G. Tsakiris

A System-based Paradigm of Drought Analysis for Operational Management

Conventionally droughts are studied in terms of their dimensions (severity, duration and areal extent), without specifying the affected system. The paper presents an innovative system-based approach for drought analysis, which can lead to rational decisions for combating drought. Concepts of water scarcity (drought, water shortage, aridity and desertification) are viewed within the perspective of this new approach. The paper focuses also on operational water management in the presence of drought. Starting from the needs for such management, the affected system is defined and the related quantities are identified. Also, sub-systems are considered which allow the establishment of the link between specific variables and drought. Some drought characterisation methods are particularly suited for the systemic approach. Finally drought is considered as a natural hazard phenomenon and its consequences are discussed. Each physical sub-system can be improved by a variety of measures aiming at decreasing its vulnerability towards drought, so that the drought risk is mitigated. It is concluded that the clear definition of the affected system on the spatial and temporal scales can significantly contribute to the rational management for combating drought.

Meteorological Drought Effect on Sediment Yield

This study introduces a continuous simulation model dealing with the reconnaissance estimation of sediment yield from a hydrological basin. Based on this model, historical precipitation data of the Mornos River Basin in western Greece, were analyzed. The analysis allowed to establish a relationship between meteorological drought and sediment yield through a dimensionless erosion index. It was indicated that, for the historical precipitation series considered, sediment yield estimations were higher during the wet period following a period of drought.

Experimental Validation of a Linearized Kinematic Wave Equation for Micro-Catchment Water Harvesting Design

A series of laboratory experiments was carried out on a sandy loam soil, for testing the predictive ability of a linearized analytical solution of the kinematic wave equation used for runoff estimation in micro-catchment water harvesting design. The experimental set-up comprised an inclined flume containing the soil sample and a rainfall simulator. The flume represented the Contributing Area (CA) of a micro-catchment. By applying various rainfall intensities, the runoff from the flume was recorded for a variety of conditions, including the initial soil water content and the slope of the flume. Comparison between experimental and predicted runoff hydrographs showed satisfactory agreement.

Micro-catchment water harvesting in semi-arid regions: Basic design considerations

In many parts of southern Europe (e.g. in most Mediterranean islands), water is not adequate for intensive irrigation development. In some other cases, due to various technico-economic reasons, water cannot be transferred over long distances. As a result, large areas remain without irrigation water and therefore they are solely dependent on rainfall. Rainwater harvesting, defined as the collection and storage of surface runoff water produced by rainfall for irrigation use, encompasses various practices, some of them having been known for many thousands of years. The great number of papers published on rainwater harvesting over the last two decades shows a renewed interest in this old technique and also its great potential under the recent socio-technico-economic conditions of many developing areas of the world. Although increasing interest is currently focussed on rainwater harvesting methods for arid climates, very little attention has been paid to semi-arid climates such as the Mediterranean climate. It is the objective of this note to discuss some of the aspects of design parameters of rainwater harvesting systems. Particular attention is focusses on the aspects of such hydrological design parameters as the expected soil moisture in the root zone at the beginning of the dry season under natural and rainwater harvesting conditions. Comparisons between these cases show a substantial improvement of the soil moisture regime under the rainwater harvesting technique and result in useful conclusions directly related to the design of rainwater harvesting systems.

Drought Risk in Agriculture in Mediterranean Regions. Case Study: Eastern Crete

The objective of this paper is to present a methodology for the quantification of drought risk in agriculture in Mediterranean regions. The methodology consists of three interrelated components: the estimation of the severity and frequency of droughts, the simulation of water use and crop yield production and the assessment of annualized risk in agriculture. Both rainfed and irrigated agriculture are considered through the concept of vulnerability. The methodology is demonstrated by a case study in Eastern Crete

Drought Severity Thresholds and Drought Management in Greece

The objective of this chapter is the analysis of the three major components of drought assessment and management in Greece. First, the legal framework and the structure of services related to the water management are presented. Second, drought characterisation is applied for two river basins, Nestos and Mornos, and thresholds for drought management are defined. A new meteorological drought index, the Reconnaissance Drought Index (RDI), similar to the well-known Standardised Precipitation Index (SPI), is introduced. Finally, the operational component for drought management is analysed. This component consists of the formulation of a preparedness master plan and the adoption of proactive and reactive actions.

Stochastic modelling of point rainfall in a Mediterranean island environment

A stochastic simulation model of daily rainfall in discrete time is proposed. The model simulates the sequence of rainfall occurrences using the method of transition probability matrices. Synthetic daily rainfall depths are then generated using sampling methods plus a two step power transformation scheme (TSPT). Rainfall data from four meteorological stations from the islands Rhodes and Chios (Aegean Sea) were used for model validation. The proposed model was also compared to a widely used TPG model. Results showed that the proposed model performed more satisfactorilly than the TPG model preserving the statistical characteristics and the total number of rainfall occurrences of the historical samples.