Dimitris Tigkas

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.

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.

An Enhanced Effective Reconnaissance Drought Index for the Characterisation of Agricultural Drought

The drought phenomenon is directly associated to the agricultural production and it is considered as one of the major water-related hazards in this sector. Conventionally, the magnitude of drought impacts on crops, taking into account the susceptibility of the plants to the meteorological and hydrological conditions, is referred to as agricultural drought. The accurate and timely assessment of agricultural drought can provide the means for taking the appropriate proactive and relief measures for the protection of the farmers’ income and supporting food security. The Reconnaissance Drought Index (RDI), incorporating the key parameters of precipitation and potential evapotranspiration, has been widely and successfully used worldwide for drought characterisation during the last decade. In this paper, a modification of this index is proposed, namely the Effective Reconnaissance Drought Index (eRDI), aiming at improving the ability to assess agricultural drought. The main aspect of this modification consists in the substitution of the total precipitation with the effective precipitation, which represents more precisely the amount of water that is productively used by the crops. Further, the estimation methods of effective precipitation and the modification of other aspects of RDI, such as the selection of the appropriate reference period, are analysed and discussed.

Impacts of Multi-year Droughts and Upstream Human-Induced Activities on the Development of a Semi-arid Transboundary Basin

This paper aims at investigating the combined impacts of basin-wide multi-year droughts and upstream human-induced activities on current and future potential development of a semi-arid transboundary basin. The approach is based on the drought analysis through three widely used drought indices (Standardised Drought Index- SPI, Reconnaissance Drought Index - RDI and Streamflow Drought Index- SDI), coupled with the current and future conceivable man-made changes upstream, taking also into account the effects of climate change. As a representative case, the Diyala river basin, shared between Iraq and Iran, is selected. A close examination of the climate trends in the study area exhibits that the basin points to be drier, with a decreasein precipitation and rise in the rates of temperature and potential evapotranspiration. The comparison between RDI and SDI indicates the cumulative drought effects on runoff during recent multi-year droughts episodes (1999–2001 and 2008–2009), which crippled the socio-economic activities and influenced the environmental system. Further, the results reveal that the combined impacts of multi-year droughts at basin scale and the river damming, water abstraction and water diversion works upstream have significant effects on water availability, especially at the middle and lower parts of the basin, with impacts on the security of the irrigated agriculture and public water supply, contributing to displacement and tribal conflicts. The projected climate change conditions along with the water withdrawal schemes upstream, which will put into operation in the foreseeable future, are expected to increase the vulnerability of water security in the portion of the basin that lies in the downstream country.

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.

Drought characterisation based on an agriculture-oriented standardised precipitation index

Drought is a major natural hazard with significant effects in the agricultural sector, especially in arid and semi-arid regions. The accurate and timely characterisation of agricultural drought is crucial for devising contingency plans, including the necessary mitigation measures. Many drought indices have been developed during the last decades for drought characterisation and analysis. One of the most widely used indices worldwide is the Standardised Precipitation Index (SPI). Although other comprehensive indices have been introduced over the years, SPI remains the most broadly accepted index due to a number of reasons, the most important of which are its simple structure and the fact that it uses only precipitation data. In this paper, a modified version of SPI is proposed, namely the Agricultural Standardised Precipitation Index (aSPI), based on the substitution of the total precipitation by the effective precipitation, which describes more accurately the amount of water that can be used productively by the plants. Further, the selection of the most suitable reference periods and time steps for agricultural drought identification using aSPI is discussed. This conceptual enhancement of SPI aims at improving the suitability of the index for agricultural drought characterisation, while retaining the advantages of the original index, including its dependence only on precipitation data. The evaluation of the performance of both SPI and aSPI in terms of correlating drought magnitude with crop yield response in four regions of Greece under Mediterranean conditions indicated that aSPI is more robust than the original index in identifying agricultural drought.