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Droughts are one of the gravest natural threats currently existing in the world and their occurrence and intensity might be exacerbated in the coming years due to climate change. The severe impacts that droughts cause to inland water resources and to the associated socio-economic activities justify the continuous monitoring of the drought. The case study presented shows a practical application of a distributed drought monitoring system implemented in a real river basin district, the Júcar River Basin District (43,000 km 2 ), where drought periods of marked intensity have occurred historically and the climate ranges from humid in the north to semiarid in the south. Five drought indices have been applied: Standardised Precipitation Index (SPI) for meteorological drought; Palmer Drought Severity Index (PDSI) and a new soil moisture index (HI), for edaphic drought; Normalised Difference Vegetation Index (NDVI) for the vegetation activity; and Spanish Status Index (SI), for the operational drought. All indices are standardised to compare them. The relationship between the standardised operational drought index SI and the long-term meteorological indices, SPI-12 or SPI-24, show that in a medium size basin the concept of “prolonged drought” required by the European Commission under the Water Framework Directive could be defined by the use of accumulated precipitation indices. The number of months to be accumulated depends on the size of the basin and the water management system properties. In large basins, such as the Júcar river basin (22,000 km 2 ), there are significant deviations due to the spatial distribution of the drought. The use of a unique aggregated indicator could hide a significant drought in a specific area, or on the other hand show a non-real drought. Evolution of drought indices for each water management system must be accompanied by spatially distributed drought maps to better understand the drought status and its evolution. [ABSTRACT FROM AUTHOR]

Summary Water represents an essential element for the life of all who inhabit our planet. But the random nature of this resource, which is manifested by the alternation of wet periods and dry periods, makes it even more precious. Whatever the approach (water planning, water management, drought, economy), in order to maximise the profit produced by the allocation of water it is necessary an understanding of the relationships between physical variables as precipitation, temperatures, streamflows, reservoir volumes, piezometric levels, water demands and infrastructures management. This paper attends to provide a review of fundamental water scarcity and drought indexes that enables to assess the status of a water exploitation system. With the aim of a better water management and governance under water scarcity conditions., this paper also presents a classification of indexes to help decision makers and stakeholders to select the most appropriate indexes, taking as the starting point the objectives of the analysis and the river basin features. [ABSTRACT FROM AUTHOR]