Hydrology

	Hydrology and Earth System Sciences
	Basic ground water hydrology
	Dams and Development Project Vision: The development and management of water and energy resources address the full range of options and are attained through institutionalised participatory and transparent decision-making processes to achieve sustainable outcomes that benefit all. Mission: Promote improved decision-making, planning and management of dams and their alternatives building on the World Commission on Dams core values and strategic priorities and other relevant reference materials through promoting multistakeholder dialogue at national, regional and global levels and producing non-prescriptive tools to help decision-makers.
	Dryland hydrology in Mediterranean regions—a review Dryland areas display high hydrological sensitivity to changes in their environment. This high sensitivity makes the survey of their water resources and hazards particularly crucial, not only in scientific terms, but also as a strategic aspect of technical and socio-political management. Being mainly semi-arid and arid, the Mediterranean basin and the Middle-East have major water needs (UNPD, 2006; Alcamo et al., 2007; Iglesias et al., 2007). During recent decades, the large increase in population, rise of living standards, development of irrigated agriculture, and new activities—especially tourism—have drastically changed the water uses. Future needs will be hard to satisfy as many aquifers are already overexploited and surface waters are endangered (Tal, 2006; Kundzewicz et al., 2007; Murad et al., 2007; Qadir et al., 2007). According to the Plan Bleu (Margat & Treyer, 2004), 60% of the world’s water-poorest population (i.e. with less than 1000 m3 per capita per year) live in the southern and eastern parts of the Mediterranean basin. Therefore, improving the identification of the main hydrological processes, and their variability and changes, is essential for better management of the water resources, and for the day-to-day life of millions of people. In recent decades, this increasing stress on the water balance has required management of local irregular resources to develop from the traditional, parsimonious management towards more intensive water resources exploitation. In many cases, the balance between water resources and needs is not achieved and numerous negative effects have emerged. Moreover, the regional climate change (Christensen et al., 2007) may have major hydrological impacts, which need to be assessed and to which water management should be adapted (Kundzewicz et al., 2007). In the framework of the international conference “Future of Drylands” organized by UNESCO and the Tunisian authorities in June 2006, in Tunis, during the International Year of Deserts & Desertification (IYDD), the G-WADI network (http://gwadi.org) of the International Hydrological Programme (IHP) initiated a side event dedicated to these issues and with a focus on the Mediterranean region. Following this event, several papers were considered for publication in Hydrological Sciences Journal and, following peer review, seven are published in this Special Section (Hreiche et al., 2007; Leduc et al., 2007; Martín-Rosales et al., 2007; McIntyre et al., 2007; Nasri, 2007; Romagny & Riaux, 2007; Slimani et al., 2007). These papers—as well as regular papers with similar focus, also published in this issue—cover several aspects of the range of current quantitative hydrological issues in the Mediterranean and Middle-East in relation to water management.
	Encyclopedia of Hydrological Sciences The definitive multi-volume treatment of Hydrological Sciences.
	Hydrologic Hazards The basis for many decisions related to hydrologic hazards lies in understanding aspects of basic hydrologic science, such as discharge probability relationships, rainfall-runoff relationships, and geomorphic processes.
	Hydrological impact simulations of climate change on Lebanese coastal rivers The significance of predicted climatic changes is still uncertain. The hydrological consequences of climatic changes on Lebanese catchments are analysed by means of different scenarios of rainfall variability and temperature increase. The conceptual rainfall–runoff model MEDOR, coupled to a stochastic model of rainfall and temperature, is used to estimate change in runoff by simulation of six scenarios. These test the response to the rainfall structure, to the duration of rainy events, their frequency, and the duration of the rainy season. The climate–runoff model is used to determine the impact of a temperature increase of 2 degrees on the flow characteristics of a watershed affected by seasonal snow cover. The modifications of the hydrological regimes are significant: droughts are predicted to occur 15 days to one month earlier; snowmelt floods are often replaced by rainfall floods; and the peak flow occurs two months earlier. These changes could have a great impact on water resources management in the future.

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