropower energy potential. The stochastic approach is employed in terms of the Monte Carlo ensemble technique in order to additionally account for the effect of the intermediate storage retention due to the thresholds of the reservoir. A synthetic river flow timeseries is simulated by preserving the marginal probability distribution function properties of the observed timeseries and also by explicitly preserving the second-order dependence structure of the river flow in the scale domain. The synthetic ensemble is used for the simulation of the reservoir water balance, and the estimation of the hydropower potential is used for covering residential energy needs. For the second-order dependence structure of the river flow, the climacogram metric is used. The proposed methodology has been implemented to assess different reservoir volume scenarios offering the associated hydropower potential for a case study at the island of Crete in Greece. The tool also provides information on the probability of occurrence of the specific volumes based on available hydrological data. Therefore, it constitutes a useful and integrated framework for evaluating the hydropower potential of any given reservoir. The effects of the intermediate storage retention of the reservoir, the marginal and dependence structures of the parent distribution of inflow and the final energy output are also discussed

Predicting Meteorological Variables on Local Level with SARIMA, LSTM and Hybrid Techniques

The choice of holiday destinations is highly depended on climate considerations. Nowadays, since the effects of the climate crisis are being increasingly felt, the need for accurate weather and climate services for hotels is crucial. Such a service could be beneficial for both the future planning of tourists’ activities and destinations and for hotel managers as it could help in decision making about the planning and expansion of the touristic season, due to a prediction of higher temperatures for a longer time span, thus causing increased revenue for companies in the local touristic sector. The aim of this work is to calculate predictions on meteorological variables using statistical techniques as well as artificial intelligence (AI) for a specific area of interest utilising data from an in situ meteorological station, and to produce valuable and reliable localised predictions with the most cost-effective method possible. This investigation will answer the question of the most suitable prediction method for time series data from a single meteorological station that is deployed in a specific location; in our case, in a hotel in the northern area of Crete, Greece. The temporal resolution of the measurements used was 3 h and the forecast horizon considered here was up to 2 days. As prediction techniques, seasonal autoregressive integrated moving average (SARIMA), AI techniques like the long short-term memory (LSTM) neural network and hybrid combinations of the two are used. Multiple meteorological variables are considered as input for the LSTM and hybrid methodologies, like temperature, relative humidity, atmospheric pressure and wind speed, unlike the SARIMA that has a single variable. Variables of interest are divided into those that present seasonality and patterns, such as temperature and humidity, and those that are more stochastic with no known seasonality and patterns, such as wind speed and direction. Two benchmark techniques are used for comparison and quantification of the added predictive ability, namely the climatological forecast and the persistence model, which shows a considerable amount of improvement over the naive prediction methods, especially in the 1-day forecasts. The results indicate that the examined hybrid methodology performs best at temperature and wind speed forecasts, closely followed by the SARIMA, whereas LSTM performs better overall at the humidity forecast, even after the correction of the hybrid to the SARIMA model. Lastly, different hybrid methodologies are discussed and introduced for further improvement of meteorological predictions

Sustainability of mining activities in the European Mediterranean region in terms of a spatial groundwater stress index

Mining activities depend significantly on water resources availability as it consists a major tool of the extraction, processing and the post closure mining operations. Especially, groundwater is the major water source in most mining areas. However, overexploitation, competition from the communities and climate change effects have caused significant stress on the groundwater resources in many areas of the Mediterranean basin. The sustainability of mining operations is threatened as well as the uninterrupted supply of raw materials to the industry. In this work spatial estimation and analysis of groundwater stress at hydrological basin-scale in the European part of the Mediterranean region is applied using local and global datasets. Aquifer productivity index and groundwater use information at monitoring sites are extracted from the River Basin Management Plans of the European Environment Agency, while groundwater recharge is considered from the World-wide Hydrogeological Mapping and Assessment Program (WHYMAP) after validation. The processing of these data using the Self Organized Maps technique and their integration within a novel function, provide the groundwater stress index. The output of this work can be used for governance and management decisions that will improve groundwater resources availability in vulnerable areas ensuring the sustainable use from the communities and the industry.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Water ResourcesHydraulic Structures and Flood Ris