George Tsakiris

On regional drought estimation and analysis

The main objective of this paper is to review the existing methodologies for the estimation and analysis of regional drought. As a first step, point drought methods are presented. Further emphasis is given to the definition and estimation of regional drought characteristics. Stochastic processes for simulating the time-space variability of drought, are presented. Finally, illustrative examples are shown and recommendations for further research are given.

Drought and climatic change impact on streamflow in small watersheds

The paper presents a comprehensive, thought simple, methodology, for forecasting the annual hydrological drought, based on meteorological drought indications available early during the hydrological year. The meteorological drought of 3, 6 and 9 months is estimated using the reconnaissance drought index (RDI), whereas the annual hydrological drought is represented by the streamflow drought index (SDI). Regression equations are derived between RDI and SDI, forecasting the level of hydrological drought for the entire year in real time. Further, using a wide range of scenarios representing possible climatic changes and drought events of varying severity, nomographs are devised for estimating the annual streamflow change. The Medbasin rainfall-runoff model is used to link meteorological data to streamflow. The later approach can be useful for developing preparedness plans to combat the consequences of drought and climate change. As a case study, the area of N. Peloponnese (Greece) was selected, incorporating several small river basins.

DrinC: a software for drought analysis based on drought indices

Drought is a complex phenomenon which can be characterised mainly by its severity, duration and areal extent. Among these three dimensions, drought severity is the key factor which can be used for drought analysis. Drought indices are typically used to assess drought severity in a meaningful way. DrinC (Drought Indices Calculator) is a software package which was developed for providing a simple, though adaptable interface for the calculation of drought indices. The paper aims at presenting the overall design and the implementation of the software along with the utilisation of various approaches for drought analysis. DrinC can be used for the calculation of two recently developed indices, the Reconnaissance Drought Index (RDI) and the Streamflow Drought Index (SDI), as well as two widely known indices, the Standardised Precipitation Index (SPI) and the Precipitation Deciles (PD). Moreover, the software includes a module for the estimation of potential evapotranspiration (PET) through temperature based methods, useful for the calculation of RDI. The software may be used in a variety of applications, such as drought monitoring, assessment of the spatial distribution of drought, investigation of climatic and drought scenarios, etc. The applications of DrinC in several locations, especially in arid and semi-arid regions, show that it is gaining ground as a useful research and operational tool for drought analysis.

Comparing Various Methods of Building Representation for 2D Flood Modelling In Built-Up Areas

Floods in built-up areas are among the most catastrophic natural hazards mainly due to the high value properties existing in these areas. The most vulnerable areas are the riverine areas with mild terrain which are often encountered in the coastal zone. Due to the mild terrain and the complicated topography caused by buildings, roads and infrastructure, a two-dimensional modelling is required for a realistic simulation of the flood evolvement. In this paper the flood simulation is performed by a recently devised fully dynamic numerical model, the FLOW-R2D, which is based on the two-dimensional Shallow Water Equations solved by the Finite Difference Method and the McCormack numerical scheme. The performance of the model is tested for three alternative representations of the resistance caused by buildings, namely, the reflection boundary, the local elevation rise, and the local increase of the Manning roughness coefficient. The model was run for three different hydrographs and produced time series of water depths and flow velocities in the entire computational domain of the inundated area for each hydrograph. The results of the model for the three alternative building representations and different building alignments were compared with the experimental data available from experiments reported in recent papers. Based on the comparison between numerical and experimental results it was concluded that the reflection boundary method proved to be the most successful building representation for the application of FLOW-R2D. Finally, the data requirements and the required density of the digital terrain model were discussed in relation to the building representation methods.

The Status of the European Waters in 2015: a Review

The paper aims at presenting the recent European developments in water resources management with particular focus on the EU policies related to floods, droughts and ecosystems and their implementation. In this context, the Water Framework Directive (WFD), the Flood Directive and the Communication on Water Scarcity and Droughts are critically presented and analysed. Also, the main methodologies endorsed by the member states for the implementation of EU directives, such as the DPSIR (Driver-Pressure-State-Impact-Response), the risk assessment and the CEA (Cost-Effectiveness Analysis) are briefly discussed. Further, the first account of the implementation of the EU directives by the member states is presented, together with the statistics that resulted from the first River Basin Management Plans of WFD and the first results from the Flood Directive. It is concluded that despite the significant progress achieved up to now on the fulfilment of the environmental objectives, there is still a long way to go particularly for the new member states of the EU. Enhanced integration of all related policies and better coordination is still required for improving the effectiveness of the Programmes of Measures (PoMs) in the River Basin Districts of the EU territory. Finally, future amendments in European policies on water resources are discussed which will lead to revised environmental objectives for the second and third stage applications of the water directives by the EU member states.

A Numerical Model for Two-Dimensional Flood Routing in Complex Terrains

In this paper, a new powerful numerical hydrodynamic in-house model is presented and tested. The model simulates flood routing in two dimensions. It is based on the solution of Shallow Water Equations using the Finite Difference Method according to the explicit McCormack numerical scheme which has shock capturing capability. The innovation of the proposed model lies in the modification of McCormack scheme by incorporating artificial viscosity through a diffusion factor in order to avoid oscillations as proposed by various researchers. Additionally, a threshold of water depth is introduced in order to distinguish the wet and dry cells of the computational domain. The model is capable of producing maps for the inundation extent, water depths and depth-averaged water velocities. Finally, the paper presents extensive testing of the model by comparison with analytical solution, experimental results and with the output of another software package in real world flood simulation studies.

Suitability of Water Quality Indices for Application in Lakes in the Mediterranean

Water quality indices (WQIs) are efficient and powerful tools for evaluating, organising and communicating information on the overall quality of surface water bodies. The use of these indices may be very helpful in evaluating the water quality of aquatic systems in relation to the EU Water Framework Directive (WFD). In this study, two well-known water quality indices have been selected for evaluation: the CCME (Canadian Council of Ministers of the Environment) and NSF (National Sanitation Foundation). These WQIs were applied in the Polyphytos reservoir-Aliakmon river in Greece where monthly water quality data were available for the period June 2004 to May 2005. The available dataset included values of the following parameters: water depth, water temperature, dissolved oxygen, electrical conductivity, pH, transparency (Secchi disk depth), BOD5, COD, total phosphorus (TP), chlorophyll-a (Chl-a), ammonium (NH4+), nitrite (NO2−) and nitrate (NO3−), and total Κjeldahl nitrogen (TKN). The application of the two WQIs was made using specialised, freely available software-tools. A comparison of their performance and a qualitative judgement on their suitability on expressing the quality of a surface water body is presented. The classification results were compared with those obtained by the WFD-ECOFRAME approach of the EU. Based on the applicability and drawbacks of the examined indices, useful conclusions were derived and discussed. Among others, it is concluded that the NSF-WQI is a more robust index and produces a classification nearer that of the WFD-ECOFRAME approach when compared to the CCME-WQI.

Eliminating the effect of temperature from unsaturated soil hydraulic functions

The effect of temperature in soil-water transfer studies is usually neglected. However, experimental research has shown that there is a strong temperature effect on the characteristic soil hydraulic functions, such as the matric potential versus water content relationship, h(θ), and the hydraulic conductivity versus water content relationship, K(θ). The objective of this study was to examine whether this effect can be isolated and explained. For this purpose, experimental h(θ) and K(θ) values from two different sandy soils at temperatures of 20, 8 and 3°C, were directly compared with predictions obtained by both the surface-tension viscous-flow model of soil moisture movement (STVF) and the empirical Gain factor model extended to include the K(θ) relationship. Results showed that the predictive efficiency of the STVF method depends upon the soil type. For fine-textured material the Gain factor model seemed to perform satisfactorily. Finally, it was shown that unique normalized functions of both characteristic soil hydraulic properties, independent of temperature, can always be obtained.

Analysing Drought Severity and Areal Extent by 2D Archimedean Copulas

Droughts can be considered as multidimensional hazardous phenomena characterised by three attributes: severity, duration and areal extent. Conventionally, drought events are assessed for their severity, using drought indices such as SPI (Standardised Precipitation Index), RDI (Reconnaissance Drought Index), PDSI (Palmer Drought Severity Index) and many others. This approach may be extended to incorporate the modelling of an additional dimension, the duration or the areal extent. Since the marginal distributions describing these dimensions of drought are often different, no simple mixed probability distribution can be used for the bivariate frequency analysis. The copula approach seems to be sufficiently general and suitable for this type of analysis. It is the aim of this paper to analyse droughts as two-dimensional phenomena, including drought severity and areal extent. In this paper, the Gumbel-Hougaard copula from the Archimedean family is used for this two-dimensional frequency analysis. Annual data on historical droughts from Eastern Crete are analysed for their severity and areal extent, producing copula-based probability distributions, incorporating Gumbel marginal probability functions. Useful conclusions are derived for estimating the «OR» return period of drought events related to both severity and areal extent.

Comparative Study of Evolutionary Algorithms for the Automatic Calibration of the Medbasin-D Conceptual Hydrological Model

The calibration of a hydrological model is an important task for obtaining accurate runoff simulation results for a specific watershed. Several optimisation algorithms have been applied during the last years for the automatic calibration of conceptual rainfall-runoff (CRR) models. The aim of this study is to compare the effectiveness and the efficiency of three evolutionary algorithms, namely the Shuffled Complex Evolution (SCE), the Genetic Algorithms (GA) and the Evolutionary Annealing-Simplex (EAS), for the calibration of the Medbasin-D daily CRR model. An improved calibration approach of Medbasin-D is presented, including a batch-processing module which enables the implementation of coupled simulation-optimisation routines. The enhanced Medbasin calibration module is employed in a watershed of the island of Crete (Greece), using several objective functions in order to test the optimisation algorithms under different hydrological flow conditions. The results reveal that, in terms of effectiveness, SCE and EAS performed equally well, while GA provided slightly worse optimal solutions. However, GA was computationally more efficient than SCE and EAS. Despite the discrepancies among the optimisation runs, the simulated hydrographs had a very similar response for the optimal parameter sets obtained by the same calibration criteria, indicating that all tested optimisation methods produce equally successful results with Medbasin-D model. Additionally, the selected objective function seems to have a more decisive effect on the final simulation outcomes.