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Abstract. The temporal and spatial characteristics of meteorological drought are investigated to provide a framework for sustainable water resources management in the region of Thessaly, Greece. Thessaly is the most intensely cultivated and productive agricultural plain region in Greece. Thessaly's total area is about 13 700 km 2 and it is surrounded by mountains and traversed by Pinios River. Using the Standardized Precipitation Index (SPI) as an indicator of drought severity, the characteristics of droughts are examined. Thessaly was divided into 212 grid-cells of 8×8 km and monthly precipitation data for the period 1960-1993 from 50 meteorological stations were used for global interpolation of precipitation using spatial co-ordinates and elevation data. Drought severity was assessed from the estimated gridded SPI values at multiple time scales. Firstly, the temporal and spatial characteristics of droughts were analyzed and then, Drought Severity -Areal extent -Frequency (SAF) annual and monthly curves were developed. The analysis indicated that moderate and severe droughts are common in Thessaly region. Using the SAF curves, the return period of selected severe drought events was assessed.

Abstract. Information on extreme precipitation for future climate is needed to assess the changes in the frequency and intensity of flooding. The primary source of information in climate change impact studies is climate model projections. However, due to the coarse resolution and biases of these models, they cannot be directly used in hydrological models. Hence, statistical downscaling is necessary to address climate change impacts at the catchment scale. This study compares eight statistical downscaling methods (SDMs) often used in climate change impact studies. Four methods are based on change factors (CFs), three are bias correction (BC) methods, and one is a perfect prognosis method. The eight methods are used to downscale precipitation output from 15 regional climate models (RCMs) from the ENSEMBLES project for 11 catchments in Europe. The overall results point to an increase in extreme precipitation in most catchments in both winter and summer. For individual catchments, the downscaled time series tend to agree on the direction of the change but differ in the magnitude. Differences between the SDMs vary between the catchments and depend on the season analysed. Similarly, general conclusions cannot be drawn regarding the differences between CFs and BC methods. The performance of the BC methods during the control period also depends on the catchment, but in most cases they represent an improvement compared to RCM outputs. Analysis of the variance in the ensemble of RCMs and SDMs indicates that at least 30% and up to approximately half of the total variance is derived from the SDMs. This study illustrates the large variability in the expected changes in extreme precipitation and highlights the need for considering an ensemble of both SDMs and climate models. Recommendations are provided for the selection of the most suitable SDMs to include in the analysis.

A modeling system was developed to evaluate the sustainability of water resources management strategies in the two major basins of Thessaly Region in Greece, namely the Pinios River and the Lake Karla basins. The intense and extensive agriculture of water demanding crops, such as cotton, and the absence of reasonable water resources management have lead to a remarkable water demand increase, which is usually fulfilled by the over-exploitation of groundwater resources. This unsustainable practice has deteriorated the already disturbed water balance and accelerated water resources degradation. The modeling system consists of a hydrological model, a reservoir operation model and methods for the estimation of water demands. The study area was sub-divided into subbasins and water balance analyses were performed for each sub-basin and each control node of the system for a number of water resources management strategies. Four strategies of hydro-technical project development were coupled with two strategies of groundwater withdrawal and three water demand strategies. In total, more than 24 water management strategies were evaluated. The results showed that, under the existing water resources management, the water deficit of the Pinios River and Lake Karla basins is very large. However, the development of proposed hydro-technical projects in the Pinios River basin coupled with water demand management measures, like improvement of existing water distribution systems, change of irrigation methods, and changes of crop cultivation could alleviate the problem and lead to sustainable and ecological use of water resources in the study area.